JP4782098B2 - Internal combustion engine provided with a secondary air passage - Google Patents

Description

  The present invention relates to an internal combustion engine including a cylinder head provided with an exhaust port that opens to a combustion chamber and a secondary air passage that guides secondary air for exhaust purification to the exhaust port.

In an internal combustion engine, it is known that a cylinder head integrated with a cylinder block is provided with an exhaust port that opens to a combustion chamber and a secondary air passage that guides secondary air for exhaust purification to the exhaust port. Yes. (For example, see Patent Documents 1 and 2)
Japanese Utility Model Publication No. 61-4647 JP 2000-73752 A

The secondary air supplied to the exhaust port provided in the cylinder head of the internal combustion engine is for purifying the exhaust gas by burning combustible components such as HC in the exhaust gas (hereinafter referred to as “combustible component”). It is air and it is desirable to burn the combustible component efficiently. For this reason, the secondary air in the secondary air passage provided in the cylinder head is heated by the heat from the combustion chamber or the exhaust port provided in the cylinder head in terms of promoting combustion of combustible components. It is preferable.
However, when the secondary air passage is provided between the combustion chamber and the exhaust port in the cylinder axial direction of the cylinder block, or when provided along the exhaust port directly below or directly above the exhaust port, There is a possibility that the secondary air is excessively heated in the air passage. And in the secondary air heated too much, the density will fall and oxygen concentration will fall, As a result, the fall of the combustion efficiency of a combustible component will be caused.
Therefore, in order to prevent excessive heating of the secondary air in the secondary air passage provided in the cylinder head, the cooling fluid passage is provided so as to surround the secondary air passage. The structure of the cylinder head becomes complicated and the cost increases.
In addition, when a passage forming portion is provided on the bottom chamber wall of the valve operating chamber formed by the cylinder head in order to form the secondary air passage, if the passage forming portion is a raised portion, the raised portion moves. Oil flow in the valve chamber may be hindered, and it may be difficult for the oil after lubrication at the lubrication point in the valve chamber to flow into the oil return passage.

  This invention is made | formed in view of such a situation, and the invention of Claims 1-6 prevents excessive heating of the secondary air by the heat from a combustion chamber and an exhaust port, and is secondary. An object is to improve the exhaust purification performance by air and to reduce the size of the cylinder head. The invention described in claim 2 further aims to further reduce the size of the cylinder head while enhancing the effect of preventing excessive heating of the secondary air in the cylinder head. The invention further aims to eliminate the oil return failure from the valve operating chamber by using an oil passage for enhancing the effect of preventing excessive heating of the secondary air. An object of the present invention is to reduce the cost of a cylinder head provided with a secondary air passage, and an object of the present invention is to facilitate formation of a bent secondary air passage.

The invention according to claim 1 includes a cylinder block and a cylinder head, and the cylinder head includes an exhaust port that opens to a combustion chamber, and a secondary air passage that guides secondary air for exhaust purification to the exhaust port. The secondary air passage has an inlet opening in the side wall of the cylinder head and an outlet opening in the exhaust port, and the secondary air passage is in the cylinder axial direction, The internal combustion engine is located far from the exhaust port with respect to the combustion chamber, and an oil passage is provided between the secondary air passage and the exhaust port.
According to a second aspect of the present invention, in the internal combustion engine according to the first aspect, the cylinder head includes a cooling fluid passage through which a cooling fluid for cooling the cylinder head flows, the combustion chamber and the secondary air passage. It is provided between.
The invention according to claim 3 is the internal combustion engine according to claim 1 or 2, wherein the cylinder head forms a valve operating chamber in which a valve operating device that drives an exhaust valve that opens and closes the exhaust port is accommodated. The oil passage guides oil collected in a recess formed by a side wall of the cylinder head and a raised portion provided with the secondary air passage in the valve operating chamber to an oil return passage provided in the cylinder head. It is.
According to a fourth aspect of the present invention, in the internal combustion engine according to the third aspect, the cylinder head is a cast product formed by casting, and the cylinder head includes an endless transmission band that drives a cam shaft of the valve gear. The oil return passage is the transmission chamber, and the oil passage is formed by a hole formed by a core that forms the transmission chamber.
According to a fifth aspect of the present invention, in the internal combustion engine according to any one of the first to fourth aspects, the secondary air passage includes an upstream passage having the inlet, a downstream passage having the outlet, and the upper portion. A bent portion where the downstream passage is bent and connected to the flow passage, and the upstream passage and the bent portion are positioned on the opposite side of the oil passage from the combustion chamber in the cylinder axial direction. The bent portion is located at a position that overlaps with the oil passage or a portion beyond the oil passage in the upstream passage extending from the inlet as viewed from the cylinder axial direction.
According to a sixth aspect of the present invention, in the internal combustion engine according to the fifth aspect, the upstream passage is a linear hole formed by machining from the side wall of the cylinder head, and the downstream passage is the It is a straight hole formed by machining from the wall surface of the exhaust port through the combustion chamber.

According to the first aspect of the present invention, since the secondary air passage is located farther from the exhaust port than the combustion chamber, the heating of the secondary air by the heat of the combustion chamber is suppressed, and the secondary air passage is Since the oil passage is provided between the exhaust port and the exhaust port, the amount of heat transferred from the exhaust port to the secondary air passage is reduced by the oil flowing through the oil passage, and the heating of the secondary air due to the heat of the exhaust port is also suppressed. . As a result, since the secondary air is suppressed from being heated excessively in the secondary air passage by the heat of the combustion chamber and the exhaust port, the oxygen concentration due to the decrease in the density of the secondary air due to excessive heating. Is prevented, combustion of combustible components in the exhaust gas by the secondary air is promoted, and the exhaust gas purification performance of the internal combustion engine is improved.
Even when the distance between the secondary air passage and the exhaust port is reduced, the oil passage can be used to prevent the secondary air from being excessively heated, so that the cylinder head can be downsized. .
According to the second aspect of the present invention, the amount of heat transferred from the combustion chamber to the secondary air passage is reduced by the cooling fluid flowing through the cooling fluid passage, so that the heating of the secondary air by the heat of the combustion chamber is suppressed. As a result, even when the interval between the combustion chamber and the secondary air passage is reduced, excessive heating of the secondary air can be prevented by utilizing the cooling fluid passage for cooling the cylinder head. The head can be downsized.
According to the third aspect of the present invention, even when a raised portion is formed in the valve operating chamber to provide the secondary air passage, and the raised portion forms a recess that accumulates oil in the valve operating chamber. Since the oil passage for guiding the oil collected in the concave portion to the oil return passage is provided, the return of the oil in the valve operating chamber is not hindered by the raised portion. As a result, by using the oil passage for enhancing the effect of preventing excessive heating of the secondary air, it is possible to eliminate the problem of oil return from the valve operating chamber. Since the amount of oil that remains stored in the valve operating chamber is reduced, the amount of oil required for the internal combustion engine can be reduced.
According to the fourth aspect of the present invention, the oil passage is formed using a core for forming a transmission chamber provided in the cylinder head. As a result, the number of machining steps for the cylinder head is reduced compared to the case where machining such as machining is required only to form the oil passage, thereby reducing the cost of the cylinder head provided with the secondary air passage. can do.
According to the fifth aspect of the present invention, since the upstream passage and the downstream passage are connected at the bent portion, the secondary air passage is bent in the cylinder head. The secondary air passage in the cylinder head has a higher degree of freedom than the secondary air passage in the shape of a cylinder, and it is possible to reduce the size of the cylinder head while preventing excessive heating of the secondary air in the cylinder head. A secondary air passage can be provided.
In addition, since the secondary air passage can be provided so as to avoid the oil passage on the side opposite to the combustion chamber with respect to the oil passage in the cylinder axis direction by utilizing the bent portion, for example, from the inlet to the outlet is almost Compared to the straight secondary air passage, the secondary air passage is less likely to restrict the arrangement of the oil passage. As a result, the passage area of the oil passage provided between the secondary air passage and the exhaust port can be increased, so that the oil in the valve operating chamber can be smoothly discharged to the oil return passage, By using an oil passage for enhancing the effect of preventing the secondary air from being excessively heated, the problem of oil return from the valve chamber is eliminated, and the cylinder head can be reduced in size.
According to the sixth aspect of the present invention, a secondary air passage having a bent portion can be formed by simple machining with a tool that forms a straight hole such as a drill. The secondary air passage can be easily formed.

Hereinafter, embodiments of the present invention will be described with reference to FIGS.
Referring to FIG. 1, an internal combustion engine E to which the present invention is applied is an air-cooled four-stroke that is mounted on a motorcycle V, which is a vehicle as a machine, in a horizontal arrangement in which a crankshaft 28 is oriented in the vehicle width direction. The power unit P is configured together with a transmission that is an internal combustion engine and includes an input shaft connected to the crankshaft 28.
In the specification, the vertical direction is the vertical direction, and in the embodiment, front and rear and left and right respectively mean front and rear and left and right when the motorcycle V including the internal combustion engine E is used as a reference. The left-right direction coincides with the vehicle width direction and the axial direction of a cam shaft 41 (see FIG. 3) described later. When one of the right side and the left side is one direction in the left-right direction, the other of the right side and the left side is the other direction in the left-right direction.

  The motorcycle V includes a vehicle body that includes a vehicle body frame F and a vehicle body cover C that covers the vehicle body frame F, and a power unit P that is supported by the vehicle body frame F. The vehicle body frame F includes a head pipe 1, a pair of left and right main frames 2 that extend rearward from the head pipe 1 and supports the fuel tank 14, and a rear side of the head pipe 1 below the main frame 2. One down tube 3 extending obliquely downward, a pair of left and right seat rails 4 connected to the rear part of each main frame 2 and extending rearward and supporting the seat 15, and rear parts of the left and right main frames 2 A pair of left and right rear frames 5 respectively connecting the rear portions of the seat rails 4 and a pair of left and right pivot plates 6 connected to the rear portions of the main frames 2 and extending downward.

  A front fork 10 having a front wheel 8 pivotally supported at the lower end and a handle 11 attached to the upper end is supported on the head pipe 1 so as to be steerable. The pivot shaft 7 supported by the left and right pivot plates 6 supports the front end portions of a pair of left and right swing arms 12 so as to be swingable. The rear end portion of each swing arm 12 is supported by the vehicle body frame F via a rear cushion 13 coupled to the rear portion of the seat rail 4 and pivotally supports the rear wheel 9.

  The power unit P disposed between the main frames 2 and the down tube 3 is attached to the down tube 3 and the pivot plate 6. An output shaft 16 of the transmission is disposed at the rear of the power unit P, and the power generated by the internal combustion engine E is input to the transmission through the crankshaft 28 and is then shifted, and then the output shaft 16 to the final reduction mechanism 17. Is transmitted to the rear wheel 9 via. The final reduction mechanism 17 includes a driving sprocket 17a coupled to the output shaft 16, a driven sprocket 17b coupled to the rear wheel 9 as a driving wheel, an endless chain 17c wound around both the sprockets 17a and 17b, Consists of

  2 and 3, the internal combustion engine E includes a cylinder block 20 having one cylinder 20a inclined forward, a cylinder head 21 disposed on the cylinder block 20, and an upper portion of the cylinder head 21. An engine body including a head cover 22 disposed and a crankcase 23 disposed below the cylinder block 20 is provided. The crankcase 23 is integrally formed with a transmission case 24 that houses the transmission.

  The cylinder head 21 and the crankcase 23 are provided with a plurality of head bolts 25 and 26, an upper end portion that is both ends in the direction of the cylinder axis Lc (hereinafter referred to as “cylinder axis direction”) with the cylinder block 20 interposed therebetween, and The cylinder block 20 is integrated with the lower end portion. The head bolt 25 is inserted into a pair of bearing portions 44a and 44b of the cam holder 44 and an insertion hole 25a (see also FIG. 4) provided in the cylinder head 21 and an insertion hole (not shown) provided in the cylinder block 20. Then, it is screwed into the crankcase 23 and tightened by the nut 25b.

  The cylinder 20a is disposed on the vehicle body with the cylinder axis Lc directed slightly obliquely forward with respect to the vertical line from the crankshaft 28 upward. A piston 27 is fitted in the cylinder bore 20b of the cylinder 20a so as to be able to reciprocate, and a crankshaft 28 to which the piston 27 is connected via a connecting rod is rotatably supported by the crankcase 23 via a main bearing.

The cylinder head 21 is provided with an intake port 30 having an intake port 30a and an exhaust port 31 having an exhaust port 31a that open to a combustion chamber 29 between the piston 27 and the cylinder head 21, respectively. Attach to 29. An intake valve 33 and an exhaust valve 34 provided in the cylinder head 21 are slidably supported by a guide cylinder 35 fixed to the cylinder head 21 and are urged by a valve spring 36 in a valve closing direction.
Here, it is assumed that the combustion chamber 29 is a space formed by the cylinder bore 20b and the concave portion of the cylinder head 21 between the piston 27 and the cylinder head 21 in the cylinder axial direction.

  The intake valve 33 and the exhaust valve 34 are driven to open and close by a valve gear 40 including a camshaft 41 that is rotationally driven by the power of the crankshaft 28 transmitted through the valve gear transmission mechanism 37, and the rotation of the crankshaft 28 The intake port 30a and the exhaust port 31a are opened and closed in synchronization with each other.

  A valve operating device 40 accommodated in the valve operating chamber 38 includes a cam shaft 41 rotatably supported by the cylinder head 21 via bearings 44a and 44b of a cam holder 44 provided integrally with the cylinder head 21. , An intake rocker arm 42i and an exhaust rocker arm 42e that are driven by an intake cam 41i and an exhaust cam 41e provided on the cam shaft 41 to swing, and a pair of rocker shafts 43i that swingably support the rocker arms 42i and 42e, 43e. The rocker shafts 43i and 43e inserted and held in the holes 44i and 44e provided in the cam holder 44 are prevented from coming off by the head bolt 25.

  The transmission mechanism 37 includes a drive sprocket provided at the shaft end of the crankshaft 28, a driven sprocket 37a provided at the shaft end of the camshaft 41 and disposed in the valve operating chamber 38, and the drive sprocket and the driven sprocket 37a. And a chain 37b, which is an endless transmission band that is stretched over.

The chain 37b includes a cavity 45a provided at one end in the direction of the rotation center line La of the cam shaft 41 in the cylinder head 21 (hereinafter referred to as “cam shaft direction”), and a cam shaft direction in the cylinder block 20. Is accommodated in a chain chamber 45 as a transmission chamber constituted by a cavity (not shown) provided at one end of the.
The cylinder block 20 and the cylinder head 21 are castings formed by casting from a light metal material, for example, an aluminum alloy material, and the cavity 45a is formed by a core that is a part of a mold for casting the cylinder head 21. The

The valve operating chamber 38 is formed by the cylinder head 21 and the head cover 22. Then, as the chamber wall of the valve operating chamber 38, a cylinder head 21 forms a bottom chamber wall 48e and a cylindrical side chamber wall 49 that rises upward from the bottom chamber wall 48e or toward the anti-combustion chamber and surrounds the cylinder axis Lc. The ceiling chamber wall 48f is formed by the head cover 22.
4 and 5 together, the side chamber wall 49 is formed by a part of the side wall 47 of the cylinder head 21 surrounding the cylinder axis Lc. In this embodiment, the side wall 47 is a front side facing in the front-rear direction. The wall 47a and the rear wall 47b are composed of a left wall 47c and a right wall 47d that face each other in the left-right direction. The side chamber wall 49 includes a front chamber wall 49a and a rear chamber wall 49b that are opposed in the front-rear direction, and a left chamber wall 49c and a right chamber wall 49d that are opposed in the left-right direction. Accordingly, the front chamber wall 49a, the rear chamber wall 49b, the left chamber wall 49c, and the right chamber wall 49d are parts of the front wall 47a, the rear wall 47b, the left wall 47c, and the right wall 47d, respectively.

  Note that the combustion chamber side with respect to the parts and members of the internal combustion engine E means a position close to the combustion chamber 29 in the cylinder axial direction (in this embodiment, it is also the lower side in the vertical direction), and anti-combustion. The chamber side means a position far from the combustion chamber 29 in the cylinder axial direction (in this embodiment, it is also an upper side in the vertical direction).

1 to 3, an internal combustion engine E includes an intake device 50 that forms an intake passage that guides intake air to the combustion chamber 29, and an air-fuel mixture forming means that supplies fuel to the intake air to form an air-fuel mixture. And an exhaust device 52 that forms an exhaust passage for guiding the exhaust gas to the outside of the internal combustion engine E.
The intake device 50 includes an air cleaner 50a for taking in outside air, a throttle body 50b provided with a throttle valve for controlling the flow rate of intake air from the air cleaner 50a, and a side wall 47 on the intake side of the throttle body 50b and the cylinder head 21. An intake pipe 50c connecting the wall 47b is provided. The throttle body 50 b is configured by the body of the carburetor 51.
The exhaust device 52 includes an exhaust pipe 52a connected to the front wall 47a, which is the side wall 47 on the exhaust side of the cylinder head 21, and an exhaust muffler 52b connected downstream of the exhaust pipe 52a.

The intake air whose flow rate is controlled by the throttle valve is mixed with the fuel supplied from the carburetor 51 to form an air-fuel mixture, and is sucked into the combustion chamber 29 via the intake port 30 when the intake valve 33 is opened. The air-fuel mixture is ignited and burned in the combustion chamber 29 by the spark plug 32, and the piston 27 driven by the generated combustion gas rotates the crankshaft 28 via the connecting rod. The combustion gas is discharged as exhaust gas to the exhaust port 31 when the exhaust valve 34 is opened, and is further discharged to the atmosphere through the exhaust pipe 52a and the exhaust muffler 52b.
The power of the crankshaft 28 is shifted by the transmission and then drives the rear wheels 9 via the final reduction mechanism 17.

3 and 4, air as a cooling fluid is provided between the bottom wall 46e and the ceiling wall 46f of the cylinder head 21 in a region overlapping the combustion chamber 29 and the valve operating chamber 38 when viewed from the cylinder axial direction. A cooling air passage 55 is provided as a cooling fluid passage through which the air flows. The cylinder head 21 is cooled by the air flowing through the cooling air passage 55, and more specifically, the combustion chamber wall 29w of the combustion chamber 29 and the exhaust port wall 31w of the exhaust port 31 are cooled.
The bottom wall 46e forms a combustion chamber wall 29w, an intake port wall 30w and an exhaust port wall 31w of the intake port 30, and the bottom chamber wall 48e of the valve operating chamber is a part of the bottom wall 46e excluding the combustion chamber wall 29w. And the ceiling wall 46f.
Here, the bottom wall 46e is a wall that is located on the combustion chamber side in the cylinder axis direction in the cylinder head 21 and has a mating surface with the cylinder block 20, and the ceiling wall 46f is a bottom wall in the cylinder axis direction in the cylinder head 21. It is a wall that is separated from the wall 46 to the anti-combustion chamber side.

  The cooling air passage 55 is located between the exhaust port 31 and the chain chamber 45 in the cam shaft direction and opens forward, and between the intake port 30 and the chain chamber 45 in the cam shaft direction. A second communication passage 55b that is located in the middle and opens rearward, and a third communication passage 55c that faces the chain chamber 45 with the combustion chamber 29 therebetween in the camshaft direction and that opens to the right. And communicates with the atmosphere that is the atmosphere of the internal combustion engine E (that is, the cooling fluid supply source) through the communication passages 55a, 55b, and 55c. A portion of the combustion chamber wall 29w that forms the third communication passage 55c is provided with a mounting portion 57 to which the spark plug 32 is screwed.

In the cooling air passage 55, a diverting wall 56 for diverting the air flow to the intake side and the exhaust side between the intake port 30 and the exhaust port 31 in the orthogonal direction connects the bottom wall 46e and the ceiling wall 46f. Provided.
Here, the orthogonal direction is a direction orthogonal to a central plane including the cylinder axis Lc and parallel to the rotation center line La of the cam shaft 41 or a plane including the cylinder axis Lc and the rotation center line La. In the form, it is parallel to the front-rear direction when viewed from the cylinder axial direction. In the internal combustion engine E, the side where the intake port 30 is located with respect to the central plane is the intake side, and the side where the exhaust port 31 is located with respect to the central plane is the exhaust side.

  During traveling of the motorcycle V (see FIG. 1), traveling wind (air) flows into the cooling air passage 55 from the communication passage 55a, and the air flowing through the cooling air passage 55 causes the combustion chamber wall 29w and the exhaust port wall. 31w and spark plug 32 are cooled. Specifically, the air flowing into the cooling air passage 55 cools the combustion chamber wall 29w and the exhaust port wall 31w on the exhaust side. Thereafter, a part of the air flows toward the communication passage 55b to cool the combustion chamber wall 29w on the intake side, and then flows backward from the communication passage 55b. Further, another part of the air is diverted to the exhaust side and the intake side by the diverting wall 56, cools the combustion chamber wall 29w and the exhaust port wall 31w, and merges on the downstream side of the diverting wall 56 to form an ignition plug After cooling 32, it flows out from the communication passage 55c to the right. Therefore, the first communication passage 55 a is an air inflow passage to the cooling air passage 55.

  Referring to FIGS. 2 and 3, oil discharged from an oil pump constituting a lubrication system provided in the internal combustion engine E is supplied to a valve operating device 40 which is a lubricating portion in the valve operating chamber 38. Specifically, the oil pumped by the oil pump driven by the crankshaft 28 (see FIG. 1) is pumped up and discharged from the oil reservoir provided in the crankcase 23 (see FIG. 1). Further, the oil is injected into the valve operating chamber 38 through an oil passage provided in the cylinder head 21, and a lubricating portion such as a sliding portion of the valve operating device 40 is lubricated. The oil after lubricating the valve operating device 40 flows on the bottom chamber wall 48e of the valve operating chamber 38, flows into the chain chamber 45 as an oil return passage, flows down the chain chamber 45, and flows into the oil reservoir. Return to.

  4 to 7, the cylinder head 21 is provided with an oil passage 60 (indicated by a thick broken line in FIG. 2) for guiding oil in the valve operating chamber 38 to the chain chamber 45. Since the cylinder 20a is inclined forward, the oil passage 60 has a bottom chamber wall 48e including an exhaust port wall 31w, a raised portion 76, which will be described later, a front chamber wall 49a and a right chamber wall in the valve chamber 38. The oil collected in the recess 65 formed by 49d is guided to the chain chamber 45. A space 66 formed by the recess 65 is the lowermost part in the valve train chamber 38.

The oil passage 60 for communicating the valve chamber 38 and the chain chamber 45 has a raised portion 76 positioned between the exhaust valve 34 and the chain chamber 45 in the cam shaft direction, and an upstream passage of the secondary air passage 80 described later. It penetrates below 81 and is constituted by a hole formed by the core used when the chain chamber 45 is formed.
The oil passage 60 has an inflow port 61 that opens into the space 66 of the recess 65 and an outflow port 62 that opens into the chain chamber 45, and is positioned above or on the anti-combustion chamber side in the vertical direction or the cylinder axis direction. It is located between the next air passage 80 and the first communication passage 55a of the cooling air passage 55 located below or on the combustion chamber side. Therefore, the oil passage 60 is located between the secondary air passage 80 and the communication passage 55a and overlaps the secondary air passage 80 and the communication passage 55a when viewed from the cylinder axial direction.

Referring to FIGS. 1 and 2, the internal combustion engine E supplies secondary air for exhaust purification to the exhaust gas in order to purify the exhaust by burning unburned components (for example, HC, CO) in the exhaust gas. A secondary air supply device 70 is provided.
The secondary air supply device 70 includes a secondary air passage 80 provided in the cylinder head 21, and a supply pipe 71 that forms a supply passage 72 that supplies air in the air cleaner 50 a as an air source to the secondary air passage 80. The control valve 73 is configured to control the amount of secondary air introduced into the exhaust gas through the secondary air passage 80.
A control valve 73 provided in the middle of the supply passage 72 is controlled by the control device, and controls the amount of air according to the engine operating state of the internal combustion engine E, for example, the engine load.

3 and 5, the supply pipe 71 has a flange 71a as a connecting portion for communicating the supply passage 72 with the secondary air passage 80 by the cylinder head 21, and the flange 71a is a cylinder. It is connected to the cylinder head 21 by being attached to a mounting seat 74 as a connecting portion provided on the front wall 47a of the head 21 with a bolt 75 screwed into the screw hole 75a.
The supply pipe 71 and the exhaust pipe 52a connected to the front wall 47a facing the down tube 3 in the front-rear direction are arranged by being distributed to the left and right of the down tube 3 with the down tube 3 sandwiched in the left-right direction (FIG. 2). reference). For this reason, an internal combustion engine E including a cylinder head 21 provided with an exhaust pipe 52a and a supply pipe 71 extending forward from the front wall 47a and a forwardly inclined cylinder 20a is brought close to the down tube 3 in the front-rear direction. Since it can arrange | position, the internal combustion engine E and by extension, the power unit P can be arrange | positioned to a vehicle body compactly in the front-back direction.

2 to 5, the secondary air passage 80 located in the cylinder head 21 has an inlet 80i that opens to the mounting seat 74 in the front wall 47a and an outlet 80o that opens near the exhaust port 31a in the exhaust port 31. Have. Specifically, the secondary air passage 80 includes a straight upstream passage 81 having an inlet 80i, a straight downstream passage 82 having an outlet 80o, and the downstream passage 82 is bent with respect to the upstream passage 81. This is a bent passage composed of a bent portion 83 which is a connecting portion to be connected. The inlet 80i opens to the outer surface of the front wall 47a, which is the side wall 47, at a position separated from the exhaust port 31 in the cylinder axis direction and the cam axis direction.
The secondary air passage 80 is located between the valve stem 34a of the exhaust valve 34 and the exhaust port 31 when viewed from the cam shaft direction (see FIG. 3), and between the exhaust valve 34 and the chain chamber 45 in the cam shaft direction. (Refer to FIG. 2).

  Referring also to FIGS. 6 and 7, the upstream passage 81, the bent portion 83, and the downstream passage 82 are passage forming portions that protrude on the anti-combustion chamber side or upward in the bottom chamber wall 48 e of the valve operating chamber 38. It is provided on a certain ridge 76. The upstream passage 81 is formed from the outer surface of the front wall 47a of the cylinder head 21, and the downstream passage 82 is formed from the wall surface of the exhaust port 31 through the combustion chamber 29 (that is, the inner surface of the exhaust port wall 31w) by machining with a drill. The bent portion 83 is an intersection of the two holes.

The upstream passage 81 extending from the inlet 80i to the bent portion 83 in the orthogonal direction is separated from the exhaust port 31 in the cam shaft direction by a minimum interval A (see FIG. 5) when viewed from the orthogonal direction.
The entire upstream passage 81 and the bent portion 83 are located farther from the exhaust port 31 with respect to the combustion chamber 29 in the cylinder axial direction, and therefore from the portion farthest from the combustion chamber 29 at the exhaust port 31 in the cylinder axial direction. Located on the anti-combustion chamber side. Therefore, the entire upstream passage 81 and the bent portion 83 are located on the opposite side of the combustion chamber 29 with respect to the communication passage 55a of the oil passage 60 and the cooling air passage 55 in the vertical direction or the cylinder axis direction. Therefore, the communication passage 55 a and the oil passage 60 are arranged in order from the vicinity of the combustion chamber 29 between the entire upstream passage 81 and the bent portion 83 and the combustion chamber 29.

  The entire upstream passage 81 is located on a specific orthogonal plane that is one of planes orthogonal to the cylinder axis Lc (hereinafter referred to as “orthogonal plane”), and is parallel or substantially parallel to the orthogonal direction. is there. Therefore, the inclination angle of the upstream passage 81 with respect to the orthogonal plane is 0 ° or extremely small, and is smaller than the inclination angle of the downstream passage 82 with respect to the orthogonal plane. As described above, the upstream passage 81 and the downstream passage 82 are formed so as to have different inclination angles with respect to the orthogonal plane, with the bent portion 83 as a boundary. Note that the entire upstream passage 81 may be inclined with respect to the orthogonal direction when viewed from the cylinder axial direction.

  The upstream passage 81 and the bent portion 83 are positioned so as to overlap with the oil passage 60 and the communication passage 55a when viewed in the vertical direction or the cylinder axis direction, while the entire upstream passage 81 and the bent portion 83 are connected to the exhaust port 31 and The combustion chamber 29 is in a position that does not partially overlap. The upstream passage 81 and the bent portion 83 are located immediately above the oil passage 60 and the communication passage 55a, and the secondary air passage 80 is bent at a position overlapping the oil passage 60 when viewed from the cylinder axial direction. Yes. For this reason, the communication passage 55a and the oil passage 60 are provided between the combustion chamber 29, the entire upstream passage 81, and the bent portion 83. The oil passage 60 is provided between the exhaust port 31 and the entire upstream passage 81 and the bent portion 83.

  A downstream passage 82 extending obliquely downward from the bent portion 83 toward the outlet 80o and the exhaust port 31a is inclined with respect to the cam shaft direction and the orthogonal direction when viewed from the cylinder axial direction, and is extended from the bent portion 83 to the exhaust port 31. It extends in the approaching direction. The downstream passage 82 is located at a position that does not overlap the exhaust port 31 and the combustion chamber 29 when viewed from the cylinder axial direction, and is located upstream of the bent portion 83 and an upstream portion 82a that is located at a position overlapping the oil passage 60 and the communication passage 55a. It is a part other than the part 82a and is composed of a downstream part 82b near the outlet 80o.

  Almost all of the upstream portion 82a is located farther from the exhaust port 31 with respect to the combustion chamber 29 in the cylinder axial direction, and therefore the counter-combustion chamber than the portion farthest from the combustion chamber 29 in the exhaust port 31 in the cylinder axial direction. Located on the side. Therefore, the upstream portion 82a is located on the opposite side of the combustion chamber 29 with respect to the oil passage 60 and the communication passage 55a in the vertical direction or the cylinder axis direction, and is located directly above the oil passage 60 and the communication passage 55a. To do. Therefore, between the upstream portion 82a and the combustion chamber 29, the communication passage 55a and the oil passage 60 are arranged in order from the vicinity of the combustion chamber 29. For this reason, the communication passage 55a and the oil passage 60 are provided between the combustion chamber 29 and the upstream portion 82a, and the oil passage 60 is provided between the exhaust port 31 and the upstream portion 82a.

  Accordingly, the secondary air passage 80 is located at a position that does not overlap the exhaust port 31 and the combustion chamber 29 when viewed from the cylinder axial direction, and at a position that overlaps the oil passage 60 and the communication passage 55a, and the first passage. It is comprised from other 2nd channel | paths. The first passage is composed of an upstream passage 81, a bent portion 83 and an upstream portion 82a, and the second passage is composed of a downstream portion 82b.

Next, operations and effects of the embodiment configured as described above will be described.
The secondary air passage 80 provided in the cylinder head 21 includes an upstream passage 81 having an inlet 80i opening in the front wall 47a which is the side wall 47 of the cylinder head 21, and a downstream passage having an outlet 80o opening in the exhaust port 31. 82 and a bent portion 83 where the downstream passage 82 is bent and connected to the upstream passage 81, and the entire upstream passage 81 is connected to the combustion chamber 29 from the exhaust port 31 in the cylinder axial direction. Are located far from each other and do not overlap with the exhaust port 31 when viewed from the cylinder axial direction, the entire upstream passage 81, which is a part of the secondary air passage 80, is exhausted from the combustion chamber 29. Since it is located farther from the port 31, heating due to the heat of the combustion gas in the combustion chamber 29 is suppressed, and the exhaust gas flowing through the exhaust port 31 is located so as not to overlap the exhaust port 31 when viewed from the cylinder axial direction. Heating due to heat is also suppressed . On the other hand, since the secondary air passage 80 is bent at the bent portion 83, the passage length of the secondary air passage 80 can be increased, so that the secondary air in the secondary air passage 80 is brought into an excessively heated state. It can be heated appropriately to such an extent that it does not become. As a result, the secondary air is prevented from being heated excessively in the secondary air passage 80 due to the heat of the combustion chamber 29 and the exhaust port 31, so the density of the secondary air is reduced due to excessive heating. Oxygen concentration is prevented from being lowered by the combustion, and combustion of combustible components in the exhaust gas by the secondary air is promoted, and the exhaust gas purification performance of the internal combustion engine E is improved.
Further, the cylinder head 21 is provided with an oil passage 60 between the secondary air passage 80 and the exhaust port 31, so that the amount of heat transferred from the exhaust port 31 to the secondary air passage 80 by the oil flowing through the oil passage 60. Therefore, the heating of the secondary air due to the heat of the exhaust port 31 is suppressed. As a result, even when the distance between the exhaust port 31 and the secondary air passage 80 is reduced, the oil passage 60 can be used to prevent excessive heating of the secondary air. Can be realized.

The cylinder head 21 is provided with a cooling air passage 55 through which cooling air for cooling the cylinder head 21 flows between the combustion chamber 29 and the secondary air passage 80, so that the air flowing through the cooling air passage 55 is provided. As a result, the amount of heat transferred from the combustion chamber 29 to the secondary air passage 80 is reduced, so that the heating of the secondary air by the heat of the combustion chamber 29 is suppressed. As a result, even when the interval between the combustion chamber 29 and the secondary air passage 80 is reduced, the secondary air is excessively heated by using the cooling air for cooling the cylinder head 21 including the combustion chamber wall 29w. Therefore, the cylinder head 21 can be downsized.
In addition, the communication passage 55a that overlaps the secondary air passage 80 when viewed from the cylinder axial direction is an air inflow passage to the cooling air passage 55, and therefore after the combustion chamber wall 29w and the exhaust port wall 31w are cooled. Since the temperature is lower than that of air, heating of the secondary air due to the heat of the combustion chamber 29 and the exhaust port 31 is further suppressed.

  Since the upstream passage 81 and the downstream passage 82 are connected by the bent portion 83, the secondary air passage 80 is bent in the cylinder head 21, so that, for example, secondary air that is substantially straight from the inlet to the outlet is provided. Compared to the passage, the degree of freedom of arrangement of the secondary air passage 80 in the cylinder head 21 is increased, and the cylinder head 21 can be reduced in size, and the secondary air in the cylinder head 21 can be prevented from being excessively heated. A secondary air passage 80 can be provided.

  The cylinder head 21 forms a valve operating chamber 38 in which a valve operating device 40 that drives an exhaust valve 34 that opens and closes the exhaust port 31 is accommodated, and the oil passage 60 defines an exhaust port wall 31w in the valve operating chamber 38. The oil collected in the recess 65 formed by the bottom chamber wall 48e including the raised portion 76 provided with the secondary air passage 80 and the front chamber wall 49a and the right chamber wall 49d of the valve operating chamber 38 is supplied to the cylinder head 21. In order to provide the secondary air passage 80, a raised portion 76 is formed in the valve operating chamber 38 by being led to the chain chamber 45 which is an oil return passage provided in the valve chamber 38. Even when the recess 65 is formed so as to collect the oil, the oil passage 60 that guides the oil collected in the recess 65 to the chain chamber 45 is provided, so that the return of the oil in the valve operating chamber 38 is caused by the raised portion 76. Is not hindered. As a result, by using the oil passage 60 for enhancing the effect of preventing the secondary air from being excessively heated, the defective oil return from the valve operating chamber 38 is eliminated. Since the amount of oil remaining in the valve operating chamber 38 is reduced, the amount of oil required for the internal combustion engine E can be reduced.

  The cylinder head 21 is a cast product formed by casting. The cylinder head 21 is formed with a chain chamber 45 in which a chain 37b for driving the cam shaft 41 of the valve gear 40 is accommodated, and the oil return passage is a chain chamber. 45, and the oil passage 60 is constituted by a hole formed by a core that forms the chain chamber 45, so that the oil passage 60 uses a core for forming the chain chamber 45 provided in the cylinder head 21. Formed. As a result, since the machining process for the cylinder head 21 is reduced as compared with the case where machining such as machining is required only for forming the oil passage 60, the cylinder head 21 provided with the secondary air passage 80 is provided. The cost can be reduced.

  The upstream passage 81 and the bent portion 83 are located on the side opposite to the combustion chamber 29 with respect to the oil passage 60 in the cylinder axis direction, and the bent portion 83 is located at a position overlapping the oil passage 60 when viewed from the cylinder axis direction. By using the bent portion 83, the secondary air passage 80 can be provided so as to avoid the oil passage 60 on the side opposite to the combustion chamber 29 with respect to the oil passage 60 in the cylinder axis direction. For example, the secondary air passage 80 is less likely to restrict the arrangement of the oil passage 60 than the secondary air passage that is substantially straight from the inlet to the outlet. As a result, the passage area of the oil passage 60 provided between the secondary air passage 80 and the exhaust port 31 can be increased, so that the oil in the valve operating chamber 38 can smoothly flow out to the chain chamber 45. This makes it possible to eliminate the oil return failure from the valve operating chamber 38 by using the oil passage 60 for enhancing the effect of preventing excessive heating of the secondary air, and to reduce the size of the cylinder head 21. it can.

  The upstream passage 81 is a straight hole formed by machining from the front wall 47 a of the cylinder head 21, and the downstream passage 82 is a straight hole formed by machining from the wall surface of the exhaust port 31 through the combustion chamber 29. The secondary air passage 80 having the bent portion 83 can be formed by simple machining with a tool that forms a linear hole such as a drill. The secondary air passage 80 can be easily formed.

Hereinafter, the configuration in which a part of the configuration of the above-described embodiment is changed will be described with respect to the changed configuration.
In the embodiment, the upstream passage 81 is substantially parallel to the orthogonal plane, but may be inclined with respect to the orthogonal plane at an inclination angle smaller than the inclination angle of the downstream passage 82 with respect to the orthogonal plane, Further, the inclination angle of the upstream passage 81 may be larger than the inclination angle of the downstream passage 82.
When viewed from the cylinder axial direction, the bent portion 83 is perpendicular to the upstream passage 81 extending from the inlet 80i so that the secondary air passage 80 extends from the inlet 80i and exceeds the oil passage 60. It may be provided in a portion beyond the oil passage 60. In this case as well, the bent portion 83 reduces the restriction of the arrangement of the oil passage 60 by the secondary air passage 80, and the passage area of the oil passage 60 can be increased. The cylinder head 21 can be reduced in size while allowing the oil inside to smoothly flow out into the oil return passage.
The endless transmission band of the transmission mechanism 37 may be a belt.
The cylinder block and the cylinder head may be integrated by forming the cylinder head integrally with the cylinder block.
The internal combustion engine may be used for a machine other than a vehicle, for example, a work machine such as a generator, may be a multi-cylinder internal combustion engine including a cylinder block having a plurality of cylinders, and is a water-cooled internal combustion engine. May be. In the case of a water-cooled internal combustion engine, the cooling fluid passage is a cooling water passage.

1 is a left side view of a motorcycle equipped with an internal combustion engine to which the present invention is applied. It is a figure of the principal part centering on a cylinder head and a valve operating apparatus in the II arrow view of FIG. It is sectional drawing in the III-III line of FIG. It is sectional drawing seen from the cylinder axial direction in the IV-IV line of FIG. It is a figure of the principal part of the cylinder head in the V arrow view of FIG. FIG. 6 is a cross-sectional view of a main part taken along line VI-VI in FIG. 2. It is principal part sectional drawing in the VII-VII line of FIG.

Explanation of symbols

21 ... Cylinder head, 22 ... Head cover, 29 ... Combustion chamber, 31 ... Exhaust port, 34 ... Exhaust valve, 38 ... Valve operated chamber, 40 ... Valve operated device, 41 ... Cam shaft, 45 ... Chain chamber, 47 ... Side wall, 55 ... Cooling air passage, 60 ... Oil passage, 65 ... Recess, 76 ... Raised portion, 80 ... Secondary air passage, 80i ... Inlet, 80o ... Outlet, 81 ... Upstream passage, 82 ... Downstream passage, 83 ... Bending portion ,
V: Motorcycle, E: Internal combustion engine.

Claims (6)

An internal combustion engine comprising a cylinder block and a cylinder head, wherein the cylinder head is provided with an exhaust port that opens to a combustion chamber, and a secondary air passage that guides secondary air for exhaust purification to the exhaust port.
The secondary air passage has an inlet opening on a side wall of the cylinder head and an outlet opening on the exhaust port;
The secondary air passage is located farther from the exhaust port in the cylinder axial direction than the exhaust port, and an oil passage is provided between the secondary air passage and the exhaust port. An internal combustion engine.   2. The internal combustion engine according to claim 1, wherein a cooling fluid passage through which a cooling fluid for cooling the cylinder head flows is provided in the cylinder head between the combustion chamber and the secondary air passage. . The cylinder head forms a valve operating chamber that houses a valve operating device that drives an exhaust valve that opens and closes the exhaust port.
The oil passage guides oil collected in a recess formed by a side wall of the cylinder head and a raised portion provided with the secondary air passage to the oil return passage provided in the cylinder head. The internal combustion engine according to claim 1 or 2, characterized by the above. The cylinder head is a cast product formed by casting,
The cylinder head is formed with a transmission chamber in which an endless transmission band for driving the camshaft of the valve gear is housed.
The oil return passage is the transmission chamber;
4. The internal combustion engine according to claim 3, wherein the oil passage is constituted by a hole formed by a core that forms the transmission chamber. The secondary air passage is composed of an upstream passage having the inlet, a downstream passage having the outlet, and a bent portion where the downstream passage is bent and connected to the upstream passage,
The upstream passage and the bent portion are located on a side opposite to the combustion chamber with respect to the oil passage in the cylinder axial direction,
5. The bent portion according to claim 1, wherein the bent portion is located at a position overlapping with the oil passage or a portion beyond the oil passage in the upstream passage extending from the inlet when viewed from the cylinder axial direction. The internal combustion engine according to any one of claims.   The upstream passage is a straight hole formed by machining from the side wall of the cylinder head, and the downstream passage is a straight line formed by machining from the wall surface of the exhaust port through the combustion chamber. 6. The internal combustion engine according to claim 5, wherein the internal combustion engine has a shape of a hole.

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