JP2014034930A - Exhaust device of engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To miniaturize an engine as a whole including an auxiliary machine while forming a collective passage where exhaust ports are collected, in a cylinder head.SOLUTION: Exhaust ports of a first combustion chamber 10a and a second combustion chamber 10b are deviated in a direction of a cylinder row with respect to centers of the combustion chambers and a direction separating from an alternator 63, a bulging portion 69 is disposed at a side of the second combustion chamber 10b, a downstream side of a second exhaust port 12b is extended to a bulging portion 69 side in a direction orthogonal to the cylinder row, and a collective passage 59 is disposed in the bulging portion 69 at the downstream side of the second exhaust portion 12b. Further in a section opposed to the alternator 63, a first exhaust port 12a of the first combustion chamber 10a is curved into the S-shape so that it passes an inner side with respect to an outer wall 70 of a cylinder head 2 of a corresponding position of the first combustion chamber 10a. Thus the alternator 63 can approach the cylinder head 2 without disturbed by the bulging portion 69 and the first exhaust port 12a.

Description

  The present invention relates to an exhaust system for an engine used in a vehicle or the like, and is particularly suitable for an exhaust system for an engine in which an exhaust collecting passage called an exhaust manifold is formed integrally with a cylinder head.

  As an example in which such an exhaust collecting passage is integrated with a cylinder head, there is one described in Patent Document 1 below, for example. Patent Document 2 below describes that the exhaust ports formed in the cylinder head are gathered in the cylinder head.

JP 2008-208738 A JP 2009-74510 A

  Incidentally, various auxiliary machines are generally arranged around the engine. In particular, an auxiliary machine driven by the rotational force of the engine, for example, an auxiliary machine driven by a belt, needs to be arranged at a position close to the engine. However, as in Patent Document 1, when the cylinder head and the exhaust manifold are simply integrated, a portion corresponding to the exhaust manifold bulges from the cylinder head body, and the bulged portion interferes with the belt drive auxiliary machine. Therefore, there is a possibility that the belt drive accessory must be arranged at a location away from the engine. That is, downsizing of the entire engine including the auxiliary machine is hindered.

  The present invention has been made paying attention to the above-mentioned problems, and it is possible to reduce the size of the entire engine including the auxiliary machine while forming a collecting passage in which the exhaust ports are gathered in the cylinder head. It is an object of the present invention to provide an engine exhaust device that can reduce the passage resistance of an exhaust port.

  In order to solve the above-described problems, an embodiment of the invention is an engine exhaust system in which a plurality of cylinders are arranged in series, and includes a combustion chamber corresponding to the number of cylinders and one exhaust port per one combustion chamber. A cylinder head, an auxiliary machine arranged on the side of the cylinder chamber orthogonal direction of the combustion chamber at one end in the cylinder row direction and driven by a belt, and a combustion arranged at the end on the auxiliary machine side in the cylinder row direction When the chamber is the first combustion chamber and the combustion chamber disposed next to the first combustion chamber is the second combustion chamber, the cylinder head expands in the direction perpendicular to the cylinder row on the side of the second combustion chamber. The first and second combustion chambers are displaced by shifting in a direction away from the auxiliary device in the cylinder row direction with respect to the center of the first and second combustion chambers. The exhaust ports formed respectively and the exhaust ports of the second combustion chamber are orthogonal to the cylinder rows A second exhaust port formed in the cylinder head so as to extend in a direction, a collecting passage formed in the bulging portion continuously downstream of the second exhaust port, and an exhaust gas in the first combustion chamber The cylinder head that communicates between the mouth and the collecting passage and is located outside the first combustion chamber at least in a section facing the auxiliary machine in a direction orthogonal to the cylinder row when viewed from the cylinder central axis direction An exhaust system for an engine, comprising: a first exhaust port that passes through an inner side of the outer wall of the gas passage and is curved in directions opposite to each other on an upstream side and a downstream side of the passage.

  Further, when viewed from the direction orthogonal to the cylinder row direction, the central axis of each cylinder is defined as the port axis adjacent to the exhaust ports of the first exhaust port and the second exhaust port and the central axis of the exhaust valve that opens and closes each exhaust port. The side away from the combustion chamber was inclined with respect to the collecting passage side.

  The engine is a two-cylinder engine.

  Thus, according to an embodiment of the invention, in the engine exhaust system in which a plurality of cylinders are arranged in series, the cylinder head has a structure having one exhaust port per combustion chamber. It is possible to reduce the volume that the passage fills in the cylinder head. For this reason, the passage shape of the exhaust port can be freely set, and the amount by which the bulging portion of the cylinder head bulges out of the cylinder head can be reduced. Further, the exhaust ports of the first combustion chamber and the second combustion chamber are shifted from the center of each combustion chamber in the direction of the cylinder row in a direction away from the auxiliary machine, and a bulging portion is formed on the side of the second combustion chamber. It is arranged and the downstream side of the second exhaust port of the second combustion chamber extends in the direction orthogonal to the cylinder row and extends toward the bulging portion, and continuously into the bulging portion downstream of the second exhaust port. Arrange the gathering passage. Therefore, at least the length of the second exhaust port that communicates between the exhaust port of the second combustion chamber and the collecting passage can be shortened to reduce the size of the bulging portion, and the passage resistance of the second exhaust port can be reduced. it can. Further, when the first exhaust port of the first combustion chamber is viewed from the cylinder central axis direction, the cylinder head located outside the first combustion chamber is at least in a section facing the auxiliary machine in a direction orthogonal to the cylinder row. The passage was curved in an S shape so that the upstream side and the downstream side were opposite to each other so as to pass inside the outer wall. As a result, the first exhaust port can be disposed closer to the first combustion chamber to reduce the size of the expansion portion, and accordingly, the auxiliary device can be disposed closer to the cylinder head. As described above, since the auxiliary machine can be arranged close to the cylinder head without being obstructed by the expansion part and the exhaust port, the engine can be downsized. Further, the passage lengths of the exhaust port and the collecting passage can be shortened as compared with the conventional one, and the ventilation resistance in the exhaust port and the collecting passage can be reduced.

  Further, when viewed from the direction perpendicular to the cylinder row, the central axis of the exhaust valve that opens and closes the ports adjacent to the exhaust ports of the first exhaust port and the second exhaust port and the respective exhaust ports is the central axis of each cylinder. On the other hand, it was inclined so that the side away from the combustion chamber was the collecting passage side. As a result, the length of the exhaust port can be made shorter than before, the degree of bending of the exhaust port can be reduced, and the passage resistance of the exhaust port can be reduced.

  Further, since the engine is a two-cylinder engine, the length in the cylinder row direction is short, the auxiliary machine can be brought close to the engine, the engine can be miniaturized, and the passage resistance of the exhaust port can be reduced.

1 is a perspective view showing an embodiment of an engine to which an exhaust device of the present invention is applied. It is a front view of the engine of FIG. It is a left view of the engine of FIG. It is a longitudinal cross-sectional view of the engine of FIG. It is a cross-sectional view of the cylinder head of the engine of FIG. It is a longitudinal cross-sectional view which shows the shape of the exhaust port of the engine of FIG.

  Next, an embodiment of an exhaust system for an engine according to the present invention will be described with reference to the drawings. 1 is a perspective view showing the appearance of the engine of the present embodiment, FIG. 2 is a front view of the engine of FIG. 1, FIG. 3 is a left side view of the engine of FIG. 1, and FIG. FIG. 5 is a cross-sectional view of the cylinder head of the engine of FIG. 1, and FIG. 6 is a vertical cross-sectional view showing the shape of the exhaust port of the engine of FIG. The engine of this embodiment is a monoblock engine in which a cylinder head, a cylinder, and an upper half of a crankcase are integrated. This monoblock engine is an in-line two-cylinder engine mounted on a vehicle such as a motorcycle or a four-wheeled vehicle or a device such as a generator, and may be mounted in various directions, as shown in FIG. The upper part of FIG. 1 is defined as the upper part of the engine. In addition, the arrows “front” and “left” in the drawing indicate “front” on the side opposite to the transmission mounting portion in the crankshaft direction and “left” on the exhaust pipe mounting side, respectively.

  Since the monoblock engine of the present embodiment is a monoblock, a cylinder head 2, a cylinder 3, and an upper crankcase (upper crankcase) 4, which are generally called, are integrated to form an engine block main portion 1. It has become. The engine block main part 1 is an aluminum die-cast part, for example. A cylinder bore 5 is formed in the cylinder 3 of the engine block main portion 1, a valve mechanism including a camshaft 6 is disposed in the cylinder head 2, and a crankshaft 7 is disposed in the upper crankcase 4. A head cover 8 is attached above the cylinder head 2 and a lower crankcase (lower crankcase half) 9 is attached below the upper crankcase 4 to constitute a monoblock engine as a whole. In FIG. 1, the symbol A indicates the joint surface between the cylinder head 2 and the head cover 8, and the symbol B indicates the joint surface between the upper crankcase 4 and the lower crankcase 9. The lower crankcase 9 also serves as an oil pan.

  Combustion chambers 10 a and 10 b are formed at the lower end portion of the cylinder head 2 corresponding to the upper end portion of the cylinder bore 5. An intake port 11 and exhaust ports 12a and 12b are connected to the combustion chambers 10a and 10b, and valve seats 13 are provided at the ends of the intake port 11 and the exhaust ports 12a and 12b on the combustion chamber 10a and 10b side, that is, the intake and exhaust ports, respectively. Is provided. A valve stem guide 14 is attached to each of the intake port 11 and the exhaust ports 12a and 12b, and the valve stems of the intake valve 15 and the exhaust valve 16 are inserted into the respective valve stem guides 14. A valve spring 17 is attached to the end of the intake valve 15 and the exhaust valve 16 opposite to the valve face, that is, the valve stem end side via a retainer and a cotter. A spark plug 51 is attached to the combustion chambers 10a and 10b.

  A cam journal 18 is rotatably supported by the cylinder head 2 and the head cover 8 via a bearing 19. The cam journal 18 is located immediately above the center of each of the two combustion chambers 10, and an intake cam 20 and an exhaust cam 21 are provided on both sides of each cam journal 18. Between the intake cam 20 and the valve stem end of the intake valve 15, and between the exhaust cam 21 and the valve stem end of the exhaust valve 16, a rocker arm 22 with a roller is interposed, and each rocker arm 22 with a roller and the cylinder head 2 are interposed. A hydraulic lash adjuster 23 is interposed between them.

  In the present embodiment, the axis of the intake valve 15 and the axis of the exhaust valve 16 are inclined radially so that the valve stem end side opens with respect to the vertical line of FIG. 4, that is, the axis (center line) 5CL of the cylinder bore 5. ing. This is also for facilitating the seat surface processing of the valve seat 13. Note that the cam surfaces of the intake cam 20 and the exhaust cam 21, the cam contact surface of the rocker arm 22 with a roller, and the valve stem end contact surface are all orthogonal to the axis of the intake valve 15 and the axis of the exhaust valve 16, that is, The contact surfaces are formed so as to be in plane contact with each other. Further, in the present embodiment, when viewed from the direction orthogonal to the cylinder row, the port portion adjacent to the valve seat 13 of the exhaust ports 12a and 12b and the central shaft 16CL of the exhaust valve 16 that opens and closes each exhaust port are provided for each cylinder. The center axis 5CL is inclined so that the side away from the combustion chambers 10a, 10b is the collecting passage side described later. As a result, the exhaust ports 12a and 12b can be shortened and the passage resistance can be reduced.

  A piston 24 is accommodated in each cylinder bore 5. The piston 24 is connected to the crankpin 25 of the crankshaft 7 by a connecting rod (connecting rod) 26. The crankshaft 7 has a crank journal 27 rotatably supported by the upper crankcase 4 and the lower crankcase 9 via a bearing metal 28. As is well known, when the piston 24 reciprocates in the cylinder bore 5 as the air-fuel mixture in the combustion chamber 10 burns and explodes, the reciprocating motion is extracted as the rotational motion of the crankshaft 7. In addition, since the monoblock engine of the present embodiment is a two-cylinder engine, the primary vibration accompanying the combustion cycle is large, and a balancer shaft (not shown) is housed in, for example, the reference numeral 52 in FIGS. Has been. As is well known, the balancer shaft 52 has the same weight as that of the crankshaft 7 and the balance is reversed. The balancer shaft 52 is connected to the crankshaft 7 by a gear (not shown) and rotates in the direction opposite to the crankshaft 7. Therefore, the drive pulley 53 shown in FIGS. 1 and 2 rotates in the counterclockwise direction of FIG. 2 together with the balancer shaft 52.

  As is well known, in a four-cycle engine, the camshaft 6 needs to rotate at a rotation speed ratio that is ½ of the rotation speed of the crankshaft 7 and at a predetermined phase with respect to the rotation angle of the crankshaft 7. Therefore, a camshaft drive mechanism that transmits the driving force of the crankshaft 7 to the camshaft 6 is required. In this embodiment, a bevel gear and an intermediate shaft are used for this cam shaft drive mechanism. The intermediate shaft 29 is arranged so that the axis thereof is orthogonal to the axis of the camshaft 6 and the axis of the crankshaft 7, that is, the shaft is arranged in the vertical direction, together with a bearing (bearing) 19 that rotatably supports the engine. It is stored in a cylindrical storage portion 31 formed integrally with the block main portion 1. As shown in FIGS. 1 and 5, the storage portion 31 is formed by adding a hollow cylindrical portion to the engine block main portion 1.

  For example, as shown in FIG. 4, a first bevel gear 32 is attached integrally with the crankshaft 7 to the left end portion of the crankshaft 7 in the drawing, so that the crankshaft 7 and the first bevel gear 32 rotate synchronously. A second bevel gear 33 that meshes with the first bevel gear 32 is attached to the lower end portion of the intermediate shaft 29 integrally with the intermediate shaft 29 by a bolt. An intermediate shaft 29 and an individual third bevel gear 34 are integrally attached to the intermediate shaft 29 by bolts at the upper end of the intermediate shaft 29. A fourth bevel gear 35 that meshes with the third bevel gear 34 is attached to the cam shaft 6 integrally with the cam shaft 6 by a bolt at the left end of the cam shaft 6 in the figure, and therefore the cam shaft 6 and the fourth bevel gear 35 are synchronized. Rotate. The gear ratio between the first bevel gear 32 and the second bevel gear 33 is 1, and the gear ratio between the third bevel gear 34 and the fourth bevel gear 35 is 2. As a result, the camshaft 6 has a rotational speed of the crankshaft 7. Rotates at a rotation speed ratio of 1/2.

  A step portion is formed above the second bevel gear 33 at the lower end portion of the intermediate shaft 29 in the storage portion 31, a disc-like plate 30 is placed on the step portion, and an oil pump case 36 is mounted above the step plate. Has been. An oil pump housing is formed at the lower end of the oil pump case 36 facing the plate 30 and houses an outer rotor 37 and an inner rotor 38 that are components of the oil pump. Among these, the inner rotor 38 is rotated by the intermediate shaft 29, and thereby, for example, a trochoid oil pump 39 is configured. A water pump case 54 is further mounted above the oil pump case 36, and a water pump housing is formed at the lower end of the water pump case 54 facing the oil pump case 36. The impeller is a component of the water pump. 55 is stored. The impeller 55 is rotated by the intermediate shaft 29, and a water pump 56 is configured by these.

  The above is the configuration of the so-called engine main machine. For example, when the monoblock engine of this embodiment is used as a vehicle engine, it is not until the auxiliary machines other than the main machine such as the intake system, the exhaust system, and the ignition system are attached. It is established as a vehicle engine. Therefore, individual intake pipes 57 are connected to the intake ports 11, and an intake manifold 58 is connected to the intake pipes 57 in the intake direction. The exhaust ports 12a and 12b are gathered at the cylinder head 2 portion of the engine block main portion 1 to form a collecting passage 59, and an exhaust pipe 60 separate from the engine block main portion 1 is formed in the collecting passage 59. A catalytic converter 61 is interposed in the middle of the exhaust pipe 60.

  An air compressor 62 is disposed above the balancer shaft 52, and an alternator 63 is disposed above the air compressor 62. A driven pulley 65 is attached to both the alternator 63 and the air compressor 62. A tensioner pulley 64 is disposed below the balancer shaft 52, and a belt 66 is wound around the driving pulley 53, the driven pulley 65 of the air compressor 62, the driven pulley 65 of the alternator 63, and the tensioner pulley 64 in this order. . In the belt layout of this embodiment, only the driving pulley 53 is in contact with the outer peripheral surface of the belt 66, and the two driven pulleys 65 and the tensioner pulley 64 are in contact with the inner peripheral surface of the belt 66. Therefore, when the driving pulley 53 rotates counterclockwise as described above, the driven pulley 65, that is, the alternator 63 and the air compressor 62 rotate clockwise, and the tensioner pulley 64 also rotates clockwise. In the figure, reference numeral 67 is an oil filter, and reference numeral 68 is a starter.

  In the present embodiment, the alternator 63 driven by the belt 66 is disposed at the height position of the cylinder head 2 of the engine block main portion 1. In the present embodiment, since the storage portion 31 for storing the intermediate shaft 29 and the bevel gear is provided at the end of the cylinder row, the alternator 63 is the first of the cylinder row end closest to the storage portion 31. It is located laterally with respect to the combustion chamber 10a in a direction perpendicular to the cylinder row. Let the combustion chamber adjacent to this 1st combustion chamber 10a be the 2nd combustion chamber 10b. For example, as clearly shown in FIG. 6, in the present embodiment, the exhaust ports of the combustion chambers 10a and 10b, that is, the valve seats 13 of the exhaust ports 12a and 12b are cylinders with respect to the centers of the combustion chambers 10a and 10b. It is shifted in the direction away from the alternator 63 in the row direction.

  A bulging portion 69 bulging from the cylinder head 2 in a direction perpendicular to the cylinder row is formed on the side of the second combustion chamber 10 b, and a collecting passage 59 is formed in the bulging portion 69. As a result, since the second exhaust port 12b of the second combustion chamber 10b is continuous with the collecting passage 59, the second exhaust port 12b is extended in a direction orthogonal to the cylinder row and is disposed on the downstream side of the second exhaust port 12b. A collecting passage 59 is formed inside 69. Note that the first exhaust port 12a of the first combustion chamber 10a also gathers in the collecting passage 59.

  In this embodiment, the cylinder head 2 and the cylinder 3 are monoblocked to form the engine block main portion 1. In a normal engine, a head bolt for fixing the cylinder head 2 to the cylinder 3 is required, but in the present embodiment, a head bolt is unnecessary. Therefore, for example, the exhaust port can be freely laid out in the cylinder head 2. Therefore, in the present embodiment, when the engine is viewed from the cylinder center axis direction, the first exhaust port 12a is curved in an S shape so that the upstream side and the downstream side of the passage are opposite to each other, and the alternator 63 In the facing section, the first exhaust port 12a passes through the inner side of the outer wall 70 of the cylinder head 2 disposed outside the first combustion chamber 10a in the direction perpendicular to the cylinder row. Therefore, the bulging portion 69 containing the collecting passage 59 is disposed in a direction away from the alternator 63, and the alternator 63 can be brought close to the cylinder head 2. Further, since the second exhaust port 12b is connected to the collecting passage 59 by a straight passage, and the first exhaust port 12a is also gently curved and gathers in the collecting passage 59, the passage resistance of each exhaust port 12a, 12b is also reduced. To reduce.

  As described above, in the engine exhaust system of the present embodiment, in the engine exhaust system in which a plurality of cylinders are arranged in series, the cylinder head 2 has the combustion chambers 10a and 10b, one exhaust port 12a and 12b per one respectively. Therefore, it is possible to reduce the volume that the exhaust ports 12a, 12b and the collecting passage 59 can fit in the cylinder head 2. Therefore, the passage shapes of the exhaust ports 12a and 12b can be freely set, and the amount by which the bulging portion 69 of the cylinder head 2 bulges out of the cylinder head 2 can be reduced. Also, the exhaust ports of the first combustion chamber 10a and the second combustion chamber 10b are shifted in the direction away from the alternator 63 in the cylinder row direction with respect to the centers of the combustion chambers 10a and 10b, and the second combustion chamber 10b side A bulging portion 69 is arranged on the side, and the downstream side of the second exhaust port 12b communicating with the second combustion chamber 10b is in a direction perpendicular to the cylinder row and extends to the bulging portion 69 side. The collecting passage 59 is disposed in the bulging portion 69 disposed on the extended downstream side of the exhaust port 12b. Therefore, the length of the second exhaust port 12b communicating at least between the exhaust port of the second combustion chamber 10b and the collecting passage 59 can be shortened to reduce the size of the bulging portion 69, and the passage resistance of the second exhaust port 12b can be reduced. Can be reduced. Further, the first exhaust port 12a of the first combustion chamber 10a is located outside the first combustion chamber 10a in a section facing the alternator 63 at least in the direction orthogonal to the cylinder row when viewed from the cylinder central axis direction. The passage was curved in an S shape so that the upstream side and the downstream side of the passage were opposite to each other so as to pass inside the outer wall 70 of the cylinder head 2. Accordingly, the first exhaust port 12a can be disposed closer to the first combustion chamber 10a to reduce the size of the expansion portion 69, and the alternator 63 can be disposed closer to the cylinder head 2 by that amount. As described above, since the alternator 63 can be disposed close to the cylinder head 2 without being obstructed by the expansion portion 69 and the exhaust ports 12a and 12b, the engine can be downsized. In addition, the passage lengths of the exhaust ports 12a and 12b and the collecting passage 59 can be made shorter than the conventional length, and the ventilation resistance in the exhaust ports 12a and 12b and the collecting passage 59 can be reduced.

  Further, when viewed from the direction orthogonal to the cylinder row, the port portion adjacent to the valve seat 13 of the first exhaust port 12a and the second exhaust port 12b and the central shaft 16CL of the exhaust valve 16 that opens and closes each exhaust port are respectively provided. The side away from the combustion chambers 10a, 10b was inclined with respect to the central axis 5CL of the cylinder so as to approach the collecting passage 59 side. As a result, the length of the exhaust ports 12a and 12b can be made shorter than before, the degree of bending of the exhaust ports 12a and 12b can be reduced, and the passage resistance of the exhaust ports 12a and 12b can be reduced.

  Further, even in a two-cylinder engine whose length in the cylinder row direction is relatively short and the collecting passage is often arranged on the side of the auxiliary machine, if the above structure is applied, the alternator 63 is brought closer to the engine and the engine is made smaller. And the passage resistance of the exhaust ports 12a and 12b can be reduced.

1 is an engine block main part 2 is a cylinder head 3 is a cylinder 4 is an upper crankcase (the upper half of the crankcase)
5 is a cylinder bore 6 is a camshaft 7 is a crankshaft 8 is a head cover 9 is a lower crankcase 10a and 10b is a combustion chamber 11 is an intake port 12a, 12b is an exhaust port 13 is a valve seat 14 is a valve stem guide 15 is an intake valve 16 is Exhaust valve 17 is a valve spring 18 is a cam journal 19 is a bearing 20 is an intake cam 21 is an exhaust cam 22 is a rocker arm with a roller 23 is a hydraulic lash adjuster 24 is a piston 25 is a crank pin 26 is a connecting rod 27 is a crank journal 28 is a bearing metal 29 is an intermediate shaft 30 is a plate 31 is a storage portion 32 is a first bevel gear 33 is a second bevel gear 34 is a third bevel gear 35 is a fourth bevel gear 36 is an oil pump case 37 is an outer rotor 38 is an inner rotor 39 Is an oil pump 51 is a spark plug 52 is a balancer shaft 53 is a drive pulley 54 is a water pump case 55 is an impeller 56 is a water pump 57 is an intake pipe 58 is an intake manifold 59 is a collecting passage 60 is an exhaust pipe 61 is a catalytic converter 62 is an air Compressor 63 is an alternator 64 is a tensioner pulley 65 is a driven pulley 66 is a belt 67 is an oil filter 68 is a starter 69 is a bulging portion 70 is an outer wall

Claims (3)

In an engine exhaust system in which a plurality of cylinders are arranged in series,
A cylinder head having a combustion chamber corresponding to the number of cylinders and one exhaust port per combustion chamber;
An auxiliary machine disposed on the side of the cylinder chamber orthogonal direction of the combustion chamber at one end in the cylinder row direction and driven by a belt;
When the combustion chamber disposed at the end on the auxiliary machine side in the cylinder row direction is the first combustion chamber and the combustion chamber disposed adjacent to the first combustion chamber is the second combustion chamber, the second combustion chamber A bulging portion that bulges from the cylinder head in a direction perpendicular to the cylinder row on the side of
Exhaust ports formed in the first combustion chamber and the second combustion chamber, respectively, shifted in the cylinder row direction in the direction away from the auxiliary machine with respect to the centers of the first combustion chamber and the second combustion chamber. When,
A second exhaust port formed in the cylinder head to extend from the exhaust port of the second combustion chamber in a direction orthogonal to the cylinder row;
A collecting passage formed inside the bulging portion continuously downstream of the second exhaust port;
The exhaust port of the first combustion chamber communicates with the collecting passage, and when viewed from the cylinder central axis direction, at least in a section facing the auxiliary machine in a direction orthogonal to the cylinder row, the first combustion chamber Engine exhaust comprising a first exhaust port that passes through the inside of the outer wall of the cylinder head located outside and whose upstream and downstream sides of the passage are curved in opposite directions. apparatus.   When viewed from the direction perpendicular to the cylinder row direction, the central axis of the exhaust valve that opens and closes the port portion adjacent to the exhaust port of each of the first exhaust port and the second exhaust port and the exhaust port is respectively set with respect to the central axis of each cylinder. 2. The exhaust system for an engine according to claim 1, wherein the exhaust system is inclined so that the side away from the combustion chamber is the collecting passage side.   The engine exhaust system according to claim 1 or 2, wherein the engine is a two-cylinder engine.

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