阅读说明：本技术 多气缸发动机的气缸盖 (Cylinder head of multi-cylinder engine ) 是由 山﨑信 竹形徳之 大田笃志 于 2021-03-16 设计创作，主要内容包括：本发明提供一种多气缸发动机的气缸盖,能够顺畅地排出排气气体且能够高效地冷却排气气体。气缸盖具有：排气通路(51),其按每个气缸而设置,从燃烧室延伸；排气集合部(52),其与多个排气通路共同连接；以及水套(30),其形成为与排气通路和排气集合部相邻。排气通路包括：从与燃烧室连通的一对排气口延伸的一对排气通路上游部(53)；和与一对排气通路上游部共同连接的排气通路中游部(54)。一对排气通路上游部在高度方向上彼此不同的高位置和低位置处与排气通路中游部连接,对于与排气集合部连通的全部排气通路上游部,高位置(53A)和低位置(53B)在气缸列方向上交替。在全部的排气通路中游部中产生相同方向的回旋流。(The invention provides a cylinder head of a multi-cylinder engine, which can smoothly discharge exhaust gas and can efficiently cool the exhaust gas. The cylinder head has: an exhaust passage (51) provided for each cylinder and extending from the combustion chamber; an exhaust collecting unit (52) connected in common to the plurality of exhaust passages; and a water jacket (30) formed adjacent to the exhaust passage and the exhaust collecting portion. The exhaust passage includes: a pair of exhaust passage upstream portions (53) extending from a pair of exhaust ports communicating with the combustion chamber; and an exhaust passage midstream portion (54) connected in common to the pair of exhaust passage upstream portions. The pair of exhaust passage upstream portions are connected to the exhaust passage midstream portion at high positions and low positions different from each other in the height direction, and the high positions (53A) and the low positions (53B) alternate in the bank direction for all the exhaust passage upstream portions communicating with the exhaust collecting portion. Swirling flows in the same direction are generated in all the exhaust passages.)

1. A cylinder head of a multi-cylinder engine, which is fastened to an upper portion of a cylinder block on which a plurality of cylinders are formed in a row, forming a combustion chamber between the cylinder head and a top surface of a piston sliding in the cylinder,

the cylinder head includes:

an exhaust passage provided for each of the cylinders and extending from the corresponding combustion chamber in a direction intersecting the direction of the bank;

an exhaust collecting unit connected in common to the plurality of exhaust passages; and

a water jacket formed adjacent to the exhaust passage and the exhaust collecting portion,

the exhaust passages each include: a pair of exhaust passage upstream portions extending from a pair of exhaust ports communicating with the corresponding combustion chambers; and an exhaust passage midstream portion connected in common to a pair of the exhaust passage upstream portions,

a pair of the exhaust passage upstream portions are connected to the corresponding exhaust passage midstream portions at high and low positions different from each other in the height direction,

the high position and the low position alternate in the bank direction for all of the exhaust passage upstream portions that communicate with the exhaust collecting portion.

2. The cylinder head of claim 1,

all of the upstream portions of the downstream portions of the exhaust passages are formed in a cross-sectional shape inclined in the same direction with respect to the cylinder row direction.

Technical Field

The present disclosure relates to a cylinder head of a multi-cylinder engine having an exhaust collecting portion formed therein.

Background

As a cylinder head of a multi-cylinder engine, a cylinder head is known in which an integrated exhaust pipe formed by merging exhaust pipes (exhaust passages) is integrally provided in the cylinder head (patent document 1). In the cylinder head, a lower coolant jacket is disposed below the exhaust pipe and an upper coolant jacket is disposed above the exhaust pipe for good cooling. Of the exhaust passages, 2 exhaust passages connected to 2 exhaust ports provided in each cylinder are joined together to form a partial collective exhaust passage, and a plurality of partial collective exhaust passages communicating with each cylinder are joined together at a collective portion to form a common collective exhaust passage downstream.

In such a cylinder head structure in which the exhaust passages are integrated in the cylinder head, generally, a pair of exhaust passages extending from the combustion chamber are integrated into 1 exhaust passage (partial integrated exhaust passage) on a plane substantially perpendicular to the cylinder axis, and then the partial integrated exhaust passages communicating with all the cylinders are integrated in the integrated portion.

On the other hand, there is known a cylinder head including: the 2 exhaust passages provided for each cylinder overlap in the cylinder axial direction at the upstream portion of the first collecting passage (partial collecting passage) so as to change from 2 circular cross sections to 2 longitudinal cross sections (patent document 2). In the cylinder head, a downstream portion of the first collecting passage is formed to have a vertically long cross section in order to reduce a ventilation resistance due to a change in a passage cross section from the exhaust port to the collecting portion, and to reduce a ventilation resistance due to interference of exhaust gas flowing from the exhaust passage to the collecting portion.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2008-309158

Patent document 2: japanese laid-open patent publication No. 2018-200017

Disclosure of Invention

Problems to be solved by the invention

However, in the cylinder head described in patent document 2, the overlapping direction of the 2 exhaust passages provided for each cylinder in the cylinder axis direction differs among the 3 cylinders. Specifically, in the rear 2 cylinders, the front exhaust ports are overlapped so as to be positioned above the rear exhaust ports, and in the front end cylinder, the rear exhaust ports are overlapped so as to be positioned above the front exhaust ports. Therefore, in this cylinder head, even if the ventilation resistance due to interference of the exhaust gas flowing from the 2 exhaust passages to the first collecting passage is reduced, the ventilation resistance due to interference of the exhaust gas flowing from the first collecting passage to the second collecting passage is not reduced. That is, the pressure loss of the exhaust gas is large, and the exhaust gas cannot be smoothly discharged.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a cylinder head capable of smoothly discharging exhaust gas and efficiently cooling the exhaust gas.

Means for solving the problems

In order to achieve the above object, one embodiment of the present invention is a cylinder head 3 of a multi-cylinder engine E fastened to an upper portion of a cylinder block 2, the cylinder block 2 having a plurality of cylinders 1 formed in a row, a combustion chamber 6 being formed between the cylinder head 3 and a top face of a piston sliding in the cylinder, the cylinder head 3 having: an exhaust passage 51 provided for each of the cylinders and extending from the corresponding combustion chamber in a direction intersecting the direction of the bank; an exhaust collecting unit 52 connected in common to the plurality of exhaust passages; and a water jacket 30 formed adjacent to the exhaust passage and the exhaust collecting portion. The exhaust passages each include: a pair of exhaust passage upstream portions 53 extending from a pair of exhaust ports 8a communicating with the corresponding combustion chambers; and an exhaust passage midstream portion 54 commonly connected to a pair of the exhaust passage upstream portions connected to the corresponding exhaust passage midstream portion at high and low positions different from each other in the height direction. The high position and the low position alternate in the bank direction for all of the exhaust passage upstream portions that communicate with the exhaust collecting portion.

According to this configuration, since the pair of exhaust passage upstream portions are connected to the corresponding exhaust passage midstream portions at the high and low positions different from each other in the height direction, the exhaust gas generates a swirling flow in each exhaust passage midstream portion. Further, since the high position and the low position alternate in the bank direction for all the exhaust passage upstream portions communicating with the exhaust collecting portion, the direction of the swirling flow generated in the upstream portion is the same in each exhaust passage. Thus, the exhaust gas flowing from the midstream portion of the exhaust passage to the exhaust collecting portion is smoothly discharged without interfering with each other. Further, since the exhaust gas flows in the exhaust passage midstream portion and the exhaust collecting portion along with the swirling flow, the contact time between the exhaust gas and the cylinder head wall surface increases. That is, without increasing the surface area of the exhaust passage and the exhaust collecting portion defined by the cylinder head, the apparent surface area of these passages, which can perform heat exchange, can be increased. Thereby, the exhaust gas is efficiently cooled.

Preferably, all of the upstream portions of the downstream portions of the exhaust passages are formed in a cross-sectional shape inclined in the same direction with respect to the bank direction.

According to this configuration, the swirling flow in the same direction can be reliably generated in the exhaust gas flowing through the downstream portion of the exhaust passage.

Effects of the invention

As described above, according to the present invention, it is possible to provide a cylinder head capable of smoothly discharging exhaust gas and efficiently cooling the exhaust gas.

Drawings

Fig. 1 is a sectional view of a main portion of an engine of the embodiment in a direction perpendicular to a cylinder row direction.

Fig. 2 is a perspective view of the cylinder head as viewed from below.

Fig. 3 is a perspective view of the water jacket of the cylinder head as viewed from above.

Fig. 4 is a perspective view of the water jacket of the cylinder head as viewed from below.

Fig. 5 is a main portion sectional view around an exhaust collecting passage of a cylinder head.

Fig. 6 is a plan view of the cylinder head.

Fig. 7 is a perspective view of an exhaust collection passage of the cylinder head.

Fig. 8 is a plan view of the exhaust collecting passage of the cylinder head.

Fig. 9 is a cross-sectional view of the exhaust manifold passage along the IXA, IXB, IXC, and IXD lines in fig. 8, showing a comparative example on the left side and the present invention on the right side.

Description of the reference symbols

1: a cylinder;

2: a cylinder block;

3: a cylinder head;

6: a combustion chamber;

8: an exhaust collection passage;

8 a: an exhaust port;

30: a water jacket;

51: an exhaust passage;

52: an exhaust gas collection portion (exhaust passage downstream portion);

53: an exhaust passage upstream portion;

53A: a first passage (an exhaust passage upstream portion connected to an exhaust passage midstream portion at a high position);

53B: a second passage (an exhaust passage upstream portion connected to the exhaust passage midstream portion at a low position);

54: an exhaust passage midstream section;

e: an engine.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the present embodiment, the invention is applied to an internal combustion engine for an automobile (hereinafter, simply referred to as engine E). Hereinafter, the description will be made in the vertical direction shown in fig. 1 with reference to a state where the engine E is mounted on the automobile.

As shown in fig. 1 and 2, the engine E is an SOHC type 4-valve in-line 4-cylinder gasoline engine. As shown in fig. 1, the engine E includes: a cylinder block 2 in which 4 cylinders 1 that house pistons are formed in a row; a box-shaped cylinder head 3 fastened to an upper portion of the cylinder block 2; and a head cover 4 fastened to an upper portion of the cylinder head 3. The engine E is mounted on the automobile in a posture in which the cylinder head 3 is disposed on the upper side in the vertical direction. The cylinder block 2 and the cylinder head 3 are cast from an aluminum alloy.

The cylinders 1 extend substantially vertically and are formed in parallel with each other in the cylinder block 2. Hereinafter, the arrangement direction of the plurality of cylinders 1 arranged in an array is referred to as a cylinder row direction. The upper end of each cylinder 1 opens to an upper end surface 2a of the cylinder block 2, and the lower end opens to a crank chamber (not shown) formed in a lower portion of the cylinder block 2. A block inner water jacket 5 (block inner cooling water passage) is formed on the side portion of the cylinder 1 of the cylinder block 2 so as to integrally surround the side peripheral portion of each cylinder 1. The block inner water jacket 5 is curved so as to follow the side peripheral portion of each cylinder 1, and the upper end of the block inner water jacket 5 opens at the upper end surface 2a of the cylinder block 2. The block inner jacket 5 is formed as a cavity by sand molding or the like at the time of molding the cylinder block 2 so as to allow cooling water (coolant) to flow therethrough.

A combustion chamber recess 3b, which is a curved recess, is formed in a portion of a joint surface of the cylinder head 3 to the cylinder block 2 (hereinafter, referred to as a cylinder block joint surface 3a) that faces each cylinder 1. Each combustion chamber recess 3b defines a combustion chamber 6 together with a portion of each cylinder 1 above the piston. That is, the cylinder head 3 defines the upper edge of the combustion chamber 6.

Inside the cylinder head 3, 4 intake passages 7 are formed. The upstream end of each intake passage 7 opens an intake air inlet 7a on one side surface (the left side surface in fig. 1) of the cylinder head 3 in the cylinder row direction. The downstream end of each intake passage 7 branches into two branches so that 2 intake ports 7b open on the wall surface of the combustion chamber recess 3 b. The 8 intake ports 7b are arranged in the cylinder row direction. Further, 1 exhaust collecting passage 8 is formed inside the cylinder head 3. The upstream end of the exhaust collecting passage 8 has 2 exhaust ports 8a each opened in the wall surface of each combustion chamber recess 3 b. The downstream end of the exhaust collection passage 8 opens a single exhaust outlet 8b on the other side surface (the right side surface in fig. 1) of the cylinder head 3 in the cylinder row direction. The 8 exhaust ports 8a are arranged in the cylinder row direction. Hereinafter, with reference to the combustion chamber recess 3b, the side provided with the intake passage 7 is referred to as the intake side, and the side provided with the exhaust collecting passage 8 is referred to as the exhaust side.

In the cylinder head 3, an intake valve 9 for opening and closing the intake port 7b and an exhaust valve 10 for opening and closing the exhaust port 8a are slidably arranged in the cylinder row direction. A valve operating chamber 11 is defined between the cylinder head 3 and the head cover 4, and a valve operating mechanism 12 for driving the intake valve 9 and the exhaust valve 10 to open is housed in the valve operating chamber 11. The valve train 12 includes: a camshaft 13 rotatably mounted to the cylinder head 3; a rocker shaft 14 disposed above the camshaft 13; the rocker arm shaft 14 supports an intake rocker arm 15, an exhaust rocker arm 16, and the like so as to be swingable. The camshaft 13 is formed with 4 valve operating cams 13a that drive the pair of intake valves 9 and exhaust valves 10 for each cylinder 1.

As shown in fig. 2, the exhaust outlet 8b is formed at a longitudinally intermediate position of the exhaust-side surface 3c of the cylinder head 3. Further, a spark plug insertion hole 17 for inserting a spark plug (not shown) is formed in the wall surface of the combustion chamber recess 3b so as to penetrate the upper surface of the cylinder head 3 at the center of the 4 intake passages 7 and the exhaust collecting passage 8.

As shown in fig. 1 and 2, the exhaust collection passage 8 is formed to extend further to the exhaust side than the cylinder block joining surface 3a of the cylinder head 3. More specifically, the exhaust outlet 8b is defined by a tubular exhaust outlet tubular portion 18 protruding from the exhaust-side surface 3c of the cylinder head 3, and the exhaust outlet tubular portion 18 of the cylinder head 3 and the vicinity thereof constitute a bulging portion 19 bulging sideward with respect to the cylinder block 2.

The end surface of the exhaust outlet tubular portion 18 constitutes a connection surface 18a of a downstream-side exhaust passage member 20 such as a turbine of a supercharger (turbocharger), not shown, an exhaust gas purification device, and the like. Further, at the tip end of the exhaust outlet tubular portion 18, a plurality of (4 in the example of the drawing) fastening bosses 21 for fastening the downstream exhaust passage member 20 with bolts are formed so as to surround the exhaust outlet 8 b. On the other hand, 2 ribs 22 are formed on the lower surface of the bulging portion 19 so as to reach the fastening bosses 21 from the peripheral edge of the cylinder block joint surface 3 a. These ribs 22 extend in the front-rear direction, which is a direction approaching or separating from the cylinder row, and these ribs 22 are tapered in shape opening from the fastening boss 21 toward the cylinder block joint surface 3 a.

As described above, the downstream-side exhaust passage member 20 such as a supercharger or an exhaust gas purification device is disposed in front of the cylinder block 2 and the cylinder head 3, and after the engine E is started, these members reach high temperatures. Therefore, the bulging portion 19 of the cylinder head 3 bulging laterally with respect to the cylinder block 2 is likely to transmit heat from the supercharger or the exhaust gas purification apparatus by heat conduction, radiation, and convection, and particularly the lower surface thereof is likely to have a high temperature. Further, when the lower surface of the bulging portion 19 is at a high temperature, the sealing property between the cylinder head 3 and the downstream exhaust passage member 20 is likely to be lowered due to deformation caused by thermal expansion. In the present embodiment, ribs 22 extending in directions approaching and separating from the banks are formed on the lower surface of the bulging portion 19, whereby deformation of the bulging portion 19 is suppressed.

As shown in fig. 1 and 3 to 4, a cylinder head inner water jacket (cylinder head inner cooling water passage) is formed inside the cylinder head 3 to suppress a temperature increase caused by heat propagation from the combustion gas in the combustion chamber 6 or in the exhaust collecting passage 8. Hereinafter, the cylinder head inner water jacket is simply referred to as the water jacket 30(31 to 36). The water jacket 30 is also formed as a cavity by sand molding or the like at the time of molding the cylinder head 3 in order to allow cooling water (coolant) to flow therethrough. In fig. 3 and 4, a water jacket 30 as a cavity portion is shown physically in a manner of perspective of the cylinder head 3.

The water jacket 30 has a main water jacket 31, an upper exhaust side water jacket 32, a lower exhaust side water jacket 33, and the like as main elements. The main water jacket 31 is disposed above the plurality of combustion chamber recesses 3b so as to be adjacent to the combustion chamber recesses 3b, and extends in the cylinder row direction (longitudinal direction) of the cylinder head 3. The upper exhaust side water jacket 32 and the lower exhaust side water jacket 33 are disposed adjacent to the exhaust collecting passage 8 so as to sandwich the exhaust collecting passage 8 from above and below, and the upper exhaust side water jacket 32 and the lower exhaust side water jacket 33 extend in the longitudinal direction of the cylinder head 3, respectively. The upper and lower exhaust side water jackets 32, 33 communicate with the main water jacket 31.

The broken line in fig. 2 indicates a portion of the upper end of the cylinder block water jacket 5 that faces the cylinder block joint surface 3a of the cylinder head 3 when the cylinder head 3 is fastened to the cylinder block 2. As indicated by hollow arrows, cooling water flows through the cylinder block inner water jacket 5. At one end in the cylinder row direction, 2 cooling water inflow passages 34 extending upward in the cylinder head 3 from the opposing block-engaging surface 3a and communicating with the water jacket 30 are formed in a portion of the upper end surface of the cylinder block inner water jacket 5 that faces the opposing block-engaging surface 3 a. The 2 cooling water inflow passages 34 communicate with one end side of the main water jacket 31 in the bank direction, respectively, and cooling water flows in from the cylinder block inner water jacket 5.

Further, a bypass passage 35 extending upward in the cylinder head 3 from the cylinder block joining surface 3a and communicating with the water jacket 30 is formed at an appropriate position on the other end side in the cylinder row direction than the cooling water inflow passage 34 in the broken line portion of the cylinder block joining surface 3a at the upper end of the cylinder block inner water jacket 5. The bypass passage 35 communicates with the main water jacket 31. Each bypass passage 35 is formed to have a smaller flow path cross-sectional area than the cooling water inflow passage 34.

As shown in fig. 3 and 4, a cooling water outflow passage 36 for discharging cooling water from the water jacket 30 is formed at the other end (end different from the side where the cooling water inflow passage 34 is provided) in the upper exhaust side water jacket 32 in the cylinder row direction. The outer end of the cooling water outflow passage 36 communicates with a radiator (not shown) via a pipe, a hose, or the like. In the main water jacket 31, the upper exhaust side water jacket 32, and the lower exhaust side water jacket 33, cooling water flows in the cylinder row direction as indicated by black arrows.

As shown in fig. 5, the upper exhaust side water jacket 32 and the lower exhaust side water jacket 33 are respectively formed inside the wall forming the bulging portion 19. That is, in the cross section shown in fig. 5, the bulging portion 19 has: an upper outer wall 41 and a lower outer wall 42 that define a pair of upper and lower exhaust side water jackets 32 and 33; and an annular inner peripheral wall 43 defining the exhaust collecting portion 52. An upper exhaust side water jacket 32 is formed between an upper outer wall 41 and an inner circumferential wall 43 which are arranged apart from each other so as to form a cavity, and a lower exhaust side water jacket 33 is formed between a lower outer wall 42 and an inner circumferential wall 43 which are arranged apart from each other so as to form a cavity. As shown in fig. 1, a side wall 23 of the cylinder head 3 defining the valve operating chamber 11 is provided upright on the upper outer wall 41.

In the cross section of fig. 5, the exhaust collection passage 8 (the downstream portion shown in fig. 5) is formed in a substantially straight line shape. That is, in this cross section, the inner peripheral surface 43i of the inner peripheral wall 43 defining the exhaust collection passage 8 is formed in a substantially parallel planar shape. The outer surface 43o of the inner peripheral wall 43 linearly extends from the combustion chamber 6 side (leftward in the drawing) toward the exhaust outlet 8b (rightward in the drawing) in parallel with the inner peripheral surface 43i to the front of the exhaust outlet 8 b. That is, the inner peripheral wall 43 is formed to have a substantially constant thickness in a linear region before reaching the distal end bending region.

On the other hand, the inner surface 41i of the upper outer wall 41 defining the upper exhaust side water jacket 32 is curved so as to have a center of curvature on the exhaust collection passage 8 side, thereby enlarging the upper exhaust side water jacket 32. Further, the inner surface 42i of the lower outer wall 42 defining the lower exhaust side water jacket 33 is curved so as to have a center of curvature on the exhaust collecting passage 8 side, thereby expanding the lower exhaust side water jacket 33.

As shown in fig. 6 to 8, the exhaust collection passage 8 includes: 4 exhaust passages 51 provided for each cylinder 1; and an exhaust gas collecting portion 52 which is connected in common to the 4 exhaust passages 51 and joins the exhaust gas flowing therethrough. Each exhaust passage 51 has 2 exhaust passage upstream portions 53(53A, 53B) communicating with the corresponding combustion chamber 6; and an exhaust passage midstream portion 54 connected in common to the 2 exhaust passage upstream portions 53(53A, 53B). The exhaust collecting portion 52 constitutes an exhaust passage downstream portion commonly connected to the 4 exhaust passage midstream portions 54, and a single exhaust outlet 8b is formed in the other side surface (the connection surface 18a in fig. 1) of the cylinder head 3. All the exhaust passage upstream portions 53 have substantially the same cross-sectional area. All the exhaust passage midstream portions 54 have a cross-sectional area of about 2 times that of the exhaust passage upstream portion 53. The exhaust collecting portion 52 has a height equal to the exhaust passage midstream portion 54 and a width and a cross-sectional area larger than the exhaust passage midstream portion 54, and the width and the cross-sectional area of the exhaust collecting portion 52 gradually decrease toward the downstream.

In fig. 9, cross-sectional views of the exhaust collecting passage 8 taken along the IXA, IXB, IXC, and IXD lines in fig. 8 are shown as a cross-section a-a, a cross-section B-B, a cross-section C-C, and a cross-section D-D, respectively, with the left side showing a comparative example and the right side showing the present invention. In the comparative example, the same or similar elements as those in the present embodiment are denoted by the same reference numerals.

As for the comparative example, the structure is such that, as in the above-described patent document 1: on a plane substantially perpendicular to the cylinder axis, a pair of exhaust passage upstream portions 53 extending from the combustion chamber 6 are collected to 1 exhaust passage midstream portion 54, and then the exhaust passage midstream portions 54 communicating with all the cylinders 1 are collected to the exhaust collecting portion 52. Therefore, in the a-a cross section, 8 exhaust passage upstream portions 53 are arranged at the same height position. In the B-B cross section, the 4 exhaust passage midstream portions 54 are arranged at the same height position, and each exhaust passage midstream portion 54 has a laterally long shape that is substantially bilaterally symmetrical. In the C-C cross section immediately downstream after the 4 exhaust passage midstream portions 54 merge, the exhaust gas collecting portion 52 has a laterally longer shape with a larger cross section area than the D-D cross section near the exhaust outlet 8b, and the cross section area is gradually reduced toward the downstream.

On the other hand, in the exhaust collecting passage 8 of the present invention, as shown in fig. 7, the 2 exhaust passage upstream portions 53 of each cylinder 1 are curved toward the exhaust outlet 8b at positions different from each other in the vertical direction (hereinafter, referred to as high position and low position), and extend forward at the high position and the low position to join each other. Therefore, in the a-a section of fig. 9, the 2 exhaust passage upstream portions 53 of each cylinder 1 are connected to the exhaust passage midstream portion 54 at positions shifted from each other in the up-down direction. Hereinafter, of the 2 exhaust passage upstream portions 53 of each cylinder 1, a passage that curves at a high position and connects to the exhaust passage midstream portion 54 at the high position is referred to as a first passage 53A, and a passage that curves at a low position and connects to the exhaust passage midstream portion 54 at the low position is referred to as a second passage 53B. In all of the 4 cylinders 1, the first passage 53A is disposed on the left side, and the second passage 53B is disposed on the right side. That is, the first passages 53A and the second passages 53B are alternately arranged in the bank direction, whereby the high positions and the low positions of the exhaust passage upstream portions 53 alternate in the bank direction for all 8 exhaust passage upstream portions 53 that communicate with the exhaust collecting portion 52. In other words, the height position of the exhaust passage upstream portion 53 is alternately set to a high position and a low position in the bank direction with respect to all the exhaust passage upstream portions 53 communicating with the exhaust collecting portion 52.

In addition, the 2 exhaust passage upstream portions 53 of each cylinder 1 merge with each other at high and low positions that are different from each other in the up-down direction. Thus, in the B-B cross section, the upstream portion of the downstream portion 54 in all the exhaust passages is formed in a cross-sectional shape in which the right side portion is lower than the left side portion and is inclined in the same direction with respect to the cylinder row direction. The exhaust collecting portion 52 is not greatly different from the comparative example, and the exhaust collecting portion 52 is formed in a laterally long shape having a larger sectional area than the D-D section in the C-C section, and the sectional area is gradually reduced toward the downstream.

Since the pair of exhaust passage upstream portions 53 are connected to the corresponding exhaust passage midstream portions 54 at the high and low positions different from each other in the height direction, a swirling flow is generated in the exhaust gas in each exhaust passage midstream portion 54. Further, since the high position and the low position alternate in the bank direction with respect to all the exhaust passage upstream portions 53 communicating with the exhaust collecting portion 52, the direction of the swirling flow generated in each exhaust passage intermediate portion 54 is the same. Thus, the exhaust gas flowing from the exhaust passage midstream portion 54 to the exhaust collecting portion 52 is smoothly discharged without interference. Further, since the exhaust gas flows through the exhaust passage midstream portion 54 and the exhaust collecting portion 52 along with the swirling flow, the contact time between the exhaust gas and the wall surface of the cylinder head 3 increases. That is, the apparent surface area of the exhaust collecting passage 8, which can perform heat exchange, can be increased without increasing the surface areas of the exhaust passage 51 and the exhaust collecting portion 52 defined by the cylinder head 3. Thereby, the exhaust gas is efficiently cooled.

Further, as shown in the B-B cross section of fig. 9, the upstream side portions of the exhaust passage intermediate stream portions 54 have a cross sectional shape inclined in the same direction with respect to the cylinder row direction, and therefore swirling flows in the same direction are reliably generated in the exhaust gas flowing through the exhaust passage intermediate stream portions 54.

The description of the specific embodiments is completed above, but the present invention is not limited to the above embodiments, and can be widely modified and implemented. For example, in the above embodiment, the present invention is applied to a 4-cylinder gasoline engine as an example, but the present invention may be applied to a multi-cylinder engine, and may be applied to a 2-cylinder, 3-cylinder, or 5-cylinder or more engine E, or a diesel engine. In the above embodiment, the single exhaust outlet 8b is formed in the side surface of the cylinder head 3, but a plurality of exhaust collecting portions 52 (in the case of 4 or more cylinders, 2 or more cylinders) may be formed in the cylinder head 3 to form a plurality of exhaust outlets 8 b. The specific configuration, arrangement, number, angle, and the like of each member and part can be appropriately changed without departing from the scope of the present invention. On the other hand, all of the components shown in the above embodiments are not necessarily required, and can be appropriately selected.