Engine

Abstract

An engine (1) is provided with a cylinder block (2) including a tubular cylinder liner (12) constituting a cylinder (11) extending in a vertical direction, and a liner cooling jacket (13) which is formed around the cylinder liner and through which a cooling liquid flows. An introduction port (14A) for introducing the cooling liquid into the liner cooling jacket and a discharge port (14B) for discharging the cooling liquid from the liner cooling jacket are formed in an upper part of the liner cooling jacket. A drain port (14C) for emptying the liner cooling jacket by discharging the cooling liquid from the liner cooling jacket is formed in a lower part of the liner cooling jacket. The flow passage cross-sectional area of the drain port is smaller than the flow passage cross-sectional area of the introduction port and the discharge port.

Description

engine

[0001] The present invention relates to an engine.

[0002] Patent Document 1 discloses an engine including a cylinder block in which cylinder liners (cylinder bores) of a plurality of vertically extending cylinders are surrounded by a water jacket through which coolant flows to cool the cylinder bores during engine operation.

[0003] Patent No. 5939176

[0004] This type of engine requires that the cylinder liners can be adequately cooled while the engine is running, and that the coolant can be drained from the water jacket to empty it when the engine is stored for an extended period of time.

[0005] The present invention has been made in consideration of these problems, and aims to provide an engine that can properly cool the cylinder liner and can drain the coolant from the water jacket to empty the water jacket.

[0006] An engine according to a first aspect of the present invention comprises a cylinder block including a cylindrical cylinder liner that forms a cylinder extending in the vertical direction, and a liner cooling jacket formed around the cylinder liner and through which a coolant flows, wherein an inlet port for introducing the coolant into the liner cooling jacket and an outlet port for discharging the coolant from the liner cooling jacket are formed at the upper part of the liner cooling jacket, and a drain port for discharging the coolant from the liner cooling jacket to empty the liner cooling jacket is formed at the lower part of the liner cooling jacket, and the flow path cross-sectional area of ​​the drain port is smaller than the flow path cross-sectional areas of the inlet port and the outlet port.

[0007] According to the present invention, the cylinder liner can be appropriately cooled, and the coolant can be discharged from the liner cooling jacket (water jacket) to empty the liner cooling jacket.

[0008] Fig. 1 is a schematic configuration diagram showing an engine system including an engine according to one embodiment of the present invention. Fig. 2 is a side view showing an engine according to one embodiment of the present invention. Fig. 3 is a cross-sectional side view with a portion of the engine of Fig. 2 broken away. Fig. 4 is a cross-sectional view taken along line IV-IV of Fig. 3. Fig. 5 is a cross-sectional view taken along line V-V of Fig. 3. Fig. 6 is a cross-sectional view taken along line VI-VI of Figs. 4 and 5. Fig. 7 is a diagram schematically showing a portion of a coolant flow portion in a cylinder block of an engine according to one embodiment of the present invention.

[0009] An engine according to an embodiment of the present invention will be described in detail below with reference to Figures 1 to 7. As shown in Figure 1, the engine 1 according to this embodiment is included in an engine system 100. The engine system 100 is mounted on any work vehicle, such as a dump truck, a wheel loader, or a motor grader. The engine system 100 includes the engine 1, a pump 101, a radiator 102, and a thermostat 103.

[0010] <Engine> First, the engine 1 will be described. In Figures 2 to 7, the up-down direction of the engine 1 is indicated as the Z-axis direction. In Figures 2 to 6, a first linear direction perpendicular to the Z-axis direction is indicated as the X-axis direction. Furthermore, a second linear direction perpendicular to the Z-axis direction and the X-axis direction is indicated as the Y-axis direction.

[0011] As shown in FIG. 2 , the engine 1 according to this embodiment includes a cylinder block 2 , a cylinder head 3 , a rocker housing 4 , and an oil pan 5 .

[0012] <Cylinder Block> As shown in Figure 3, cylinders 11 are formed inside the cylinder block 2. Each cylinder 11 is a space that extends in the vertical direction (Z-axis direction) and opens to the top surface 2a of the cylinder block 2. The upper end of each cylinder 11 is covered by a cylinder head 3. A piston 6 is disposed inside each cylinder 11. The piston 6 reciprocates in the vertical direction under the pressure of combustion gas combusted inside the cylinder 11. The space above the piston 6 in each cylinder 11 functions as a combustion chamber 11A.

[0013] The cylinders 11 are arranged at intervals in the first linear direction (X-axis direction). In the illustrated example, the number of cylinders 11 is six, but is not limited to this.

[0014] <Liner Cooling Jacket> As shown in Figures 4 to 6, the cylinder block 2 includes a cylinder liner 12 and a liner cooling jacket 13. The cylinder liner 12 is formed in a cylindrical shape that constitutes the cylinder 11. The upper end of the cylinder liner 12 is exposed on the upper surface 2a of the cylinder block 2. The liner cooling jacket 13 is a cylindrical space formed around the cylinder liner 12. Coolant flows through the liner cooling jacket 13.

[0015] 6 and 7, the upper end of the liner cooling jacket 13 is located below the upper end of the cylinder liner 12 (the upper surface 2a of the cylinder block 2). Note that the upper end of the liner cooling jacket 13 may be located at the upper end of the cylinder liner 12, for example. In Fig. 6, the lower end of the liner cooling jacket 13 is located above the lower end of the cylinder liner 12. Note that the lower end of the liner cooling jacket 13 may be located at the lower end of the cylinder liner 12, for example, as shown in Fig. 7.

[0016] 6 and 7, an inlet 14A for introducing the coolant into the liner cooling jacket 13 and an outlet 14B for discharging the coolant from the liner cooling jacket 13 are formed in the upper part of the liner cooling jacket 13. The flow of the coolant through these inlet 14A and outlet 14B is mainly performed when the cylinder liner 12 is cooled by the coolant.

[0017] The upper part of the liner cooling jacket 13 is, for example, the part of the liner cooling jacket 13 where, with the positions of the inlet 14A and the outlet 14B in the vertical direction as the reference positions, the length from the reference position to the lower end of the liner cooling jacket 13 is longer than the length from the reference position to the upper end of the liner cooling jacket 13.

[0018] The inlet 14A and the outlet 14B may be located in a range from the upper end of the liner cooling jacket 13 to a position that is at least half the vertical dimension of the liner cooling jacket 13 (the vertical dimension of the jacket). The positions of the inlet 14A and the outlet 14B are preferably closer to the upper end of the liner cooling jacket 13. For example, the inlet 14A and the outlet 14B are more preferably located in a range from the upper end of the liner cooling jacket 13 to a position that is one-third of the vertical dimension of the jacket, and even more preferably to a position that is one-quarter of the vertical dimension. In Figures 6 and 7, the inlet 14A and the outlet 14B are located below the upper end of the liner cooling jacket 13, but they may also be located at the upper end of the liner cooling jacket 13, for example.

[0019] <Drain Port> A drain port 14C is formed in the lower part of the liner cooling jacket 13. The drain port 14C is formed to drain the coolant from the liner cooling jacket 13 and empty the liner cooling jacket 13 when the engine 1 is stored for a long period of time. For this reason, it is preferable that the drain port 14C be located closer to the lower end of the liner cooling jacket 13. In Figures 6 and 7, the drain port 14C is located above the lower end of the liner cooling jacket 13, but it may also be located at the lower end of the liner cooling jacket 13, for example. As shown in Figure 7, the flow path cross-sectional area S3 of the drain port 14C is smaller than the flow path cross-sectional areas S1 and S2 of the inlet port 14A and the outlet port 14B.

[0020] 4 and 5 , the cylinder liners 12 and liner cooling jackets 13 correspond to individual cylinders 11. That is, the cylinder block 2 has multiple sets of cylinder liners 12 and liner cooling jackets 13. In this embodiment, the multiple sets of cylinder liners 12 and liner cooling jackets 13 are arranged at intervals in the first linear direction (X-axis direction), similar to the cylinders 11.

[0021] As shown in Fig. 4, the inlet 14A and the outlet 14B are formed in each of the multiple liner cooling jackets 13. As shown in Fig. 5, the drain port 14C is formed in only one liner cooling jacket 13A. In Fig. 5, the drain port 14C is formed in the liner cooling jacket 13A located in the middle of the multiple liner cooling jackets 13 in the arrangement direction (X-axis direction), but it may also be formed in, for example, a liner cooling jacket 13 located at an end of the multiple liner cooling jackets 13 in the arrangement direction.

[0022] 5 to 7 , the cylinder block 2 has a connection flow path 21 that connects the lower portions of adjacent liner cooling jackets 13. Specifically, the connection flow path 21 connects the lower portions of adjacent liner cooling jackets 13 in the first linear direction (X-axis direction). As a result, the multiple liner cooling jackets 13 are connected to each other by the connection flow path 21.

[0023] The connecting flow passage 21 serves to flow the coolant from the liner cooling jackets 13 that do not have a drain port 14C toward the liner cooling jackets 13 that have a drain port 14C when the coolant is discharged from the multiple liner cooling jackets 13 to empty the multiple liner cooling jackets 13. For this reason, the position of the connecting flow passage 21 is preferably closer to the lower end of the liner cooling jacket 13. In Fig. 7, the connecting flow passage 21 is located above and spaced apart from the lower end of the liner cooling jacket 13, but it may be located at the lower end of the liner cooling jacket 13, for example. Also, in Fig. 7, the connecting flow passage 21 is located at the same height as the drain port 14C in the vertical direction, but it may be located above the drain port 14C, for example.

[0024] 7, the cross-sectional area S4 of the connecting flow path 21 is larger than the cross-sectional area S3 of the drain port 14C, and smaller than the cross-sectional areas S1 and S2 of the inlet 14A and the outlet 14B.

[0025] 1, 4, and 6, the cylinder block 2 is formed with an inlet passage 22 for introducing coolant into the liner cooling jacket 13. The inlet passage 22 in this embodiment includes a main inlet passage 221 and a plurality of branch inlet passages 222.

[0026] The main inlet flow passage 221 extends linearly in the first linear direction. The main inlet flow passage 221 is located at an interval on one side (negative Y-axis direction side) of the multiple liner cooling jackets 13 in the second linear direction. The upstream end of the main inlet flow passage 221 opens to the outside of the cylinder block 2. In FIG. 4 , the upstream end of the main inlet flow passage 221 is located at the end of one side (negative X-axis direction side) of the cylinder block 2 in the first linear direction. A connection pipe 111 extending to a pump 101 (described later) is connected to the upstream end of the main inlet flow passage 221. This allows coolant to be supplied from the pump 101 to the main inlet flow passage 221. In the main inlet flow passage 221, the coolant supplied from the pump 101 flows from the upstream end to the downstream end of the main inlet flow passage 221 (positive X-axis direction). In FIG. 4 , the connection pipe 111 extends linearly in the second linear direction along the side surface of the cylinder block 2, but this is not limiting.

[0027] The number of branch introduction channels 222 corresponds to the number of liner cooling jackets 13. The branch introduction channels 222 are aligned at intervals in the first linear direction. Each of the branch introduction channels 222 extends from the main introduction channel 221 to the inlet 14A of the corresponding liner cooling jacket 13. As shown in Fig. 4 , each branch introduction channel 222 is inclined in the first linear direction from the upstream end toward the downstream end of the main introduction channel 221 as it moves away from the main introduction channel 221 in the second linear direction. This makes it easier for the coolant flowing from the upstream end toward the downstream end in the main introduction channel 221 to enter each branch introduction channel 222.

[0028] The coolant supplied from the pump 101 to the main inlet flow path 221 is introduced into each of the plurality of liner cooling jackets 13 through the plurality of branch inlet flow paths 222. As shown in Fig. 6, the inlet flow path 22 including the main inlet flow path 221 and the plurality of branch inlet flow paths 222 is located at a height corresponding to the upper part of the liner cooling jacket 13, similar to the inlet port 14A.

[0029] <Liner Discharge Flow Passage> As shown in Figures 1, 4, and 6, the cylinder block 2 is formed with a liner discharge flow passage 23 (discharge flow passage) that extends from the discharge port 14B of the liner cooling jacket 13 and opens to the outside of the cylinder block 2. The liner discharge flow passage 23 guides the coolant discharged from the discharge port 14B of the liner cooling jacket 13 to the outside of the cylinder block 2. In this embodiment, the liner discharge flow passage 23 opens to the upper surface 2a of the cylinder block 2. The liner discharge flow passage 23 guides the coolant discharged from the discharge port 14B of the liner cooling jacket 13 to a head cooling jacket 31 of the cylinder head 3, which will be described later. The liner discharge flow passage 23 is connected to each of the multiple liner cooling jackets 13. In other words, the cylinder block 2 is formed with a number of liner discharge flow passages 23 corresponding to the number of liner cooling jackets 13.

[0030] 1 , 5 , and 6 , the cylinder block 2 is formed with a drain passage 24 extending from the drain port 14C of the liner cooling jacket 13. The drain passage 24 guides the coolant discharged from the drain port 14C of the liner cooling jacket 13 to the outside of the cylinder block 2. In the present embodiment, the drain passage 24 is connected to the first oil cooler 7, which will be described later. Therefore, the coolant discharged from the drain port 14C of the liner cooling jacket 13 is guided to the first oil cooler 7.

[0031] 2 and 4 to 6, a first oil cooler 7 (oil cooler) is integrally provided on the cylinder block 2 of this embodiment. The first oil cooler 7 cools the lubricating oil used to lubricate various parts of the engine 1 by using the coolant discharged from the liner cooling jacket 13 and the head cooling jacket 31 (described later).

[0032] 3 and 6, the cylinder head 3 is disposed on the upper surface 2a of the cylinder block 2 and covers the upper ends of the multiple cylinders 11. Although not shown, the cylinder head 3 is formed with intake ports and exhaust ports that communicate with the combustion chambers 11A of the cylinders 11. In addition, the cylinder head 3 is fitted with intake valves that open and close the openings of the intake ports on the cylinder 11 side, and exhaust valves that open and close the openings of the exhaust ports on the cylinder 11 side.

[0033] 1 and 6 , the cylinder head 3 is formed with a head cooling jacket 31 through which coolant flows. The head cooling jacket 31 is formed around, for example, the portions of the cylinder head 3 where exhaust ports are formed and the mounting portions of intake valves and exhaust valves. This allows these mounting portions and mounting portions to be cooled by the coolant flowing through the head cooling jacket 31. The cylinder head 3 is formed with a head discharge passage 32 extending from the head cooling jacket 31. The head discharge passage 32 guides the coolant discharged from the head cooling jacket 31 to the first oil cooler 7.

[0034] 2, 3, and 6, the rocker housing 4 is provided on the upper part of the cylinder head 3. Inside the rocker housing 4, valve train components (not shown) such as a camshaft and a rocker arm are arranged.

[0035] 2 and 3, the oil pan 5 is provided below the cylinder block 2. Lubricating oil is stored inside the oil pan 5. The lubricating oil stored in the oil pan 5 is supplied to various parts of the engine 1 (inside the cylinder block 2, inside the rocker housing 4, etc.) by an oil pump (not shown).

[0036] <Pump> As shown in Fig. 1 , the pump 101 discharges coolant to supply it to the engine 1. A connection pipe 111 extending from the pump 101 to the main inlet flow path 221 of the cylinder block 2 is connected to the discharge port of the pump 101. The pump 101 is driven by the power of the engine 1. The pump 101 operates constantly while the engine 1 is running. In Figs. 2 , 4 and 5 , the pump 101 is attached to the outer surface of the cylinder block 2 of the engine 1, but it may be attached to another part of the engine 1 or may be located away from the engine 1, for example.

[0037] 1 , the radiator 102 exchanges heat between the coolant and outside air to cool the coolant that has been heated by circulating through various parts of the engine 1 (the liner cooling jacket 13, the head cooling jacket 31, and the first oil cooler 7). A coolant outlet 102b of the radiator 102 is connected to the suction port of the pump 101 described above. Therefore, the coolant cooled in the radiator 102 flows toward the pump 101. The outlet 102b of the radiator 102 may be connected directly to the pump 101, for example, but in this embodiment, it is connected to the pump 101 via a second oil cooler 104, which will be described later.

[0038] <Second Oil Cooler> The engine system 100 of this embodiment further includes a second oil cooler 104. The second oil cooler 104 cools brake oil used in the brakes of the work vehicle. The second oil cooler 104 is connected to a coolant outlet 102b of the radiator 102. As a result, the coolant from the radiator 102 passes through the second oil cooler 104, and heat exchange occurs between the coolant and the brake oil, thereby cooling the brake oil. The coolant discharged from the second oil cooler 104 flows toward the pump 101.

[0039] <Thermostat> The thermostat 103 is provided midway along the coolant path leading from the engine 1 to the radiator 102, that is, between the engine 1 and the radiator 102. A radiator connection flow path 113 is provided between the thermostat 103 and the radiator 102 to connect them. In addition, a bypass flow path 114 is provided between the thermostat 103 and the second oil cooler 104 to connect them.

[0040] The thermostat 103 switches the flow path of the coolant from the engine 1 so that the coolant flows through the radiator-connecting flow path 113 or the bypass flow path 114 depending on the temperature of the coolant. Specifically, when the coolant is below a predetermined temperature, such as during warm-up of the engine 1, the thermostat 103 flows the coolant through the bypass flow path 114. Furthermore, when the coolant is at or above the predetermined temperature, the thermostat 103 flows the coolant only through the radiator-connecting flow path 113.

[0041] 2, 4, and 5, the thermostat 103 is attached to the outer surface of the cylinder block 2 of the engine 1 and is disposed adjacent to the first oil cooler 7. Note that the thermostat 103 may be attached to, for example, another part of the engine 1, or may be located away from the engine 1.

[0042] <Operation and Effect> In engine system 100 configured as described above, when engine 1 is running, coolant circulates between engine 1 and pump 101 by the operation of pump 101. Specifically, when the coolant is below a predetermined temperature, the coolant passes from pump 101 through engine 1 and second oil cooler 104 in this order, and then returns to pump 101. When the coolant is at or above the predetermined temperature, the coolant passes from pump 101 through engine 1, radiator 102, and second oil cooler 104 in this order, and then returns to pump 101.

[0043] Next, the flow of coolant within the engine 1 will be described. When the engine 1 is running, the operation of the pump 101 introduces coolant into the inlet flow passage 22 of the engine 1. As shown in FIGS. 4 to 7 , the coolant is introduced from the inlet flow passage 22 into the multiple liner cooling jackets 13 through their respective inlets 14A and is discharged from the multiple liner cooling jackets 13 through their respective outlets 14B. Here, because the inlets 14A and outlets 14B are located at the top of each liner cooling jacket 13, the coolant flows more actively in the upper parts of each liner cooling jacket 13 than in the lower parts. This allows the upper parts of the cylinder liners 12 to be cooled more actively than the lower parts.

[0044] When the engine 1 is running, fuel burns (explodes) in the combustion chamber 11A above the cylinder liner 12 (cylinder 11), causing the upper part of the cylinder liner 12 to become hotter than the lower part. Therefore, by actively cooling the upper part of the cylinder liner 12 more than the lower part, the cylinder liner 12 can be cooled appropriately.

[0045] Furthermore, in the engine 1 of this embodiment, the drain port 14C is formed in the lower part of the liner cooling jacket 13. Therefore, when the engine 1 is stored for a long period of time, the coolant can be discharged from the drain port 14C of the liner cooling jacket 13 to empty the liner cooling jacket 13.

[0046] During long-term storage of the engine 1, the coolant discharged from the drain port 14C may be discharged at least to the outside of the engine 1. In the engine system 100 of this embodiment, the coolant discharged from the drain port 14C may be discharged from an openable / closable outlet (not shown) provided at the lowest position in the vertical direction of the flow path through which the coolant circulates. The outlet may be provided, for example, midway through the flow path connecting the second oil cooler 104 and the pump 101. The outlet may be openable / closable by a predetermined sealing member (a cock or a plug).

[0047] Furthermore, in the engine 1 of this embodiment, the flow path cross-sectional area S3 of the drain port 14C is smaller than the flow path cross-sectional areas S1 and S2 of the inlet port 14A and the outlet port 14B. Therefore, the flow rate of the coolant passing through the drain port 14C can be made smaller than the flow rate of the coolant passing through the inlet port 14A and the outlet port 14B. Therefore, even without providing a valve or other component for opening and closing the drain port 14C at or near the drain port 14C, the amount of coolant introduced into the liner cooling jacket 13 from the inlet port 14A and discharged from the outlet port 14B to the outside of the liner cooling jacket 13 is greater than the amount discharged from the drain port 14C. Therefore, even if the drain port 14C remains open, the upper part of the cylinder liner 12 can be actively cooled by the coolant. In other words, the open drain port 14C is prevented from interfering with proper cooling of the cylinder liner 12.

[0048] The engine 1 of this embodiment also has multiple sets of cylinder liners 12 and liner cooling jackets 13 corresponding to the multiple cylinders 11. Each liner cooling jacket 13 is formed with an inlet 14A and an outlet 14B. This allows the multiple cylinder liners 12 to be appropriately cooled while the engine 1 is running.

[0049] Furthermore, in the engine 1 of this embodiment, the lower portions of adjacent liner cooling jackets 13 are connected to each other by the connecting flow path 21. Furthermore, the drain port 14C is formed in only one liner cooling jacket 13. Therefore, when draining the coolant from multiple liner cooling jackets 13 for long-term storage of the engine 1, the coolant can flow from a liner cooling jacket 13 that does not have a drain port 14C through the connecting flow path 21 to a liner cooling jacket 13 that has a drain port 14C. This allows the coolant to be drained from multiple liner cooling jackets 13 through a single drain port 14C. In other words, multiple liner cooling jackets 13 can be emptied.

[0050] Furthermore, in the engine 1 of this embodiment, only one drain port 14C is formed for each of the multiple liner cooling jackets 13, each of which has an inlet port 14A and an outlet port 14B formed therein. Therefore, the ratio of the flow path cross-sectional area S3 of the drain port 14C to the flow path cross-sectional areas S1, S2 of the inlet port 14A and the outlet port 14B of each liner cooling jacket 13 is smaller than when a drain port 14C is formed in each liner cooling jacket 13. This more effectively prevents the open drain port 14C from interfering with proper cooling of the cylinder liner 12, even if the drain port 14C is left open.

[0051] Furthermore, in the engine 1 of this embodiment, the flow path cross-sectional area S4 of the connecting flow path 21 is larger than the flow path cross-sectional area S3 of the drain port 14C. Therefore, when the coolant is discharged from the multiple liner cooling jackets 13 to empty them, the flow rate of the coolant flowing from the liner cooling jacket 13 without the drain port 14C to the liner cooling jacket 13A with the drain port 14C (a specific liner cooling jacket 13A) is larger than the flow rate of the coolant flowing from the drain port 14C to the outside. This makes it easier for the coolant to collect in the specific liner cooling jacket 13A. Therefore, the coolant can be efficiently discharged from the multiple liner cooling jackets 13.

[0052] Furthermore, in the engine 1 of this embodiment, the flow path cross-sectional area S4 of the connecting flow path 21 is smaller than the flow path cross-sectional areas S1, S2 of the inlet 14A and the outlet 14B. Therefore, the flow rate of the coolant passing through the connecting flow path 21 can be made smaller than the flow rate of the coolant passing through the inlet 14A and the outlet 14B of the liner cooling jacket 13. As a result, the coolant introduced from the inlet 14A to the liner cooling jacket 13 flows more actively from the outlet 14B toward the outside of the liner cooling jacket 13 than through the connecting flow path 21. Therefore, even if the connecting flow path 21 is connected to the lower part of the liner cooling jacket 13, the upper part of the cylinder liner 12 can be actively cooled by the coolant.

[0053] Other Embodiments Although the embodiments of the present invention have been described above, the present invention is not limited to these and can be modified as appropriate within the scope of the technical concept of the invention.

[0054] In the present invention, the first oil cooler is not limited to being disposed downstream of the liner cooling jacket or the head cooling jacket, but may be disposed, for example, downstream of the pump and upstream of the intake passage (engine).

[0055] The number of cylinders in the engine of the present invention may be, for example, one.

[0056] 1... engine, 2... cylinder block, 11... cylinder, 12... cylinder liner, 13, 13A... liner cooling jacket, 14A... inlet, 14B... outlet, 14C... drain port, 21... connecting flow path, S1... flow path cross-sectional area of ​​inlet 14A, S2... flow path cross-sectional area of ​​outlet 14B, S3... flow path cross-sectional area of ​​drain port 14C, S4... flow path cross-sectional area of ​​connecting flow path 21

Claims

1. An engine comprising: a cylinder block including a cylindrical cylinder liner that constitutes a cylinder extending in the vertical direction; and a liner cooling jacket formed around the cylinder liner and through which a coolant flows, wherein an inlet port for introducing the coolant into the liner cooling jacket and an outlet port for discharging the coolant from the liner cooling jacket are formed at an upper portion of the liner cooling jacket; and a drain port for discharging the coolant from the liner cooling jacket to empty the liner cooling jacket is formed at a lower portion of the liner cooling jacket, and the flow path cross-sectional area of ​​the drain port is smaller than the flow path cross-sectional areas of the inlet port and the outlet port.

2. An engine as described in claim 1, wherein the cylinder block has a plurality of sets of the cylinder liners and the liner cooling jackets, and a connecting flow passage connecting the lower parts of adjacent liner cooling jackets, the inlet and the outlet are formed in each of the plurality of liner cooling jackets, and the drain port is formed in only one of the liner cooling jackets.

3. The engine according to claim 2, wherein the flow passage cross-sectional area of ​​the connecting flow passage is larger than the flow passage cross-sectional area of ​​the drain port.

4. An engine according to claim 2 or 3, wherein the flow passage cross-sectional area of ​​the connecting flow passage is smaller than the flow passage cross-sectional areas of the inlet and the outlet.

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