Marine engine scavenging chamber structure

Abstract

To improve scavenging efficiency while restraining the manufacturing cost.SOLUTION: A scavenging chamber 100 of an engine 1 includes a cylinder jacket 13, and a cylindrical cylinder liner 14 inserted into the cylinder jacket 13, and sucks air from the cylinder jacket 13 into the cylinder liner 14 by reciprocating a piston 21 along the cylinder liner 14. The cylinder liner 14 includes scavenging ports 14a which are arranged along a circumferential direction of the cylinder liner 14. An inner wall 13e of the cylinder jacket 13 forms a circular shape coaxial with the cylinder liner 14 when viewed from a cross section orthogonal to a direction of a center axis C of the cylinder liner 14 and passing through the scavenging port 14a.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present disclosure relates to a scavenging chamber structure for a marine engine. [Background technology]

[0002] For example, Patent Document 1 discloses a cylinder jacket having a spiral-shaped inner wall. Specifically, the inner wall of the cylinder jacket according to Patent Document 1 forms an involute curve when viewed in cross section. That is, this inner wall is not a circular curve with a constant distance from the center (particularly the center of the cylinder liner), but is formed to draw a curve that gradually increases in distance.

[0003] Furthermore, the cylinder jacket according to Patent Document 1 has an inlet that is inclined along the spiral shape of the inner wall. According to Patent Document 1, when air flows in from the inlet of the cylinder jacket, a swirl is formed by the inlet, and the swirl thus formed is guided along the spiral inner wall, thereby making it possible to uniform the amount of air flowing into each scavenging port of the cylinder liner.

[0004] Also, another example of a cylinder jacket is disclosed in Patent Document 2. Specifically, the internal space (scavenging chamber) of the cylinder jacket according to Patent Document 2 is formed in a rectangular shape when viewed in a cross section perpendicular to the central axis direction of the cylinder liner and passing through the scavenging port.

[0005] Furthermore, a guide plate for controlling the direction of the scavenging flow is provided at the scavenging air inlet of the scavenging chamber according to Patent Document 2. According to this document, by providing a guide plate at the scavenging air inlet, the distribution of the scavenging air in the circumferential direction of the cylinder liner in the scavenging chamber can be made uniform. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 62-174534 [Patent Document 2] Japanese Patent Application Publication No. 6-221220 Summary of the Invention [Problem to be solved by the invention]

[0007] However, when an internal space having a rectangular cross section is used as in the cylinder jacket of Patent Document 2, the scavenging flow may become non-uniform at the corners of the internal space, which may adversely affect the scavenging efficiency. For this reason, it is possible to provide a guide plate at the scavenging intake as disclosed in the same document. However, providing a guide plate increases the number of parts, which is undesirable in terms of manufacturing costs.

[0008] Therefore, it is conceivable to form the inner wall of the cylinder jacket into a spiral shape and to form an inlet that is inclined along the spiral shape, as disclosed in the above-mentioned Patent Document 1. However, the configuration disclosed in the above-mentioned Patent Document 1 is also undesirable in terms of manufacturing costs, since it requires highly accurate curved surface processing of the inner wall and the inlet of the cylinder jacket.

[0009] In addition, the configuration disclosed in Patent Document 1 is based on the premise that scavenging air flows in from the inlet of the cylinder jacket. Therefore, there is a problem that the shape and arrangement of the inlet are limited. This is inconvenient for use in a wide variety of engines.

[0010] The present disclosure has been made in consideration of the above points, and an object of the present disclosure is to improve scavenging efficiency while suppressing manufacturing costs. [Means for solving the problem]

[0011] A first aspect of the present disclosure relates to a scavenging chamber structure for a marine engine, comprising: a cylinder jacket connected to a scavenging trunk; and a cylindrical cylinder liner inserted into the cylinder jacket, wherein air is sucked out from the cylinder jacket into the cylinder liner as a piston reciprocates along the cylinder liner.

[0012] According to a first aspect of the present disclosure, the cylinder liner is provided with scavenging ports arranged along the circumferential direction of the cylinder liner, and the inner wall portion of the cylinder jacket has a circular shape coaxial with the cylinder liner when viewed in a cross section perpendicular to the central axial direction of the cylinder liner and passing through the scavenging ports.

[0013] According to the first aspect, the inner wall of the cylinder jacket has a circular shape coaxial with the cylinder liner when viewed in a predetermined cross section. With this configuration, the air flowing from the scavenging trunk into the cylinder jacket flows along the circular inner wall. This allows a uniform scavenging flow flowing along the circumferential direction to be realized in the cylinder jacket. This makes it possible to make the scavenging flow uniform, and thus improve the scavenging efficiency. Furthermore, by configuring the inner wall and the cylinder liner coaxially, the distance between the inner wall of the cylinder jacket and the outer wall of the cylinder liner can be kept approximately constant. This also contributes to making the scavenging flow uniform.

[0014] Furthermore, the first aspect does not require a separate part such as a guide plate or any special design for the shape of the inlet of the cylinder jacket, which contributes to reducing manufacturing costs.

[0015] In this way, according to the first aspect, it is possible to improve the scavenging efficiency while suppressing the manufacturing cost.

[0016] According to a second aspect of the present disclosure, the inner wall portion of the cylinder jacket may be formed into a conical shape whose diameter increases downward.

[0017] According to the second aspect, the volume in the vicinity of the cross section can be increased, which can increase the fluidity of the scavenging flow, and is further advantageous in improving the scavenging efficiency.

[0018] According to a third aspect of the present disclosure, a portion of an outer wall portion of the cylinder liner that is located above the scavenging ports may be defined as a first portion, and a portion that is located below the scavenging ports may be defined as a second portion. At least a part of the second portion may be formed to have a smaller diameter than the first portion.

[0019] According to the third aspect, the inner wall of the cylinder jacket is expanded downward and at least a part of the second portion is formed to have a relatively small diameter, which increases the space between the inner wall of the cylinder jacket and the outer wall of the cylinder liner as much as possible, thereby increasing the fluidity of the scavenging flow and further improving the scavenging efficiency.

[0020] According to a fourth aspect of the present disclosure, when viewed in a cross section perpendicular to the central axis direction of the cylinder liner and passing through the scavenging port, the cross-sectional area of ​​the cylinder jacket is A1 and the cross-sectional area of ​​the cylinder liner is A2, A1-A2≧A2 The following relationship may be satisfied.

[0021] According to the fourth aspect, the volume between the inner wall of the cylinder jacket and the outer wall of the cylinder liner can be increased, and the fluidity of the scavenging flow can be increased, which is more advantageous in improving the scavenging efficiency.

[0022] According to a fifth aspect of the present disclosure, the scavenging port may extend along the up-down direction, and the relationship may be satisfied both when viewed in a cross section perpendicular to the central axial direction of the cylinder liner and passing through an upper end of the scavenging port, and when viewed in a cross section perpendicular to the central axial direction of the cylinder liner and passing through a lower end of the scavenging port.

[0023] According to the fifth aspect, the volume between the inner wall of the cylinder jacket and the outer wall of the cylinder liner can be maximized, and the fluidity of the scavenging flow can be increased, which is more advantageous in improving the scavenging efficiency. Effect of the Invention

[0024] As described above, according to the present disclosure, it is possible to improve scavenging efficiency while suppressing manufacturing costs. [Brief description of the drawings]

[0025] [Figure 1] FIG. 1 is a schematic diagram illustrating the configuration of a marine engine. [Diagram 2] FIG. 2 is a perspective view illustrating a scavenging chamber structure of a marine engine. [Diagram 3] FIG. 3 is a vertical sectional view illustrating a scavenging chamber structure of a marine engine. [Figure 4] FIG. 4 is a cross-sectional view illustrating an example of a scavenging chamber structure of a marine engine. [Diagram 5] FIG. 5 is a view corresponding to FIG. 4 and showing a conventional example of a scavenging chamber structure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. Note that the following description is an example. Fig. 1 is a schematic diagram illustrating the configuration of a marine engine (hereinafter, simply referred to as "engine 1").

[0027] The engine 1 is an in-line multi-cylinder diesel engine equipped with multiple cylinders 16. The engine 1 is configured as a uniflow scavenging two-stroke one-cycle engine, and is installed on large ships such as tankers, container ships, and car carriers.

[0028] The engine 1 installed on a ship is used as a main engine for propelling the ship. To this end, the output shaft of the engine 1 is connected to a propeller (not shown) of the ship via a propeller shaft (not shown). When the engine 1 is operated, its output is transmitted to the propeller, propelling the ship.

[0029] In particular, the engine 1 according to the present disclosure is configured as a so-called crosshead type internal combustion engine in order to realize a long stroke. That is, in this engine 1, a piston rod 22 that supports a piston 21 from below and a connecting rod 24 that is connected to a crankshaft 23 are connected by a crosshead 25.

[0030] (1)Main configuration The main parts of the engine 1 will be described below.

[0031] As shown in Fig. 1, the engine 1 includes a base plate 11 located below, a frame 12 provided on the base plate 11, and a cylinder jacket 13 provided on the frame 12. The base plate 11, the frame 12, and the cylinder jacket 13 are fastened together by a plurality of tie bolts and nuts extending in the vertical direction. The engine 1 also includes a cylinder 16 provided in the cylinder jacket 13, a piston 21 provided in the cylinder 16, and an output shaft (e.g., a crankshaft 23) that rotates in conjunction with the reciprocating movement of the piston 21.

[0032] The base plate 11 constitutes the crankcase of the engine 1, and houses a crankshaft 23 and a bearing 26 that rotatably supports the crankshaft 23. The lower end of a connecting rod 24 is connected to the crankshaft 23 via a crank 27.

[0033] The frame 12 houses a pair of guide plates 28, the connecting rod 24, and a crosshead 25. Of these, the pair of guide plates 28 are made of a pair of plate-shaped members provided along the piston axial direction, and are arranged at an interval in the width direction of the engine 1 (the left-right direction on the paper surface of FIG. 1). The connecting rod 24 is arranged between the pair of guide plates 28 with its lower end connected to the crankshaft 23. The upper end of the connecting rod 24 is connected to the lower end of the piston rod 22 via the crosshead 25.

[0034] Specifically, the crosshead 25 is disposed between a pair of guide plates 28, and slides up and down along each of the guide plates 28. That is, the pair of guide plates 28 are configured to guide the sliding of the crosshead 25. The crosshead 25 is connected to the piston rod 22 and the connecting rod 24 via a crosshead pin 29. The crosshead pin 29 is connected to the piston rod 22 so as to move up and down integrally therewith, and is connected to the connecting rod 24 so as to rotate the connecting rod 24 about the upper end of the connecting rod 24 as a fulcrum.

[0035] The cylinder jacket 13 supports a cylinder liner 14 as an inner cylinder. The cylinder liner 14 is formed in a cylindrical shape and is inserted into the cylinder jacket 13. The internal space S1 of the cylinder jacket 13 communicates with the internal space S2 of the cylinder liner 14 (see Figures 3 and 4). The above-mentioned piston 21 is disposed inside the cylinder liner 14. This piston 21 reciprocates up and down along the inner wall of the cylinder liner 14. In addition, a cylinder cover 15 is fixed to the upper part of the cylinder liner 14. The cylinder cover 15, together with the cylinder liner 14, constitutes the cylinder 16.

[0036] In addition, the cylinder cover 15 is provided with an exhaust valve 18 that is operated by a valve train (not shown). The exhaust valve 18, together with a cylinder 16 formed by the cylinder liner 14 and the cylinder cover 15, and the top surface of a piston 21, defines a combustion chamber 17. The exhaust valve 18 opens and closes between the combustion chamber 17 and an exhaust pipe 19. The exhaust pipe 19 has an exhaust port that communicates with the combustion chamber 17, and the exhaust valve 18 is configured to open and close the exhaust port.

[0037] Further, the cylinder cover 15 is provided with a fuel injection valve 31 for supplying fuel to the combustion chamber 17. The fuel injection valve 31 injects diesel fuel into the combustion chamber 17.

[0038] Furthermore, the engine 1 according to this embodiment is provided with a fuel pump 32 that pressure-feeds diesel fuel to the fuel injection valve 31. As shown in Fig. 1, the fuel pump 32 is laid out in the vicinity of the cylinder 16, and is fluidly connected to the fuel injection valve 31 via a fuel injection pipe (not shown).

[0039] An exhaust manifold 41 is also disposed near the cylinder 16. This exhaust manifold 41 is connected to the combustion chamber 17 via the exhaust pipe 19. The exhaust manifold 41 receives exhaust gas from the combustion chamber 17 through the exhaust pipe 19, temporarily stores the received exhaust gas, and converts the dynamic pressure of the exhaust gas into static pressure.

[0040] The engine 1 further includes a turbocharger 42 that supercharges a combustion gas such as air, and a scavenging trunk 43 that temporarily stores the combustion gas compressed by the turbocharger 42. The turbocharger 42 rotates a compressor (not shown) together with a turbine (not shown) by utilizing the pressure of the exhaust gas, and the combustion gas is compressed by the compressor. The scavenging trunk 43 is provided so as to communicate with the internal space S1 of the cylinder jacket 13. The combustion gas compressed by the turbocharger 42 (hereinafter also referred to as "compressed gas") flows from the scavenging trunk 43 into the internal space S1 of the cylinder jacket 13, and is fed from this internal space S1 to the internal space S2 of the cylinder liner 14 through the scavenging port 14a.

[0041] When the engine 1 is in operation, diesel fuel is supplied into the combustion chamber 17 from the fuel injection valve 31, and compressed gas is supplied from the scavenging trunk 43 through the cylinder jacket 13, etc. As a result, in the combustion chamber 17, the diesel fuel is combusted by the compressed gas.

[0042] The energy generated by the combustion of diesel fuel causes the piston 21 to reciprocate up and down along the cylinder liner 14. At this time, when the exhaust valve 18 operates to open the combustion chamber 17, exhaust gas generated by the combustion is pushed out into the exhaust pipe 19. In addition, as the piston 21 reciprocates along the cylinder liner 14, compressed gas (air) is sucked out from the cylinder jacket 13 into the cylinder liner 14, and the piston 21 pushes this in, introducing new compressed gas into the combustion chamber 17. By repeating these processes, the combustion of diesel fuel and scavenging of the cylinder 16 are repeatedly performed.

[0043] Furthermore, when the piston 21 reciprocates due to combustion, the piston rod 22 reciprocates up and down together with the piston 21. This causes the crosshead 25 connected to the piston rod 22 to reciprocate up and down. This crosshead 25 allows the connecting rod 24 to rotate, and rotates the connecting rod 24 around the connection point with the crosshead 25 as a fulcrum. Then, the crank 27 connected to the lower end of the connecting rod 24 performs crank motion, and the crankshaft 23 rotates in response to this crank motion. In this way, the crankshaft 23 converts the reciprocating movement of the piston 21 into rotational motion, and rotates the propeller of the ship together with the propeller shaft. This propels the ship.

[0044] Incidentally, the scavenging efficiency in the cylinder 16 depends on the state of the air flow (hereinafter also referred to as the "scavenging flow") that flows from the scavenging trunk 43 through the cylinder jacket 13 into the cylinder liner 14.

[0045] The inventors of the present application have improved the scavenging efficiency by devising a structure of the scavenging chamber 100 constituted by the cylinder jacket 13 and the cylinder liner 14.

[0046] The structure of each part related to the scavenging chamber 100 will be described in detail below.

[0047] (2) Engine scavenging chamber structure Fig. 2 is a perspective view illustrating the scavenging chamber structure of the engine 1. Fig. 3 is a vertical cross-sectional view illustrating the scavenging chamber structure of the engine 1, and Fig. 4 is a horizontal cross-sectional view thereof. As described above, the scavenging chamber 100 of the engine 1 is composed of the cylinder jacket 13 connected to the scavenging trunk 43 and the cylindrical cylinder liner 14 inserted into the cylinder jacket 13.

[0048] The cylinder jacket 13 functions as an outer garment that covers the lower part of the cylinder liner 14. Specifically, the cylinder jacket 13 is configured as a substantially rectangular box, as shown in Figs. 2 and 3 .

[0049] As shown in Figures 2 and 3, the cylinder jacket 13 has a first opening 13a opening to one side of the box body, a second opening 13b opening to the side opposite the first opening 13a, a third opening 13c opening to the bottom surface of the box body, a fourth opening 13d opening to the top surface of the box body, and an inner wall portion 13e that defines an internal space S1.

[0050] Of these, the first opening 13a and the second opening 13b are each formed in an elliptical shape extending in the vertical direction. As shown in FIG. 3, the dimension of the first opening 13a in the vertical direction is longer than the dimension of the second opening 13b in the same direction. Of the first opening 13a and the second opening 13b, the first opening 13a is connected to the scavenging trunk 43 (not shown). This connection allows the scavenging trunk 43 to communicate with the internal space S1 of the cylinder jacket 13. The second opening 13b is closed by a lid or the like (not shown).

[0051] As shown in Fig. 3, the third opening 13c is configured so that the piston rod 22 can be inserted therein. The piston rod 22 is supported by a bearing (not shown) disposed near the third opening 13c so as to be movable up and down.

[0052] 3, the fourth opening 13d is configured so that the lower part of the cylinder liner 14 (specifically, the part located below the supported part 14c) can be inserted into the fourth opening 13d. The peripheral part of the fourth opening 13d supports the supported part 14c of the cylinder liner 14 from below.

[0053] As shown in Fig. 3, the inner wall portion 13e communicates with the outside through the first opening 13a, the second opening 13b, the third opening 13c, and the fourth opening 13d. The inner wall portion 13e is adapted to surround and cover the lower portion of the cylinder liner 14. As shown in Fig. 3, the inner wall portion 13e according to this embodiment is tapered upward. That is, the cross section of the inner wall portion 13e in the vicinity of the fourth opening 13d is smaller than the cross section of the inner wall portion 13e in the vicinity of the third opening 13c.

[0054] The cylinder liner 14 functions as an inner cylinder that guides the reciprocating movement of the piston 21. Specifically, as shown in Figures 2 and 3, the cylinder liner 14 is formed in a cylindrical shape that extends in the up-down direction.

[0055] As shown in FIGS. 2 and 3, the cylinder liner 14 has a scavenging port 14a provided in the lower part of the cylinder liner 14, a liner inner wall part 14b that defines the internal space S2 of the cylinder liner 14, and a supported part 14c that is supported by the cylinder jacket 13.

[0056] Among these, the scavenging ports 14a are arranged along the circumferential direction of the cylinder liner 14. In detail, the scavenging ports 14a according to the present embodiment are formed in an elliptical shape extending in the up-down direction as illustrated in Fig. 2 and the like, and a plurality of the scavenging ports 14a are arranged along the circumferential direction of the cylinder liner 14 as illustrated in Fig. 4.

[0057] In addition, in the vertical direction, each scavenging port 14a is disposed in a portion of the cylinder liner 14 inserted into the cylinder jacket 13 (corresponding to the lower part of the cylinder liner 14 and equivalent to the portion located below the supported portion 14c).

[0058] Specifically, as shown in Fig. 3, each scavenging port 14a is located above the piston 21 located at the bottom dead center and below the fourth opening 13d in the cylinder jacket 13. Furthermore, as shown in Fig. 3, the dimension of each scavenging port 14a in the vertical direction is shorter than the dimensions of the first opening 13a and the second opening 13b in the same direction. Each scavenging port 14a communicates the internal space S1 of the cylinder jacket 13 with the internal space S2 of the cylinder liner 14. Each scavenging port 14a is opened when the piston 21 is located near the bottom dead center, and communicates the scavenging trunk 43 with the combustion chamber 17 via the cylinder jacket 13 and the cylinder liner 14.

[0059] The liner inner wall portion 14b guides the reciprocating movement of the piston 21. Specifically, as shown in Fig. 3, the liner inner wall portion 14b according to this embodiment is formed in a cylindrical shape having a central axis C along the moving direction of the piston 21, and the piston 21 is slidably inserted therein.

[0060] The supported portion 14c is provided on the outer wall of the cylinder liner 14. Specifically, the supported portion 14c according to this embodiment is formed by protruding radially outward from the outer wall of the cylinder liner 14. The supported portion 14c is formed with a larger diameter than the fourth opening 13d of the cylinder jacket 13, and is supported from below by the periphery of the fourth opening 13d.

[0061] As described above, the portion of the cylinder liner 14 located below the supported portion 14c is inserted into the cylinder jacket 13. As illustrated in Fig. 3, the portion located below the supported portion 14c is divided into two portions, a portion located above the scavenging port 14a and a portion located below the scavenging port 14a.

[0062] Here, if a portion of the outer wall of the cylinder liner 14 located above the scavenging ports 14a is defined as a first portion P1, and a portion located below the scavenging ports 14a is defined as a second portion P2, at least a part of the second portion P2 is formed to have a smaller diameter than the first portion P1. Specifically, a reduced diameter portion 14d is provided near the upper end portion (boundary with the scavenging ports 14a) of the second portion P2, the diameter of which is reduced from the second portion P2. As a result, a portion of the second portion P2 located below the reduced diameter portion 14d has a smaller diameter than the first portion P1.

[0063] As described above, the liner inner wall portion 14b is formed in a cylindrical shape. In this embodiment, the inner wall portion 13e of the cylinder jacket 13 is also formed in a circular shape, similar to the liner inner wall portion 14b.

[0064] Specifically, the inner wall portion 13e of the cylinder jacket 13 has a circular shape coaxial with the cylinder liner 14 when viewed in a cross section (the cross section shown in FIG. 4) perpendicular to the direction of the central axis C of the cylinder liner 14 and passing through the scavenging port 14a.

[0065] More specifically, the inner wall portion 13e of the cylinder jacket 13 has a conical shape whose diameter increases downward (in other words, toward the bottom dead center of the piston 21). The upper end of this cone is cut away by the fourth opening 13d. The central axis of this cone coincides with the central axis C of the cylinder liner 14.

[0066] In this embodiment, when viewed in the cross section shown in FIG. 4, if the cross-sectional area of ​​the cylinder jacket 13 is A1 and the cross-sectional area of ​​the cylinder liner 14 is A2, A1-A2≧A2…(1) Specifically, the distance (=R2) between the inner wall portion 13e of the cylinder jacket 13 and the outer wall portion of the cylinder liner 14 is determined according to the outer diameter (=2R1) of the cylinder liner 14 and the inner diameter (=2R1+2R2) of the cylinder jacket.

[0067] The relationship in (1) above can be expressed as follows by using R1 and R2: (R1+R2) 2 -R1 2 ≧R1 2 …(2) It can also be expressed as:

[0068] As described above, the inner wall portion 13e of the cylinder jacket 13 expands in diameter downward. Therefore, the cross-sectional areas A1 and A2 are different in size when viewed in a cross section passing through the upper end of the scavenging port 14a (cross section passing through the dashed line H1 in FIG. 3) and when viewed in a cross section passing through the lower end of the scavenging port 14a (cross section passing through the dashed line H2 in FIG. 3).

[0069] In this embodiment, the relationships (1) and (2) are established both when viewed in a cross section perpendicular to the direction of the central axis C of the cylinder liner 14 and passing through the upper end of the scavenging port 14a, and when viewed in a cross section perpendicular to the direction of the central axis C of the cylinder liner 14 and passing through the lower end of the scavenging port 14a.

[0070] (3) Scavenging efficiency Fig. 5 is a view corresponding to Fig. 4 showing a conventional example of a scavenging chamber structure. As in this embodiment, a scavenging chamber 100' according to this conventional example includes a cylinder jacket 13' connected to a scavenging trunk (not shown) and a cylindrical cylinder liner 14' inserted into the cylinder jacket 13', and is configured so that air is sucked from the cylinder jacket 13' into the cylinder liner 14' by a piston (not shown) reciprocating along the cylinder liner 14'.

[0071] Also, similarly to this embodiment, the cylinder liner 14' according to the conventional example is provided with scavenging ports 14a' arranged along the circumferential direction of the cylinder liner 14'.

[0072] However, the inner wall portion 13e' of the cylinder jacket 13' in the conventional example is formed in a rectangular shape, unlike the present embodiment, when viewed in a cross section (cross section shown in FIG. 5) perpendicular to the direction of the central axis C of the cylinder liner 14' and passing through the scavenging port 14a'.

[0073] In the conventional example, as shown by the arrows f1' to f3' in Fig. 5, there was a problem that the scavenging flow was not uniform around the corners of the inner wall portion 13e' and became non-uniform. If the scavenging flow becomes non-uniform, it is inconvenient for improving the scavenging efficiency.

[0074] On the other hand, according to the present embodiment, the inner wall portion 13e of the cylinder jacket 13 has a circular shape coaxial with the cylinder liner 14 when viewed in a cross section as illustrated in FIG. 4. With this configuration, as shown by arrows f1 to f3 in FIG. 4, the air flowing from the scavenging trunk 43 into the cylinder jacket 13 flows along the circular inner wall portion 13e. This allows a uniform scavenging flow flowing along the circumferential direction to be realized in the cylinder jacket 13. This makes it possible to uniformize the scavenging flow, and thus improve the scavenging efficiency. In addition, by configuring the inner wall portion 13e and the cylinder liner 14 coaxially, the interval (=R2) between the inner wall portion 13e of the cylinder jacket 13 and the outer wall portion of the cylinder liner 14 can be kept approximately constant. This also contributes to uniformizing the scavenging flow.

[0075] Furthermore, in this embodiment, there is no need to use a separate part such as a guide plate, and there is no need to elaborate on the shape of the inlet (first opening 13a) of the cylinder jacket 13. This also contributes to reducing manufacturing costs.

[0076] In this manner, according to this embodiment, it is possible to improve the scavenging efficiency while suppressing the manufacturing cost.

[0077] 3, the volume near the cross section can be increased by expanding the diameter of the inner wall portion 13e of the cylinder jacket 13 downward. This increases the fluidity of the scavenging flow, which is more advantageous in improving the scavenging efficiency.

[0078] 3, the inner wall portion 13e of the cylinder jacket 13 is expanded in diameter downward, and at least a part of the second portion P2 is formed to have a relatively small diameter, which combines to maximize the space (distance R2) between the inner wall portion 13e of the cylinder jacket 13 and the outer wall portion of the cylinder liner 14. This increases the fluidity of the scavenging flow, which is further advantageous in improving the scavenging efficiency.

[0079] 4, by designing the scavenging chamber 100 so that the relationships (1) and (2) are satisfied, the volume between the inner wall 13e of the cylinder jacket 13 and the outer wall of the cylinder liner 14 can be increased. This increases the fluidity of the scavenging flow, which is more advantageous in improving the scavenging efficiency. [Explanation of symbols]

[0080] 1. Marine engines 13 Cylinder jacket 13e Inner wall of cylinder jacket 14 Cylinder liner 14a Scavenging port 14d Reduced diameter part 21 Piston 43 Scavenging trunk 100 Scavenging air chamber C Cylinder liner central axis P1 Part 1 P2 2nd part

Claims

1. A scavenging chamber structure for a crosshead type marine engine, comprising: a cylinder jacket connected to a scavenging trunk; and a cylindrical cylinder liner inserted into the cylinder jacket, wherein a piston reciprocates along the cylinder liner to suck air from the cylinder jacket into the cylinder liner, and the piston is supported by a piston rod connected to a connecting rod by a crosshead, The cylinder liner is provided with scavenging ports arranged along a circumferential direction of the cylinder liner, the cylinder jacket has a first opening connected to the scavenging trunk; When viewed in a cross section perpendicular to a central axis direction of the cylinder liner and passing through the first opening and the scavenging port, the first opening is inclined with respect to an opening direction of the scavenging port and opens so as to face the central axis of the cylinder liner, An air flow flows into the cylinder jacket from one direction through the first opening, The inner wall portion of the cylinder jacket has a circular shape coaxial with the cylinder liner when viewed in the cross section so that the air flow supplied from the first opening and reaching the cylinder liner through the scavenging port is uniform in the circumferential direction. A scavenging chamber structure for a marine engine.

2. The scavenging chamber structure for a marine engine according to claim 1, The inner wall of the cylinder jacket is conically shaped so that the diameter of the inner wall increases downward. A scavenging chamber structure for a marine engine.

3. The scavenging chamber structure for a marine engine according to claim 2, In the outer wall portion of the cylinder liner, a portion located above the scavenging port is defined as a first portion, and a portion located below the scavenging port is defined as a second portion. At least a part of the second portion is formed to have a smaller diameter than the first portion. A scavenging chamber structure for a marine engine.

4. The scavenging chamber structure for a marine engine according to any one of claims 1 to 3, When viewed in the cross section, the distance between the inner wall of the cylinder jacket and the outer wall of the cylinder liner is R ２ The outer diameter of the cylinder liner is 2R １ Then, (R １ +R ２ ) ２ -R １ ２ ≧R １ ２ The relationship is established. A scavenging chamber structure for a marine engine.

5. The scavenging chamber structure for a marine engine according to claim 4, The scavenging port extends along the up-down direction, The relationship holds both when viewed in a cross section perpendicular to the central axis direction of the cylinder liner and passing through the upper end of the scavenging port, and when viewed in a cross section perpendicular to the central axis direction of the cylinder liner and passing through the lower end of the scavenging port. A scavenging chamber structure for a marine engine.

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