Engine

Abstract

An engine (1) is provided with: a cylinder unit (2); a rocker housing (3) which is provided on an upper part of the cylinder unit and the inside of which constitutes a valve system accommodation space (3A); and an oil pan (4) which is provided on a lower part of the cylinder unit and the inside of which constitutes an oil storage space (4A). An oil drain flow path (31) and a discharge flow path (32) are formed inside the cylinder unit. The oil drain flow path penetrates from an upper end to a lower end of the cylinder unit, and communicates with the valve system accommodation space and the oil storage space. The discharge flow path extends upward from the lower end of the cylinder unit, opens at the lower end of the cylinder unit, and communicates with the oil storage space. An upper end of the discharge flow path is closed. A gas discharge port (32O) that opens to the outside is provided at a position in the discharge flow path that is separated upward from the lower end of the cylinder unit.

Description

engine

[0001] The present invention relates to an engine.

[0002] Patent Document 1 discloses an engine that releases blow-by gas into the atmosphere. Blow-by gas is exhaust gas that leaks from the combustion chamber into other internal spaces of the engine (for example, the space inside the crankcase or rocker housing). The blow-by gas that leaks into other internal spaces of the engine atomizes the lubricating oil present in the vicinity and mixes with the atomized oil (oil mist).

[0003] Japanese Patent Application Publication No. 11-107737

[0004] In order to comply with exhaust gas regulations, it is desirable to further reduce the oil mist contained in the blow-by gas released to the atmosphere.

[0005] The present invention has been made in view of the above-mentioned problems, and has an object to provide an engine that can effectively reduce oil mist contained in blow-by gas that is released into the atmosphere.

[0006] An engine according to a first aspect of the present invention comprises a cylinder unit having cylinders extending vertically therein, a rocker housing provided on the upper part of the cylinder unit and having a valve system accommodating space on the inside, and an oil pan provided on the lower part of the cylinder unit and having an oil storage space on the inside, wherein an oil drain passage and an exhaust passage are formed inside the cylinder unit, each of which is partitioned for each cylinder, and the oil drain passage penetrates from the upper end to the lower end of the cylinder unit and communicates with the valve system accommodating space and the oil storage space, the exhaust passage extends upward from the lower end of the cylinder unit at a position horizontally spaced from the oil drain passage, opens at the lower end of the cylinder unit and communicates with the oil storage space, the upper end of the exhaust passage is closed, and a gas exhaust port opening to the outside is provided in the exhaust passage at a position above the lower end of the cylinder unit.

[0007] According to the present invention, it is possible to more effectively reduce oil mist contained in blow-by gas released to the atmosphere.

[0008] Fig. 1 is a side view showing an engine unit including an engine according to an embodiment of the present invention. Fig. 2 is a side cross-sectional view of the engine of Fig. 1. Fig. 3 is a cross-sectional view taken along III-III in Fig. 1. Fig. 4 is a cross-sectional view taken along IV-IV in Fig. 1. Fig. 5 is a cross-sectional view taken along V-V in Fig. 1. Fig. 6 is a schematic view corresponding to the engine unit of Fig. 1. Fig. 7 is a schematic view corresponding to the cylinder unit of Fig. 5.

[0009] An engine according to one embodiment of the present invention will be described in detail below with reference to FIGS. 1 to 7. In FIGS. 1 to 7, the vertical direction of the engine 1 is indicated as the Z-axis direction. A first linear direction perpendicular to the Z-axis direction is defined as the X-axis direction. A second linear direction perpendicular to the Z-axis direction and the X-axis direction is defined as the Y-axis direction. In the following description, any direction within the XY plane including the X-axis direction and the Y-axis direction may be referred to as the "horizontal direction." As shown in FIG. 1, the engine 1 according to this embodiment includes a cylinder unit 2, a rocker housing 3, and an oil pan 4.

[0010] <Cylinder Unit> As shown in Figure 2, a cylinder 11 is formed inside the cylinder unit 2. The cylinder 11 is located in the upper part of the cylinder unit 2. The cylinder 11 is a space in which a piston 5 is disposed, and extends in the vertical direction (Z-axis direction). The piston 5 reciprocates in the vertical direction under the pressure of combustion gas combusted in the cylinder 11. The space above the piston 5 in the cylinder 11 functions as a combustion chamber 11A.

[0011] 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 this is not limited to six. As shown in FIG. 5 , each cylinder 11 is circular when viewed from the top-bottom direction. Therefore, the distance between the cylinders 11 in the first linear direction is wider at both sides of the cylinders 11 in the second linear direction (Y-axis direction) than at the middle of the cylinders 11 in the second linear direction (Y-axis direction).

[0012] 2, the lower part of the cylinder unit 2 is configured as a crankcase 12 that houses a crankshaft (not shown). An internal space 12A of the crankcase 12 that houses the crankshaft is connected to the lower ends of the cylinders 11. The lower end of the crankcase 12 is open and is covered by an oil pan 4, which will be described later.

[0013] 1 and 3 to 5, an oil drain passage 31, a discharge passage 32, and a horizontal passage 33 are formed inside the cylinder unit 2. As shown in Figures 3 to 5, the oil drain passage 31 is defined for each cylinder 11 and penetrates from the upper end to the lower end of the cylinder unit 2. The oil drain passage 31 communicates with a valve train accommodating space 3A in the rocker housing 3, which will be described later, and an oil storage space 4A in the oil pan 4.

[0014] In this embodiment, multiple oil drain passages 31 are formed inside the cylinder unit 2. The multiple oil drain passages 31 are positioned at intervals in the horizontal direction. As shown in FIGS. 5 and 7 , the oil drain passages 31 are arranged on both sides of the cylinder 11 in the second linear direction. In the following description, the oil drain passage 31 arranged on one side of the cylinder 11 in the second linear direction (the positive Y-axis side) may be referred to as the first oil drain passage 31A. Furthermore, the oil drain passage 31 arranged on the other side of the cylinder 11 in the second linear direction (the negative Y-axis side) may be referred to as the second oil drain passage 31B.

[0015] As shown in Figures 1 and 5 to 7, the oil drain passages 31 are arranged at intervals in the first linear direction. Specifically, the multiple first oil drain passages 31A are arranged at intervals in the first linear direction on one side of the cylinders 11 in the second linear direction. The multiple first oil drain passages 31A are located between adjacent cylinders 11 in the first linear direction. The number of first oil drain passages 31A is two less than the number of cylinders 11. Therefore, there are gaps between the cylinders 11 in the first linear direction where no first oil drain passages 31A are located.

[0016] The second oil drain passages 31B are arranged at intervals in the first linear direction on the other side of the cylinders 11 in the second linear direction. The second oil drain passages 31B are located between adjacent cylinders 11 in the first linear direction. The number of second oil drain passages 31B is one less than the number of cylinders 11. Therefore, the second oil drain passages 31B are located in all of the gaps between the cylinders 11 arranged in the first linear direction.

[0017] In Fig. 5, the shape of the second oil drain passage 31B in plan view when viewed from the top and bottom is different from that of the first oil drain passage 31A, but may be the same as, for example, the first oil drain passage 31A. Also, in Fig. 5, the shape of some second oil drain passages 31B in plan view is different from that of other second oil drain passages 31B, but the shape of multiple second oil drain passages 31B in plan view may be the same as each other.

[0018] 4 and 5 , the discharge passage 32 is defined for the cylinder 11 and extends upward (in the positive direction of the Z axis) from the lower end of the cylinder unit 2. The discharge passage 32 opens at the lower end of the cylinder unit 2 and communicates with the oil storage space 4A of the oil pan 4. The discharge passage 32 does not open at the upper end of the cylinder unit 2, and does not communicate with the valve train accommodating space 3A of the rocker housing 3. In other words, the upper end of the discharge passage 32 is closed.

[0019] As shown in FIG. 4 , a gas exhaust port 32O that opens to the outside of the engine 1 is provided in the exhaust flow passage 32 at a position spaced above the lower end of the cylinder unit 2 .

[0020] As shown in FIGS. 1 and 5 to 7 , the discharge flow passage 32 is positioned at a distance in the horizontal direction from the oil drain flow passage 31. Specifically, the discharge flow passage 32 is positioned only on one side (one side) of the cylinders 11 in the second linear direction. Furthermore, the discharge flow passage 32 is positioned in a gap between the cylinders 11 on one side of the cylinders 11 where the first oil drain flow passage 31A is not positioned. Therefore, the discharge flow passage 32 is positioned at a distance in the first linear direction from the first oil drain flow passage 31A located on one side of the cylinders 11. Furthermore, the discharge flow passage 32 is positioned at a distance in the second linear direction from the second oil drain flow passage 31B.

[0021] The horizontal flow passage 33 is defined with respect to the cylinder 11, extends horizontally, and connects the plurality of oil drain flow passages 31 and the exhaust flow passage 32. As shown in Figures 1, 4, and 6, the horizontal flow passage 33 is positioned at a distance from the upper and lower ends of the exhaust flow passage 32 in the vertical direction. The gas exhaust port 32O is positioned above the connection position between the exhaust flow passage 32 and the horizontal flow passage 33.

[0022] As shown in Figures 5 and 7, the horizontal flow passage 33 includes a first horizontal flow passage 33A and a second horizontal flow passage 33B. The first horizontal flow passage 33A is arranged on both sides of the cylinder 11 in the second linear direction and extends in the first linear direction. The first horizontal flow passage 33A arranged on one side of the cylinder 11 communicates with the plurality of first oil drain flow passages 31A and the discharge flow passage 32 arranged in the first linear direction. The first horizontal flow passage 33A arranged on the other side of the cylinder 11 communicates with the plurality of second oil drain flow passages 31B arranged in the first linear direction. In Figure 5, the two first horizontal flow passages 33A arranged on both sides of the cylinder 11 have different shapes, but they may also have the same shape, for example.

[0023] The second horizontal flow passage 33B connects the first horizontal flow passages 33A located on both sides of the cylinder 11 in the second linear direction. The second horizontal flow passage 33B extends from one side of the cylinder 11 to the other side in the second linear direction. The second horizontal flow passage 33B is located between adjacent cylinders 11 in the first linear direction and on both sides of multiple cylinders 11 lined up in the first linear direction. In FIGS. 5 and 7 , the second horizontal flow passage 33B extends in a curved manner along the outer periphery of the cylinder 11 from one side of the cylinder 11 to the other side in the second linear direction. Note that the second horizontal flow passage 33B may extend linearly along the second linear direction, for example, or may be formed in any other shape.

[0024] 2, the cylinder unit 2 of this embodiment includes a cylinder block 21 and a cylinder head 22. The cylinder block 21 includes a plurality of cylinders 11 and a crankcase 12. Each of the plurality of cylinders 11 opens to an upper surface 21a of the cylinder block 21.

[0025] The cylinder head 22 is disposed on the upper surface 21a of the cylinder block 21 and covers the upper ends of the multiple cylinders 11. Although not shown, the cylinder head 22 is formed with intake ports and exhaust ports that communicate with the combustion chambers 11A of the cylinders 11. The cylinder head 22 is also 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.

[0026] 3 and 4, the plurality of oil drain passages 31 described above are each composed of a lower oil drain passage 311 formed in the cylinder block 21 and an upper oil drain passage 312 formed in the cylinder head 22. The lower oil drain passage 311 is formed to penetrate the cylinder block 21 from its upper end to its lower end. The upper oil drain passage 312 is formed to penetrate the cylinder head 22 from its upper end to its lower end. The upper oil drain passage 312 communicates with the lower oil drain passage 311 when the cylinder head 22 is disposed on the upper surface 21a of the cylinder block 21. This forms an oil drain passage 31 that penetrates the cylinder unit 2 from its upper end to its lower end.

[0027] As shown in Fig. 4, the aforementioned discharge passage 32 is formed penetrating the cylinder block 21 from the upper end to the lower end, similar to the lower oil drain passage 311. The upper end of the discharge passage 32 is closed by the cylinder head 22 disposed on the upper surface 21a of the cylinder block 21. As shown in Figs. 3 to 5, the aforementioned horizontal passages 33 (first horizontal passage 33A and second horizontal passage 33B) are formed only in the cylinder block 21.

[0028] 1 and 5, ribs 15 are provided on two side surfaces 21b, 21c of the cylinder block 21 that face opposite each other in the second linear direction. The ribs 15 are strip-shaped portions of the cylinder block 21 that protrude or bulge from the side surfaces 21b, 21c of the cylinder block 21. A lower oil drain passage 311, a discharge passage 32, and a first horizontal passage 33A are formed inside the ribs 15.

[0029] The ribs 15 include a first rib 15A and a second rib 15B that extend in the vertical direction, and a third rib 15C that extends in the first linear direction. The first rib 15A and the second rib 15B each extend from the lower end to the upper end of the cylinder block 21. The first rib 15A and the second rib 15B are each located between adjacent cylinders 11 in the first linear direction. The first rib 15A is disposed in a position corresponding to the lower oil drain passage 311. Therefore, the first ribs 15A are provided on both of the two side surfaces 21b, 21c of the cylinder block 21, and multiple first ribs 15A are arranged at intervals in the first linear direction on each side surface 21b, 21c. In addition, a lower oil drain passage 311 is formed inside each first rib 15A.

[0030] The second rib 15B is disposed at a position corresponding to the exhaust flow passage 32. Therefore, the second rib 15B is provided on the side surface 21b of the cylinder block 21 located on one side of the cylinder 11 in the second linear direction. The exhaust flow passage 32 is then formed inside the second rib 15B. The third rib 15C is disposed at a position corresponding to the first horizontal flow passage 33A. Therefore, the third rib 15C is provided on both of the two side surfaces 21b, 21c of the cylinder block 21. The first horizontal flow passage 33A is then formed inside each third rib 15C.

[0031] 2 to 4 and 6, the rocker housing 3 is provided on the upper part of the cylinder unit 2. The inside of the rocker housing 3 is a valve train accommodation space 3A. Valve train components (not shown), such as a camshaft and a rocker arm, are mainly disposed in the valve train accommodation space 3A.

[0032] <Oil Pan> The oil pan 4 is provided below the cylinder unit 2. The inside of the oil pan 4 is an oil storage space 4A. Lubricating oil is stored in the oil storage space 4A. In the engine 1, the oil stored in the oil storage space 4A is supplied to the valve train housing space 3A and the like by an oil pump (not shown).

[0033] 2 and 6, a gear case 13 is provided at one end of the cylinder block 21 in the first linear direction (the X-axis positive direction side). The inside of the gear case 13 defines a gear accommodating space 13A in which various gears are disposed for transmitting the rotation of the crankshaft to the camshaft, oil pump, etc. The upper end of the gear accommodating space 13A is connected to the valve train accommodating space 3A via a through hole 221 formed in the cylinder head 22. The lower end of the gear accommodating space 13A is connected to the oil reservoir space 4A.

[0034] <Oil Mist Separator> As shown in Figures 1 and 6, an oil mist separator 112 is connected to the gas exhaust port 32O via an exhaust pipe 111. The oil mist separator 112 is a device for separating oil mist contained in blow-by gas exhausted from the gas exhaust port 32O to the outside of the engine 1. An open pipe 113 and an oil return pipe 114 are connected to the oil mist separator 112. The open pipe 113 is a pipe that releases the blow-by gas exhausted from the oil mist separator 112 to the atmosphere. The oil return pipe 114 is a pipe that returns the oil mist (or oil) separated from the blow-by gas in the oil mist separator 112 to the oil storage space 4A. In Figure 1, the oil return pipe 114 is hidden by the oil mist separator 112.

[0035] 1, a breather 115 is provided between the gas exhaust port 32O and the exhaust pipe 111. The breather 115 separates oil mist from the blow-by gas discharged from the gas exhaust port 32O, but has a simpler structure and lower oil mist separation accuracy than the oil mist separator 112. However, providing the breather 115 can reduce the load of oil mist separation on the oil mist separator 112. The oil mist separator 112 and breather 115, which are provided outside the engine 1, together with the engine 1 of this embodiment described above, constitute the engine unit 100.

[0036] <Oil Flow> In the engine 1 and engine unit 100 including the engine 1 shown in Figure 6, lubricating oil is supplied to the valve train accommodation space 3A by an oil pump. Some of the oil stored in the valve train accommodation space 3A flows back to the oil storage space 4A through the gear accommodation space 13A. As a result, some of the oil is also supplied to the various gears arranged in the gear accommodation space 13A. Some of the oil stored in the valve train accommodation space 3A also flows back to the oil storage space 4A through the oil drain passage 31. The arrows in Figure 6 indicate the above-mentioned oil flow direction.

[0037] <Discharge of Blow-by Gas> In addition, in the engine 1, blow-by gas that leaks from the combustion chamber 11A of the cylinder 11 shown in FIG. 2 into the valve train accommodation space 3A or the oil storage space 4A can be released to the atmosphere through the gas discharge port 32O. This point will be described below. As shown in FIG. 6, blow-by gas that leaks into the valve train accommodation space 3A or the oil storage space 4A can reach the discharge passage 32 via the oil drain passage 31 and the horizontal passage 33. In addition, blow-by gas that leaks into the oil storage space 4A can also enter the discharge passage 32 directly. Then, the blow-by gas rises in the discharge passage 32, and can be discharged to the outside of the engine 1 (i.e., the atmosphere) through the gas discharge port 32O.

[0038] Even if the blow-by gas contains oil mist, the density of the oil mist is greater than that of the blow-by gas, and the oil mist is more affected by gravity than the blow-by gas. Therefore, the oil mist is less likely to rise in the exhaust passage 32 than the blow-by gas, i.e., it is less likely to be discharged to the outside of the engine 1 through the gas exhaust port 32O.

[0039] The blow-by gas discharged from the gas discharge port 32O is released to the atmosphere after passing through the breather 115 (see FIG. 1) and the oil mist separator 112 in that order. Therefore, even if the blow-by gas discharged from the gas discharge port 32O contains oil mist, the breather 115 and the oil mist separator 112 can separate the oil mist from the blow-by gas, thereby suppressing or preventing the oil mist from being released to the atmosphere.

[0040] <Operation and Effect> As described above, according to the engine 1 of this embodiment, blow-by gas that leaks from the combustion chamber 11A of the cylinder 11 into the valve train accommodation space 3A or the oil storage space 4A can reach the discharge passage 32 through the oil drain passage 31 and the horizontal passage 33. In addition, the blow-by gas that leaks into the oil storage space 4A can also enter the discharge passage 32 directly. Then, by causing the blow-by gas to rise in the discharge passage 32, it can be released to the atmosphere from the gas discharge port 32O. On the other hand, oil mist contained in the blow-by gas does not easily rise in the discharge passage 32, and therefore is not easily discharged to the outside from the gas discharge port 32O. Therefore, the oil mist contained in the blow-by gas released to the atmosphere from the engine 1 can be effectively reduced.

[0041] Furthermore, in the engine 1 of this embodiment, the oil drain passage 31 and the discharge passage 32 are connected via the horizontal passage 33. Therefore, blow-by gas leaking into the valve train accommodating space 3A passes through the oil drain passage 31 and the horizontal passage 33 in that order, and then rises in the discharge passage 32, thereby being discharged to the outside of the engine 1 through the gas discharge port 32O. As a result, the blow-by gas leaking into the valve train accommodating space 3A can reach the gas discharge port 32O without passing through the oil storage space 4A. In other words, compared to a case where the horizontal passage 33 is not provided, the blow-by gas leaking into the valve train accommodating space 3A can reach the gas discharge port 32O via a shorter path and be released to the atmosphere.

[0042] Furthermore, in the engine 1 of this embodiment, the horizontal flow path 33 allows the blow-by gas present in the oil storage space 4A to reach the gas discharge port 32O from the lower end openings of both the oil drain flow path 31 and the discharge flow path 32. As a result, even if the opening areas of the oil drain flow path 31 and the discharge flow path 32 at the lower end of the cylinder unit 2 are small, the blow-by gas can be efficiently discharged from the oil storage space 4A to the outside of the engine 1.

[0043] Furthermore, according to the engine 1 of this embodiment, multiple oil drain passages 31 are formed. The horizontal passage 33 connects the multiple oil drain passages 31. Therefore, blow-by gas leaking into the valve train accommodating space 3A can be guided from the upper openings of the multiple oil drain passages 31 through the horizontal passage 33 and the discharge passage 32 to the gas discharge port 32O. Similarly, blow-by gas present in the oil storage space 4A can be guided from the lower openings of the multiple oil drain passages 31 and the discharge passage 32 to the gas discharge port 32O. Therefore, even if the opening areas of the oil drain passages 31 at the upper and lower ends of the cylinder unit 2 are small, blow-by gas can be efficiently discharged from the valve train accommodating space 3A and the oil storage space 4A to the outside of the engine 1.

[0044] In addition, according to the engine 1 of this embodiment, multiple oil drain passages 31 are formed that penetrate from the upper end to the lower end of the cylinder unit 2, so that oil can be efficiently returned from the valve system accommodating space 3A to the oil storage space 4A through the multiple oil drain passages 31.

[0045] Furthermore, according to the engine 1 of this embodiment, the oil drain passages 31 are arranged on both sides of the cylinder 11 in the second linear direction. Therefore, the number of oil drain passages 31 can be increased compared to when the oil drain passages 31 are arranged on only one side of the cylinder 11 in the second linear direction. This allows blow-by gas to be efficiently discharged from the valve train accommodation space 3A and the oil storage space 4A to the outside of the engine 1.

[0046] Furthermore, according to the engine 1 of this embodiment, the oil drain passages 31 arranged on both sides of the cylinder 11 in the second linear direction are connected by the horizontal passages 33 (first and second horizontal passages 33A and 33B). Therefore, even if the exhaust passages 32 and the gas discharge ports 32O are arranged on only one side of the cylinder 11, all of the oil drain passages 31 can be connected to the same exhaust passage 32. In other words, blow-by gas leaking into the valve train accommodation space 3A and the oil storage space 4A can be discharged from the gas discharge port 32O provided in the same exhaust passage 32. This simplifies the piping structure (including the exhaust pipe 111, the oil mist separator 112, etc.) that processes the blow-by gas downstream of the gas discharge port 32O, compared to when the exhaust passages 32 and the gas discharge ports 32O are arranged on both sides of the cylinder 11.

[0047] In addition, all of the oil drain passages 31 are connected to one discharge passage 32 located on one side of the cylinder 11. This allows the number of oil drain passages 31 to be increased compared to when the discharge passages 32 and the gas discharge ports 32O are located on both sides of the cylinder 11. This allows oil to be efficiently returned from the valve train accommodating space 3A to the oil storage space 4A through more oil drain passages 31.

[0048] Furthermore, according to the engine 1 of this embodiment, the strength of the engine 1 (particularly the cylinder block 21) can be improved by forming the ribs 15 on the side surfaces 21b, 21c of the cylinder block 21. Furthermore, by arranging the lower oil drain passage 311, the discharge passage 32, and the first horizontal passage 33A inside the ribs 15, the lower oil drain passage 311, the discharge passage 32, and the first horizontal passage 33A can be easily formed in the cylinder block 21 while minimizing the impact on the internal shape of the cylinder block 21. In other words, it becomes possible to easily design the cylinder block 21 including the lower oil drain passage 311, the discharge passage 32, and the first horizontal passage 33A.

[0049] Furthermore, according to the engine 1 of this embodiment, the ribs 15 (first and second ribs 15A, 15B) containing the lower oil drain passage 311 and the discharge passage 32 therein are positioned in the gaps between adjacent cylinders 11 in the first linear direction. This makes it possible to suppress an increase in the volume of the cylinder unit 2 due to the formation of the ribs 15 containing the lower oil drain passage 311 and the discharge passage 32 therein.

[0050] Furthermore, according to the engine 1 of this embodiment, the exhaust passage 32 is formed penetrating from the upper end to the lower end of the cylinder block 21. The upper end of the exhaust passage 32 is closed by the cylinder head 22 disposed on the upper surface 21a of the cylinder block 21. This makes it possible to easily form the exhaust passage 32 with a closed upper end without making the shape of the cylinder unit 2 complex.

[0051] 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.

[0052] In the present invention, the number of oil drain passages formed inside the cylinder unit may be, for example, one.

[0053] In the present invention, it is sufficient that at least an oil drain passage and a discharge passage are formed inside the cylinder unit, and for example, a horizontal passage does not have to be formed. In this configuration, blow-by gas leaking into the valve train housing space can move to the oil storage space through the oil drain passage. The blow-by gas can also move to the oil storage space through the gear housing space, which functions as an oil drain passage. The blow-by gas in the oil storage space then rises in the discharge passage and can be discharged to the outside of the engine through the gas discharge port.

[0054] In the present invention, the number of exhaust passages formed inside the cylinder unit may be, for example, plural. In this case, the exhaust passages may be arranged on only one side of the cylinder in the second linear direction, or on both sides of the cylinder.

[0055] The present invention is not limited to engines in which the camshaft is disposed in the valve train housing space, but may also be applied to engines in which the camshaft is disposed in the internal space of the crankcase (or a space adjacent thereto). In an engine in which the camshaft is disposed in the internal space of the crankcase, a pushrod that moves up and down as the camshaft rotates is passed through a through-hole that penetrates from the lower end to the upper end of the cylinder unit. In this case, the through-hole of the cylinder unit through which the pushrod passes may be used as the oil drain passage of the present invention.

[0056] The number of cylinders in the engine of the present invention may be, for example, one.

[0057] The engine of the present invention may be applied to any work vehicle such as a dump truck, a hydraulic excavator, a bulldozer, or an engine-powered forklift.

[0058] DESCRIPTION OF SYMBOLS 1...engine, 2...cylinder unit, 3...rocker housing, 3A...valve train accommodating space, 4...oil pan, 4A...oil storage space, 11...cylinder, 15...rib, 15A...first rib, 15B...second rib, 15C...third rib, 21...cylinder block, 21a...top surface, 21b, 21c...side surface, 22...cylinder head, 31...oil drain passage, 32...exhaust passage, 32O...gas exhaust port, 33...horizontal passage, 33A...first horizontal passage, 33B...second horizontal passage

Claims

an oil pan provided at the bottom of the cylinder unit, the inside of which serves as an oil storage space; wherein an oil drain passage and a discharge passage are formed inside the cylinder unit, the oil drain passage penetrating the cylinder unit from its upper end to its lower end and communicating with the valve system storage space and the oil storage space; the discharge passage extending upward from the lower end of the cylinder unit at a position horizontally spaced from the oil drain passage, and opening at the lower end of the cylinder unit to communicate with the oil storage space; the upper end of the discharge passage being closed; and a gas discharge port opening to the outside being provided in the discharge passage at a position above the lower end of the cylinder unit.

2. An engine as described in claim 1, wherein a horizontal flow passage is formed inside the cylinder unit, which is partitioned with respect to the cylinder, extends horizontally and connects the oil drain flow passage and the exhaust flow passage, and the gas exhaust port is located above the connection position of the exhaust flow passage with the horizontal flow passage.

3. An engine as set forth in claim 2, wherein a plurality of the oil drain passages are formed inside the cylinder unit, and the horizontal passage connects the plurality of the oil drain passages.

4. An engine as described in claim 2 or 3, wherein the cylinders are arranged at intervals in a first linear direction perpendicular to the up-down direction, the oil drain passage is arranged on both sides of the cylinder in a second linear direction perpendicular to the up-down direction and the first linear direction, the exhaust passage is arranged on at least one side of the cylinder in the second linear direction, and the horizontal passages include first horizontal passages arranged on both sides of the cylinder in the second linear direction and extending in the first linear direction, and a second horizontal passage connecting the first horizontal passages located on both sides of the cylinder in the second linear direction.

5. An engine as claimed in claim 2 or 3, wherein the cylinder unit comprises a cylinder block including the cylinders, and a cylinder head disposed on the upper surface of the cylinder block and covering the upper ends of the cylinders, and the oil drain passage, the discharge passage and the horizontal passage are formed inside a rib provided on the side surface of the cylinder block.

6. An engine as described in claim 5, wherein the cylinders are arranged at intervals in a first linear direction perpendicular to the vertical direction, and the ribs extending in the vertical direction and including the oil drain passage and the discharge passage therein are each positioned between the cylinders adjacent to each other in the first linear direction.

7. An engine as claimed in any one of claims 1 to 3, wherein the cylinder unit includes a cylinder block including the cylinders opening to an upper surface thereof, and a cylinder head disposed on the upper surface of the cylinder block and covering the upper ends of the cylinders, the exhaust passage is formed penetrating the cylinder block from the upper end to the lower end, and the upper end of the exhaust passage is closed by the cylinder head.

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