JPH0316503B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a cylinder structure for a liquid-cooled internal combustion engine.

Prior Art A typical prior art is shown in FIG.
At the top of the cylinder liner 2 is a cylinder head 3.
A combustion chamber 1 is formed above a piston 4 to which a piston 4 is fixed and guided by a cylinder liner 2. The cylinder liner 2 is supported by a cylinder jacket 5. A portion 2a surrounding the combustion chamber 1 at the upper part of the cylinder liner 2 is thick. A coolant passage 6 formed in the circumferential direction between the inner circumferential surface of the cylinder jacket 5 and the outer circumferential surface of the cylinder liner 2 connects a plurality of coolant passages 7 formed in the cylinder liner upper part 2a. Then, the coolant is led to a coolant passage 10 formed in the cylinder head 3 from a coolant passage 9 of a passage fitting 8 fitted over the cylinder liner upper part 2a.

5 shows the vicinity of the upper part 2a of the cylinder liner in the prior art of FIG. 4, FIG. 6 shows the outer peripheral surface of the upper part 2a of the cylinder liner developed in the circumferential direction, and FIG. 7 shows the upper part 2a of the cylinder liner. shows a cross section of A coolant passage 6 in the lower part of the cylinder liner is provided in the thick part of the upper part 2a of the cylinder liner.
A passage portion 7a that communicates with and extends across the axial direction of the cylinder liner 2, and a passage portion 7b that communicates with the coolant passage 9 of the passage hardware 8 and extends in the radial direction.
are formed, and these passage portions 7a and 7b constitute the above-mentioned coolant passage 7.

In this prior art, when the cylinder liner upper part 2a is sandwiched between the cylinder head 3 and the cylinder jacket 5 and firmly tightened with bolts or the like in order to keep the combustion chamber 1 airtight, the passage portions 7a, 7
There is a problem in that a large stress concentration phenomenon occurs at the intersection portion 11 of the cylinder liner, and the strength of the cylinder liner upper part 2a decreases. In addition, the passage portions 7a, 7b have a relatively small diameter, and therefore, during the tightening process, stress concentration tends to occur in these passage portions 7a, 7b, resulting in a decrease in strength.

In another prior art, as shown in FIG. 8, an annular coolant passage 12 that extends in the circumferential direction is formed on the outer periphery of the cylinder liner upper part 2a. This cylinder liner upper part 2a is surrounded by a passage metal fitting 13 and is held between the cylinder head 3 and the cylinder jacket 5.

In this prior art, since the coolant passage 12 is annular and the strength of the cylinder liner upper part 2a is small, a bolt is used between the cylinder head 3 and the cylinder jacket 5 to clamp the cylinder liner upper part 2a. Then, cylinder liner upper part 2a
may be deformed.

Problems to be Solved by the Invention An object of the present invention is to provide a cylinder structure for a liquid-cooled internal combustion engine in which the strength of the upper part of the cylinder liner is improved and there is no deformation.

Means for Solving the Problems The present invention provides (a) a cylinder liner 17, which includes: (a1) a cylinder liner cylindrical portion 17b, which is connected to the upper portion thereof and has an outer diameter larger than that of the cylinder liner cylindrical portion 17b; (a2) The cylinder liner upper part 17a has a plurality of flat notches 24 that are open radially outward and extend in the axial direction of the cylinder liner 17.
Upper end surface 17a1 of cylinder liner upper part 17a
(a3) These notches 24 are formed at a first interval l1 downward from the cylinder liner upper part 17a, at a interval l2 upward from the lower end surface 17a2 of the cylinder liner upper part 17a, and at approximately equal intervals in the circumferential direction. , (a3 1) extends in the radial direction of the cylinder liner 17,
An upper surface 24 having an upwardly convex arc shape in a plane substantially parallel to the axis 41 of the cylinder liner 17
c and (a3 2) from the radially inner end of this upper surface 24c,
a first connecting surface 24e that extends downward in a circular arc shape within a plane passing through the axis 41 of the cylinder liner 17; (a3 3) a first connecting surface 24e that extends downward from the first connecting surface 24e;
As it goes downwards, it becomes radially outward;
(a3 4) A first inner surface 24d having an arcuate shape convex radially inward in a plane perpendicular to the axis 41 of the cylinder liner 17; A second connecting surface 24 that extends in an arc shape so as to become radially outward toward the bottom within the one plane passing through the plane.
(a3 5) within the one plane passing from the second connecting surface 24g to the axis 41 of the cylinder liner 17,
It has a first lower surface 24f that is inclined radially outward toward the lower side and has a downwardly convex arc shape in the plane parallel to the axis 41 of the cylinder liner 17, and further has (a4 ) A passage 26 that opens to the second connecting surface 24g near the lower end of the second inner surface 24d and extends radially outward as it goes downward; (a5) a lower end surface 17a of the cylinder liner upper part 17a;
(a5 1) At the upper part of this annular groove 27, an annular groove 27 continues downward in an arc shape from the lower end surface 17a2 within the one plane passing through the axis 41 of the cylinder liner 17. , a third connecting surface 27a where the passage 26 is open; (a5 2) continuing downward from the third connecting surface 27a;
The annular groove 27 has a second inner surface 27b that is substantially parallel to the axis 41 of the cylinder liner 17, and (a5 3) a second lower surface 27c that extends radially outward from the lower end of the second inner surface 27b. (b) a reinforcing cylinder 18; (b1) a cylinder liner upper part 17a extending downward from its lower end surface 17a2 to surround the annular groove 27; Step 28 that comes into contact with end surface 17a2
and (b3) a coolant inflow hole 30 facing the lower part of the annular groove 27
(b4) A groove 33 facing the upper part of the notch 24 and continuous in the circumferential direction; (b5) A coolant discharge path continuous with the groove 33 and formed at intervals in the circumferential direction. 31, 32, 34,
35; (b6) a reinforcing ring 18 having a lower supporting surface 40 facing downward; (c) abutting against the lower supporting surface 40 of the reinforcing ring 18;
A cylinder block 2 that extends below the reinforcing ring 18 and surrounds the cylinder liner cylindrical portion 17b.
(d) Upper end surface 17a1 of cylinder liner upper part 17a
(e) cylinder block 20 and cylinder head 19;
This is a cylinder structure for a liquid-cooled internal combustion engine, characterized in that it includes a bolt 22 that tightens the two in a direction toward each other.

Effects According to the present invention, the following effects (a), (b), and (c) are realized. (a) Cylinder block 2 by bolt 22
0 and the cylinder head 19 in a direction close to each other, it is possible to suppress the occurrence of a stress concentration phenomenon in the state where the cylinder liner upper part 17a of the cylinder liner 17 is sandwiched, and to improve the strength, (b) It is possible to improve the strength of the cylinder liner upper part 17a against stress generated in the circumferential direction due to explosive force within the combustion chamber during operation of the internal combustion engine.
That is, according to the present invention, (a) when the cylinder liner upper part 17a of the cylinder liner 17 is clamped between the cylinder block 20 and the cylinder head 19 using the bolt 22, stress is concentrated on the cylinder liner upper part 17a. What happens is suppressed,
We will discuss how its strength is improved. A notch 24 is formed in the cylinder liner upper part 17a, and the upper surface 24c of this notch 24 has an upwardly convex arc shape within a substantially plane parallel to the axis 41 of the cylinder liner 17, and has a first connecting surface. The cylinder liner 17 extends downward from the upper surface 24c in a circular arc shape within a plane passing through the axis 41 of the cylinder liner 17.
The first inner surface 24d, which is an arcuate convex radially inward, is continuous in a plane perpendicular to the axis 41 of the cylinder liner 17, and the second connecting surface 24g passes through the axis 41 of the cylinder liner 17 from the first connecting surface 24d. The first lower surface 24f, which extends in an arc shape in a plane and continues to the second connecting surface 24g, has a downwardly convex arc shape in the plane parallel to the axis 41 of the cylinder liner 17, so that the bolt 22 When the cylinder block 24 and the cylinder head 19 are tightened in the direction of mutual proximity using a compressive force applied to the cylinder liner upper part 17a of the cylinder liner 17, a stress concentration phenomenon occurs near the notch 24. can be suppressed, and thereby the strength can be improved.

Furthermore, according to the present invention, (b) during operation of the internal combustion engine, the cylinder liner upper part 1 of the cylinder liner 17
The strength against the explosive forces generated within the combustion chamber formed by 7 is also improved. The reason for this is that due to the explosive force within the combustion chamber, stress mainly acts on the inner circumferential surface of the cylinder liner 17 in the circumferential direction. In the present invention, the cylinder liner upper part 17
The notch 24 formed in the cylinder liner upper part 17a is spaced downwardly from the upper end surface 17a1 of the cylinder liner upper part 17a by a first distance l1, and the notch 24 is also formed in the lower end surface 17a2 of the cylinder liner upper part 17a.
Therefore, in the part of the cylinder liner upper part 17a where these intervals l1 and l2 exist, the stress in the circumferential direction generated during the explosion stroke of the internal combustion engine can be reduced, and the Cylinder liner upper part 17 against explosive force
The strength of a can be improved.

In this way, in the present invention, it is possible to improve the strength against the tightening force of the bolt 22 and against the explosive force during operation of the internal combustion engine.

Furthermore, according to the present invention, (c) the cooling effect can be improved. The reason for this is that in order to achieve sufficient cooling in the present invention, it is necessary to increase the surface area of the notch 24 for contact with the cooling fluid, and for this reason, the notch 24 is located in the cylinder liner 17.
A plurality of cutouts 24 are formed at approximately equal intervals in the circumferential direction. In order to increase the contact area of the notch 24 with the coolant, the upper part 1 of the cylinder liner is
The outer diameter of 7a is made larger than that of the cylinder liner cylindrical portion 17b, and this notch 24
It is configured to extend in a radial direction. In this way, the notch 24 can sufficiently cool the cylinder liner upper part 17a.
By increasing the outer diameter and wall thickness, it is possible to further improve the strength against the tightening force of the bolt 22 and against the explosive force.

In the present invention, since a plurality of flat notches 24 are formed in the cylinder liner upper part 17a at approximately equal intervals in the circumferential direction, the portion of the cylinder liner 17 between the notches 24 is so-called a fin. In this state, the cooling liquid supplied to the notch 24 efficiently cools the housing.

Next, other effects of the present invention will be supplementarily described.

According to the present invention, the coolant flows from the coolant inflow hole 30 formed in the reinforcing link 18 to the annular groove 27 formed in the inner circumferential surface of the reinforcing ring 18 and the cylinder liner cylindrical portion 17b, and further flows into the cylinder liner cylindrical portion 17b. Coolant flows from the passage 26 in the upper part 17a to the flat notches 24, and this coolant flows through each of the plurality of notches 24.
The coolant flows through the grooves 33 formed continuously in the circumferential direction, and further flows through the coolant discharge paths 31, 32, 34, 35.
It is then discharged. In this way, the cylinder liner 17 is cooled by the cooling fluid.

Further, according to the present invention, the support portion 20 and the cylinder head 19 are tightened in the direction toward each other by the bolt 22, and thereby the cylinder head 19
and the upper end surface 17a1 of the cylinder liner upper part 17a.
and the lower end surface 17 of this cylinder liner upper part 17a.
a2, the step 28 of the reinforcing link 18, the lower support surface 40 of the reinforcing ring 18, and the cylinder block 20.
are in contact and fixed. This makes the bolt 22 relatively long. Therefore, the load sharing ratio at the time of explosion in the combustion chamber inside the cylinder liner 17 becomes small, and therefore the bolt 22
fatigue of the bolt 22 can be prevented as much as possible, and the safety factor of the bolt 22 can be increased.
Furthermore, the cylinder liner upper part 17a and the reinforcing ring 18 are held between the cylinder head 19 and the cylinder block 20 by the bolts 22.
The elasticity of a and the reinforcing ring 18 also reduces the load sharing of the bolt 22.

Embodiment FIG. 1 shows a longitudinal section of an embodiment of the present invention. FIG. 2 shows a cross section taken along the cutting line - in FIG. 1, and the upper half shows the cylinder head 19.
The lower half shows the cylinder liner upper part 17a. Cylinder liner upper part 17 of liquid-cooled internal combustion engine
The cylinder liner upper part 17a and the cylinder liner cylindrical part 17b connected to the cylinder liner upper part 17a are surrounded by a reinforcing ring 18 that is commonly fitted on the outside. There is. A cylinder head 19 is arranged above the cylinder liner upper part 17a, and a reinforcing ring 1
8, surrounding the cylinder liner 17,
A cylinder block 20 is arranged. An annular gasket 21 is interposed between the upper end surface 17a1 of the cylinder block upper part 17a of the cylinder liner 17 and the cylinder head 19, and a bolt 22 is inserted between the cylinder head 19 and the reinforcing ring 18.
The threaded portion 23 of this bolt 22 is screwed into the cylinder block 20. In this way, the cylinder liner 17, reinforcing ring 18, cylinder head 19, and cylinder block 20 are integrally fixed.

FIG. 3 shows a partial perspective view of the vicinity of the upper part 17a of the cylinder liner according to the embodiment of the present invention. A relatively deep and narrow notch 2 is formed on the outer periphery of the cylinder liner upper part 17a by milling or the like.
4 are arranged in large numbers at approximately equal intervals. The shape of the notch 24 is open to the outside in the radial direction of the cylinder liner 17 and extends in parallel to the axial direction of the cylinder liner 17. Cylinder liner upper part 17a
The lower end surface 1 opposite to the cylinder head 19 of
Facing 7a2, a coolant passage 26 connected to the notch 24 is formed by drilling or the like.

An annular groove 27 having a smaller diameter is formed in the cylinder liner cylindrical portion 17b connected to the cylinder liner upper part 17a, and the above-mentioned coolant passage 26 is open to the annular groove 27. The reinforcing ring 18 has a step 28 that comes into contact with the lower end surface 17a2 of the cylinder liner upper part 17a. This reinforcing ring 18 is
The reinforcing ring 18 has a cooling fluid passage 29 together with the annular groove 27, and at least one cooling fluid inflow hole 30 communicating with the cooling fluid passage 29 is formed in the circumferential direction of the reinforcing ring 18.

Coolant passages 31 are also formed in the upper part of the reinforcing ring 18 and extend in the axial direction at intervals in the circumferential direction. The lower end of this coolant passage 31, that is, the lower end in FIG. 1, is connected to a notch 32 that widens in the circumferential direction as it goes radially inward. This notch 32 is connected to a groove 33 that is continuously formed in the circumferential direction of the inner circumferential surface of the reinforcing ring 18 . The groove 33 commonly communicates with the end of the notch 24 in the cylinder liner upper part 17a closer to the cylinder head 19. Further, the upper end portion of the cooling liquid passage 31 formed in the reinforcing ring 18, that is, the first
The upper end in the figure is connected to a notch 34 that widens in the circumferential direction as it goes radially inward. This notch 34 is connected to a concave groove 34 that is continuous in the circumferential direction.
The groove 35 communicates with a coolant passage 36 formed in the cylinder head 19. A fuel injection valve 37 is attached to the cylinder head 19.

By tightening the cylinder head 19 and the support part 20 in the direction toward each other with the bolts 22, the cylinder block 20 is tightened by the reinforcing ring 18.
The step 28 of the reinforcing ring 18 is in contact with the support surface 40 in FIG.
a, and the upper end surface 17 of this cylinder liner upper part 17a in FIG.
a1 is connected to the cylinder head 1 via the gasket 21.
Contact with 9. In this way, cylinder liner 1
7, reinforcing ring 18, and cylinder head 19
and the cylinder block 20 are integrally fixed as described above.

The coolant is guided from the inflow hole 30 to the coolant passage 29 . The coolant from the coolant passage 29 flows through the coolant passage 26 formed in the cylinder liner upper part 17a.
It flows from the notch 24 into the notch 24, rises while removing heat, and then flows from the notch 33 through the notch 32 and the coolant passage 31, and then from the notch 34 to the notch 35.
The coolant is then guided to the coolant passage 36 of the cylinder head 19. Cooling by the coolant is thus achieved.

In the notch 24 formed in the upper part 17a of the cylinder liner, in order to prevent stress concentration from occurring when the bolt 22 is tightened, the cylinder head 1 is inserted between the side walls 24a and 24b of the notch 24.
The connecting surface 24e that extends from the upper surface 24c near the axis 9 to the inner surface 24d near the axis, the connecting surface 24g that extends from the lower surface 24f near the lower end surface 17a2, and the like are formed in an arc shape as described later. Therefore bolt 2
During tightening according to No. 2, the occurrence of stress concentration phenomenon is suppressed.

The notches 24 are elongated and narrow in the axial direction, and are arranged in large numbers at approximately equal intervals around the outer periphery of the cylinder liner upper part 17a. Therefore, the cross-sectional area of the cylinder liner upper part 17a is not reduced much, and its rigidity is not significantly reduced. In addition, a reinforcing ring 1 is used to reinforce this rigidity.
8 is used. The inner circumferential surface of this reinforcing ring 18 is dimensioned to be in contact with the outer circumferential surface of the cylinder liner upper part 17a, and to have a certain interference in the radial direction of the cylinder liner 17 under the temperature conditions during operation of the internal combustion engine. . Therefore, a precompression force is applied to the cylinder liner upper part 17a. Therefore, the cylinder liner upper part 17a has a structure that can withstand large tensile stress in the circumferential direction.

To further describe the configuration of the above-mentioned embodiment, the cylinder liner upper part 17a is
The cylinder liner cylindrical portion 17 is connected to the upper part of b.
The outer diameter is larger than that of b. Notch 24
are formed on the cylinder liner upper part 17a at approximately equal intervals in the circumferential direction, are flat, open radially outward, and extend in the axial direction of the cylinder liner 17. This notch 24 is
As shown in FIG.
The cylinder liner upper part 17a is formed at a first interval 11 downward from the upper end surface 17a1, and at a distance 12 upward from the lower end surface 17a2 of the cylinder liner upper part 17a. The upper surface 24c of the notch 24 extends in the radial direction of the axis of the cylinder liner 17. This upper surface 24c
has an upwardly convex arc shape in a plane substantially parallel to the axis 41 of the cylinder liner 17. Connecting surface 24e
is downward within a plane passing through the axis 41 of the cylinder liner 17 from the radially inner end of the upper surface 24c,
Connected in an arc shape. The inner surface 24d continues downward from the connecting surface 24e, and becomes radially outward as it goes downward. The inner surface 24d has a circular arc shape that is convex radially inward within a plane perpendicular to the axis 41 of the cylinder liner 17. The connecting surface 24g is the inner surface 24d.
In a plane passing through the axis 41 of the cylinder liner 17 from the lower end of the cylinder liner 17, the cylinder liner 17 continues in an arc shape so as to move downwardly and outwardly in the radial direction. The lower surface 24f is inclined radially outward as it goes downward within the plane passing from the connecting surface 24g to the axis 41 of the cylinder liner 17, and is parallel to the axis 41 of the cylinder liner 17. It has a downward convex arc shape.

Passage 2 formed in the cylinder liner upper part 17a
6 is the second connecting surface 24 near the lower end of the inner surface 24d.
g, and extends radially outward toward the bottom.

The annular groove 27 is formed in a continuous manner downward from the lower end surface 17a2 of the cylinder liner upper part 17a. This annular groove 27 has a connecting surface 27a and an inner surface 27.
b and a lower surface 27c. The connecting surface 27a is an upper portion of the annular groove 27, and extends downward in the plane from the lower end surface 17a2 in an arc shape, and the passage 26 is open. The inner surface 27b continues downward from the connecting surface 27a and is formed substantially parallel to the axis 41 of the cylinder liner 17. The lower surface 27c extends radially outward from the lower end of the inner surface 27b.

The reinforcing ring 18 is attached to the cylinder liner upper part 17a.
and the lower end surface 17 of the cylinder liner upper part 17a.
It extends below a2 and surrounds the annular groove 27. This reinforcing ring 18 has the lower end surface 17a2
It has a step 28 that comes into contact with. Furthermore, the annular groove 2
An inflow hole 30 is formed facing the lower part of 7. Further, a groove 33 is formed continuously in the circumferential direction facing the upper part of the notch 34 . The coolant discharge path, which is continuous with the groove 33 and is formed at intervals in the circumferential direction, includes a coolant passage 31, a notch 32, a notch 34,
It is formed by the groove 35. Lower support surface 40
is formed facing downward from the reinforcing ring 18.

The cylinder block 20 contacts the lower support surface 40 of the reinforcing ring 18, extends below the reinforcing ring 18, and surrounds the cylinder liner cylindrical portion 17b. An annular gasket 21 is provided on the upper part of the cylinder liner upper part 17a. Cylinder head 19
is placed on the gasket 21. bolt 22
The cylinder block 20 and cylinder head 19 are
and tighten in the direction of mutual proximity.

Effects of the Invention As described above, according to the present invention, the following effects are achieved.

(a) In the present invention, stress concentration phenomenon in the notch 24 is suppressed when the cylinder liner upper part 17a is clamped and tightened between the cylinder block 20 and the cylinder head 19 using the bolt 22. As a result, the strength can be improved.

(b) Furthermore, according to the present invention, even if circumferential stress is applied to the cylinder liner upper part 17a due to explosive force during the explosion stroke during operation of the internal combustion engine, the upper and lower parts of the notch 24 are Interval l1,l
2 exists respectively, and the strength against the explosive force can be improved.

(c) Furthermore, according to the present invention, the notches 24 are flat and are formed in plurality, so that the spaces between the notches 24 in the upper part 17a of the cylinder liner function as fins and improve the heat dissipation effect. The cooling effect is great.

(d) As described above, a plurality of flat notches 24 are formed in the cylinder liner upper part 17a, and in order to increase the surface area of the notches 24 that comes into contact with the coolant, the outer diameter of the cylinder liner upper part 1a is Since it is made to be large, it becomes possible to further improve the strength. Therefore, the outer diameter of the cylinder liner upper part 17a is made larger than that of the cylinder liner cylindrical part 17b, and a flat notch 24 is formed in the cylinder liner upper part 17a, which has a large diameter.
By forming the grooves at approximately equal intervals in the circumferential direction, a decrease in strength due to the notches 24 is suppressed,
Moreover, it becomes possible to achieve a sufficient cooling effect.

(e) Since the bolts 22 are relatively long, the load sharing ratio of the bolts can be reduced and fatigue can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of one embodiment of the present invention, FIG. 2 is a cross-sectional view taken along the cutting line in FIG. 1, FIG. 3 is a perspective view of the vicinity of the upper part 17a of the cylinder liner, and FIG. A vertical sectional view of the technology, FIG. 5 is a perspective view of the vicinity of the upper part 2a of the cylinder liner of the prior art in FIG. 4, and FIG.
The figure is a developed view in the circumferential direction of the cylinder liner upper part 2a of the prior art, FIG. 7 is a plan view of the cylinder liner upper part 2a of the prior art, and FIG. 8 is a longitudinal sectional view of another prior art. 17...Cylinder liner, 17a...Cylinder liner upper part, 18...Reinforcement ring, 19...Cylinder head, 20...Cylinder block, 24...
...Notch.

Claims (1)

[Scope of Claims] 1 (a) A cylinder liner 17, which includes (a1) a cylinder liner cylindrical portion 17b, and a cylinder liner that is connected to the upper part of the cylinder liner cylindrical portion 17b and has an outer diameter larger than that of the cylinder liner cylindrical portion 17b. (a2) The cylinder liner upper part 17a has a plurality of flat notches 24 that are open radially outward and extend in the axial direction of the cylinder liner 17.
Upper end surface 17a1 of cylinder liner upper part 17a
(a3) These notches 24 are formed at a first interval l1 downward from the cylinder liner upper part 17a, at a interval l2 upward from the lower end surface 17a2 of the cylinder liner upper part 17a, and at approximately equal intervals in the circumferential direction. , (a3 1) extends in the radial direction of the cylinder liner 17,
An upper surface 24 having an upwardly convex arc shape in a plane substantially parallel to the axis 41 of the cylinder liner 17
c and (a3 2) from the radially inner end of this upper surface 24c,
a first connecting surface 24e that extends downward in a circular arc shape within a plane passing through the axis 41 of the cylinder liner 17; (a3 3) a first connecting surface 24e that extends downward from the first connecting surface 24e;
As it goes downwards, it becomes radially outward;
(a3 4) A first inner surface 24d having an arcuate shape convex radially inward in a plane perpendicular to the axis 41 of the cylinder liner 17; A second connecting surface 24 that extends in an arc shape so as to become radially outward toward the bottom within the one plane passing through the plane.
(a3 5) within the one plane passing from the second connecting surface 24g to the axis 41 of the cylinder liner 17,
It has a first lower surface 24f that is inclined radially outward toward the lower side and has a downwardly convex arc shape in the plane parallel to the axis 41 of the cylinder liner 17, and further has (a4 ) A passage 26 that opens to the second connecting surface 24g near the lower end of the second inner surface 24d and extends radially outward as it goes downward; (a5) a lower end surface 17a of the cylinder liner upper part 17a;
(a5 1) At the upper part of this annular groove 27, an annular groove 27 continues downward in an arc shape from the lower end surface 17a2 within the one plane passing through the axis 41 of the cylinder liner 17. , a third connecting surface 27a where the passage 26 is open; (a5 2) continuing downward from the third connecting surface 27a;
The annular groove 27 has a second inner surface 27b that is substantially parallel to the axis 41 of the cylinder liner 17, and (a5 3) a second lower surface 27c that extends radially outward from the lower end of the second inner surface 27b. (b) a reinforcing cylinder 18; (b1) a cylinder liner upper part 17a extending downward from its lower end surface 17a2 to surround the annular groove 27; Step 28 that comes into contact with end surface 17a2
and (b3) a coolant inflow hole 30 facing the lower part of the annular groove 27
(b4) A groove 33 facing the upper part of the notch 24 and continuous in the circumferential direction; (b5) A coolant discharge path continuous with the groove 33 and formed at intervals in the circumferential direction. 31, 32, 34,
35; (b6) a reinforcing ring 18 having a lower supporting surface 40 facing downward; (c) abutting against the lower supporting surface 40 of the reinforcing ring 18;
A cylinder block 2 that extends below the reinforcing ring 18 and surrounds the cylinder liner cylindrical portion 17b.
(d) Upper end surface 17a1 of cylinder liner upper part 17a
(e) cylinder block 20 and cylinder head 19;
A cylinder structure for a liquid-cooled internal combustion engine, characterized in that the cylinder structure includes a bolt 22 which is tightened in a direction toward each other.