1. A cylinder head of a multi-cylinder engine, which is fastened to an upper portion of a cylinder block in which a plurality of cylinders are formed in a row, and combustion chambers are formed between the cylinder head and top surfaces of pistons sliding in the cylinders, characterized in that,

the cylinder head has:

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 part which is connected with the plurality of exhaust passages together and forms a single exhaust outlet; and

a water jacket formed adjacent to the exhaust collecting portion,

an annular concave-convex portion extending in the circumferential direction is formed on an inner circumferential surface of the exhaust collecting portion in the vicinity of the exhaust outlet.

2. The cylinder head of a multi-cylinder engine according to claim 1,

the concave-convex portion includes an annular protrusion protruding from the inner peripheral surface of the exhaust collecting portion.

3. The cylinder head of the multi-cylinder engine according to claim 2,

the protruding strip has a flat annular top surface extending in parallel with the inner peripheral surface of the exhaust collecting portion in the exhaust flow direction.

4. The cylinder head of the multi-cylinder engine according to claim 2 or 3,

the inner peripheral surface of the exhaust collecting portion is formed with a plurality of the ribs at predetermined intervals in the exhaust flow direction.

5. The cylinder head of the multi-cylinder engine according to claim 4,

the interval is larger than a width of the bead in the exhaust gas flow direction.

6. The cylinder head of the multi-cylinder engine according to claim 2,

the water jacket is disposed in a manner surrounding the protrusion.

Background

As a cylinder head of a diesel engine, there is known a structure in which: an exhaust passage and a water jacket surrounding the exhaust passage are formed, and a plurality of protrusions are formed on an inner wall of a wall forming the exhaust passage (patent document 1). In the cylinder head, a plurality of columnar or mesa-shaped protrusions having a protrusion height larger than the wall thickness are formed from the portion directly behind the exhaust port to substantially the entire inner wall of the wall forming the exhaust passage in order to increase the heat receiving area in contact with the exhaust gas and to reduce the flow resistance flowing in the exhaust passage as much as possible. Alternatively, a plurality of ridges or plate-like projections are formed along the flow direction of the exhaust gas.

In addition, in a cylinder head in which a plurality of exhaust ports (exhaust passages) are formed, the exhaust ports being branched from an upstream portion at an upstream end to a middle portion and being grouped into 1 downstream portion at a middle portion to a downstream end, a cylinder head in which a plurality of protrusions are provided along an exhaust gas flow direction on an inner peripheral surface of the exhaust port is known (patent document 2). In the cylinder head, the short-sized protrusions are provided in the upper half region of the downstream portion of the exhaust passage in the vertical direction, and the long-sized protrusions are provided at least as many as the number of the upstream portions in the exhaust gas flow direction on both sides of the short-sized protrusions from the upstream portion to the downstream portion.

Further, among cylinder heads in which collective exhaust ports (exhaust gas collecting portions) communicating with a plurality of exhaust ports (exhaust passages) provided for each cylinder are formed, a cylinder head in which a plurality of ridges in the form of gentle ridge-like dams are provided on the upper and lower surfaces of the collective exhaust ports is known (patent document 3). In this cylinder head, when the exhaust gas flows out from the exhaust port to the exhaust passage on the downstream side, the presence of the ridge leads the exhaust gas to the center of the exhaust passage.

Documents of the prior art

Patent document

Patent document 1: japanese examined patent publication (Kokoku) No. 1-35164

Patent document 2: japanese patent No. 5786663

Patent document 3: japanese patent laid-open publication No. 2013-155690

Disclosure of Invention

Problems to be solved by the invention

However, in the cylinder heads described in patent documents 1 and 2, the exhaust gas temperature is reduced by promoting heat exchange with the projection portions, and on the other hand, there is a problem that: the exhaust gas flows to the downstream side without sufficient heat exchange because the exhaust gas flows smoothly.

Further, the technique described in patent document 3 is intended to prevent exhaust gas from colliding with the upper inner surface of the leading end portion of the exhaust passage on the downstream side, and a plurality of ridges are formed near the exhaust outlet. Therefore, in the cylinder head, the amount of heat received around the exhaust outlet increases, and local overheating occurs in this portion. In addition, the pressure loss of the exhaust gas increases.

In view of such a background, an object of the present invention is to provide a cylinder head capable of suppressing local overheating around an exhaust outlet and reducing the temperature of 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 part 52 which is connected to the plurality of exhaust passages in common and forms a single exhaust outlet 8 b; and a water jacket 30 formed adjacent to the exhaust collecting portion, and having an annular concave-convex portion 60 extending in the circumferential direction formed on an inner peripheral surface 43i of the exhaust collecting portion in the vicinity of the exhaust outlet.

According to this configuration, the exhaust gas flow velocity is increased and decreased by the convex portion formed by narrowing the exhaust gas flow passage, and the exhaust gas having the increased flow velocity actively transfers heat to the convex portion. The heat transferred to the convex portion is transferred to the water jacket. Therefore, it is possible to suppress overheating around the exhaust outlet and reduce the exhaust gas temperature.

Preferably, the concave-convex portion includes an annular ridge 60 protruding from the inner peripheral surface of the exhaust collecting portion.

According to this configuration, the ridges can be formed at a shorter distance in the exhaust gas flow direction than in the case where the recessed grooves are provided on the inner peripheral surface and the exhaust gas actively transfers heat to the ridges formed between the recessed grooves. Further, the reduction in the exhaust passage area due to the formation of the ribs increases the flow velocity of the exhaust gas in contact with the ribs. Therefore, heat transfer from the exhaust gas to the ridge can be activated, and the exhaust gas temperature can be effectively reduced.

Preferably, the ridge has a flat annular top surface 63 extending in parallel with the inner peripheral surface of the exhaust collecting portion in the exhaust flow direction.

According to this configuration, since the exhaust gas having an increased flow velocity flows along the annular top surfaces of the ridges, heat transfer from the exhaust gas to the ridges via the annular top surfaces can be efficiently performed while suppressing pressure loss of the exhaust gas. In addition, the heat transfer efficiency is also improved due to the collision of the exhaust gas against the front surface of the bead.

Preferably, the inner peripheral surface of the exhaust collecting portion has a plurality of the ridges formed thereon at predetermined intervals L in the exhaust gas flow direction.

The grooves formed between the ribs function as retention portions having a length corresponding to the interval between the ribs, and retain the exhaust gas. According to this configuration, the exhaust gas is temporarily retained in the retention portion, and the flow velocity of the portion is reduced, whereby the time for which the exhaust gas exchanges heat with the inner peripheral surface between the bead can be increased, and heat can be efficiently transferred from the exhaust gas to the cylinder head. In addition, by forming a plurality of ridges, the exhaust gas temperature can be further reduced.

Preferably, the interval L is larger than a width W of the bead in the exhaust gas flow direction.

According to this configuration, the turbulent flow of the exhaust gas in the grooves between the ridges functioning as the retention portions is likely to become a clean flow at the portions in contact with the ridges, and an increase in the pressure loss of the exhaust gas can be suppressed, and the flow velocity of the exhaust gas in contact with the ridges can be reliably increased. This makes it possible to reliably perform active heat transfer from the exhaust gas to the ridge.

Preferably, the water jacket is disposed in a manner surrounding the protrusion.

According to this structure, the heat transferred from the exhaust gas to the bead can be transferred to the water jacket. Therefore, overheating around the exhaust outlet of the cylinder head can be suppressed.

Effects of the invention

Thus, according to the present invention, it is possible to provide a cylinder head capable of suppressing local overheating around the exhaust outlet and reducing the temperature of 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 perspective view of an exhaust collection passage of the cylinder head.

Fig. 7 is an enlarged view of a main portion of the exhaust collecting passage shown in fig. 6.

Fig. 8 is a schematic cross-sectional view of the exhaust collecting portion.

Fig. 9 is a graph showing the correlation between the exhaust gas temperature and the crank angle, the thin line showing the conventional example, and the thick line showing the present invention.

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;

8 b: an exhaust outlet;

30: a water jacket;

32: an upper exhaust side water jacket;

33: a lower exhaust side water jacket;

43: an inner peripheral wall;

43 i: an inner peripheral surface;

51: an exhaust passage;

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

60: a ridge (concave-convex portion);

63: an annular top surface;

64: a groove;

e: an engine;

l: spacing of the ribs;

w: the width of the ridge.

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, 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 communicating with the corresponding combustion chambers 6; and an exhaust passage midstream portion 54 commonly connected to the 2 exhaust passage upstream portions 53. 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 of the cylinder head 3. All the exhaust passage upstream portions 53 have substantially the same cross-sectional area. The entire exhaust passage midstream portion 54 has a cross-sectional area approximately 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 are gradually reduced toward the downstream. The exhaust gas collecting portion 52 has a substantially fan-shaped upstream portion 55 in which the flow passage area sharply decreases toward the downstream, and a substantially tubular downstream portion 56 in which the flow passage area gently decreases toward the downstream.

As shown in fig. 5 to 7, a plurality of annular ridges 60 extending in the circumferential direction are formed on the inner circumferential surface 43i (see fig. 5) defining the inner circumferential wall 43 of the exhaust collecting portion 52 at portions corresponding to the downstream side portions 56. In the example of the figure, 3 ribs 60 are formed. As shown in fig. 5, these ribs 60 are arranged at positions between the upper exhaust side water jacket 32 and the lower exhaust side water jacket 33. In other words, the upper exhaust side water jacket 32 and the lower exhaust side water jacket 33 are disposed in a manner surrounding the ribs 60.

As shown in fig. 7 and 8, the 3 ribs 60 have substantially the same cross-sectional shape and are arranged at a predetermined interval L in the exhaust gas flow direction. Each of the ribs 60 has a rectangular shape having a width W (length in the exhaust gas flow direction) larger than a projection height H from the inner peripheral surface 43 i. Each of the ribs 60 has: a front surface 61 and a rear surface 62 substantially perpendicular to the inner peripheral surface 43i (exhaust gas flow); and an annular top surface 63 joining front surface 61 and rear surface 62. The front surface 61 and the rear surface 62 have substantially the same height, and the annular top surface 63 extends in parallel with the inner peripheral surface 43i of the exhaust collecting portion 52 in the exhaust flow direction. The interval L between 2 ribs 60 adjacent to each other in the exhaust gas flow direction is set larger than the width W of the ribs 60. Between 2 ribs 60 adjacent to each other in the exhaust gas flow direction, a groove 64 having a length corresponding to the interval L is formed. The concave groove 64 functions as a retention portion for retaining the exhaust gas.

The cylinder head 3 is configured as described above. The operational effects of the cylinder head 3 configured as described above will be described below. In the cylinder head 3, an annular bead 60 extending in the circumferential direction is formed on the inner circumferential surface 43i of the exhaust collecting portion 52 in the vicinity of the exhaust outlet 8 b. Therefore, in the portion where the annular ridge 60 is formed, the cross-sectional area of the exhaust collecting passage 8 (hereinafter referred to as the exhaust passage area) is reduced, and the exhaust gas having an increased flow velocity is actively transferred to the ridge 60 by the ridge 60 portion where the exhaust passage is reduced. The heat transmitted to the ribs 60 is transmitted to the upper exhaust side water jacket 32 and the lower exhaust side water jacket 33. Therefore, overheating around the exhaust outlet 8b is suppressed, and the exhaust gas temperature decreases.

Fig. 9 is a graph showing the correlation between the exhaust gas temperature at the exhaust outlet 8b of the cylinder head 3 of the embodiment and the crank angle. In the graph, the case of the cylinder head 3 according to the present embodiment in which the 3 beads 60 are formed on the inner peripheral surface 43i of the exhaust collecting portion 52 is represented as "the present invention", indicated by a thick line, and the case in which the beads 60 are not formed is represented as "the conventional example", indicated by a thin line. As shown in fig. 9, in the cylinder head 3 of the present embodiment, the exhaust gas temperature indicated by a thick line is reduced by about 5 degrees in average of 1 cycle (2 crank rotations of 720 degrees) as compared with the conventional example.

As shown in fig. 6 to 8, in the present embodiment, an annular ridge 60 (instead of the annular groove portion) is formed to extend in the circumferential direction on the inner circumferential surface 43i of the exhaust collecting portion 52. With such a configuration, the ridges 60 can be formed at a shorter distance in the exhaust gas flow direction than in a configuration in which the concave portions are provided on the inner peripheral surface 43i and the exhaust gas actively transfers heat to the ridge portions formed between the concave portions. Further, the reduction in the exhaust passage area due to the formation of the ribs 60 increases the flow velocity of the exhaust gas in contact with the ribs 60. Therefore, heat transfer from the exhaust gas to the ribs 60 becomes active, and the exhaust gas temperature effectively decreases.

The bead 60 has a flat annular top surface 63 extending in parallel with the inner peripheral surface 43i of the exhaust collecting portion 52 in the exhaust gas flow direction, and this structure allows the exhaust gas having an increased flow velocity to flow along the annular top surface 63 of the bead 60. Therefore, heat can be efficiently transferred from the exhaust gas to the ribs 60 via the annular top surface 63 while suppressing the pressure loss of the exhaust gas. In addition, the heat transfer efficiency is also improved by the collision of the exhaust gas against the front surface 61 of the ridge 60.

The plurality of ribs 60 are formed at predetermined intervals L in the exhaust gas flow direction, and with this structure, the exhaust gas temporarily stays in the retention portion and the flow velocity of the exhaust gas decreases in this portion. Therefore, the time for the exhaust gas to exchange heat with the inner peripheral surface 43i of the bead 60 becomes longer, and heat is efficiently transferred from the exhaust gas to the cylinder head 3. In addition, by forming the plurality of ribs 60, the exhaust gas temperature is further lowered.

The interval L between the ridges 60 is larger than the width W of the ridges 60 in the exhaust gas flow direction, and with this configuration, the flow of the exhaust gas that is disturbed in the concave grooves 64 between the ridges 60 functioning as the retention portions is easily rectified at the portions that are in contact with the ridges 60. This suppresses an increase in the pressure loss of the exhaust gas, reliably increases the flow velocity of the exhaust gas contacting the ribs 60, and reliably transfers active heat from the exhaust gas to the ribs 60.

The upper exhaust side water jacket 32 and the lower exhaust side water jacket 33 are disposed in such a manner as to surround the ribs 60. Therefore, the heat transferred from the exhaust gas to the ribs 60 is transferred to the upper exhaust side water jacket 32 and the lower exhaust side water jacket 33. Thereby, overheating around the exhaust outlet 8b of the cylinder head 3 is suppressed.

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 annular bead 60 may be formed on the inner peripheral surface 43i of the exhaust collecting portion 52 in the vicinity of the exhaust outlet 8b, and an annular uneven portion may be formed on the portion. For example, instead of the ridge 60, a plurality of annular groove portions may be formed, and a ridge portion may be formed between 2 groove portions adjacent to each other in the exhaust gas flow direction. 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.