JPH11182341A - Sealing structure for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sealing structure of an engine which can prevent the reduction of sealing property and the shortening of a service life of a gasket by a simple structure thereof. SOLUTION: In a sealing structure of an engine in which a gasket 91 having a bead part 91a formed so as to surround a piston slide face 22a is provided between a cylinder block in which a sleeve 27 constituting the piston slide face 22a is arranged in a cylinder main body part 22c made of aluminum alloy and a cylinder head 23 made of aluminum alloy, the cylinder main body part 22c and the cylinder head 23 are made of materials having substantially equal coefficient of thermal expansion, and the bead part 91a of the gasket 91 is arranged in such a way that it does not reach the sleeve 27 but comes into contact with the cylinder main body part 22c only.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a seal structure for an engine in which a gasket is interposed between a cylinder block and a cylinder head.

[0002]

2. Description of the Related Art In an engine, a gasket is conventionally interposed between a cylinder block and a cylinder head as a sealing structure between the cylinder block and the cylinder head, and both are firmly fastened by a head bolt. The structure is common.

In this type of engine, as a structure for forming a piston sliding surface in a cylinder block, a separate sleeve having a piston sliding surface is disposed in the cylinder block by press-fitting or casting. is there.

[0004]

In the case of a structure in which a separate sleeve is inserted into the cylinder body, depending on the linear expansion coefficient of the cylinder body and the sleeve, or the structure of the gasket. However, there is a problem that the sealing performance is reduced and the life of the gasket is shortened.

SUMMARY OF THE INVENTION An object of the present invention is to provide an engine seal structure which can prevent problems such as a reduction in sealability and a shortened gasket life with a simple structure.

[0006]

According to the first aspect of the present invention, an aluminum alloy cylinder head is provided between an aluminum alloy cylinder head and a cylinder block in which a sleeve constituting a piston sliding surface is disposed within an aluminum alloy cylinder main body. In an engine seal structure in which a gasket having a bead portion formed to surround a piston sliding surface is interposed, the cylinder body and the cylinder head are formed of materials having substantially equal thermal expansion coefficients, and It is characterized in that the bead portion is disposed so as to abut only the cylinder body without passing over the sleeve.

According to a second aspect of the present invention, in the first aspect, the sleeve is cast in the cylinder main body, and a thin portion for retaining is formed at an end of the cylinder head on the side of the cylinder head. The cylinder body portion has a thick portion covering the thin portion of the sleeve at the cylinder head side end portion, and the bead portion of the gasket abuts the mating surface of the thick portion on the cylinder head side. It is characterized by having.

A third aspect of the present invention is characterized in that, in the first or second aspect, a portion of the gasket on the inner peripheral side of the cylinder from the bead portion faces the end face of the sleeve on the cylinder head side.

A fourth aspect of the present invention is characterized in that, in any one of the first to third aspects, the piston sliding surface of the sleeve is formed by forming a plating film on the inner peripheral surface of the sleeve. I have.

[0010]

According to the first aspect of the present invention, the cylinder body and the cylinder head are formed of a material having substantially the same coefficient of linear expansion, and only the cylinder body is provided without passing the bead portion of the gasket over the sleeve. , The sealing performance can be ensured and the life of the gasket can be ensured.

That is, since the sleeve must form the piston sliding surface, the coefficient of linear expansion often differs from that of the cylinder main body. There may be a step in the cylinder axis direction between the mating surface (upper end surface) of the sleeve and the sleeve.
If the seal point of the bead portion on the cylinder block side is in contact with both the cylinder body and the sleeve, a force in the shear direction acts on the bead portion of the gasket due to the step, and the life of the bead portion is reduced. There is a concern that it may be shortened or the sealing property may be reduced. However, in the present invention, since the bead portion of the gasket abuts only on the mating surface of the cylinder main body portion, the above problem does not occur even if the step is formed.

Further, since the cylinder body and the cylinder head are formed of a material having substantially the same linear expansion coefficient, a thermal expansion dimension difference occurs in the cylinder radial direction between the cylinder body and the cylinder head in a hot operation state. No force acts in the cylinder radial direction between the cylinder side and the cylinder head side of the gasket bead, and no stress is generated in the cylinder radial direction of the gasket. And the service life can be secured.

According to the second aspect of the present invention, a thin portion is provided at the end of the sleeve on the cylinder head side where the outer peripheral surface is stepped down, and the sleeve is provided at the end of the cylinder body on the cylinder head side. Since the thick portion covering the thin portion is provided, and the bead portion of the gasket is brought into contact with only the mating surface of the thick portion on the cylinder head side, it is easy to secure a space for disposing the bead portion, and the sealing property is improved. Can be improved.

According to the third aspect of the present invention, since the inner peripheral side portion of the cylinder from the bead portion of the gasket faces the cylinder head side end surface of the sleeve, the space created between the cylinder head and the sleeve is reduced. It is possible to fill the inner circumferential portion of the cylinder, secure the compression ratio, and prevent the generation of unnecessary concave portions in the surface shape of the combustion chamber. In this case, even if the end surface of the sleeve extends in the cylinder axis direction from the end surface of the cylinder main body and a step occurs, the end surface of the sleeve does not hit the bead portion of the gasket, and there is no problem in sealing performance. .

According to the fourth aspect of the present invention, the sliding surface of the piston is formed by forming a plating film on the inner peripheral surface of the sleeve. In some cases, a so-called flower bloom to which a plating film adheres may be formed, and the flower bloom is not removed even by a honing in a subsequent process, so that there is a concern that sealing performance may be affected. However, in the present invention, since the bead portion of the gasket does not touch the mating surface of the sleeve on the cylinder head side, even when the flower is formed, the sealing performance is not affected.

[0016]

Embodiments of the present invention will be described below with reference to the accompanying drawings. 1 to 21 are views for explaining a cylinder block of a motorcycle engine according to an embodiment of the present invention. FIG. 1 is a left side view of a motorcycle on which the engine is mounted, and FIG. FIG. 3 is a right side view of a cylinder block, a cylinder head, and a head cover portion of the engine, FIG. 4 is a cross-sectional rear view of the engine, FIG. 5 is a cross-sectional view showing a communication hole portion of the cylinder block, 6 is a bottom view of the cylinder block viewed from the crankshaft side, FIG. 7 is a cross-sectional side view of a right end cylinder portion of the cylinder block, FIG. 8 is a cross-sectional side view of a second cylinder portion from the right of the cylinder block, and FIG. FIG. 10 is a plan view of a head gasket of the cylinder block viewed from the cylinder head side, and FIG. 11 is an enlarged view showing a sealing state of a mating surface of the cylinder block on the head side. 2 is an enlarged view showing a rib-shaped weir of a cylinder block, FIGS. 13 and 14 are diagrams showing a manufacturing process, FIGS. 15 to 18 are diagrams showing the results of a drilling test of a communication hole, and FIG. 19 is a honing process of FIG. FIGS. 20 and 21 are schematic diagrams showing a plating apparatus. Note that the terms front, rear, left and right in this embodiment mean front, rear, left, and right when viewed in a seated state.

In FIG. 1, reference numeral 1 denotes a motorcycle, and a vehicle body frame 2 has a seat rail 4 extending rearward of the vehicle body at a rear end of a pair of left and right main frames 3 having a substantially inverted L shape in side view. The fuel tank 5 is mounted on the upper part of the main frame 3, and the main seat 6 and the tandem seat 7 are mounted on the upper part of the seat rail 4, respectively.

A front fork 9 is pivotally supported at the front end of the main frame 3 by a head pipe 8, and a front wheel 10 is pivotally supported at the lower end of the front fork 9. A rear arm 11 is pivotally supported by a pivot shaft 12 on a rear arm bracket 3a below the rear end of the main frame 3 so as to be able to swing up and down.
A rear wheel 13 is pivotally supported at the rear end.

A rear cushion 14 is provided between the rear arm 11 and the vehicle body frame 2. The lower end of the rear cushion 14 is connected to the lower end of a first link 14a which is arranged upright on the rear side and is supported by the rear arm 11, and the upper end is supported by the body frame. The upper end of the first link 14a is connected to the vehicle body frame via a second link 14b provided upright on the rear side of the rear cushion 14, and the second link 14b and the first link 14a are connected to the rear cushion 14. Is forming a triangle. As described above, the lower end of the rear cushion 14 is supported by the first and second links 14a and 14b which are arranged upright, so that a large space is secured below the rear cushion 14 while ensuring so-called progressive characteristics. ing.

An engine unit 15 is suspended below the main frame 3.
A radiator 16 is provided on the front side of 5. The exhaust device of the engine unit 15 is disposed between an exhaust pipe 141 connected to each exhaust port opened to the front wall of the cylinder head 23, the engine unit 15 and the rear wheel 13, and below the rear cushion 14. The first muffler 14
2 and a second muffler 1 arranged on the upper right side of the rear wheel 13
43.

The engine unit 15 is a water-cooled 4-cycle parallel 4-cylinder 5-valve engine, and has a cylinder axis 20
Is mounted forward with the crankshaft 21 oriented in the vehicle width direction. As shown in FIG. 2, the engine unit 15 has an aluminum alloy cylinder head 23 on the upper mating surface of the aluminum alloy cylinder block 22.
And the cylinder head 2 is fastened with a head bolt.
3 Attach the aluminum alloy head cover 24 to the upper mating surface,
Further, it has a schematic structure in which an aluminum alloy oil pan 28 is connected to a lower portion of the cylinder block 22.

The cylinder block 22 is composed of a cylinder body 22a and a unit case 27 integrally formed by die casting using an aluminum alloy. The unit case 27 is provided with the crankshaft 21.
And a transmission case 26 for accommodating the transmission, and the crankcase 25 and the transmission case 26
Is divided into upper and lower parts by upper and lower crankcase parts 25a and 25b and upper and lower transmission case parts 26a and 26b.

The crankshaft 21 is supported via a bearing 30 by a plurality of bearing bosses 29 formed on the surface of the upper and lower crankcase portions 25a and 25b. In addition, the boss portion 29 allows the crank chamber 19 for each cylinder,
Are partitioned into independent chambers and communicate with each other through a communication hole 52 described later.

In the cylinder block wall 22d of the cylinder body 22c of the cylinder block 22, four sleeves 27 made of a drawn pipe material made of aluminum alloy are cast in parallel and at equal intervals. On the inner surface at the lower end of the sleeve 27, a relief portion 27a for relieving the cutting tool during honing is formed to have a larger diameter than the other portion, and on the outer surface, a surface for preventing the sleeve 27 from coming off to the crankshaft side. A receiving portion 27b is formed. The inner surface of the upper end of the sleeve 27 has a chamfered portion 2 serving as a relief when the piston is inserted and assembled.
7c is formed, and on the outer surface, a locking step portion (a thin portion for retaining) 27d for preventing the sleeve 27 from coming off toward the cylinder head side is formed to have a smaller diameter than other portions.
By providing this step 27d, the cylinder body 2
The cylinder head mating surface 22f on the 2c side is thick, and as a result, a bead portion 9 of a gasket 91a described later is formed.
The contact space of 1a can be easily secured.

The sleeve 27 has a piston sliding surface 22a having a plating film a formed on the inner surface. The piston sliding surface 22a is
7 is cast into the cylinder main body 22c, a boring process is performed to remove thermal strain during the casting, an etching process is performed on the processed surface by a method described later, and a plating film a is formed. The film a is formed by performing honing processing.

Here, as shown in FIG. 12, the etching process is performed in the region h1 from the upper end to the lower end of the sleeve 27.
And the plating film a is formed over a region h2 from the upper end of the sleeve 27 to the middle of the escape portion 27a. A small end of a connecting rod 32 is connected to a piston 31 slidably inserted in the piston sliding surface 22a via a piston pin 31b, and the lower end 31e of the piston 31 is plated with the plating. It slides in a region h4 'overlapping with the lower end a' of the film a. The honing is performed over a region h3 'from the upper end of the sleeve 27 to the corner of the escape portion 27a.

The large end of the connecting rod 32 is of an upper and lower split type including a main body portion and a cap member. The main body portion is located above the crankpin 21a of the crankshaft 21, and the cap member is located below the crankpin 21a. Are respectively connected to the crankshaft 21 by bolting and fixing. When assembling the piston 31, the main body of the connecting rod 32 is assembled to the piston 31, the main body and the piston 31 are inserted into the sleeve 27 from the cylinder head side, and the main body is connected to the cap member with the cap member. It will be connected to the crank pin 21a.

The piston 31 has a piston skirt 3
1a piston pin 31b notch recess 31 at the shaft end
This is a so-called slipper type formed by forming c. When the piston 31 descends to its bottom dead center position, the lower end 31e of the piston skirt 31a
A clearance c is opened in the escape portion 27a of the vehicle. That is, by providing the gap c, the piston 31 does not contact the lower edge a 'of the plating film a.

In FIG. 6 showing the cylinder block 22 as viewed from the crankshaft side, the opening of the sleeves 27, 27, 27 of the three cylinders from the right end on the crankshaft side is the front side wall of the upper crankcase portion 25a. 25c, a partition wall 25d defining a crank chamber and a transmission chamber, and a crankshaft bearing boss 29 surround the periphery, so that an etchant or the like overflows in the plating film forming step as described later. , Mission room 26d
It can be prevented from flowing into the side.

On the other hand, the sleeve 27 of the left end cylinder in FIG. 6 corresponds to the above-mentioned partition wall 25d because it is necessary to secure a space for disposing the reduction gear 82 and the reduction gear 82 connecting the crankshaft 21 and the main shaft 72. Not equipped. Therefore, in the left end cylinder, the effect of preventing the etching liquid and the like from flowing into the mission chamber by the partition wall 25d in the plating film forming step cannot be obtained.

Therefore, in this embodiment, in the cylinder for the left end, the sleeve 27
Retaining chamfered portion 27b formed on the outer surface of the lower end of the
The portion is covered with an aluminum alloy, and a rib-shaped dam portion 25d 'is formed integrally with the other portion and protrudes slightly toward the crankshaft from the other portions. The dam portion 25d 'prevents the etchant or the like from overflowing to the transmission case 26d side in the plating process.

Each combustion recess 23 of the cylinder head 23
The three intake ports and two exhaust ports opening to a can be opened and closed by an intake valve 35 and an exhaust valve 36. The valves 35, 36 are opened and closed by an intake camshaft 40 and an exhaust camshaft 41 via bottomed tubular valve lifters 37, 37 mounted on the upper ends. Each camshaft 40, 41
Sprocket 40 attached to the axial right end of the
a, 41a and a crank sprocket 21b formed integrally with the right end of the crankshaft 21
They are connected by two.

The cam sprockets 40a, 41a and the timing chain 4 of the camshaft driving mechanism constructed as described above.
2 and the crank sprocket 21b are accommodated in a chain arrangement chamber 43 integrally formed on the right outer end surfaces of the cylinder block 22 and the cylinder head 23. A rotor 44 having outer peripheral teeth is mounted inside the crank sprocket 21b of the crankshaft 21, and a pickup 45 for detecting a crank rotation angle is opposed to the rotor 44. An auto-tensioner 46 automatically adjusts the tension of the timing chain 42.
7 is a chain guide.

An opening 50 for assembling the camshaft drive mechanism is formed in a portion of the outer wall 22b of the cylinder block 22 that constitutes the chain arrangement chamber 43, facing the shaft end of the crankshaft 21. The opening 50 has a lid member 5.
1 is detachably bolted. By communicating the adjacent crank chambers 19 with each other, the communication hole 52 for reducing the pumping loss due to the reciprocating movement of the piston is positioned in the assembling opening 50 when viewed in the crankshaft direction. And is formed so as to form the same axis parallel to the crankshaft 21.

The communication hole 52 has a circular cross section formed by inserting a long drill from the assembling opening 50 in a step between the plating process and the honing process. It is. And the communication hole 5
The machining center point 2 is set at a position deviated toward the cylinder head from the crankshaft end 27e of the sleeve 27. The sleeve 27 has a higher hardness than the upper crankcase portion 25a.

As described above, in this embodiment, when a circular hole is formed by drilling so as to extend over both the upper crankcase portion 25a and the sleeve 27 having different hardnesses,
Since the center of the drill is set to be deviated toward the high-hardness sleeve 27 side, escape of the drill can be avoided, and workability can be improved. This escape avoidance effect is achieved by the overhang portion (region 52 in FIG. 7) that prevents the drill from moving toward the high-hardness member because the center of the drill is located on the high-hardness member side.
It is considered to be obtained by the presence of part (b). By the way, when the processing center point b is deviated toward the upper crankcase portion 25a side with low hardness, there is a possibility that the drill processing center may be shifted away from the high hardness sleeve.

Further, the communication hole 52 is disposed so as to face the notch 31c and the piston pin 31b when the piston 31 descends to the bottom dead center.
The distance from the upper edge 52a to the lower edge of the oil ring 31d at the lower end of the piston 31 located at the bottom dead center is 3
The center position b and the hole diameter are set to be not less than mm, preferably not less than 7 mm.

The center position of the communication hole 52 is set as described above for the following reason. That is, the communication hole 52
Is formed, burrs and deformations of an unacceptable degree occur on the periphery as a piston sliding surface. The burrs and the like are removed by a subsequent honing process. However, in a range of about 3 mm from the periphery of the communication hole 52, it may not be possible to sufficiently remove the burrs as a piston sliding surface. Because it turned out.

FIGS. 15 to 19 show the results of experiments conducted to investigate the occurrence of burrs and the like when the through-hole 52 is formed and the surface finish by honing. In addition,
In each of the figures, the actual dimensions are shown in the vertical direction (cylinder axial direction), while 10 mm in the horizontal direction.
It is shown enlarged to 00 times.

FIGS. 15 to 18 show first to fourth cases in which a plated film is formed on each sleeve of the experimental cylinder block and a drill is inserted in the direction of the arrow to form the above-mentioned through-hole.
This shows the occurrence of burrs and the like in the cylinder. In each figure,
The right part shows the situation when the drill penetrates the plating film and enters the sleeve, and the left part shows the situation when the drill penetrates the plating film from inside the sleeve and enters the cylinder body. Burr etc. is 5-30μ in any cylinder
m.

FIG. 19 shows the state of the piston sliding surface after honing. As is apparent from the figure, the burrs and the like are removed by honing, and in a portion above a point 3 mm from the upper edge 52a of the through hole 52, α μm (for example, set as an allowable dimension as a piston sliding surface) (for example, 5 μm). Therefore, when the piston 31 is located at the bottom dead center, the lower edge of the oil ring 31d disposed at the bottom and the upper edge 5 of the through hole 52
By setting the dimension 2a to be larger than 3 mm, the gap between the oil ring 31d and the piston sliding surface can be set within an allowable range, and the occurrence of output loss due to an increase in sliding resistance can be prevented.

As shown in FIG. 5, each of the bearing bosses 29 of the upper crankcase portion 25a has
A lubricating oil passage 53 is formed to communicate the bearing 30 with the inner peripheral surface of the communication hole 52. A cooling nozzle 54 is inserted into the lubricating oil passage 53, and an injection port 54a of the nozzle 54 is directed so as to jet lubricating oil from the notch 31c of the piston 31 located at the bottom dead center to the back surface of the piston. doing. The thickness of the bearing boss portion 29 in the direction of the crankshaft at the communication hole 52 is W2 on the crankshaft side and W1 on the piston side. Therefore, the lubricating oil injected from the injection port 54a
Is reliably supplied to the back surface of the piston without being hindered by the periphery of the piston or the piston skirt, and the piston 31 can be cooled reliably.

The cylinder block 22 has a sleeve 2
7, a water cooling jacket 90 is formed.
The inside of the water cooling jacket 90 is a cylinder bore wall 22d. The depth of the water cooling jacket 90 except for the side of the chain arrangement chamber 43 is set so as to coincide with the upper end surface of the piston 31 which is located 116 ° below the top dead center by a crank angle of 116 °. On the other hand, the depth of the portion 90a of the water cooling jacket 90 on the side of the chain arrangement chamber 43 is set so as to coincide with the vicinity of the upper end surface of the piston 31 located at the bottom dead center, and the bottom wall 90b of the water cooling jacket portion 90a is formed. The height in the cylinder axial direction is
0 is set to be slightly lower than the height of the upper edge 50a. The water-cooled jacket 90 is open over the entire circumference at the head-side mating surface, and is closed by a gasket 91 described later.

As described above, since the portion 90a of the water cooling jacket 90 on the side of the chain arrangement chamber 43 is formed deeper than other portions, the provision of the chain arrangement chamber 43 improves the cooling performance of the arrangement chamber 43 of the cylinder block. It can compensate for the decrease. That is, the portion surrounding the sleeve 27 of the cylinder block 22 is also cooled by direct contact with the traveling wind, but the right end portion of the cylinder block 22 in FIG. , And there is a concern that the cooling performance is reduced. In the present embodiment, the chain arrangement chamber side portion 90 of the cooling jacket 90 is used.
Since a is formed deeper, it is possible to compensate for a decrease in cooling performance due to the absence of the traveling wind.

The height of the bottom wall 90b of the water cooling jacket portion 90a of the cylinder block 22 in the cylinder axial direction is set to be slightly lower than the height of the upper edge 50a of the assembling opening 50 (see FIG. 4). Therefore, the casting mold of the portion can be simplified. That is, the bottom wall 90
When b is higher than the upper edge 50a, a slide mold is required. However, in the present embodiment, the bottom wall 90b can be formed by a mold that moves in the crankshaft direction for forming the opening 50. The slide type is not required.

A gasket 91 is interposed between the mating surfaces of the cylinder block 22 and the cylinder head 23.
The gasket 91 has three thin plates 92, 93, 94 cut in accordance with the mating surface shape of the cylinder block 22.
While overlapping with the same gap as the thin plate,
A concentric bore bead portion 91a having a diameter larger than that of the sleeve 27 is formed so as to surround the sourb 27, and a peripheral bead portion 91b having a shape along the periphery of the mating surface and a shape along the opening edge of the chain arrangement chamber 43 are formed. The chain chamber bead portion 91c and the like are formed by press molding or the like. In each of the bead portions 91a to 91c, the central thin plate 93 is kept flat and the upper and lower thin plates 92 and 94 are connected to the central thin plate 9.
3 and is formed by fixing portions other than the bead portion by caulking or the like. FIG. 11 is schematically shown to emphasize the bead portion and the gap.

The gasket 91 is connected to the cylinder block 2
2 and the cylinder head 23 are interposed between the mating surfaces, and the two are tightened with a head bolt.
The bending point p of 1b is pressed on the mating surface, and at the same time, the upper and lower thin plates 92 and 94 are pressed against the central thin plate 93, whereby the cylinder block 22 and the cylinder head 2 are pressed.
The space between the three is sealed. The cylinder inner peripheral portion 91d of the gasket 91 faces the cylinder head side joint surface 22f of the sleeve 27.

In FIGS. 2 and 4, reference numeral 70 denotes a transmission mainly disposed in the upper transmission case 26a.
And a drive shaft (output shaft) 74 provided with an output gear group 73 which meshes with the input gear group 71 below the main shaft 72. They are arranged in parallel.

The drive shaft 74 is connected to the crankshaft 2.
1 is disposed between bearing surfaces of the upper and lower transmission case portions 26a and 26b in the same manner as that of the upper and lower crankcase portions 25a and 25b. Supported. The main shaft 72
Are arranged in the upper transmission case 26a,
The left end of the main shaft 72 is the upper transmission case 26a.
Are supported via bearings 76. The right side portion is supported by a right side wall 26g of the upper transmission case portion 26a via a bearing 77 and a flange 78, and the flange 78 is bolted and fixed to the right side wall 26g.

The left end of the drive shaft 74 protrudes outward from the transmission case 26, and a drive sprocket 79 mounted on the protrusion is connected to the rear wheel sprocket 13a of the rear wheel 13 via a chain 80. Have been. A clutch mechanism 8 is provided at the right end of the main shaft 72.
1 is attached. The clutch mechanism 81 meshes with a reduction gear 82 of the crankshaft 21, and is connected to an outer drum 84 via a damper to a reduction gear 83 supported on the main shaft 72, and is spline-connected to the main shaft 72. It has a structure in which a number of clutch plates 86 are interposed between the inner drum 85 and the clutch plate 86. The clutch mechanism 81 turns off and on the engine power by rotating a push lever 87 connected to the inner drum 85.

A shift drum 90, an input-side fork shaft 91, and an output-side fork shaft 92 are disposed in parallel with the main shaft 72 and the drive shaft 74 on the rear rear side of the main shaft 72 and the drive shaft 74. The right and left ends of the fork shafts 91 and 92 are supported by right and left bosses integrally formed with the upper transmission case 26a.

The input side fork shaft 91 has one input side shift fork 93 and the output side fork shaft 9
2, two output-side shift forks 94, 94 are mounted movably in the axial direction. The shift fork 93,
The forked claw portion 94 has an input gear group 71 and an output gear group 73.
An engagement pin slidably engaged with the sliding grooves 71b, 73b formed on the gears of the first and second shift forks 93, 94 is formed on the outer peripheral surface of the shift drum 90. It is slidably engaged with the guide groove. By rotating the shift drum 90 by a change mechanism (not shown), the shift forks 93 and 94 slide in the axial direction to move the gears of the input gear group 71 and the output gear group 73, and as a result, Switching is performed between the lowest speed stage and the highest speed stage.

Next, the crankshaft 21, the main shaft 72,
The positional relationship between the drive shaft 74 and the drive shaft 74 will be described mainly with reference to FIG. In the main shaft 72, the first shaft angle θ1 formed between the crankshaft / main shaft straight line A connecting the shaft center of the main shaft and the shaft center of the crankshaft 21 and the cylinder axis 20 on the cylinder head side and the main shaft side is an acute angle. In other words, it is disposed at a position closer to the cylinder head 23 side than a straight line C passing through the axis of the crankshaft 21 and perpendicular to the cylinder axis 20.

The drive shaft 74 has a main shaft / drive shaft straight line B and a crank shaft / main shaft straight line A connecting the shaft center of the drive shaft 74 and the shaft center of the main shaft 72. Are arranged so that the second axis angle θ2 formed by the first angle becomes an acute angle. In this manner, the main shaft 72 and the drive shaft 74 are arranged so as to be carried on the back surface of the cylinder block 22.

The maximum outer peripheral surface (the outer peripheral surface of the large reduction gear) 81a of the clutch mechanism 81 is formed by a straight line D passing through the top surface of the piston 31 'located at the bottom dead center and making a right angle with the cylinder axis 20. Located on the side. The main shaft 72, the shift drum 90, the fork shafts 91 and 92, and the drive shaft 74 are located in the axial projection plane of the reduction gear 83 of the clutch mechanism 81.

As shown mainly in FIG. 2, the cooling water pump 100 and the lubricating oil pump of this embodiment are both housed in the lower transmission case portion 26b, and the pump shaft 102 common to both pumps is connected to the crankshaft. It is arranged below and parallel to the shaft 21 and the drive shaft 74.
The driven sprocket 108 attached to the right end of the pump shaft 102 is connected to the main shaft 7 via a chain 109.
It is connected to a drive sprocket 110 mounted on a portion outside the second flange 78. The cooling water discharged from the cooling water pump 100 is supplied to the cooling water passages 119, 123a,
It is supplied to the cooling jacket 90 via 123b.

The lubricating pump sucks the lubricating oil in the oil pan 28 through the oil strainer 120 and removes the lubricating oil from the oil filter 121 attached to the front wall of the lower crankcase portion 25b to the main gallery 122. Via the crankshaft 21, the main shaft 72, the drive shaft 7
4 and the camshafts 40, 41 and the like to each engine lubrication section.

As shown in FIG. 3, the lubricating oil for the valve mechanism is supplied from an oil passage 126 opened between the first cylinder intake side of the cylinder head 23 and the chain arrangement chamber 43 to the intake camshaft. The oil is supplied to an oil passage 127 extending along 40 and is supplied to an oil passage 129 extending along the exhaust camshaft 41 by an oil passage 128.
The lubricating oil that has lubricated the camshaft bearings is recovered into the oil pan 28 through an oil return passage formed between the exhaust sides of the third and fourth cylinders of the cylinder head 23.

In FIG. 2, reference numeral 135 denotes a starting motor, which is arranged in parallel to the crankshaft 21 on the back surface of the cylinder body 22c of the upper transmission case 26a. The output of the starting motor 135 is an intermediate gear 138, a starting gear 139, a one-way clutch 140,
The power is transmitted to the crankshaft 21 via the large reduction gear 83.

Next, the manufacturing process of the cylinder block 22 of this embodiment will be described. Cylinder block 22 of the present embodiment
As the aluminum alloy for die-casting of the cylinder body portion 22c, the upper crankcase portion 25a, and the upper transmission case portion 26a (hereinafter, sometimes referred to as a cylinder block base material), the aluminum alloy of JIS standard shown in Table 1 below is used. The alloys shown in Table 2 can be used as the aluminum alloy for the cylinder head 23, and the alloys shown in Table 3 can be used as the aluminum alloy for the sleeve 27.

[0061]

[Table 1]

[0062]

[Table 2]

[0063]

[Table 3] As shown in Tables 1 to 3, the base aluminum alloy contains 5 to 20% (% by weight) of Si,
As the aluminum alloy, an aluminum alloy having a Si content such that 50 <α <150, where α is (weight content of Si in sleeve 27 / weight content of base material) × 100, is used.
By forming each of the base material and the sleeve using the aluminum alloy having such a configuration, the difference in the coefficient of thermal expansion between the base material and the sleeve is reduced, and a heat spot is generated between the base material and the sleeve, and the inner circumference of the sleeve is reduced. Thermal deformation of the surface is reduced, and peeling of the plating film a applied to the inner peripheral surface of the sleeve is suppressed.

When the cylinder block base material is formed by AC4C shown in Table 2, the Si content by weight of the base material is 6.5 to 7.5%. , Si content is, for example, 3.75 to 9.75.
The alloy changed to wt.% Is used to satisfy the condition of Si weight content of the sleeve / Si weight content of the base material. Similarly, when the cylinder block base material 60 is formed by the ADC 10, the Si content in the base material 60 is 7.5 to 9.5%. For example, 4.75-15
The alloy changed to wt.% Is used to satisfy the condition of Si weight content of the sleeve / Si weight content of the base material.

Further, as shown in Table 3, the aluminum alloy of the sleeve has a C content of at least 0.2 or more and 10 or less.
Contains both u and Mg. Thereby, the hardness can be easily increased to HB70 or more by performing the T6 treatment as described below. Even when only one of Cu and Mg is contained, the hardness can be easily increased to HB 70 or more by performing T6 treatment. Further, as shown in Tables 1 and 2, the base aluminum alloy contains one or both of Cu and Mg. This makes it possible to easily increase the hardness by performing T6 treatment on the base material together with the sleeve as described below, and to increase the rigidity of the entire cylinder block while improving the plating holding capacity of the plating layer support portion of the sleeve. And the durability of the engine can be improved.

FIG. 13 is a flow chart for explaining a process of manufacturing the cylinder block 22 by casting the sleeve 27. In this flow, the T6 treatment (steps S2, S4, S6) is performed in order to increase the surface hardness of the inner peripheral surface serving as the plating film support of the sleeve.
In accordance with S Standard H5202, the sleeve alone or the entire cylinder block into which the sleeve is cast is solution-hardened at a predetermined temperature and then age-hardened. Steps S2, S4, S
6 may be performed once or may be omitted.
By such a T6 treatment, the surface hardness of the sleeve is reduced to HB70.
It is desirable to make the above (70 to 150). When the surface hardness of the inner peripheral surface is set to HB70 or more by extrusion or drawing of the sleeve, the surface hardening treatment can be omitted by the subsequent T6 treatment.

It should be noted that any one of T in steps S2 and S4
According to the sixth treatment, the hardness of only the sleeve can be increased. At the time of casting, the hardness of the sleeve slightly decreases due to the heat of the base material in the molten state, but the casting time itself is shorter than that of the T6 treatment, and the hardness of the inner peripheral side of the sleeve can be maintained at HB70 or more. Further, according to the T6 process in step S6, the hardness of the base material of the cylinder block can be increased in addition to the increase of the hardness of the sleeve, the rigidity of the entire cylinder block can be increased, and the sliding of each part due to the engine vibration. It is possible to prevent a decrease in engine durability due to, for example, an increase in sliding wear due to a decrease in clearance of the portion.

Outer peripheral shot blast (step S3)
Is for forming fine irregularities on the outer peripheral surface of the sleeve to improve the bonding property with the base material. By forming the irregularities on the outer peripheral surface of the sleeve before casting the sleeve, the sleeve can be reliably prevented from coming off even if the tension force is reduced due to the difference in the coefficient of thermal expansion between the base material and the sleeve during operation. Such irregularities on the outer peripheral surface of the sleeve can be formed by other mechanical processing other than shot blasting, or by pickling (etching) the entire sleeve. Note that the shot blast processing (step S3) may be omitted. Further, instead of a method of forming irregularities on the outer periphery of the sleeve by shot blasting or the like to enhance the bonding property with the base material, the sleeve and the base material may be bonded by using low melting point solder to prevent the sleeve from coming off. .

Here, shot blasting refers to steel balls, carbide beads, stainless steel balls, zinc beads, glass beads having a particle size of 50 to 150 μm, river sand containing a large amount of quartz having a slightly larger particle size, and the like. With a projector, for example, 40-8
It refers to an object that projects a workpiece at a projection speed of 0 m / s.

FIG. 14 shows the plating process (step S).
8) is a detailed flowchart, and FIGS. 20 and 21 are block diagrams of a plating apparatus for performing this plating process.
In the flowchart of FIG. 14, the plating process on the inner surface of the sleeve is basically performed by a degreasing process (step S11).
Alkali etching treatment (Step S13), mixed acid etching treatment (Step S15), alumite treatment (Step S17), and composite plating treatment (Step S19)
After each step, a water washing process (steps S12, S14, S16, S18, S20) is performed.

In the above-mentioned water-washing treatment, the entire cylinder block is immersed in the two water tanks in order and moved up and down using two separate water tanks (total of 10 tanks) for each step to remove the processing liquid of the preceding step. Things. The water in the aquarium is regularly replaced with fresh clean water. It is desirable to move to the next step as soon as possible after completion of each water washing treatment, and to carry out the next treatment with a water film on the surface. Accordingly, it is possible to prevent dust or the like from adhering to the processing unit and to prevent oxygen in the air from directly touching, thereby preventing formation of an oxide film and the like, and improving reliability of processing in a later step. This is particularly effective in the case of plating.

As shown in FIGS. 20 and 21, the sleeve 2
The cylinder block 22 in which the base material 7 is cast is used to perform various treatments on the inner peripheral surface of the sleeve 27.
The gasket 101 for sealing is placed on a dedicated apparatus main body 100a, 100b in each process with the mating surface of 2c facing downward.
a, 101b. In each process, the processing solution 105a in the dedicated processing solution tank 102a, 102b,
105b is supplied into the apparatus main bodies 100a and 100b by dedicated pumps 106a and 106b,
7 and returns to the processing liquid tanks 102a and 102b through the inner cylinders 107a and 107b.

FIG. 20 shows the state of the alkali etching and the mixed acid etching. Since the range of the etching process needs to have a margin with respect to the range of formation of the plating film, the range of the etching process is set to the vicinity of the end of the escape portion 27a of the sleeve 27 on the crankshaft side. The management of the processing range in this case is performed by the upper end surface 107a of the inner cylinder 107a.
The process is performed by controlling the liquid level of the processing liquid 105a according to the height position of '. However, there is a limit in performing this method with high accuracy. If the etching liquid 105a overflows to the transmission case 26 side or the like, the processed surface on the transmission case 26 side of the cylinder at the left end in FIG. 6 may be roughened.

Therefore, in the present embodiment, the left end cylinder is formed with a rib-shaped dam 25d 'on the transmission case 26 side portion as described above, so that the etching solution is transferred to the transmission case side. Overflow can be prevented.

The gaskets 101a and 101b are sealing materials for preventing the processing liquid from leaking in each processing step, and are used in the alumite processing step (step S1).
7) and in the composite plating step (step S19), it functions as an insulating material for electrolytic action. In the alumite treatment step and the composite plating step, for example, as shown in FIG.
A DC voltage is applied between the cylinder main body 22c and the inner cylinder 107 via the control circuit 110 to flow a DC current into the electrolyte. In the other steps, no DC current is passed through the processing solution.

The composite plating process is a high-speed plating process. Under a predetermined plating condition, a plating solution 105b in a dedicated processing solution tank 102b is pumped by a pump 106b into the main assembly 10 of the apparatus.
0b, and is supplied through the inner cylinder 107b.
A plating film is formed on the inner surface of the sleeve 27 while circulating a path such as returning to b at a high speed. In this high-speed plating step, the inner cylinder 107b is placed on the (+) side of the power supply circuit.
The cylinder body 22c is connected to the (-) side, and a direct current flows through the plating solution. As a result, Ni ⁺ and P ^{+ in} a plating solution having a composition described later adhere to the inner peripheral surface of the sleeve, and accordingly, SiC particles serving as a dispersant are caught in the plating layer. Thus, the plating film a containing SiC and having excellent wear resistance and lubricity is formed on the inner peripheral surface of the sleeve.
It is formed to a thickness of 150 μm.

In the high-speed plating process in step S19, the cover 111 is attached to the upper end of the sleeve 27. This cover 111 is used for the plating solution 10 circulating at high speed.
5b is prevented from being scattered and spouted, and the plating range on the inner surface of the sleeve 27 is restricted. Plating range is sleeve 2
7 is restricted to the range from the gasket 101b which is the boundary with the cylinder head to the O-ring 112 of the cover 111. Therefore, by setting the position of the O-ring 112 in the middle of the escape portion 27a, the lower end of the outer peripheral surface of the piston 31 can be prevented from contacting the lower end a 'of the plating film a as described above.

After the composite plating process in step S19, the washing process is again performed in step S20 to remove the plating solution, and the water adhering to the cylinder block 22 is removed by air blowing in step S21. After the above-described plating process step S8, after processing the through-hole 52, a honing step is performed on the plating layer on the inner peripheral surface of the sleeve 27 in a honing step S9, and the thickness of the plating film is preferably about 50 μm, and in some cases, 20 μm.
m to 100 μm, and the surface roughness of the plating layer is set to 1.0 μmRz or less. As a result, the surface of the plating layer can be surely smoothed, the coefficient of friction at the time of sliding of the piston 31 and the piston ring 31d can be reduced, and the retention of engine oil is improved and lubricity is improved. be able to. Note that Rz is J
It is defined in B0601 of the IS standard.

Next, the operation and effect of this embodiment will be described. In the present embodiment, the cylinder body 22c, the upper crankcase 25a, and the upper transmission case 26a are integrally formed by die-casting of an aluminum alloy, so that the number of parts can be reduced, and the thickness of each part can be reduced, thereby reducing the weight. be able to.

Further, a sleeve 27 made of an aluminum alloy drawn pipe material is cast into the cylinder main body 22c, and a plating film a is formed on the inner surface of the sleeve 27. Since there is no pit as in the case where a plating film is directly formed on a casting surface, the adhesion of plating is good and the defective production rate can be reduced.

In forming the plating film a,
Since the high-speed plating method in which the plating solution is circulated at a high speed between the inner surface of the sleeve 27 and the processing solution layer is adopted, the productivity is reduced as compared with the method of immersing the entire work in the stationary bath and plating. Can be improved.

The upper edge 26c of the upper transmission case 26a for accommodating the transmission is connected to the cylinder body 22c.
20 and 21, it is mounted on the plating apparatus main bodies 100a and 100b with the cylinder head side facing downward in the plating process as shown in FIGS. In this case, the upper edge portion 26c of the upper mission case portion 26a is
a, 100b, so that the work can be easily supported in the plating process, and the workability of the plating process can be improved.

Further, as shown in FIG. 2, the crankshaft 21, the main shaft 72, and the drive shaft 74 are connected to a first shaft angle θ1 between the crankshaft / main shaft straight line A and the cylinder axis 20; A and main axis / drive axis straight line B
Are arranged so as to form an acute angle with each other, the distance between the crankshaft 21 and the drive shaft 74 can be reduced, and the longitudinal length of the engine can be shortened. The amount of overhang from the portion 22c can be reduced, and from this point, the work can be easily supported, and the workability of the plating process can be improved.

Since the main shaft 72 is arranged closer to the cylinder head 23 side than the right-angled straight line C passing through the crankshaft 21, the main shaft 72 is arranged to be carried on the back of the cylinder block 22. 15 can be further reduced. Further, since the clutch mechanism 81 is disposed such that its maximum outer peripheral surface 81a is located on the cylinder head 23 side with respect to the right-angled straight line D passing through the piston top surface at the bottom dead center, the engine unit 15 can be downsized from this point as well.

Since the main shaft 72, the shift drum 90, the fork shafts 91 and 92, and the drive shaft 74 are arranged in the axial projection plane of the largest diameter portion of the clutch mechanism 81,
The arrangement of each shaft is compact, the protrusion of the unit case 25 can be reduced, and the engine can be downsized from this point as well.

The lower end of the sleeve 27 (cylinder inner wall) constituting the piston sliding surface 22a of the cylinder body 22c and a portion on the transmission case 26 side protrudes toward the crankshaft 21 as compared to the anti-transmission case portion. Since the rib-shaped weir portion 25d 'is provided, it is necessary to extend the sleeve 27 to the crankshaft 21 side more than necessary in the above-described plating process, especially when the processing liquid such as the etchant liquid overflows to the transmission case 26 side. It is possible to prevent the already processed surface from being roughened by an etching solution or the like.

In providing the weir 25d ',
The weir portion 25d 'is provided only on the transmission case side portion of the cylinder having the output take-out portion between the crankshaft bearing boss portions 29, and the other cylinders are partitioned between the crank chamber and the transmission chamber for the other cylinders. The partition wall 25d, which is higher than the lower end of the piston sliding surface 22a (sleeve 27) in the direction of the cylinder axis 21, is provided.
d 'can also be used. The original purpose of the partition 25d is to improve the case rigidity.

Further, the sleeve 27 (cylinder inner wall)
A relief 27a having a diameter larger than that of the piston sliding surface 22a is formed at the end of the cran shaft side, and the plating film a is removed from the relief 27a.
To the middle part (h2) of the piston 3
1 lowers to the bottom dead center position, a gap c is formed between the lower end 31e of the piston 31 and the lower edge a 'of the plating film.
Formed at the edge a ′ of the plating film a.
Does not come into contact with the cutting tool and the outer peripheral surface of the piston 31 during the honing process S9, and the problem of peeling and falling off from the edge of the plating film a can be avoided.

When the piston 31 descends to the bottom dead center, the lower end 31e of the piston 31
The height of the engine can be reduced while maintaining the same piston stroke. That is, when the relief portion is not provided, it is necessary to increase the length of the sleeve in order to prevent the lower end of the piston from contacting the edge of the plating film. In the embodiment, this problem can be avoided.

For example, in FIG. 12, when the plating film is provided up to h2, the honing region must be set to h3 with a margin so that the cutting tool does not hit the lower edge a 'of the plating film. Since the area needs to have a margin from the honing processing area, the area is h4, and the engine height is increased by (h4'-h4) as compared with the present invention.

When a communication hole 52 having a circular cross section for communicating the cylinder crank chambers 19 with each other is formed at the boundary between the sleeve 27 inserted into the cylinder body 22c and the crankcase 25 by a drill. Machining center point b
Is displaced toward the sleeve 27 from the boundary between the sleeve 27 and the crankcase portion 25, so that the communication hole 52 can be easily and reliably formed at a predetermined position. Incidentally, when the processing center point b is deviated toward the upper rank case portion 25a side of low hardness, the drill processing center may be shifted away from the sleeve.

When the communication hole 52 is formed so as to penetrate the piston sliding surface 22a of the sleeve 27, the piston 31 at the bottom dead center position from the communication hole upper edge 52a of the piston sliding surface 22a. Oil ring 31a at the lower end
Is set to 3 mm or more, the piston ring can be slid only in the portion where the surface roughness or the like is within an allowable range by honing the piston sliding surface 22a. The problem that the gap with 22a becomes narrower than the allowable dimension can be solved.

Further, since the communication hole 52 is formed so as to be located in the assembling opening 50 of the camshaft drive mechanism provided on the outer wall 22b of the cylinder block 22 when viewed in the crankshaft direction. The communication hole 52 can be formed by machining using the assembling opening 50, and an extra opening such as forming a separate opening for machining or embedding a hole opened by machining can be provided. There is no need for processing, and therefore, it is not necessary to close the processing opening with a dedicated lid member, and the manufacturing cost can be reduced.

Further, in the case where the lubricating oil passage 53 is formed in each boss portion 29 of the upper case 26 so as to open to the inner peripheral surface of the communication hole 52, and the lubricating oil is injected to the back surface of the piston through the passage 53. The width W of the upper part of the communication hole 52
1 is smaller than the lower width W2, the injected lubricating oil is reliably supplied to the back surface of the piston without being interrupted by the upper edge of the communication hole 52. The notch need not be formed,
The piston 31 can be efficiently cooled without increasing the cost.

Further, in the present embodiment, a slipper type piston 31 having a notch concave portion 31c formed in the piston skirt 31a is employed, and the injection port 54a of the lubricating oil passage 53 is set to the position of the piston 31 located at the bottom dead center. Since the piston skirt 31a is directed toward the back surface of the piston through the notch 31c, the injection flow of the lubricating oil is not interrupted by the piston skirt 31a, and the cooling efficiency can be improved from this point as well. Further, since the notch recess 31c is provided, the piston skirt 3
The problem that the effective area of the communication hole 52 is reduced by 1a can also be avoided. Alternatively, it is not necessary to lengthen the connecting rod in order to avoid area reduction due to the skirt.

Aluminum alloy cylinder block body 22
When a gasket 91 is interposed between the cylinder block 22 formed by casting the sleeve 27 constituting the piston sliding surface in the cylinder c and the aluminum alloy cylinder head 23,
The cylinder block body 22c and the cylinder head 2
3 and a material having substantially the same coefficient of linear expansion.
Since the sealing points p, p on the cylinder block side of the bead portion 91a of the gasket 91 are brought into contact with only the mating surface 22f on the cylinder body portion 22a side without crossing over the sleeve 27, the sealing performance can be ensured and the gasket can be secured. Life can be ensured.

That is, the sleeve 27 is attached to the piston sliding surface 22.
a, it is often the case that the linear expansion coefficient is different from that of the cylinder body 22c. Therefore, in the hot operating state, the cylinder axial direction is set between the mating surfaces of the cylinder body 22c and the sleeve 27. Step may occur. If the seal points p, p of the bead portion 91 on the cylinder block side are assumed to be
When the contact is made over both of the above cases, a force in the shearing direction acts on the bead portion 91a of the gasket 91 due to the step, and there is a concern that the life of the bead portion 91a may be shortened or the sealing property may be reduced.

In the present embodiment, the cylinder inner peripheral portion 91d of the gasket 91 faces the cylinder head side end surface (the mating surface 27f) of the sleeve 27.
1d fills the space between the sleeve 27 and the cylinder head 23, so that the compression ratio can be increased accordingly, and unnecessary combustion is not generated in the surface shape of the combustion chamber, so that good combustion can be achieved.

Further, even when the cylinder inner peripheral side portion 91d of the gasket 91 faces the mating surface 27f of the sleeve 27, the bead portion 91a is connected to the mating surface 2c of the cylinder body 22c.
Since it is in contact with only 2f, there is no effect on the sealing performance, gasket and life. Furthermore, even when a so-called flower bloom is formed on the end face of the sleeve when the plating film is formed, there is no problem in the sealing performance.

[Brief description of the drawings]

FIG. 1 is a left side view of a motorcycle equipped with an engine according to an embodiment of the present invention.

FIG. 2 is a right side view of the engine.

FIG. 3 is a right side view showing a structure around a chain arrangement chamber of the engine.

FIG. 4 is a sectional rear view of the engine.

FIG. 5 is a sectional view showing a communication hole portion of the engine.

FIG. 6 is a bottom view of the cylinder block of the engine as viewed from a crankshaft side.

FIG. 7 is a sectional side view of a right end cylinder portion of the cylinder block.

FIG. 8 is a sectional side view of a second cylinder portion from the right end of the cylinder block.

FIG. 9 is a plan view of the cylinder block.

FIG. 10 is a plan view of a gasket between the cylinder block and the cylinder head.

FIG. 11 is an enlarged sectional view showing a seal structure between the cylinder block and a cylinder head.

FIG. 12 is an enlarged sectional view showing a lower end of a sleeve of the cylinder block.

FIG. 13 is a flowchart showing a manufacturing process of the cylinder block.

FIG. 14 is a flowchart showing details of a plating process in the manufacturing process.

FIG. 15 is a view showing a result of an experiment for forming a communication hole in the cylinder block.

FIG. 16 is a view showing a result of an experiment for forming a communication hole in the cylinder block.

FIG. 17 is a view showing a result of an experiment for forming a communication hole in the cylinder block.

FIG. 18 is a view showing a result of an experiment for forming a communication hole in the cylinder block.

FIG. 19 is a diagram showing a state after honing in an experiment for forming a communication hole in the cylinder block.

FIG. 20 is a schematic view showing an etching apparatus in the plating step.

FIG. 21 is a schematic view showing a high-speed plating apparatus in the plating step.

[Explanation of symbols]

15 Engine 22 Cylinder block 22a Piston sliding surface 22c Cylinder main body 22f Mating surface (cylinder head side end surface of cylinder main body) 23 Cylinder head 27 Sleeve 27d Retaining thin portion 27f Mating surface (sleeve cylinder head side end surface) 91 Gasket 91a Bead part 91d Cylinder inner peripheral part 91d Cylinder inner peripheral part a Plating film

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F16J 15/08 F16J 15/08 F // F16J 10/04 10/04

Claims (4)

[Claims] 1. A piston sliding surface is formed between an aluminum alloy cylinder head and a cylinder block in which a sleeve forming a piston sliding surface is disposed in an aluminum alloy cylinder main body. In an engine seal structure in which a gasket having a bead portion is interposed,
The cylinder body and the cylinder head are formed of a material having substantially the same coefficient of linear expansion, and the bead portion of the gasket is disposed so as to contact only the cylinder body without passing over the sleeve. Engine seal structure. 2. The cylinder according to claim 1, wherein the sleeve is cast in the cylinder main body, and has a thin portion for retaining at a cylinder head side end, the outer peripheral surface of which is stepped down. The main body portion has a thick portion covering the thin portion of the sleeve at an end portion on the cylinder head side, and a bead portion of the gasket is in contact with a mating surface of the thick portion on the cylinder head side. The engine seal structure. 3. The engine seal structure according to claim 1, wherein a portion of the gasket on the inner peripheral side of the bead portion of the gasket faces an end surface of the sleeve on the cylinder head side. 4. The engine sealing device according to claim 1, wherein the piston sliding surface of the sleeve is formed by forming a plating film on an inner peripheral surface of the sleeve. .