JP2015028331A - Multicylinder internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure the ventilation of a crank chamber in a simple structure.SOLUTION: To a crank chamber 5, upper and lower fresh air introduction ports 14a, 14b and a blow-by gas exhaust passage 13 are opened in the state of coming close thereto. The crank chamber 5 is partitioned into a plurality of unit spaces 5a with a partition wall 10. A vent hole 15, which is provided in the partition wall 10, is formed into a tapered shape largely opened to the side of the upper fresh air introduction port 14b. The vent hole 15 has an easy-to-flow directional property, and so an air flow 16 directed to move away from the upper fresh air introduction port 14b is created in a group of the unit spaces 5a. With the creation of the air flow 16 in the group of the unit spaces 5a, a counter flow 17 to move toward the blow-by gas exhaust passage 13 is generated in the crank chamber 5. The ventilation of the crank chamber 5 is therefore ensured in a simple structure.

Description

  The present invention relates to a multi-cylinder internal combustion engine, and is particularly characterized by the ventilation of the crankcase.

  In an internal combustion engine, a phenomenon occurs in which combustion gas or unburned gas (blow-by gas) blows through the gap between the piston and the cylinder bore into the crank chamber. Therefore, in order to prevent deterioration of the lubricating oil and to recover unburned fuel, fresh air is introduced into the crank chamber from the intake system, and blow-by gas is returned to the intake system from the blow-by gas discharge passage. However, the air may not be sufficiently circulated in the crank chamber, and blow-by gas may stay in the corners of the crank chamber.

  On the other hand, when the piston descends, the air in the crankcase acts as a resistance. Therefore, in order to reduce the pumping loss by suppressing the resistance against the downward movement of the piston, a communication hole is also provided in a partition wall between adjacent cylinder bores. As an example, Patent Document 1 discloses that the opening degree of the communication hole is adjusted according to the rotational speed of the engine. Patent Document 2 discloses that a fresh air introduction hole and a blow-by gas discharge hole are provided for each partition wall that divides the cylinder bore so as to ventilate each cylinder bore.

JP 2010-180834 A JP 2009-293549 A

  Patent Document 1 is intended to reduce pumping loss and does not teach ventilation. On the other hand, Patent Document 2 is an invention for the purpose of ventilation, and it can be said that each cylinder bore can be properly ventilated. However, since the structure becomes very complicated, the manufacturing cost increases, The presence of a large number of blow-by gas passages may reduce the strength of the cylinder block. To avoid this, the engine may be increased in size.

  The present invention has been made to improve such a current situation, and aims to improve ventilation performance with a simple structure.

  The present application is multifaceted and typical examples are specified in four claims. Of these, the invention of claim 1 has a crank chamber in which a crankshaft is disposed and a plurality of cylinder bores communicating with the crank chamber, and each cylinder bore is connected to the crankshaft by a connecting rod. A piston is removably inserted, and a partition wall is formed integrally between adjacent cylinder bores in the crank chamber, and a fresh air inlet and a blow-by gas outlet are opened. In the configuration, a vent hole communicating with the adjacent cylinder bore is formed in the partition wall that partitions the crank chamber so that air can easily flow in one direction facing the axial direction of the crankshaft as the piston moves. ing.

  The invention of claim 2 has a crank chamber in which a crankshaft is disposed, and a plurality of cylinder bores communicating with the crank chamber, and each cylinder bore is connected to the crankshaft by a crank arm and a connecting rod. The piston is reciprocally inserted into the crank arm, and a counterweight is integrally provided on the crank arm, while the crank chamber has a portion of each cylinder bore as viewed from the axial direction of the crankshaft. The basic structure is such that a unit space partitioned by front and rear partition walls is formed and a fresh air inlet and a blow-by gas outlet are opened.

  Further, in the basic configuration, a ventilation hole penetrating the partition wall is formed on both the front and rear partition walls sandwiching the unit space when viewed from the axial direction of the crankshaft so that the counterweight rotates when the piston is lowered. In this way, the air flow rate of both the vent holes is shifted so as to change, so that the air is directed so as to flow from one adjacent unit space to the other unit space in accordance with the movement of the piston.

  According to a third aspect of the present invention, in the same basic configuration as in the second aspect, the partition wall separating the unit spaces has a vent hole communicating with an adjacent unit space, and the counterweight has air when the piston is lowered. The guide part which guide | induces so that many may flow toward the adjacent unit space is formed.

  According to a fourth aspect of the present invention, in the same basic structure as in the second aspect, a partition wall separating the unit spaces has a vent hole communicating with an adjacent unit space, and the counterweight or crank arm has the counterweight Or the blade | wing part which sends air toward the adjacent unit space with the rotation of a crank arm is provided.

  In the present invention, the inventions of claims 1 to 4 can be appropriately combined. For example, a stronger air flow can be formed by combining the invention of claim 1 and the invention of claim 4.

  In any of the inventions, since the direction of the air can be imparted so that the air in the crank chamber flows from one unit space adjacent to the next to the next unit space, a crank having a plurality of unit spaces arranged in the axial direction of the crankshaft. An air flow flowing in the axial direction of the crankshaft can be formed in the chamber.

  For this reason, it is easy to create a strong fresh air flow by applying a fresh air to the air flow that flows across the unit space, or to generate an air flow that flows through the inside of the crank chamber. . Then, by directing the air flow generated in the crank chamber toward the blow-by gas discharge port, the crank chamber can be thoroughly ventilated to accurately recirculate the blow-by gas. Thereby, deterioration of oil can be suppressed.

  In addition, since the air flow is formed using the vent holes provided in the partition wall, the pumping loss can be reduced. From another viewpoint, it is possible to improve ventilation by using a vent hole for reducing pumping loss. Therefore, it is possible to prevent the structure from becoming complicated. There will be no problems such as a significant increase in cost and a decrease in the strength or size of the cylinder block.

  According to the first to third aspects of the present invention, directionality is imparted to the air flow (particularly, the flow when the piston descends) due to the movement of the piston. Since there is no need for special processing, the conventional crank arm and counterweight can be used as they are.

  On the other hand, according to the third and fourth aspects of the present invention, the counterweight or the crank arm is processed, and the cylinder block does not need to be specially processed. Therefore, there is an advantage that the processing is easy. Moreover, since the invention of claim 4 forcibly forms an air flow, it can be said that the ventilation performance is particularly excellent.

  In any of the inventions, when the fresh air introduction port is arranged at the start end portion of the air flow that flows across the unit space of the crank chamber, the blow-by gas is put into the blow-by gas discharge port on the air flow containing the fresh air. It is particularly suitable because it can be accurately guided.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows 1st Embodiment, (A) is a vertical front view of an internal combustion engine, (B) (C) is a figure which shows the flow of the gas between cylinder bores. (A) is the IIA-IIA sectional view taken on the line of FIG. 1 (A), (B) is the BB sectional view taken on the line (A). It is a figure which shows 2nd-4th embodiment which is a modification of 1st Embodiment. (A) is a figure which shows 5th Embodiment, (B) is a figure which shows 6th Embodiment. (A) is a figure which shows 7th Embodiment, (B) is a figure which shows 8th Embodiment. (A1) is a partial front view of the ninth embodiment, (A2) is a view taken along A2-A2 of (A1), (B1) is a partial front view of the tenth embodiment, and (B2) is B2- of (B1). B2 view and (C) are side views of the eleventh embodiment. It is a figure which shows 12th Embodiment, (A) is a front view, (B) is a top view of (A). It is a figure which shows 13th Embodiment, (A) is a side view of a crank arm, (B1)-(B3) are each the other examples which looked at (A) from the BB view direction.

(1) Structure of First Embodiment Next, an embodiment of the present invention will be described with reference to the drawings. First, the first embodiment shown in FIGS. The first embodiment embodies the invention of claim 1. In the following description, the terms “front”, “side”, and “plane” are used, but the front view is defined as a state viewed from a direction orthogonal to the axis of the crankshaft and the axis of the cylinder bore as shown in FIG. The side view is defined as viewed from the axial direction of the crankshaft, and the plan view is defined as viewed from above the axial direction of the cylinder bore.

  The internal combustion engine of the present embodiment has four cylinders. Therefore, four cylinder bores 2 are arranged in series in the cylinder block 1 in a plan view, and a piston 3 is slidably fitted in each cylinder bore 2. . A cylinder head 4 is fixed to the upper surface of the cylinder block 1. A lower portion of the cylinder block 1 is a crank chamber 5, and a crankshaft 6 that is long in the direction in which the cylinder bores 2 are arranged is rotatably held in the crank chamber 5. Each piston 3 is connected to the crankshaft 6 through a pair of crank arms 7 and connecting rods 8. As shown in FIG. 2A, the crank arm 7 is integrally formed with a counterweight 7a that protrudes to the opposite side of the crankpin 9 with the rotational axis interposed therebetween.

  The crank chamber 5 is partitioned by a partition wall 10 for each cylinder bore 2. In addition, although the left and right ends of the crank chamber 5 are constituted by outer walls, for convenience, the left and right outer walls are also referred to as partition walls 10. Therefore, the crank chamber 5 has a unit space 5 a that communicates with each cylinder bore 2, and each unit space 5 a is partitioned by a partition wall 10 that is positioned forward and backward when viewed from the axial direction of the crankshaft 6.

  An intermediate crank journal 4 a excluding both ends of the journals of the crankshaft 6 is rotatably held via an intermediate bearing 11 at the partition 10. An oil pan 1 c is fixed to the lower surface of the cylinder block 1.

  The blow-by gas blown into the crank chamber 5 returns to the intake system. Therefore, a blow-by gas discharge passage 13 is provided in the vicinity of the partition wall 10 near the chain case 12 in the side surface of the cylinder block 1. Accordingly, the lower end of the blow-by gas discharge passage 13 opens into the crank chamber 5 as a blow-by gas discharge port 13a. Although not shown, the blow-by gas discharge passage 13 communicates with a gas-liquid separation chamber provided in the cylinder head cover, and after oil is collected in the gas-liquid separation chamber, it is sent to the intake system.

  Further, fresh air is introduced into the crank chamber 5 from the intake system in order to prevent the deterioration of the lubricating oil. For this reason, the crankshaft is connected to the counterweight (outer wall) 1a of the cylinder block 1 on which the chain case 12 overlaps. The lower fresh air inlet 14a located below 6 and the upper fresh air inlet 14b located above the crankshaft 6 are vacant in a state of penetrating inward and outward. Therefore, in the present embodiment, the blow-by gas discharge passage 13 and the fresh air inlets 14 a and 14 b are arranged in a state that is substantially close to the axial direction of the crankshaft 6.

  In this embodiment, the chain case 12 forms a fresh air introduction passage (more precisely, the space between the cylinder block 1 and the cylinder head 10), and the upper fresh air introduction port 14b is a unit at the left end. It opens to the space 5a. The fresh air introduction passage may be a vertically long through hole formed in the cylinder block 1 and the cylinder head 4. Alternatively, the fresh air introduction passage may be constituted by a pipe or a tube and connected to the cylinder block 1 via a joint. On the other hand, the blow-by gas discharge passage 13 can also be an external structure constituted by a pipe or a tube.

  Each partition wall 10 is provided with a vent hole 15 communicating with the adjacent unit space 5a. This vent hole 15 is provided on the side close to the upper fresh air introduction port 14b (the side close to one end 1a of the cylinder block 1). The opening area is large, and the opening area on the side far from the upper fresh air inlet 14b (the side close to the other end 1b of the cylinder block 1) is tapered. The upper fresh air inlet 14 b is also tapered with the same posture as each vent hole 15.

(2) Summary of First Embodiment In the above configuration, during the downward stroke of the piston 3, the air in the unit space 5a in the crank chamber 5 tends to escape from the two vent holes 15 located on both sides thereof. Since the vent hole 15 is tapered, as shown in FIG. 1 (B), the vent hole 15 that is greatly opened toward the unit space 5a has an inductive effect, and the amount of inflowing air is increased so that the vent hole 15 is directed toward the unit space 5a. The amount of inflow into the vent hole 15 having a small opening area is small.

  Therefore, as a result, directionality is imparted so that a large amount of air flows in the unit space 5a on the side farther from the upper fresh air inlet 14b in the adjacent unit spaces 5a. That is, as indicated by the white arrow, in one unit space 5a, directionality is imparted so that air flows from the unit space 5a close to the upper fresh air inlet 14b toward the unit space 5a, and as a result. In the group of unit spaces 5a, an air flow 16 that flows from the one end 1a side of the cylinder block 1 toward the other end 1b side is generated.

  Since the upper fresh air inlet 14b has the same shape as each vent hole 15, in the leftmost unit space 5a, fresh air sent from the upper fresh air inlet 14b is introduced into the adjacent unit space 5a by the air flow 16. It will receive a suction action that flows toward you. As a result, fresh air is sent into the crank chamber 5.

  Further, in the ascending stroke of the piston 3, a phenomenon occurs in which air is sucked from the adjacent cylinder bore 2, but as shown in FIG. While a large amount of air is sucked from the unit space 5a, the amount of air from the vent hole 15 that is largely open to the unit space 5a is small. Therefore, even in the upward stroke of the piston 3, it is close to the upper fresh air inlet 14b. Air 16 is provided with directionality so as to flow toward the unit space 5a far from the unit space 5a on the side.

  Since the piston 3 moves in the opposite direction in the adjacent cylinder bore 2, the air pushing action and the pulling action are alternately generated in the adjacent unit space 5a. For this reason, in the adjacent unit space 5a, It is presumed that the air amount 16 is generated more strongly due to the synergistic effect that the strongly pressed air in one unit space 5a is pulled strongly in the other unit space 5a.

  The movement of the piston 3 generates an air flow 16 in the group of unit spaces 5a, which is directed to flow from the one end 1a side of the cylinder block 1 to the other end 1b side. As shown in FIG. 1A, a countercurrent (circulation flow) 17 of air flowing from the other end 1b side of the cylinder block 1 toward the one end 1a side is generated below the group of unit spaces 5a. However, the countercurrent 17 and the flow of fresh air from the lower fresh air inlet 14a collide with each other below the blow-by gas discharge passage 13, whereby the flow of fresh air from the countercurrent 17 and the lower fresh air inlet 14a. And flows into the blow-by gas discharge passage 13 while changing the direction upward.

  In this way, since an air flow that flows so as to lick the inside of the crank chamber 5 is generated, the blow-by gas does not stay in the crank chamber 5, and the blow-by gas can be accurately recirculated to the intake system. For this reason, the crank chamber 5 can be maintained in a ventilated state to prevent the deterioration of the lubricating oil, and the blow-by gas can be reliably discharged to contribute to the improvement of fuel consumption. Moreover, since the air pushed by the piston 3 quickly escapes to the adjacent unit space 5a, the resistance to the piston 3 is reduced and the pumping loss can be reduced.

  In the present embodiment, the upper fresh air introduction port 14b and each vent hole 15 are all tapered in the same posture. However, when the number of cylinder bores is large, such as 6 cylinders, the central partition 10 is formed. It is also possible to reverse the taper of the vent hole 15 and provide the blow-by gas discharge passages 13 at two locations on the one end 1a side and the other end 1b side. The fresh air inlet is preferably provided in the vicinity of the central partition 10.

  It is also possible to provide fresh air inlets at a plurality of locations separated in the axial direction of the crankshaft 6. Alternatively, it is also possible to provide a plurality of both blow-by gas and lower fresh air inlets separated in the axial direction of the crankshaft 6. When a plurality of both are provided, the number can be varied.

(3). Second to Fifth Embodiments The second to fourth embodiments shown in FIG. 3 also embody Claim 1. Among these, in 2nd Embodiment of FIG. 3 (A), the air flow 16 which flows into the other unit space 5a from one unit space 5a is changed by changing the opening area of the vent hole 15 of the two adjacent partition walls 10. FIG. It is composed. On the other hand, in the third embodiment shown in FIG. 3B, the air flow 16 flowing in the unit space 5a is formed by changing the number of the vent holes 15. Needless to say, the second embodiment, the third embodiment, and the first embodiment can be combined.

  In the fourth embodiment shown in FIG. 3C, by forming a recess 19 that communicates with one of the vent holes 15 and partially reducing the width of the partition wall 10 at the one vent hole 15, The flow resistance of the one vent hole 15 is reduced. Therefore, the air tends to flow from the vent hole 15 provided with the recess 18, and as a result, the air flow 16 is generated.

  The air flow 16 is generated by a difference in flow resistance between the vent holes 15 of the two partition walls 10 sandwiching the cylinder bore 2. Therefore, as a means for giving a difference in flow resistance, it is also possible to change the lengths of the two vent holes 15 arranged with the unit space 5a interposed therebetween. Although illustration is omitted, it is also possible to provide a check valve such as a rotary type that allows only ventilation to one side in the ventilation hole 15, and such a configuration is also included in claim 1.

(4). Fifth to eighth embodiments (FIGS. 4 and 5)
Next, fifth to eighth embodiments shown in FIGS. These embodiments embody the invention of claim 2. 4 and 5, the partition wall 10 is viewed from the axial direction of the crankshaft 6, and the vent hole 15 ′ indicated by a white circle is the partition wall 10 (not shown in the drawing) on the front side of the cylinder bore 2 shown in the figure. The ventilation hole 15 ″ indicated by a shaded circle is opened in the partition wall 10 on the other side of the cylinder bore 2 shown in the figure.

  In the fifth embodiment shown in FIG. 4 (A), the two ventilation holes 15 'and 15 "are both located in the area inside the rotation locus 20 on the outer periphery of the counterweight 7a, and on the near side. The vent hole 15 ′ and the vent hole 15 ″ on the other side are displaced along the rotational direction of the counterweight 7a.

  In the illustrated example, the two ventilation holes 15 ′ and 15 ″ are provided at symmetrical positions with respect to the axis 21 of the cylinder bore 2 when viewed from the axial direction of the crankshaft 6. It is also possible to say that the hole 15 ′ is disposed in the vicinity of the axis 21 of the cylinder bore 2 and the vent hole 15 ″ on the other side is disposed on the right side thereof. It is also possible to make the distances from the rotation axis of the crankshaft 6 to both the vent holes 15 ′ and 15 ″ different.

  In the embodiment shown in FIG. 4A, the front vent hole 15 'is closed first by the rotation of the crank arm 7 during the downward stroke of the piston 3, so that the front side is kept in a state where the dynamic pressure of air is high. The vent hole 15 'is blocked. Therefore, the air is difficult to escape from the front vent hole 15 'and is easy to escape from the far vent hole 15' '. Therefore, the air is directed so as to flow from the front side to the other side toward the paper surface. Is granted.

  That is, in this embodiment, the air flow rate of the two vent holes 15 is different due to the difference in the timing of closing by the two vent holes 15 or the counterweight 7a. As a result, the one cylinder bore 2 of the crankshaft 6 A large air flow 16 is generated. In this embodiment, it is preferable to provide the upper fresh air introduction port 14b in the partition wall 10 on the near side of the unit space 5a located on the most front side.

  In the sixth embodiment shown in FIG. 4B, the front vent hole 15 ′ is positioned inside the rotation locus 20 of the counterweight 7a, and the other vent hole 15 ″ is the rotation locus 20 of the counterweight 7a. In other words, in this embodiment, the arrangement area of the vent hole 15 'on the near side and the vent hole 15 "on the far side is separated into the outer side and the inner side of the rotation locus 20 of the counterweight 7a. doing.

  Accordingly, when the piston 3 descends, a large amount of air flows through the far side vent hole 15 'and hardly flows into the near side vent hole 15 ". Therefore, also in this embodiment, the front side is orthogonal to the paper surface. An air flow is formed that flows from one side to the other.

  The seventh embodiment shown in FIG. 5 (A) is a combination of the fifth embodiment and the sixth embodiment, and the vent hole 15 ′ on the near side is inside the rotation locus of the counterweight 7 a and the cylinder bore 2. While the counterweight 7a is positioned on the front side in the rotational direction of the counterweight 7a with respect to the shaft center 21, the far side vent hole 15 ″ is located outside the rotational locus of the counterweight 7a and on the counterweight than the shaft center 21 of the cylinder bore 2. 4A, in this embodiment, when the piston 3 moves downward, air flows from the near side to the far side perpendicular to the paper surface.

In the eighth embodiment shown in FIG. 5B, the front side vent hole 15 'and the far side vent hole 15''both have a reference hole 15a at a common position indicated by a black circle. 15a is located on the inner side of the rotation locus of the counterweight 7a and at the position of the axis 21 of the cylinder bore 2. The vent hole 15 ″ on the far side extends upward in communication with the reference hole 15a. In this embodiment, the opening area of the vent hole 15 'on the near side is smaller than the opening area of the vent hole 15''on the far side. Therefore, when the piston 3 descends, a large amount of air flows through the vent hole 15 ″ on the other side. Accordingly, an air flow is generated between the adjacent unit spaces 5a from the near side perpendicular to the paper surface to the other side.

  The extended portion 15b of the vent hole 15 ″ on the far side may extend toward the front in the rotational direction of the counterweight 7a, as shown by the alternate long and short dash line. Since air easily flows, an air flow is generated from the near side toward the other side toward the paper surface.

(5) Ninth to eleventh embodiments Next, ninth to eleventh embodiments shown in FIG. 6 will be described. These embodiments embody the invention of claim 3. In the ninth embodiment shown in FIGS. 6A1 and 6A2, corners are diagonally formed on one side of the two outer circumferences of the counterweight 7 a as an example of the guide portion. A cut portion 23 is provided. Although not shown, each partition wall 10 has a vent hole 15 in the same portion as viewed from the axial direction of the crankshaft 6.

  On the other hand, in the tenth embodiment shown in FIG. 6 (B), a sunk portion 23 having a half circumference is formed on one of the pair of counterweights 7a. Further, in the eleventh embodiment shown in FIG. 6 (C), when forming the Nusumi portion 23 over the entire length of the counterweight 7a in the circumferential direction, the depth (or width) gradually decreases from one end to the other end. It is set to become (or become larger).

  In these embodiments, when the crank arm 7 moves upward in accordance with the downward movement of the piston 3, the air pushed by the piston 3 has a counterweight as shown in FIGS. 6 (A1) and (B1). 7a is guided by the nose portion 23. As a result, in one unit space 5a, there is a tendency that a large amount of air flows on one side of the two unit spaces 5a located on both sides of the unit space 5a, and as a result, a unidirectional air flow 16 flows in the group of unit spaces 5a. It is formed.

(6). Twelfth to Thirteenth Embodiment FIG. 7 shows a twelfth embodiment that embodies the invention of claim 4. In this embodiment, as the blade means is formed as an example of the blade means on the outer periphery of the counterweight 7a, a slant cut portion 23 is formed, so that the counterweight 7a is rotated to rotate in one direction toward the axial direction of the crankshaft 6. The air flow 16 is forcibly generated.

  The Nusumi portion 23 is set so that the depth and width gradually decrease in the direction opposite to the rotation direction. For this reason, the air flow 16 flowing in one direction is forced by the rotation of the counterweight 7a. Generated. In the example of FIG. 7, the Nusumi portion 23 is formed on both of the two counterweights 7a, but it may be formed only on one side. In addition, when the Nusumi portion 23 is formed on an uneven surface as shown in FIG.

  The thirteenth embodiment shown in FIG. 8 also embodies claim 4, and in this embodiment, the stepped crushed portion 23 a as shown in (B1) on the outer peripheral surface of the counterweight 7 a and (B1) By forming such a slanted ridged portion 23b or a sawtooth-shaped crushed portion 23c as shown in (B3), the counterweight 7a has a blade function to push air sideways.

  In this embodiment, since the base end edge 23d of the Nusumi parts 23a to 23c is orthogonal to the longitudinal line 24 of the crank arm 7 when viewed from the axial direction of the crankshaft 6, the air is removed by the rotation of the counterweight 7a. 23a, 23b, and 23c are subjected to a pushing action in the axial direction of the crankshaft 6, thereby generating an air flow 16 in the axial direction of the crankshaft 6. Instead of forming the nosumi part 23, a blade part may be projected.

  The present invention can actually be embodied in an internal combustion engine. Therefore, it can be used industrially.

1 Cylinder block 2 Cylinder bore (cylinder bore)
3 Piston 5 Crank chamber 5a Unit space 6 Crankshaft 7 Crank arm 7a Counterweight 10 Bulkhead 12 Chain case 13 Blow-by gas discharge passages 14a, 14b Fresh air inlet 15 Ventilation hole 16 Air flow generated in the unit space 17 Generated in the crank chamber Counter-current 20 Rotation trajectory of counterweight outer circumference 23, 23a-23c

Claims (4)

It has a crank chamber in which a crankshaft is disposed, and a plurality of cylinder bores communicating with the crank chamber, and a piston connected to the crankshaft by a connecting rod is fitted into each of the cylinder bores so as to freely reciprocate. In the crank chamber, a partition located between adjacent cylinder bores is integrally formed, and a fresh air introduction port and a blow-by gas discharge port are opened,
The partition wall partitioning the crank chamber is formed with a vent hole communicating with an adjacent cylinder bore in a form that allows air to easily flow in one direction facing the axial direction of the crankshaft as the piston moves.
Multi-cylinder internal combustion engine. It has a crank chamber in which a crankshaft is disposed, and a plurality of cylinder bores communicating with the crank chamber, and a piston connected to the crankshaft by a crank arm and a connecting rod is reciprocally movable in each cylinder bore. The crank arm is integrally provided with a counterweight. On the other hand, the crank chamber is partitioned by front and rear partitions for each cylinder bore as viewed from the axial direction of the crankshaft. A unit space is formed, and a fresh air inlet and a blow-by gas outlet are open,
A ventilation hole penetrating the partition wall on both front and rear sides sandwiching the unit space when viewed from the axial direction of the crankshaft, and a ventilation amount of both the ventilation holes due to the rotation of the counterweight when the piston is lowered Is arranged so that the air flows from one unit space adjacent to the other unit space in accordance with the movement of the piston.
Multi-cylinder internal combustion engine. It has a crank chamber in which a crankshaft is disposed, and a plurality of cylinder bores communicating with the crank chamber, and a piston connected to the crankshaft by a crank arm and a connecting rod is reciprocally movable in each cylinder bore. The crank arm is integrally provided with a counterweight. On the other hand, the crank chamber is partitioned by front and rear partitions for each cylinder bore as viewed from the axial direction of the crankshaft. A unit space is formed, and a fresh air inlet and a blow-by gas outlet are open,
The partition that separates the unit spaces has a vent hole communicating with an adjacent unit space, and guides the counterweight so that a large amount of air flows toward the adjacent unit space when the piston is lowered. Forming the
Multi-cylinder internal combustion engine. It has a crank chamber in which a crankshaft is disposed, and a plurality of cylinder bores communicating with the crank chamber, and a piston connected to the crankshaft by a crank arm and a connecting rod is reciprocally movable in each cylinder bore. The crank arm is integrally provided with a counterweight. On the other hand, the crank chamber is partitioned by front and rear partitions for each cylinder bore as viewed from the axial direction of the crankshaft. A unit space is formed, and a fresh air inlet and a blow-by gas outlet are open,
The partition wall separating the unit spaces has a vent hole communicating with the adjacent unit space, and the counter weight or crank arm is directed toward the adjacent unit space as the counter weight or crank arm rotates. The blades to send
Multi-cylinder internal combustion engine.

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