Cylinder block

Abstract

To provide a technique that enables accurate gas liquid separation without causing complication of a structure and increase in sizes of components in the future, even in the case where generation amount of blow-by gas is large like a hybrid engine.SOLUTION: A blow-by gas passage 17 penetrating vertically is formed on a side wall 1a of a cylinder block 1. The blow-by gas passage 17 is partitioned into a first portion 19 and a second portion 20 while sandwiching a lateral hole-shaped expansion chamber 18. The first portion 19 is narrowed upwardly and has step parts 26, 27 whose cross sectional area is sharply changed. Since a lower end of the first portion 19 is expanded, inflow speed of blow-by gas is low. Thus, even if foamy oil mist is generated in a crank chamber, inflow to the first portion 19 is inhibited so that clogging can be prevented. Since blow-by gas collides with the step parts 26, 27 while increasing the inflow speed, an oil mist collection effect is high.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an engine cylinder block, and is characterized by the structure of a blow-by gas passage. [Background technology]

[0002] In gasoline and diesel engines, a phenomenon occurs in which blow-by gas (PCV gas) blows through the gap between the piston and the cylinder bore into the crankcase during the combustion process. To prevent this, the blow-by gas is recirculated to the intake system to return unburned gas to the cylinder bore. However, since the blow-by gas contains oil, an oil separator (gas-liquid separation chamber) is installed in the middle of the recirculation of the blow-by gas to remove oil mist. collection is doing.

[0003] The placement position of the oil separator can be roughly divided into two cases: one where it is provided on one side of the cylinder block (for example, Patent Document 1) and one where it is provided on the head cover (for example, Patent Document 2). When the oil separator is provided on the head cover, the volume of the oil separator can be increased, so the oil collection It has excellent performance.

[0004] And the oil separator is installed in the head cover. case The cylinder block is formed with a blow-by gas passage that penetrates vertically. Established in The blow-by gas passage and a blow-by gas passage provided in the head cover are connected via the cylinder head, and the blow-by gas is guided to the oil separator. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-092729 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-250159 Summary of the Invention [Problem to be solved by the invention]

[0006] Now, hybrid engines are becoming more popular to improve fuel efficiency and reduce carbon dioxide emissions, but hybrid engines tend to be operated at high loads more frequently to charge the battery, and to be operated in cold environments more frequently, which tends to increase the amount of blow-by gas generated compared to conventional engines. For this reason, the oil separator in the head cover separates the oil. collection There is a concern that the PCV valve may not be able to fully release the oil, causing oil mist to spray out.

[0007] Furthermore, when the amount of blow-by gas generated increases, the blow-by gas and oil mist tend to mix and generate foamy mist, which can clog the blow-by gas passage in the cylinder block, blocking the passage or restricting the flow of blow-by gas in the passage. When this phenomenon occurs, the intake negative pressure causes a sudden rise in the negative pressure in the oil separator, and a large amount of foamy mist containing oil in the blow-by gas passage is sucked into the oil separator, causing the oil mist to be generated. collection There is also the problem of further deterioration of performance.

[0008] One solution to this problem would be to increase the size of the head cover to increase the volume of the oil separator, but this would raise new problems such as increased costs and weight, which would worsen fuel economy.

[0009] The present invention was made against the background of the current situation, and aims to disclose a technique that can deal with an increase in blow-by gas with a simple structure. [Means for solving the problem]

[0010] The present invention is "A cylinder block in which a blow-by gas passage is formed in part of the peripheral wall, the lower end of which opens into the crank chamber and the upper end of which opens onto the upper surface." This cylinder block is intended for: "At least a part of the blow-by gas passage is formed with an upper narrowed portion whose cross-sectional area at the upper end is smaller than that at the lower end, The upper narrowed portion has a plurality of stepped discontinuous portions with abrupt changes in cross-sectional area, each having a different height. That In the basic configuration, "An expansion chamber is formed in the blow-by gas passage at a height position located to the side of the cylinder bore, extending from the outer surface of the cylinder block toward the cylinder bore so as to cross the blow-by gas passage, and the open end of the expansion chamber is closed with a plug, Furthermore, the discontinuous portions of the plurality of stages are formed in a portion below the extension chamber. It has the following characteristics.

[0011] In the present invention, although it is possible to form the entire length of the blow-by gas passage as a narrowed portion at the top (widened portion at the bottom), it is preferable to form at least a part of the passage near the bottom as a narrowed portion at the top, i.e., it is preferable that the widest part of the passage is open to the crank chamber.

[0012] Claim 2 Now, the claim 1 In The configuration adopted is that "the multi-stage discontinuous portion includes a first step portion and a second step portion, and the first step portion and the second step portion are formed on opposing surfaces across the axis of the blow-by gas passage." [Effects of the Invention]

[0013] In the present invention, first, by forming an upper narrowing portion (or a lower widening portion) in the blow-by gas passage, the flow velocity of the blow-by gas entering the blow-by gas passage can be reduced. Therefore, even if oil mist turns into foam in the crankcase, the foamy oil mist can be prevented or significantly suppressed from entering the blow-by gas passage. This makes it possible to prevent or significantly suppress the phenomenon of the blow-by gas passage being blocked or the phenomenon of an increase in the flow resistance of the blow-by gas.

[0014] In particular, it is preferable to align the lower end of the upper narrowing portion with the lower end of the blow-by gas passage and set the opening area of ​​the lower end of the blow-by gas passage to the largest possible value, as this effectively prevents foamy oil mist from entering (being sucked up) into the blow-by gas passage.

[0015] Furthermore, in the present invention, since the upper narrowed portion is formed in the blow-by gas passage, the opportunity for the blow-by gas to come into contact with the inner surface of the upper narrowed portion increases, and the oil Collection It can improve functionality.

[0016] Furthermore, in the present invention, since the upper narrowed portion has a plurality of discontinuous portions, the blow-by gas flowing upward through the upper narrowed portion collides with the plurality of discontinuous portions, increasing the chance of oil mist coming into contact with the inner surface of the upper narrowed portion. collection The enhancement effect can be greatly enhanced by a step-like discontinuity.

[0017] As described above, the present invention can prevent or significantly suppress the flow of foamy oil mist into the blow-by gas passage, and can also prevent or significantly suppress the flow of oil mist into the blow-by gas passage. collection Combined with the ability to improve performance, this allows the gas-liquid separation function of the oil separator to be ensured and the necessary ventilation performance to be ensured, even in engines that generate a large amount of blow-by gas, such as hybrid engines, without enlarging the head cover.In fact, by forming the blow-by gas passage so that it widens downward, the cylinder block can be made thinner and lighter, which also contributes to improved fuel efficiency. In particular, claims 2 When the first step portion and the second step portion are arranged to face each other as described above, a strong direction change effect is given to the blow-by gas, and the opportunity for the blow-by gas to come into contact with the blow-by gas passage is increased. collection This can greatly improve the effect (adhesion).

[0018] Furthermore, in the present invention,The flow velocity of the blow-by gas decreases in the expansion chamber while ascending through the blow-by gas passage, increasing the chances of the blow-by gas coming into contact with the inner surface of the expansion chamber, resulting in the generation of oil mist. collection This further improves the functionality. In other words, the oil mist is released in two stages, at the upper narrowing section and the expansion chamber. collection There is no increase in flow resistance of blow-by gas (increase in pressure loss). Also, even if foamy oil mist rises, it is reliably contained in the expansion chamber. capture This effectively prevents the blow-by gas passage from being blocked by foamy oil mist.

[0019] And because the expansion chamber is positioned across the blow-by gas passage, the blow-by gas is forced into the dead-end expansion chamber, preventing oil mist from entering. collection In particular, if the blow-by gas passages are offset horizontally (in a direction intersecting the blow-by gas passages) above and below the extension chamber as in the embodiment, the blow-by gas does not pass through the extension chamber but is guided toward the inner part of the extension chamber, which increases the chance of the blow-by gas coming into contact with the inner surface of the extension chamber, thereby reducing the amount of oil mist. collection This can significantly enhance the performance improvement effect.

[0020] Furthermore, The present invention When the expansion chamber is formed in such a position that it crosses the blow-by gas passage, it has the effect of being able to increase the volume of the expansion chamber reasonably, it has the effect of making the cylinder block lighter by reducing its thickness, and it also has the effect of transferring the heat of the cylinder bore to the blow-by gas during cold starting and cold operation, facilitating oil drainage.

[0021] The expansion chamber can be formed by a protrusion on the side of the mold when the cylinder block is cast. However, the protrusions are This serves as a tip holding member for the butt joint of the cast pin of the blow-by gas passage inserted from the top and bottom of the cylinder block during casting. And even if burrs are generated by providing the protrusions, After casting, the butt joint of the core pin can be deburred by drilling or punching, so processing is easy and no manufacturing problems arise. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a bottom view of the embodiment. [Figure 2] 2A is a cross-sectional view taken along line II-II in FIG. [Figure 3] 1A is a cross-sectional view taken along line IIIA-IIIA in FIG. 1, and FIG. 1B is a cross-sectional view taken along line IIIB-IIIB in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0023] (1) Structure of the embodiment Next, an embodiment of the present invention will be described with reference to the drawings. This embodiment is applied to a hybrid engine. In the following, the terms "front-rear" and "left-right" are used to specify directions, but the front-rear direction is the crankshaft direction, and the left-right direction is the direction perpendicular to the crankshaft direction and the cylinder bore axis (the width direction of the engine). Regarding "front" and "rear," the side where the timing chain is located is referred to as the front, and the side where the transmission is located is referred to as the rear. Directions are indicated in the drawings as necessary.

[0024] The basic structure of the cylinder block 1 is the same as that of a conventional cylinder block, with a plurality of cylinder bores 2 arranged in the crankshaft direction. Next door A partition wall 3 is formed between the aligned cylinder bores 2, and the crank journals of the crankshaft 6 are rotatably held in crank journal receiving portions 5 provided on the end wall 4 and the partition wall 3 via crank caps 7 and metal bearings 8. The crank caps 7 are fixed to the cylinder block 1 with bolts 9, and the underside of the cylinder block 1 is provided with a group of female threaded holes 9a into which the crank cap bolts 9 are screwed.

[0025] An oil pan 10 is fastened to the underside of the cylinder block 1 with oil pan bolts 11. Therefore, on the underside of a flange provided on the side wall 1a of the cylinder block 1, a group of oil pan female threaded holes 12 into which the oil pan bolts 11 are screwed are arranged.

[0026] 2, a cylinder head 13 is fastened to the top surface of the cylinder block 1 by a group of head bolts 15 via a gasket 14. Furthermore, the cylinder block 1 is formed with a water jacket 16 that surrounds the group of cylinder bores 2.

[0027] A blow-by gas passage 17 is formed to penetrate vertically through a portion of the intake-side side wall 1a of the cylinder block 1 that partially overlaps with the rear-positioned partition wall 3. As shown in Fig. 2, the blow-by gas passage 17 is made up of an extension chamber 18 located at an intermediate height position, a first portion 19 located below the extension chamber 18, and a second portion 20 located above the extension chamber 18. Note that the second portion 20 is not visible in the bottom view of Fig. 1.

[0028] The cylinder block 1 is made up of an upper die that overlaps the product from above and an upper die that overlaps the product from below. and Multiple overlapping sides Type Use hand, It is manufactured by casting or die casting. The first portion 19 of the blow-by gas passage 17 is formed by a core pin (or protrusion) provided on the lower mold, the second portion 20 is formed by a core pin (or protrusion) provided on the upper mold, and the expansion chamber 18 is formed by a protrusion provided on one of the horizontal molds.

[0029] The horizontal protrusions for forming the expansion chamber 18 serve as retaining members against which the tips of the core pins provided in the upper and lower dies come into contact, making it easy to form the blow-by gas passage 17 by casting or die-casting. Furthermore, even if burrs occur in the overlapping areas between the core pins of the upper and lower dies and the horizontal protrusions, they can be removed by drilling or punching after molding, making post-processing easy.

[0030] In this embodiment, the first portion 19 corresponds to the upper narrowed portion described in the claims. The second portion 20 is depicted as having a straight shape, but in reality, it has a slightly upwardly tapered shape due to the draft angle of the core pin used during manufacturing.

[0031] The second portion 20 is disposed closer to the cylinder bore 2 than the first portion 19. Therefore, the first portion 19 is offset relative to the second portion 20. In this case, the first portion 19 and the second portion 20 are offset so as not to overlap across the expansion chamber 18 in a plan view (and a bottom view), but they may also be configured so as to partially overlap. In addition, the plan area (cross-sectional area) of the second portion 20 is smaller than the plan area of ​​the upper end of the first portion 19.

[0032] The expansion chamber 18 is a circular horizontal hole that crosses the blow-by gas passage 17 and opens toward the outer wall of the cylinder block 1, with the open end being closed by a plug 21. The expansion chamber 18 is composed of a main portion 18a that communicates with the first portion 19 and the second portion 20, and a rear portion 18b that is smaller in diameter than the main portion 18a, and the rear portion 18b extends to below the head bolt 15 and the water jacket 16. Therefore, the expansion chamber 18 is located at the same height as the lower portion of the cylinder bore 2. The cross-sectional area of ​​the main portion 18a that constitutes the expansion chamber 18 (the cross-sectional area when the expansion chamber 18 is cut vertically) is 1 / 2 times that of the first portion 19. Top It is larger than the planar area (see especially Figure 3(B)).

[0033] The first portion 19 of the blow-by gas passage 17 is formed across the partition wall 3 and the outer wall of the cylinder block 1, and is basically shaped approximately symmetrically in the front-to-rear direction across the center line that divides the partition wall 3 into front and rear halves.

[0034] 3(A) and 2, the first portion 19 is composed of a lower stage 23 whose inner surface 23a is generally parallel to the axis of the cylinder bore 2, a middle stage 24 whose inner surface 24a is continuous with the upper end of the lower stage 23 and slopes outward, and an upper stage 25 whose inner surface 25a is continuous with the upper end of the middle stage 24 and is generally parallel to the axis of the cylinder bore 2.

[0035] In a vertical cross section cut along a plane including the center line of the partition wall 3 (as shown in Figure 3(A)), the outer surfaces 23b, 24b, 25b of the respective step portions 23, 24, 25 are continuous as a series of inclined surfaces tilting inward at a constant rate.

[0036] Therefore, the first portion 19 of the blow-by gas passage 17 narrows upward (widens downward) when cut along a plane including the center line of the partition wall 3. The inner surface 23a of the lower stage portion 23 and the inner surface 25a of the upper stage portion 25 are slightly inclined outward due to the draft angle provided to the core pin during manufacturing.

[0037] On the other hand, in the state shown in FIG. 3(B), the first portion 19 is cut along a vertical plane parallel to the crank axis. (Longitudinal side view) In the example, rear surfaces 23c, 24c of the lower stage 23 and middle stage 24 are continuous as inclined surfaces tilted forward at a fixed rate, but the front surface 23d of the lower stage 23 and the front surface 24d of the middle stage 24 are discontinuous such that the front surface 24d of the middle stage 24 is shifted backward. Therefore, a first step portion 26, which is an example of a discontinuous portion as defined in the claims, is formed at the boundary between the two.

[0038] 3(B), the relationship between the middle stage portion 24 and the upper stage portion 25 is such that the front surface 24d of the middle stage portion 24 and the front surface 25d of the upper stage portion 25 are continuous as an inclined surface tilted backward at a certain rate, but the rear surface 24c of the middle stage portion 24 and the rear surface 25c of the upper stage portion 25 are discontinuous such that the rear surface 25c of the upper stage portion 25 is shifted forward. Therefore, the boundary between the two also forms a second step portion 27, which is an example of a discontinuous portion as defined in the claims.

[0039] 1, lower stage 23 of first portion 19 expands to surround one oil pan female threaded hole 12. Therefore, lower stage 23 has outward bulges 23e that expand outward in the left-right direction on both the front and rear sides of oil pan female threaded hole 12.

[0040] 2, the outer surface of the outwardly bulging portion 23e of the lower portion 23 appears. Longitudinal rear viewIn the example, the outer surface 24b of the middle stage 24 and the outer surface 25b of the upper stage 25 are inclined inward at the same rate, while the outer surface 23b' of the lower stage 23 is shifted outward relative to the outer surface 24b of the middle stage 24. Therefore, a first step 26 also exists at the boundary between the outer surface 23b' of the outward bulge 23e of the lower stage 23 and the outer surface 24b of the middle stage 24.

[0041] 2, the cylinder head 13 also has a blow-by gas passage 17 that communicates with the blow-by gas passage 17 of the cylinder block 1. A head cover (not shown) is fixed to the top surface of the cylinder head 13, and the head cover also has a blow-by gas passage that communicates with the blow-by gas passage 27 of the cylinder head 13, and the blow-by gas passage of the head cover communicates with an oil separator formed by the head cover and a baffle plate. The blow-by gas that passes through the oil separator flows into the intake system (e.g., intake manifold) via the PCV valve.

[0042] 2, a baffle plate 28 against which the blow-by gas collides can be disposed below the blow-by gas passage 17. The baffle plate 28 can be provided independently, or can be attached to the oil level control baffle plate.

[0043] (2) Summary This embodiment has the above-described configuration, and compared to conventional non-hybrid engines, the cross-sectional area of ​​the second portion 20 is the same as conventional engines, but the area of ​​the lower end of the first portion 19 (the opening area of ​​the lower end of the blow-by gas passage 17) is significantly increased.

[0044] And the first part 19 as a whole AboveAlthough the opening area at the lower end of the first portion 19 is narrower than in the past, the opening area at the lower end of the first portion 19 is larger than in the past, and therefore, as shown by the arrow in Fig. 2, the flow rate of the blow-by gas when it flows into the first portion 19 is significantly lower than in the past. Therefore, even if the blow-by gas becomes turbid with the oil mist and a large amount of foamy oil mist is generated in the crankcase, the foamy oil mist has low buoyancy (because it is heavier than simple oil mist), so the flow of the foamy oil mist into the first portion 19 is prevented or significantly suppressed. This makes it possible to prevent the first portion 19 from becoming clogged.

[0045] In addition, in this embodiment, since the two-stepped portions 26, 27 are formed, the blow-by gas that flows into the first portion 19 collides with the two step portions, the first step portion 26 and the second step portion 27, and is subjected to a direction change action, so that the chance of contact with the first portion 19 increases, resulting in a high oil mist. collection In particular, even if oil mist in a foam state flows into the first portion 19, it collides with the step portions 26, 27 and is destroyed, so that the occurrence of a blockage phenomenon can be reliably prevented.

[0046] In particular, in this embodiment, the first step portion 26 and the second step portion 27 are arranged on both the front and rear sides (opposite each other), so that a strong direction change effect is given to the blow-by gas, and the opportunity for the blow-by gas to come into contact with the first portion 19 increases. collection This can greatly improve the effect (adhesion).

[0047] In further detail, since the first portion 19 is tapered upward as a whole, the flow velocity of the blow-by gas increases as it rises, but since the blow-by gas collides alternately with the front and rear step portions 26, 27 while increasing its flow velocity, the direction change action is ensured and the contact opportunity of the oil mist with the first portion 19 can be increased. collection It is highly effective.

[0048] Furthermore, in this embodiment, the extension chamber 18 is provided at a mid-height portion of the blow-by gas passage 17, so that the flow velocity of the blow-by gas that has passed through the blow-by gas passage 17 decreases in the extension chamber 18, and the contact opportunity of the blow-by gas with the inner surface of the extension chamber 18 increases. collection can.

[0049] In particular, when the first portion 19 and the second portion 20 are offset to the left and right across the expansion chamber 18 as in the embodiment, the blow-by gas flows into the expansion chamber 18, changes direction in a crank-like manner, and becomes turbulent. This further increases the chance of oil mist coming into contact with the inner surface of the expansion chamber 18, and the oil mist Collection The functionality can be significantly improved.

[0050] Furthermore, since the extension chamber 18 has a deep portion 18b that is deeper inward than the second portion 20, the blow-by gas that has flowed into the main portion 18a of the extension chamber 18 tends to flow into the deep portion 18b of the extension chamber 18. collection Furthermore, since the innermost portion 18b of the extension chamber 18 is close to the inter-bore portion 1b, the heat of the cylinder bore 2 can heat the blow-by gas during operation in a low-temperature environment, thereby improving the adhesion of oil mist to the extension chamber 18.

[0051] Furthermore, since the cross-sectional area of ​​the expansion chamber 18 is sufficiently larger than the cross-sectional area of ​​the upper end of the first portion 19 and the cross-sectional area of ​​the lower end of the second portion 20, there is no increase in flow resistance (increase in pressure loss) when the blow-by gas changes direction in the expansion chamber 18 and flows into the second portion 20.

[0052] As described above, in this embodiment, even if a large amount of blow-by gas is generated or oil mist is combined with the blow-by gas to form bubbles, the blow-by gas passage 17 is not clogged, and the blow-by gas is sucked up into the blow-by gas passage 17, and a large amount of oil mist is removed in the blow-by gas passage 17. collection Therefore, a large amount of oil mist is released into the oil separator installed in the head cover. collection It is possible to send blow-by gas in a sealed state.

[0053] Therefore, in this embodiment, even in a hybrid engine that generates a large amount of blow-by gas, the blow-by gas can be properly treated without increasing the size of the head cover.In fact, the weight reduction achieved by increasing the volume of the blow-by gas passage 17 and by providing the extension chamber 18 contributes to improving fuel efficiency.

[0054] One possible way to increase the volume of the first portion 19 in the blow-by gas passage 17 is to widen the lower end of the first portion 19 inward, but this would result in a problem of the partition wall 3 becoming thick in parts.

[0055] In contrast, by expanding the lower stage 23 of the first portion 19 in the circumferential direction of the oil pan female threaded hole 12 as in this embodiment, the area of ​​the lower end of the first portion 19 can be expanded without reducing the fastening strength between the oil pan 10 and the cylinder block 1 or adding a part that increases the weight, such as an additional boss portion. This is also one of the advantages of this embodiment.

[0056] As mentioned above, the expansion chamber 18 is a high oil collection However, if the expansion chamber 18 is provided at the middle of the upper or lower part of the blow-by gas passage 17, a considerable proportion of oil mist will be released from the expansion chamber 18 before the blow-by gas reaches the cylinder head 13. collection This allows the oil mist to fall or trickle down from the first portion 19. In other words, a considerable proportion of the oil mist from the blow-by gas can be pre-treated in the first portion 19 and the expansion chamber 18. This reduces the burden on the oil separator provided in the head cover, and the overall oil mist can be reduced. collection It can demonstrate its performance.

[0057] When the blow-by gas passage 17 is provided at the partition wall 3 as in the embodiment, the space below the blow-by gas passage 17 is covered from the inside by the crank cap 7, which has the advantage of preventing splashes generated by the rotation of the crankshaft 6 from directly entering the blow-by gas passage 17.

[0058] Although the embodiments of the present invention have been described above, the present invention can be embodied in various other ways. For example, it is possible to form the entire length of the blow-by gas passage so that it tapers upward. It is also possible to form the lower end of the blow-by gas passage in a straight shape and form the portion above that in an upward tapered portion. It is also possible to form a discontinuous portion such as a step portion. is 3 It is also possible to form more than one step.

[0059] In the embodiment, the blow-by gas passage is formed in the side wall of the cylinder block 1, but the blow-by gas passage can also be formed in the end wall (front wall) of the cylinder block. The present invention can also be applied to cylinder blocks of non-hybrid engines. [Industrial Applicability]

[0060] The present invention can be embodied in a cylinder block, and is therefore industrially applicable. [Explanation of symbols]

[0061] 1 Cylinder block 1a Cylinder block side wall 2 cylinder bore 3 Bulkhead 4 End Wall 6 crankshaft 10 Oil pan 11 Oil pan bolt 12 Female threaded hole for oil pan 13 Cylinder head 15 head bolts 16 Water Jacket 17 Blow-by gas passage 18 Expansion Room 19 Part 1 20 Part 2 21 Plug 23 Lower part of the first section 24 Middle section of the first section 25 Upper part of the first section 26 First step 27 Second step

Claims

1. A blow-by gas passage is formed in a part of the peripheral wall, the lower end of which opens to the crank chamber and the upper end of which opens to the upper surface. an upper narrowed portion having a cross-sectional area at an upper end smaller than a cross-sectional area at a lower end is formed in at least a part of the blow-by gas passage, a cylinder block in which a stepped discontinuous portion in which the cross-sectional area changes suddenly is formed at a plurality of levels with varying heights in the upper tapered portion, an expansion chamber extending from an outer surface of the cylinder block toward the cylinder bore is formed in the blow-by gas passage at a height position located to the side of the cylinder bore so as to cross the blow-by gas passage, and an open end of the expansion chamber is closed by a plug, The discontinuous portions of the plurality of stages are formed in a portion below the extension chamber. Cylinder block.

2. The discontinuous portion of the plurality of stages includes a first step portion and a second step portion, and the first step portion and the second step portion are formed on opposing surfaces sandwiching the axis of the blow-by gas passage.

2. The cylinder block according to claim 1.

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