Exhaust gas recirculation device and engine

Abstract

To provide an exhaust gas recirculation device capable of effectively mixing outside air and exhaust recirculation gas, and an engine.SOLUTION: An exhaust gas recirculation device 3 comprises: a mixing unit 31 that is connected to a front stage of an intake manifold 22 of an engine 2, and sends a mixture of outside air and exhaust recirculation gas from a mixture outlet 311 to the intake manifold 22 side; an exhaust recirculation pipe 27 that guides the exhaust recirculation gas to the mixing unit 31; and an intake pipe 21 that guides the outside air to the mixing unit 31. The intake pipe 21 has: a first intake pipe that is arranged inside the mixing unit 31, and has a discharge port 217 that discharges the outside air into the mixing unit 31; and a second intake pipe that is arranged outside the mixing unit 31, and connected to an air supply side of the first intake pipe. The first intake pipe is formed to protrude toward the inside of the mixing unit 31. The discharge port 217 is formed so that its opening faces in a direction different from a direction from the first intake pipe to the mixture outlet 311 inside the mixing unit 31.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an exhaust gas recirculation device and an engine equipped with the exhaust gas recirculation device.

Background Art

[0002] As a means for reducing nitrogen oxides (NOx) contained in the exhaust gas of an engine, exhaust gas recirculation (EGR) is generally known. An exhaust gas recirculation device recirculates a part of the exhaust flowing through the exhaust system of the engine as exhaust reflux gas (i.e., EGR gas) to the intake system of the engine, and mixes the exhaust reflux gas with fresh intake air (i.e., intake air (also referred to as outside air)). Compared with the case where the exhaust gas recirculation device is not provided, the exhaust gas recirculation device can lower the combustion temperature in the cylinder and suppress the generation of NOx.

[0003] Patent Document 1 discloses an intake manifold of a multi-cylinder engine that can promote the concentration distribution of EGR gas in the intake air and the uniformity of the distribution of EGR gas to each cylinder. This intake manifold is provided with an EGR gas guide portion in the intake introduction cylinder portion. The EGR gas guide portion includes an upstream EGR gas discharge port and a downstream EGR gas discharge port. The upstream EGR gas discharge port is provided on the passage outlet side of the EGR gas introduction passage, and the downstream EGR gas discharge port is provided on the opposite side of the upstream EGR gas discharge port with the central portion of the intake introduction cylinder portion interposed therebetween. For the intake air passing through the central portion of the intake introduction cylinder portion, the EGR gas introduced into the intake introduction cylinder portion from the passage outlet of the EGR gas introduction passage is configured to be discharged from both the upstream EGR gas discharge port and the downstream EGR gas discharge port.

[0004] Thus, in order to recirculate the EGR gas to the intake system of the engine, it is necessary to equalize the concentration distribution of the EGR gas and the distribution to each cylinder. However, for example, in a small two-cylinder engine, the intake and exhaust pulsations are larger than those of an engine with three or more cylinders. Therefore, a generally used flow sensor is not suitable as a sensor used for controlling the amount of EGR gas (i.e., controlling the opening degree of the EGR valve), and thus, for example, a NOx sensor (see FIG. 1) may be used. In this case, it is necessary to branch off and recirculate the EGR gas from the downstream side (i.e., immediately before the atmosphere is released) of the NOx sensor in the exhaust system of the engine. At this branching position, since the introduction pressure of the EGR gas becomes close to (i.e., becomes lower than) the atmospheric pressure, effective mixing of the intake air (outside air) and the exhaust recirculation gas is required.

[0005] In addition, if the pulsation of the engine intake air or the like is small and the EGR valve can be controlled based on a flow sensor that measures the intake air amount, taking FIG. 1 as an example, the EGR gas can be recirculated by branching off from the upstream side of the DOC261 in the exhaust pipe 26. Then, since the introduction pressure of the EGR gas becomes close to (i.e., becomes higher than) the pressure on the upstream side of the DOC261, effective mixing of the intake air (outside air) and the exhaust recirculation gas becomes possible as compared with the case where the EGR gas is recirculated by branching off from the downstream side of the NOx sensor.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] The present invention has been made in view of the above circumstances, and an object thereof is to provide an exhaust gas recirculation device and an engine capable of effectively mixing outside air and exhaust recirculation gas.

Means for Solving the Problems

[0008] A first aspect of the present invention is an exhaust gas recirculation device that recirculates a part of the exhaust flowing through the exhaust system of an engine as exhaust recirculation gas to the intake system of the engine. The device is connected to the front stage of the intake manifold of the engine and includes a mixing unit that sends a mixture of outside air and the exhaust recirculation gas from a mixture outlet to the intake manifold side, an exhaust recirculation pipe that is connected between the exhaust manifold of the engine and the mixing unit and guides the exhaust recirculation gas to the mixing unit, and an intake pipe that is connected to the mixing unit and guides the outside air to the mixing unit. The intake pipe has a first intake pipe that is disposed inside the mixing unit and has an exhaust outlet for discharging the outside air into the mixing unit, and a second intake pipe that is disposed outside the mixing unit and is connected to the air supply side of the first intake pipe. The first intake pipe is formed to protrude toward the inside of the mixing unit, and the exhaust outlet is formed such that the opening faces in a direction different from the direction from the first intake pipe to the mixture outlet inside the mixing unit. This is the exhaust gas recirculation device according to the present invention.

[0009] A second aspect of the present invention is an engine provided with an exhaust gas recirculation device that recirculates a part of the exhaust flowing through the exhaust system as exhaust recirculation gas to the intake system. The exhaust gas recirculation device is connected to the front stage of the intake manifold of the engine and includes a mixing unit that sends a mixture of outside air and the exhaust recirculation gas from a mixture outlet to the intake manifold side, an exhaust recirculation pipe that is connected between the exhaust manifold of the engine and the mixing unit and guides the exhaust recirculation gas to the mixing unit, and an intake pipe that is connected to the mixing unit and guides the outside air to the mixing unit. The intake pipe has a first intake pipe that is disposed inside the mixing unit and has an exhaust outlet for discharging the outside air into the mixing unit, and a second intake pipe that is disposed outside the mixing unit and is connected to the air supply side of the first intake pipe. The first intake pipe is formed to protrude toward the inside of the mixing unit, and the exhaust outlet is formed such that the opening faces in a direction different from the direction from the first intake pipe to the mixture outlet inside the mixing unit. This is the engine according to the present invention.

Advantages of the Invention

[0010] According to the present invention, it is possible to provide an exhaust gas recirculation device and an engine that can effectively mix outside air and exhaust reflux gas.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. It should be noted that the embodiments described below are preferred specific examples of the present invention, and thus various technically preferable limitations are imposed. However, the scope of the present invention is not limited to these aspects unless there is a description specifically limiting the present invention in the following description. Also, in each drawing, the same reference numerals are assigned to the same components, and detailed descriptions thereof are appropriately omitted.

[0013] FIG. 1 is a schematic diagram illustrating the engine according to the present embodiment. FIG. 2 is a perspective view illustrating the engine according to the present embodiment.

[0014] The engine 2 according to the present embodiment is an internal combustion engine and is a naturally aspirated small engine. The engine 2 shown in FIG. 1 is an in-line two-cylinder engine. However, the number of cylinders is not particularly limited and may be three or more. The displacement of the engine 2 is about 500 cc. However, the displacement is not limited to about 500 cc. The timing deviation between the combustion process of the first cylinder 241, which is one of the two cylinders, and the combustion process of the second cylinder 242, which is the other one, is, for example, 180 degrees as the angle of the crankshaft. However, the timing deviation between the combustion process of the first cylinder 241 and the combustion process of the second cylinder 242 is not limited to this and may be 360 degrees as the angle of the crankshaft. Note that the engine 2 according to the present embodiment does not include a turbocharger for supercharging.

[0015] As shown in FIG. 1, the engine 2 includes an intake manifold 22, a cylinder block 24, and an exhaust manifold 25. The intake manifold 22 is connected to the intake pipe 21 and a cylinder head (not shown) and has a first branch pipe 221 and a second branch pipe 222. The cylinder block 24 has a first cylinder 241 and a second cylinder 242. The first cylinder 241 is connected to the first branch pipe 221 via an intake port (not shown) of the cylinder head. The second cylinder 242 is connected to the second branch pipe 222 via an intake port of the cylinder head.

[0016] The exhaust manifold 25 is connected to the cylinder head and the exhaust pipe 26. Specifically, the exhaust manifold 25 is connected to the first cylinder 241 and the second cylinder 242 via exhaust ports of the cylinder head. Note that the exhaust pipe 26 may be included in an exhaust gas recirculation device 3 described later.

[0017] In addition, the engine 2 includes a rail 23, a first injector 231, and a second injector 232. The rail 23 is formed in a cylindrical shape and distributes the high-pressure fuel supplied from a fuel pump (not shown) to a plurality of paths according to the number of cylinders of the engine 2. That is, the rail 23 supplies the high-pressure fuel supplied from the fuel pump to the first injector 231 and the second injector 232.

[0018] The first injector 231 is attached to the rail 23 and is provided so as to protrude toward the combustion chamber formed in the upper part of the first cylinder 241. The first injector 231 opens and closes a needle valve by, for example, a solenoid based on a signal transmitted from the control device 4, and injects the fuel supplied from the rail 23 into the combustion chamber formed in the upper part of the first cylinder 241 through an injection hole (not shown). Examples of the control device 4 include an electronic control unit (ECU).

[0019] The second injector 232 is attached to the rail 23 and is provided so as to protrude toward the combustion chamber formed in the upper part of the second cylinder 242. The second injector 232 opens and closes a needle valve by, for example, a solenoid based on a signal transmitted from the control device 4, and injects the fuel supplied from the rail 23 into the combustion chamber formed in the upper part of the second cylinder 242 through the injection hole.

[0020] The fuel pressure inside the rail 23 is measured by a pressure sensor 55 attached to the rail 23. The pressure sensor 55 measures the fuel pressure inside the rail 23 and outputs a signal regarding the fuel pressure to the control device 4.

[0021] As shown by the arrow A1 in FIG. 1, the fresh intake air (i.e., the inhaled air, also referred to as the outside air) passes through the intake pipe 21, passes through the air cleaner 211 provided in the intake pipe 21, and is guided toward the intake manifold 22 side. The intake pipe 21 is a component included in the engine 2 and is also a component included in the exhaust gas recirculation device 3 described later. The intake air guided to the intake manifold 22 is distributed to the first branch pipe 221 and the second branch pipe 222, and is guided to the first cylinder 241 through the first branch pipe 221 and to the second cylinder 242 through the second branch pipe 222.

[0022] The exhaust gas discharged from the first cylinder 241 and the second cylinder 242 passes through the exhaust manifold 25 and is guided to the exhaust pipe 26. The exhaust gas guided to the exhaust pipe 26 passes through the diesel oxidation catalyst (DOC) 261, which is a purification unit provided in the exhaust pipe 26. At this time, the diesel oxidation catalyst 261 oxidizes the SOF (soluble organic fraction), CO (carbon monoxide), and HC (hydrocarbon) in the PM (particulate matter) contained in the exhaust gas. As shown by the arrow A2 in FIG. 1, the exhaust gas that has passed through the diesel oxidation catalyst 261 is discharged to the outside of the engine 2 through the exhaust discharge pipe 29 from the branch portion 32. Note that the diesel oxidation catalyst 261 may be included in the exhaust gas recirculation device 3 described later.

[0023] Furthermore, the engine 2 includes an exhaust gas recirculation device 3. The exhaust gas recirculation device 3 recirculates a part of the exhaust gas flowing through the exhaust system of the engine 2 as exhaust reflux gas to the intake system of the engine 2 to reduce the nitrogen oxides (NOx) contained in the exhaust gas.

[0024] The exhaust gas recirculation device 3 according to this embodiment includes a mixing unit 31, an exhaust reflux pipe 27, and an intake pipe 21. The mixing unit 31 is connected to the front stage of the intake manifold 22 of the engine 2, and sends the mixture of outside air and exhaust reflux gas from the mixture outlet 311 to the intake manifold 22 side. The exhaust reflux pipe 27 is connected between a branch portion 32 provided at the rear stage of the diesel oxidation catalyst 261 and the mixing unit 31, and guides the exhaust reflux gas, which is a part of the exhaust that has passed through the diesel oxidation catalyst 261, to the mixing unit 31. A flow rate adjusting means 28 is provided in the exhaust reflux pipe 27. The flow rate adjusting means 28 is called, for example, an EGR valve. The flow rate adjusting means 28 adjusts the flow rate of the exhaust reflux gas flowing through the exhaust reflux pipe 27 based on a signal transmitted from the control device 4.

[0025] The intake pipe 21 is connected to the mixing unit 31 and guides the outside air to the mixing unit 31. That is, the intake pipe 21 is a pipe that sends the outside air that has passed through the air cleaner 211 to the inside of the mixing unit 31. In the mixing unit 31, the outside air sent from the intake pipe 21 to the inside of the mixing unit 31 and the exhaust reflux gas sent from the exhaust reflux pipe 27 to the inside of the mixing unit 31 are mixed. The mixture of the outside air and the exhaust reflux gas is sent from the mixture outlet 311 provided in the mixing unit 31 to the intake manifold 22.

[0026] Further, the engine 2 includes a control device 4, a rotation sensor 51, a NOx sensor 53, a temperature sensor 54, a water temperature sensor 56, and an accelerator opening sensor (not shown). In addition, the engine 2 includes various sensors such as a cam angle sensor and a pressure sensor (not shown). The control device 4 performs calculations based on signals from various sensors, controls the fuel injection by the first injector 231 and the second injector 232, and controls the flow rate of the exhaust reflux gas by the flow rate adjusting means 28.

[0027] As shown in FIG. 2, with the direction along the crankshaft of the engine 2 being the front-rear direction, the direction orthogonal to the crankshaft of the engine 2 being the left-right direction, and the direction orthogonal to the front-rear direction and the left-right direction being the up-down direction, the intake manifold 22 is arranged on one side (for example, the right side) in the left-right direction of the engine 2, and the exhaust manifold 25 is arranged on the other side (for example, the left side) in the left-right direction of the engine 2. The diesel oxidation catalyst 261 is arranged on the flywheel 201 side (the rear of the engine 2) of the engine 2 and above the flywheel 201.

[0028] Accordingly, the exhaust gas passes from the exhaust manifold 25 arranged on the other side in the left-right direction of the engine 2 through the diesel oxidation catalyst 261 at the rear (above the flywheel 201) of the engine 2 and is guided to one side in the left-right direction of the engine 2. A part of the exhaust gas reflux gas, which is a part of the exhaust gas guided to one side in the left-right direction of the engine 2, is sent to the intake manifold 22 side arranged on one side in the left-right direction of the engine 2, and the rest is discharged to the outside from one side in the left-right direction of the engine 2 through the exhaust discharge pipe 29. With such an arrangement of the exhaust manifold 25, the intake manifold 22, and the diesel oxidation catalyst 261, the configuration of the exhaust gas recirculation device 3 can be effectively laid out, and the engine 2 equipped with the exhaust gas recirculation device 3 can be downsized.

[0029] FIG. 3 is a perspective view illustrating the mixing portion and its peripheral configuration. FIG. 4 is a partially broken perspective view illustrating the mixing portion. The mixing portion 31 is provided in a box shape separate from the intake manifold 22 (see FIG. 1). The intake pipe 21 connected to the mixing portion 31 has a first intake pipe 215 arranged inside the mixing portion 31 and a second intake pipe 216 arranged outside the mixing portion 31. The first intake pipe 215 and the second intake pipe 216 may be provided as an integral pipe, or may be provided to connect separate pipes to each other.

[0030] The second intake pipe 216 is connected between the air cleaner 211 (see FIG. 1) and the mixing section 31, and communicates with the first intake pipe 215 disposed inside the mixing section 31. The first intake pipe 215 is provided so as to communicate with the second intake pipe 216 and protrude inside the mixing section 31.

[0031] The first intake pipe 215 is provided with a discharge port 217 for discharging the outside air that has passed through the second intake pipe 216 to the inside of the mixing section 31. The discharge port 217 is formed such that the opening faces in a direction different from the direction from the first intake pipe 215 toward the air-fuel mixture outlet 311 inside the mixing section 31. In the example shown in FIG. 4, the air-fuel mixture outlet 311 is provided below the mixing section 31, and the discharge port 217 provided in the first intake pipe 215 is provided such that the opening faces in a direction other than downward (for example, upward).

[0032] The mixing section 31 is provided with an inlet 312 for the exhaust reflux gas. The inlet 312 is an opening provided in the housing of the mixing section 31, and the exhaust reflux pipe 27 is connected to this inlet 312. In the example shown in FIG. 4, the inlet 312 is provided on one side surface of the substantially rectangular parallelepiped housing constituting the mixing section 31, and the first intake pipe 215 is provided on the other side surface.

[0033] In this way, the mixing section 31 is provided in a box shape separate from the intake manifold 22 at the front stage of the intake manifold 22, the first intake pipe 215 is disposed so as to protrude inside the mixing section 31, and further, the discharge port 217 of the first intake pipe 215 opens in a direction different from the air-fuel mixture outlet 311. Thus, the outside air discharged from the discharge port 217 into the inside of the mixing section 31 is likely to disperse and diffuse inside the mixing section 31.

[0034] In the example shown in FIG. 4, the discharge port 217 and the upper inner wall of the housing of the mixing section 31 face each other. For this reason, the outside air discharged from the discharge port 217 collides with the upper inner wall of the housing of the mixing section 31 and diffuses into the inside of the mixing section 31 so as to turn downward from the side. Then, the exhaust reflux gas is introduced from the inlet 312 into the inside of the mixing section 31 where the outside air has diffused, so that the outside air and the exhaust reflux gas are effectively (with high uniformity) mixed.

[0035] Here, in the engine 2 where the pulsation of the intake air or the like is large and the introduction pressure of the exhaust gas recirculation gas is low, it is not desired to affect the introduction pressure of the exhaust gas recirculation gas. On the other hand, even if the pulsation of the intake air or the like is large, a certain degree of introduction pressure can be expected for the intake air. Therefore, in the present embodiment, when introducing outside air into the mixing section 31, by protruding the first intake pipe 215 into the mixing section 31 or providing an exhaust port 217 in the first intake pipe 215, while fully utilizing the dispersion effect of the outside air introduced into the mixing section 31, it is ensured that the introduction pressure of the exhaust gas recirculation gas is not affected, and the outside air is sufficiently guided to the mixing section 31, enabling effective mixing of the outside air and the exhaust gas recirculation gas.

[0036] The mixing section 31 according to the present embodiment is separate from the intake manifold 22 and has a different function. That is, the collecting section of the intake manifold 22 (the main pipe section of the intake manifold 22, the collector section, etc.) has the function of evenly distributing the intake air to each cylinder while avoiding interference between cylinders of the intake air. On the other hand, the mixing section 31 is installed in the front stage of the intake manifold 22 and is not configured as a part of the aggregate of the intake manifold 22. By installing the mixing section 31 in the front stage of the intake manifold 22, it is possible to exert a function of suppressing the variation in the concentration of the exhaust gas recirculation gas between cylinders within a range where the control of the flow rate adjusting means 28 based on the NOx sensor 53 does not cause practical problems.

[0037] Also, from the viewpoint of suppressing the loss of the introduction pressure of the exhaust gas recirculation gas to the mixing section 31, it is preferable that the diameter of the introduction port 312 of the exhaust gas recirculation gas is equal to or larger than the inner diameter of the exhaust gas recirculation pipe 27. This is particularly effective in the engine 2 where the introduction pressure of the exhaust gas recirculation gas is low.

[0038] Also, the internal volume of the mixing section 31 is preferably equal to or larger than the total exhaust volume of the engine 2. For example, in a four-stroke one-cycle two-cylinder engine where the respective strokes (strokes) of each cylinder are shifted from each other by 180 degrees in terms of the crank rotation angle, the states of the first cylinder 241 and the second cylinder 242 in each stroke are as follows. (First Stroke) When the angle of the crankshaft is 0° (720°) or more and less than 180° Intake of the first cylinder 241 + Exhaust of the second cylinder 242 (Second Stroke) When the angle of the crankshaft is 180° or more and less than 360° Compression of the first cylinder 241 + Intake of the second cylinder 242 (Third Stroke) When the angle of the crankshaft is 360° or more and less than 540° Explosion of the first cylinder 241 + Compression of the second cylinder 242 (Fourth Stroke) When the angle of the crankshaft is 540° or more and less than 720° (0°) Exhaust of the first cylinder 241 + Explosion of the second cylinder 242

[0039] Also, in this cycle, the inflow state of the outside air and the exhaust recirculation gas into the mixing section 31 arranged in the front stage of the intake manifold 22 is as follows. (First Stroke) When the angle of the crankshaft is 0° (720°) or more and less than 180° Introduction of fresh intake air by the intake of the first cylinder 241 + Introduction of exhaust recirculation gas by the exhaust of the second cylinder 242 (Second Stroke) When the angle of the crankshaft is 180° or more and less than 360° Introduction of fresh intake air by the intake of the second cylinder 242 (Third Stroke) When the angle of the crankshaft is 360° or more and less than 540° Neither fresh intake air nor exhaust recirculation gas is introduced (Fourth Stroke) When the angle of the crankshaft is 540° or more and less than 720° (0°) Introduction of exhaust recirculation gas by the exhaust of the first cylinder 241

[0040] If the internal volume of the mixing section 31 is sufficiently large, the concentration of the exhaust recirculation gas in the intake air flowing from the mixing section 31 into the intake manifold 22 becomes uniform regardless of the operating state of each cylinder. In this case, the concentration converges to the average value over the entire engine cycle.

[0041] For example, when the total displacement of a two-cylinder engine is 0.5 L (0.25 L × 2), the concentration of the exhaust gas recirculation gas in the intake air flowing from the mixing section 31 into the intake manifold 22 (EGR concentration = amount of exhaust gas recirculation gas / (amount of exhaust gas recirculation gas + amount of fresh intake air)) is calculated as follows. In the following calculations, it is assumed that the amount of exhaust gas recirculation gas in one cylinder is 0.1 L and the amount of fresh intake air is 0.15 L. (First stroke) When the angle of the crankshaft is 0° (720°) or more and less than 180° EGR concentration = 0.1 / (0.1 + 0.15) = 40% (Second stroke) When the angle of the crankshaft is 180° or more and less than 360° EGR concentration = 0 / (0 + 0.15) = 0% (Third stroke) When the angle of the crankshaft is 360° or more and less than 540° None (Fourth stroke) When the angle of the crankshaft is 540° or more and less than 720° (0°) EGR concentration = (0.1 × 2) / (0.1 × 2 + 0.15 × 2) = 40%

[0042] According to the above calculation example, in order to have no practical problem in the introduction control of the exhaust gas recirculation gas by the flow rate adjusting means 28, the internal volume of the mixing section 31 should be a volume that can level out the variation for two rotations (one engine cycle) of the crankshaft of the engine 2 to a certain extent, that is, it should be equal to or greater than the displacement of the engine 2. Note that the opening shape, arrangement, and number of openings of the discharge port 217 of the first intake pipe 215 are not limited to the above. For example, it may be circular or there may be a plurality of them as long as the opening area is equal to or greater than that shown in the drawing.

[0043] FIG. 5 is a perspective view illustrating the branch portion. FIG. 6 is a plan view illustrating the branch portion. FIG. 6 shows a plan view of the branch portion as viewed from above. The branch portion 32 has a connecting portion 320 provided between the diesel oxidation catalyst 261, the first branch portion 321, and the second branch portion 322. That is, the downstream of the diesel oxidation catalyst 261 is branched into the first branch portion 321 and the second branch portion 322 via the connecting portion 320. The first branch portion 321 side is connected to the exhaust gas reflux pipe 27, and the second branch portion 322 side is connected to the exhaust discharge pipe 29 side.

[0044] In the layout of the engine 2 as described above, the first branch portion 321 downstream of the connecting portion 320 is formed to guide the exhaust gas above the diesel oxidation catalyst 261, and the second branch portion 322 is formed to guide the exhaust gas below the diesel oxidation catalyst 261.

[0045] Specifically, the connecting portion 320 is provided to guide the exhaust gas in the extending direction of the diesel oxidation catalyst 261 (for example, the right direction). The first branch portion 321 has a curved body portion 323 that bends the flow direction of the exhaust gas from the end of the connecting portion 320 in the extending direction toward the exhaust gas reflux pipe 27. As shown in FIG. 5, the first branch portion 321 is bent approximately 90° forward by the curved body portion 323 and is bent above the diesel oxidation catalyst 261 and connected to the exhaust gas reflux pipe 27. The second branch portion 322 is connected to a port 324 (see FIG. 6) provided on the side surface of the connecting portion 320 located closer to the diesel oxidation catalyst 261 than the curved body portion 323.

[0046] Due to the first branch portion 321 of the branch portion 32 like this, the exhaust gas reflux gas is sent above the diesel oxidation catalyst 261, mixed with the outside air above the intake manifold 22, and the air-fuel mixture can be sent to the intake manifold 22 side. In this way, while the exhaust gas reflux gas is sent to the intake manifold 22 from above and mixed with the outside air, even when, for example, the pulsation of intake and exhaust is large and it is difficult to uniformly mix the outside air and the exhaust gas reflux gas, a sufficient mixing path can be secured, and a uniform air-fuel mixture can be sent to the intake manifold 22.

[0047] Further, by providing the curved body portion 323 at the end of the connecting portion 320 in the extending direction, the exhaust gas that has passed through the diesel oxidation catalyst 261 advances straight through the connecting portion 320 and is smoothly bent forward and upward by the curved body portion 323 provided in the front in the advancing direction and sent to the exhaust gas reflux pipe 27. The exhaust gas sent from the diesel oxidation catalyst 261 to the connecting portion 320 easily advances straight due to the inertial force and is led from the first branch portion 321 to the exhaust gas reflux pipe 27 with a small pressure loss. If the first branch portion 321 is connected to the side surface of the connecting portion 320, the exhaust gas is difficult to branch, and a large pressure loss will occur while the exhaust gas is sent to the exhaust gas reflux pipe 27.

[0048] In the configuration of the branch portion 32 of the present embodiment, the pressure loss of the exhaust gas due to the first branch portion 321 is smaller than the pressure loss of the exhaust gas due to the second branch portion 322. Thereby, for example, even in the engine 2 with a low introduction pressure of the exhaust gas reflux gas, the exhaust gas reflux gas can be effectively sent to the intake manifold 22 side, and the reduction effect of nitrogen oxides (NOx) can be exhibited.

[0049] Next, the attachment of the diesel oxidation catalyst 261 will be described. FIG. 7 is a perspective view illustrating an attachment portion on the rear stage side of the diesel oxidation catalyst. FIG. 8 is a front view illustrating an attachment portion on the rear stage side of the diesel oxidation catalyst. FIG. 8 shows a front view as seen from the exhaust gas outlet side of the diesel oxidation catalyst 261. FIG. 9 is a perspective view illustrating an attachment portion on the front stage side of the diesel oxidation catalyst. FIG. 10 is a front view illustrating an attachment portion on the front stage side of the diesel oxidation catalyst. FIG. 10 shows a front view as seen from the inlet side of the second flange portion 62 of the diesel oxidation catalyst 261. FIG. 11 is a perspective view illustrating a flange portion in the attachment of the diesel oxidation catalyst.

[0050] The diesel oxidation catalyst 261 has a cylindrical (e.g., substantially cylindrical) body portion 2610 and first and second end portions 2611 and 2612 that are parallel to each other and are at both ends of the body portion 2610. A first flange portion 61 for fastening the diesel oxidation catalyst 261 and the branch portion 32 is provided at the first end portion 2611. The first flange portion 61 is fastened to a mating flange portion 71 provided on the side of the connecting portion 320.

[0051] A second flange portion 62 is connected to the second end portion 2612 of the diesel oxidation catalyst 261 via an extension pipe 63. Note that the extension pipe 63 may be common to all or part of the exhaust pipe 26. One end of the extension pipe 63 is connected to the second end portion 2612, and the second flange portion 62 is connected to the other end of the extension pipe 63. The first flange portion 61 and the second flange portion 62 are preferably of the same shape as each other. Thereby, the first flange portion 61 and the second flange portion 62 can be made into common parts, and the number of parts can be reduced.

[0052] Also, the first flange portion 61 is attached to the first end portion 2611 of the body portion 2610. Thereby, the attachment plane of the first flange portion 61 is provided substantially parallel to the first end portion 2611 of the body portion 2610. On the other hand, the second flange portion 62 is attached to the end of the extension pipe 63 bent from the extending direction of the body portion 2610 of the diesel oxidation catalyst 261. Thereby, the attachment plane of the second flange portion 62 is provided non-parallel to the second end portion 2612 of the body portion 2610.

[0053] The extension pipe 63 is formed into a bent tubular shape by, for example, sheet metal working of a metal material. The extension pipe 63 is provided so as to bend about 90° from the extending direction of the body portion 2610 of the diesel oxidation catalyst 261. By connecting the second flange portion 62 to the end of this extension pipe 63, the attachment surface of the second flange portion 62 becomes substantially orthogonal to the second end portion 2612 of the body portion 2610.

[0054] At the end of the exhaust manifold 25 that extends rearward and is provided on the other side (e.g., the left side) in the left-right direction of the engine 2, a flange portion 72 that mates with the second flange portion 62 is provided. As a result, it is not necessary to bend the extending end side of the exhaust manifold 25 rearward of the engine 2, and the shape is simplified.

[0055] Also, as shown in FIGS. 8 and 10, each of the first flange portion 61 and the second flange portion 62 has three fastening portions 65a, 65b, and 65c that are arranged at the positions of the vertices of a triangle. The fastening portions 65a, 65b, and 65c are, for example, fastening holes. And as shown in FIG. 8, in the first flange portion 61, when looking at the first end portion 2611 (the exhaust gas outlet side) of the diesel oxidation catalyst 261 from the front, each of the first branch portion 321 and the second branch portion 322 is arranged so as not to overlap any of the three fastening portions 65a, 65b, and 65c.

[0056] Also, as shown in FIG. 10, in the second flange portion 62, when looking at the second end portion 2612 (the exhaust gas inlet side) of the diesel oxidation catalyst 261 from the front, the extension pipe 63 is arranged so as not to overlap any of the three fastening portions 65a, 65b, and 65c. Thereby, when fastening is performed by the first flange portion 61 and the second flange portion 62, it becomes possible to access the fastening portions 65a, 65b, and 65c from the front of each of the first flange portion 61 and the second flange portion 62.

[0057] The arrangement of each of the three fastening portions 65a, 65b, and 65c is preferably an isosceles triangle, and more preferably an equilateral triangle. Note that the shape of the triangle in the arrangement of the three fastening portions 65a, 65b, and 65c is not limited to these.

[0058] By arranging the three fastening parts 65a, 65b, and 65c at the positions of the vertices of a triangle, it is possible to achieve space savings while ensuring reliable fastening to the front and rear members. That is, in the case of two-point fixing or less, the reliability of fastening is likely to be insufficient. On the other hand, in the case of four-point fixing or more, the interval between adjacent fastening parts becomes narrow, interference with peripheral members is likely to occur during fastening, and sufficient freedom in layout cannot be ensured. Therefore, in the case of three-point fixing, it is possible to avoid interference with peripheral members during fastening while achieving reliable fastening and space savings.

[0059] In the present embodiment, as shown in FIG. 8, when the first flange portion 61 is viewed from the front, two fastening parts 65a and 65b are arranged vertically on the left side, and the remaining one fastening part 65c is arranged on the right side so as to be between the two fastening parts 65a and 65b on the left side in the vertical direction. As a result, when the first flange portion 61 is viewed from the front, the exhaust reflux pipe 27 extends obliquely upward so as to pass between the fastening part 65a and the fastening part 65c, and the exhaust discharge pipe 29 extends obliquely downward so as to pass between the fastening part 65b and the fastening part 65c.

[0060] Also, as shown in FIG. 10, when the second flange portion 62 is viewed from the front, two fastening parts 65a and 65b are arranged vertically on the left side, and the remaining one fastening part 65c is arranged on the right side so as to be between the two fastening parts 65a and 65b on the left side in the vertical direction. As a result, when the second flange portion 62 is viewed from the front, the extension pipe 63 and the intake manifold 22 extend so as to pass between the fastening part 65a and the fastening part 65b.

[0061] By making the first flange portion 61 and the second flange portion 62 have the same shape and arranging the three fastening parts 65a, 65b, and 65c in this way, it is possible to reduce the number of parts by commonizing the parts, improve the attachment workability by the first flange portion 61 and the second flange portion 62, and optimize the layout of the peripheral piping.

[0062] As described above, according to the present embodiment, it is possible to provide an exhaust gas recirculation device 3 and an engine 2 that can effectively mix outside air and exhaust reflux gas.

[0063] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments, and various changes can be made without departing from the scope of the claims. The configurations of the above embodiments can be partially omitted or arbitrarily combined differently from the above.

Explanation of Reference Numerals

[0064] 2: Engine, 3: Exhaust gas recirculation device, 4: Control device, 21: Intake pipe, 22: Intake manifold, 23: Rail, 24: Cylinder block, 25: Exhaust manifold, 26: Exhaust pipe, 27: Exhaust reflux pipe, 28: Flow rate adjustment means, 29: Exhaust discharge pipe, 31: Mixing section, 32: Branch section, 51: Rotation sensor, 53: NOx sensor, 54: Temperature sensor, 55: Pressure sensor, 56: Water temperature sensor, 61: First flange section, 62: Second flange section, 63: Extension pipe, 65a: Fastening section, 65b: Fastening section, 65c: Fastening section, 71: Flange section, 72: Flange section, 201: Flywheel, 211: Air cleaner, 215: First intake pipe, 216: Second intake pipe, 217: Discharge port, 221: First branch pipe, 222: Second branch pipe, 231: First injector, 232: Second injector, 241: First cylinder, 242: Second cylinder, 261: Diesel oxidation catalyst, 311: Mixture outlet, 312: Inlet, 320: Connection section, 321: First branch section, 322: Second branch section, 323: Curved body section, 324: Port, 2610: Body section, 2611: First end, 2612: Second end

Claims

1. An exhaust gas recirculation device that recirculates a part of the exhaust flowing through the exhaust system of an engine as exhaust recirculation gas to the intake system of the engine, a mixing section connected to the front stage of the intake manifold of the engine, which sends a mixture of outside air and the exhaust recirculation gas from a mixture outlet to the intake manifold side; an exhaust recirculation pipe connected between the exhaust manifold of the engine and the mixing section, which guides the exhaust recirculation gas to the mixing section; an intake pipe connected to the mixing section, which guides the outside air to the mixing section; characterized by comprising: the intake pipe a first intake pipe disposed inside the mixing section and having an outlet for discharging the outside air into the mixing section; a second intake pipe disposed outside the mixing section and connected to the air supply side of the first intake pipe; and having: the first intake pipe is formed to project toward the inside of the mixing section; the exhaust gas recirculation device, wherein the outlet is formed such that the opening faces a direction different from the direction from the first intake pipe to the mixture outlet inside the mixing section.

2. The exhaust gas recirculation device according to claim 1, wherein the mixture outlet is provided on the side opposite to the opening of the outlet in the mixing section.

3. The exhaust gas recirculation device according to claim 1, wherein the diameter of the inlet of the exhaust recirculation gas in the mixing section is equal to or larger than the inner diameter of the exhaust recirculation pipe.

4. The exhaust gas recirculation device according to claim 1, wherein the mixing section is provided in a box shape separate from the intake manifold.

5. The exhaust gas recirculation device according to claim 1, wherein the internal volume of the mixing section is equal to or larger than the total exhaust volume of the engine.

6. An engine equipped with an exhaust gas recirculation device that recirculates a part of the exhaust flowing through the exhaust system as exhaust recirculation gas to the intake system, wherein the exhaust gas recirculation device a mixing section connected to the front stage of the intake manifold of the engine, which sends a mixture of outside air and the exhaust recirculation gas from a mixture outlet to the intake manifold side; an exhaust recirculation pipe connected between the exhaust manifold of the engine and the mixing section, which guides the exhaust recirculation gas to the mixing section; an intake pipe connected to the mixing section, which guides the outside air to the mixing section; characterized by comprising: the intake pipe a first intake pipe disposed inside the mixing section and having an outlet for discharging the outside air into the mixing section; a second intake pipe disposed outside the mixing section and connected to the air supply side of the first intake pipe; and having: The first intake pipe is formed to protrude toward the inside of the mixing section. An engine, wherein the discharge port is formed such that an opening faces in a direction different from a direction from the first intake pipe toward the air-fuel mixture outlet inside the mixing section. **Claim 7** The engine according to claim 6, wherein an internal volume of the mixing section is equal to or greater than a total exhaust volume of the engine. **Claim 8** The engine according to claim 6 or 7, which is a two-cylinder type of four-stroke one-cycle, and strokes of respective cylinders are shifted from each other by 180 degrees in terms of a crank rotation angle.

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