Internal Combustion Engine

Abstract

An in-line four-cylinder internal combustion engine wherein exhaust ports (8, 9) of a pair of cylinders positioned at the center are connected to a single merged exhaust port (11) and this merged exhaust port (11) is connected through a first exhaust pipe (19) to a catalytic converter (18). On the other hand, exhaust ports (7, 10) of pairs of cylinders positioned at the two ends are connected through a second exhaust pipe (21) to a catalytic converter (18). A length of the first exhaust pipe (19) from the merged exhaust port (11) to the catalytic converter (18) is made shorter than the length of the second exhaust pipe (21) from the exhaust ports (7, 10) to the catalytic converter (18).

Description

TECHNICAL FIELD

[0001] The present invention relates to an internal combustion engine.

BACKGROUND ART

[0002] In in-line four-cylinder internal combustion engines, there is known an internal combustion engine in which a pair of cylinders positioned at the center have exhaust ports merged into a single merged exhaust port inside the cylinder head and opening on the side wall surface of the cylinder head and in which pairs of cylinders positioned at the two ends have exhaust ports opening on the side wall surface of the cylinder head at the two sides of the opening part of the merged exhaust port as independent exhaust ports (see Japanese Patent Publication (A) No. 2003-176722).

[0003] In this internal combustion engine, an exhaust manifold common to all cylinders is attached to the side wall surface of the cylinder head.

DISCLOSURE OF THE INVENTION

[0004] An object of the present invention is to provide an optimum layout and structure of a first exhaust pipe connected to a merged exhaust port and a second exhaust pipe connected to a pair of independent exhaust ports when constructing a double system of these exhaust pipes in the case of an internal combustion engine having one merged exhaust port and a pair of independent exhaust ports such as explained above.

[0005] According to the present invention, there is provided an in-line four-cylinder internal combustion engine wherein exhaust ports of a pair of cylinders positioned at the center merge inside a cylinder head into a single merged exhaust port and open on a side wall surface of the cylinder head, exhaust ports of pairs of cylinders positioned at the two ends open on the side wall surface of the cylinder head at the two sides of an opening part of the merged exhaust port as independent exhaust ports, and the opening part of said merged exhaust port is connected through a first exhaust pipe to either an exhaust inflow part of a catalytic converter or an exhaust inflow part of an exhaust turbocharger, the opening parts of said pair of independent exhaust port being connected through a second exhaust pipe merged midway to the same exhaust inflow part, and a length of the first exhaust pipe from the corresponding opening part to said exhaust inflow part being made shorter than the length of the second exhaust pipe from the corresponding opening parts to said exhaust inflow part.

[0006] In the present invention, the exhaust gas temperature of the exit part of the merged exhaust port is higher than the exhaust gas temperature at the exit part of the independent exhaust port. The higher temperature exhaust gas is fed through the first exhaust pipe with the shorter pipe length, that is, the smaller temperature drop, to a catalytic converter or exhaust turbocharger. That is, since the first exhaust pipe can feed high temperature exhaust gas to the catalytic converter or exhaust turbocharger, warmup of the catalyst can be promoted or the efficiency of the exhaust turbocharger can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIG. 1 is a plan cross-sectional view of a cylinder head.

[0008] FIG. 2 is a cross-sectional view of a cylinder head as seen along II-II of FIG. 1.

[0009] FIG. 3 is a perspective view showing the contour shapes of exhaust ports.

[0010] FIG. 4 is a front view of the side wall surface of a cylinder head.

[0011] FIG. 5 is a perspective view of an internal combustion engine.

[0012] FIG. 6 is a side view of the internal combustion engine shown in FIG. 5.

[0013] FIG. 7 is a side view of another embodiment of an internal combustion engine.

BEST MODE FOR WORKING THE INVENTION

[0014] FIG. 1 and FIG. 2 show a cylinder head 1 integrally cast from for example an aluminum alloy. Note that the circles shown by broken lines in FIG. 1 show the positions of the No. 1 cylinder #1, No. 2 cylinder #2, No. 3 cylinder #3, and No. 4 cylinder #4. Therefore, it is learned that the internal combustion engine provided with the cylinder head 1 shown in FIG. 1 is an in-line four-cylinder internal combustion engine. In FIG. 1, 2 shows a valve port opened and closed by an intake valve, while 3 shows a valve port opened and closed by an exhaust valve. Therefore, it is learned that each cylinder #1, #2, #3, and #4 is provided with a pair of intake valves and a pair of exhaust valves.

[0015] Note that the cylinder head 1 actually has cooling water passages extending along complicated paths, support parts of the valve trains, insertion parts for spark plugs, insertion parts for fuel injectors, etc. formed in it, but in FIG. 1 and FIG. 2, these are omitted.

[0016] The cylinder head 1 has side wall surfaces 4 and 5 substantially in parallel at the two sides of a plane including the cylinder axial lines of the cylinders #1, #2, #3, and #4. The intake ports 6 of the cylinder #1, #2, #3, and #4 formed in the cylinder head 1 open on the side wall surface 4.

[0017] Further, the cylinder head 1 has exhaust ports 7 of the No. 1 cylinder #1, exhaust ports 8 of the No. 2 cylinder #2, exhaust ports 9 of the No. 3 cylinder #3, and exhaust ports 10 of the No. 4 cylinder #4 formed in it. FIG. 3 is a perspective view of the contour shapes of such exhaust ports. As will be explained from FIG. 1, the pairs of exhaust ports 7, 8, 9, and 10 are separate near the corresponding pairs of valve ports 3, but when leaving the valve ports 3 a bit become single exhaust ports.

[0018] Now, as will be understood from FIG. 1, the exhaust ports of the pair of cylinders positioned at the center, that is, the exhaust ports 8 of the No. 2 cylinder #2 and the exhaust ports 9 of the No. 3 cylinder #3 are merged inside the cylinder head 1 to form a single merged exhaust port 11. This merged exhaust port 11 is extended to the side wall surface 5 of the cylinder head 1. In FIG. 1, if the plane extending through the center between the No. 2 cylinder #2 and No. 3 cylinder #3 in the cylinder axial line direction and perpendicular to the plane including the cylinder axial lines of the cylinders #1, #2, #3, and #4 is referred to as the "symmetrical plane K-K", the exhaust ports 8 of the No. 2 cylinder #2 and the exhaust ports 9 of the No. 3 cylinder #3 are arranged symmetrically with respect to the symmetrical plane K-K. The merged exhaust port 11 extends along the symmetrical plane K-K to the side wall surface 5 of the cylinder head 1.

[0019] On the other hand, the exhaust ports of the pairs of cylinders positioned at the two ends, that is, the exhaust ports 7 of the No. 1 cylinder #1 and the exhaust ports 10 of the No. 4 cylinder #4, are also arranged symmetrically with respect to the symmetrical plane K-K. In this case, the exhaust ports 7 of the No. 1 cylinder #1 extend from the No. 1 cylinder #1 toward the merged exhaust port 11, then extend along the merged exhaust port 11 separated from the merged exhaust port 11 by a thin wall 12 at the side of the merged exhaust port 11 until the side wall surface 5 of the cylinder head 1, while the exhaust ports 10 of the No. 4 cylinder #4 extend from the No. 4 cylinder #4 toward the merged exhaust port 11, then extend along the merged exhaust port 11 separated from the merged exhaust port 11 by a thin wall 13 at the side of the merged exhaust port 11 until the side wall surface 5 of the cylinder head 1.

[0020] As shown from FIG. 1 to FIG. 4, the merged exhaust port 11 opens on the side wall surface 5 of the cylinder head 1 at 14, while the pairs of independent exhaust ports, that is, the exhaust ports 7 of the No. 1 cylinder #1 and the exhaust ports 10 of the No. 4 cylinder #4, open at the two sides of the opening part 14 of the merged exhaust port 11 at the side wall surface 5 of the cylinder head 1 as shown by 15 and 16. Note that as will be understood from FIG. 3 and FIG. 4, the opening area of the opening part 14 of the merged exhaust port 11 is larger than the opening part 15, 16 of the pairs of independent exhaust ports 7, 10.

[0021] FIG. 5 shows part of an internal combustion engine, while FIG. 6 is a side view of the internal combustion engine shown in FIG. 5. Note that in FIG. 5 and FIG. 6, 17 shows a cylinder block, while 18 shows a catalytic converter. As will be understood from FIG. 4, FIG. 5, and FIG. 6, according to the present invention, the opening part 14 of the merged exhaust port 11 is connected through a first exhaust pipe 19 to an exhaust inflow part 20 of the catalytic converter 18, while the opening parts 15, 16 of the pairs of independent exhaust ports 7, 10 are connected through a second exhaust pipe 21 merged midway to the exhaust inflow part 20 of the catalytic converter 18. In this case, the pipe length of the first exhaust pipe 19 from the corresponding opening part 14 to the exhaust inflow part 20 is formed shorter than the pipe length of the second exhaust pipe 21 from the corresponding opening parts 15, 16 to the exhaust inflow part 20.

[0022] Explaining this in slightly more detail, the first exhaust pipe 19 and the second exhaust pipe 21 are bent downward in the middle of their distance from the corresponding opening parts 14, 15, 16 to the exhaust inflow part 20. The second exhaust pipe 21 extends along the outside of the first exhaust pipe 19 after the branches of the second exhaust pipe 21 merge at the outside of the first exhaust pipe 19. Further, the catalytic converter 18 is provided with a pair of exhaust inflow openings 22, 23. The first exhaust pipe 19 and second exhaust pipe 21 are connected to corresponding exhaust inflow openings 22, 23.

[0023] However, in this embodiment according to the present invention, the firing sequence of the cylinders is made #1.fwdarw.*#3.fwdarw.#4.fwdarw.#2 or #1.fwdarw.#2.fwdarw.#4.fwdarw.#43. In both cases, the pairs of cylinders at every other place in the firing sequence become the pair of the No. 2 cylinder #2 and No. 3 cylinder #3 positioned at the center and the pair of the No. 1 cylinder #1 and No. 4 cylinder #4 positioned at the two ends. In this case, if all of the exhaust ports were merged inside the cylinder head 1 or if all of the exhaust ports were opened inside an exhaust manifold with a manifold chamber extending along the side wall surface 5 of the cylinder head 1, the positive pressures generated inside exhaust ports at the time of an exhaust stroke of a certain cylinder would act at the time of the exhaust stroke in the exhaust ports of the cylinder next fired and as a result the problem would arise of the exhaust action of the burned gas from the combustion chamber being impaired.

[0024] As opposed to this, as shown in the embodiment of the present invention, if merging the exhaust ports of only the cylinders at every other place in the firing sequence, that is, merging the exhaust ports 8 of the No. 2 cylinder #2 and the exhaust ports 9 of the No. 3 cylinder #3, merging the exhaust ports 7 of the No. 1 cylinder #1 and the exhaust ports 10 of the No. 4 cylinder #4, and keeping the merged exhaust passages, that is, the exhaust passage in the first exhaust pipe 19 and the exhaust passage in the second exhaust pipe 21, separate until the exhaust inflow part 20 of the catalytic converter 18, the positive pressure generated inside the exhaust ports of the other cylinders will not act on the exhaust ports where an exhaust action is being performed at the time of an exhaust stroke, therefore burned gas will no longer be exhausted well from the combustion chamber. That is, exhaust interference can be prevented, so a high charging efficiency can be secured.

[0025] Now, here, if comparing the flow of exhaust gas in the merged exhaust port 11 and the flows of exhaust gas in the independent exhaust ports 7, 10, exhaust gas flows to the exit part of the merged exhaust port 11 two times in each cycle, while exhaust gas only flows to the exit parts of the independent exhaust ports 7, 10 once in each cycle. Therefore, the wall temperature of the exit part of the merged exhaust port 11 becomes considerably higher than the wall temperatures of the exit parts of the independent exhaust ports 7, 10. Further, the lengths of the passages of the exhaust ports 7, 10 are long, so the exhaust gas exhausted inside the exhaust ports 7, 10 is considerably cooled inside the cylinder head 1. As opposed to this, the length of the passage of the merged exhaust port 11 is short, so the exhaust gas exhausted inside the merged exhaust port 11 is not cooled much at all inside the cylinder head 1. Therefore, the temperature of the exhaust gas flowing out from the opening part 14 of the merged exhaust port 11 becomes considerably higher than the temperature of the exhaust gas flowing out from the opening parts 15, 16 of the independent exhaust ports 7, 10.

[0026] On the other hand, as explained above, the length of the first exhaust pipe 19 is shorter than the length of the second exhaust pipe 21, therefore when exhaust gas flows inside the exhaust pipes 19, 21, the amount of drop of the exhaust gas temperature in the first exhaust pipe 19 is smaller than the amount of drop of the exhaust gas temperature in the second exhaust pipe 21. In this way, high temperature exhaust gas is exhausted from the merged exhaust port 11 into the first exhaust pipe 19. At this time, the amount of drop of the exhaust gas temperature in the first exhaust pipe 19 is small, so the temperature of the exhaust gas flowing from the first exhaust pipe 19 into the catalytic converter 18 becomes considerably high. Therefore, it is possible to quickly warm up the catalyst in the catalytic converter 18.

[0027] On the other hand, the amount of exhaust gas flowing out from the opening part 14 of the merged exhaust port 11 becomes two times the amount of exhaust gas from the opening part 15, 16 of each of the independent exhaust ports 7, 10, so the opening area of the opening part 15 of the merged exhaust port 11 is formed larger than the opening area of the opening part 15, 16 of each of the independent exhaust ports 7, 10. Therefore, the flow area of the first exhaust pipe 19 also is formed larger than the flow area of each of the two branch parts 21a of the second exhaust pipe 21. As will be understood from FIG. 5, in this embodiment according to the present invention, to hold the temperature of the first exhaust pipe 19 at as high a temperature as possible and prevent the temperature of the exhaust gas flowing in the first exhaust pipe 19 from dropping as much as possible, the first exhaust pipe 19 is surrounded at its outside by the second exhaust pipe 21.

[0028] FIG. 7 shows another embodiment. In this embodiment, the first exhaust pipe 19 and second exhaust pipe 21 are connected to the exhaust inflow part 25 of the exhaust turbocharger 24. In this case, the first exhaust pipe 19 and the second exhaust pipe 21 are bent upward from the corresponding opening parts 14, 15, 16 toward the exhaust inflow part 25, while the second exhaust pipe 21 extends along the outside of the first exhaust pipe 19 after the branches of the second exhaust pipe 21 merge at the outside, of the first exhaust pipe 19.

[0029] In this embodiment as well, the length of the first exhaust pipe 36 from the corresponding opening part 14 to the exhaust inflow part 25 is formed shorter than the length of the second exhaust pipe 21 from the corresponding opening parts 15, 16 to the exhaust inflow part 25. Further, the exhaust turbocharger 24 is comprised of a twin entry type turbocharger provided with a pair of exhaust inflow openings 26, 27. The first exhaust pipe 19 and second exhaust pipe 21 are connected to the respective corresponding exhaust inflow openings 26, 27.

[0030] In this embodiment as well, high temperature, that is, high pressure, exhaust gas is fed from the first exhaust pipe 19 into the exhaust turbocharger 24, so the speed of the exhaust turbocharger 24 can be raised and therefore the efficiency of the exhaust turbocharger 24 can be enhanced. Note that in FIG. 5 and FIG. 6, instead of the catalytic converter 18, it is possible to attach an exhaust turbocharger 24. In this case, a catalytic converter 18 can also be connected to the exhaust outflow part of the exhaust turbocharger 24. Further, similarly, in FIG. 7, a catalytic converter 18 can be attached instead of the exhaust turbocharger 24.

LIST OF REFERENCE NUMERALS

[0031] 1 cylinder head [0032] 7,8,9,10 exhaust port [0033] 11 merged exhaust port [0034] 14,15,16 opening part [0035] 18 catalytic converter [0036] 19 first exhaust pipe [0037] 20,25 exhaust inflow part [0038] 21 second exhaust pipe [0039] 22,23,26,27 exhaust inflow openings [0040] 24 exhaust turbocharger

Claims

1. An in-line four-cylinder internal combustion engine wherein central exhaust ports of a pair of cylinders positioned at the center open on a side wall surface of the cylinder head, exhaust ports of a pair of cylinders positioned at the two ends open on the side wall surface of the cylinder head at the two sides of the opening part of the central exhaust ports as independent exhaust ports, and the opening part of said central exhaust ports is connected through a first exhaust pipe to an exhaust inflow part of a catalytic converter, the opening parts of said pair of independent exhaust ports being connected through a second exhaust pipe merged midway to the same exhaust inflow part, and a length of the first exhaust pipe from the corresponding opening part to said exhaust inflow part being made shorter than the length of the second exhaust pipe from the corresponding opening parts to said exhaust inflow part, characterized in that the central exhaust ports (8, 9) of a pair of the cylinders (#2, #3) positioned at the center merge inside the cylinder head (1) into a single merged exhaust port (11) which has the single opening part (14) connected to the first exhaust pipe (19), and the exhaust ports (7, 10) of a pair of the cylinders (#1, #4) at the two ends extend along the merged exhaust port (11) separated from the merged exhaust port (11) by corresponding thin walls (12, 13) at the sides of the merged exhaust port (11) until the side wall surface (5) of the cylinder head (1).

2. An internal combustion engine as set forth in claim 1, wherein the catalytic converter (18) is provided with a pair of exhaust inflow openings (22, 23), and said first exhaust pipe (19) and second exhaust pipe (21) are connected to the corresponding exhaust inflow openings (22, 23).

3. An internal combustion engine as set forth in claim 1, wherein an exhaust turbocharger (24) is provided in place of a catalytic converter and is provided with a pair of exhaust inflow openings (26, 27), and said first exhaust pipe (19) and second exhaust pipe (21) are connected to the corresponding exhaust inflow openings (26, 27).

4. An internal combustion engine as set forth in claim 1, wherein said first exhaust pipe (19) and second exhaust pipe (21) are bent in the middle of the distance from the corresponding opening parts (14, 15, 16) toward said exhaust inflow part toward the same direction, and said second exhaust pipe (21) extends along the outside of the first exhaust pipe (19) after branches of said second exhaust pipe (21) merge at the outside of the first exhaust pipe (19).

5. An internal combustion engine as set forth in claim 1, wherein the opening area of the opening part (14) of said merged exhaust port (11) is larger than the opening area of the opening part (15, 16) of each independent exhaust port (7, 10).