JP6369523B2 - Engine exhaust system - Google Patents

Description

  The present invention relates to an exhaust system for an engine having a cylinder in which a mixture of predetermined fuel and air burns.

  In general, an exhaust passage of a multi-cylinder engine includes an exhaust port of a cylinder head connected to an exhaust opening of each cylinder, an exhaust manifold connected to an upstream end of each exhaust port, and a common exhaust pipe connected to a downstream end of the exhaust manifold. The common exhaust pipe generally incorporates a catalyst device that purifies exhaust gas, but may also incorporate an exhaust heat recovery device that collects thermal energy held in the exhaust gas. A silencer for silencing is assembled at the downstream end of the common exhaust pipe.

  In the exhaust passage, suppression of heat dissipation of exhaust heat (decrease in exhaust temperature) may be required. For example, in order to activate the catalyst in the catalyst device early when the engine is started or to maintain the activation temperature of the catalyst, it is required to guide the exhaust to the catalyst device without releasing the exhaust heat as much as possible. . Alternatively, in the exhaust heat recovery apparatus, in order to increase the amount of heat to be recovered, it is required to guide the exhaust to the exhaust heat recovery apparatus without releasing the exhaust heat as much as possible. Patent Document 1 discloses an exhaust system in which a coating layer formed of a material having a lower thermal conductivity than the exhaust pipe is provided on the inner wall surface of the exhaust pipe connecting the engine and the catalyst device. The coating layer suppresses the heat release of the exhaust heat to the outside of the exhaust pipe, so that the exhaust heat is kept warm.

JP 2012-172580 A

  However, when the coating layer is provided on the inner wall surface of the exhaust pipe as in the exhaust device of Patent Document 1, the preparation of the material for forming the coating layer and the process of forming the coating layer are required. These increase the cost and man-hour of the exhaust device.

  An object of the present invention is to provide an engine exhaust device that can suppress the release of exhaust heat in the exhaust passage without greatly increasing the cost and the number of manufacturing steps.

An exhaust system for an engine according to one aspect of the present invention is an exhaust system for an engine including a cylinder in which a mixture of fuel and air burns, and includes an exhaust passage through which exhaust discharged from the cylinder passes. In at least a part of the exhaust passage, an exhaust passage inner wall surface defining the exhaust passage has a groove in which a plurality of fine grooves having a groove width of 100 μm to 700 μm extending in the flow direction of the exhaust gas are densely arranged. It is an inner wall surface.

  Exhaust gas passing through the exhaust passage has a flow rate of about 10 to 70 m / s when the engine speed is about 1000 to 6000 rpm in a general passenger car, for example. According to the knowledge of the present inventors, such an exhaust flow in the exhaust passage is a main flow that travels downstream of the exhaust passage and a secondary flow that accompanies the main flow around the axis of travel of the main flow. Including swirling vortex flow (longitudinal vortex). The vortex is characterized by a strong property of transporting heat. As the flow velocity of the exhaust flow increases, the diameter (scale) of the vortex tends to decrease.

  According to the exhaust device described above, in at least a part of the exhaust passage, the inner wall surface of the exhaust passage defining the exhaust passage is a grooved inner wall surface in which a plurality of fine grooves are densely arranged. When the fine groove is present, the eddy current having a high heat transfer property remains at the top of the fine groove. As a result, the vortex is separated from the inner wall surface of the exhaust passage, and heat radiation (exhaust loss) of the exhaust heat passing through the wall surface of the exhaust passage is reduced. Therefore, the exhaust gas can be circulated downstream of the exhaust passage while keeping the heat of the exhaust gas. Further, it is possible to obtain the heat insulation effect of the exhaust gas simply by forming the fine groove on the inner wall surface of the exhaust passage, and the cost and the number of manufacturing steps can be reduced as compared with the case where a coating layer or the like is separately provided on the inner wall surface.

  The engine exhaust device further includes a catalyst device that is incorporated in the exhaust passage and purifies the exhaust gas, and at least a part of the exhaust passage that connects the outlet of the cylinder to the catalyst device in the exhaust passage. It is desirable that the inner wall surface of the exhaust passage in the section is the grooved inner wall surface.

  According to this exhaust device, the heat radiation of the exhaust heat in the exhaust passage leading to the catalyst device can be suppressed. Therefore, it is possible to contribute to the early activation of the catalyst in the catalyst device when the engine is started and to maintaining the activation temperature of the catalyst.

  The engine exhaust apparatus further includes an exhaust heat recovery device that is incorporated in the exhaust passage and recovers thermal energy held by the exhaust, and includes an exhaust passage from the cylinder outlet to the exhaust heat recovery device. It is desirable that the inner wall surface of the exhaust passage in at least a part of the exhaust passage connecting the two is the grooved inner wall surface.

  According to this exhaust device, heat radiation of the exhaust heat in the exhaust passage leading to the exhaust heat recovery device can be suppressed. Therefore, it is possible to contribute to increasing the amount of heat recovered from the exhaust in the exhaust heat recovery apparatus.

  In the exhaust system for an engine described above, a catalyst device that is incorporated in the exhaust passage and purifies the exhaust, and thermal energy that is incorporated in the exhaust passage on the downstream side in the exhaust flow direction from the catalyst device and that the exhaust holds. An exhaust heat recovery device for recovering the exhaust gas, and an exhaust passage inner wall surface in at least a part of the first exhaust passage connecting the outlet of the cylinder to the catalyst device in the exhaust passage, and the catalyst It is desirable that an exhaust passage inner wall surface in at least a part of the second exhaust passage connecting the device to the exhaust heat recovery device is the grooved inner wall surface.

  According to this exhaust device, heat dissipation of the exhaust heat in the first exhaust passage from the outlet of the cylinder to the catalyst device, and heat dissipation of the exhaust heat in the second exhaust passage from the catalyst device to the exhaust heat recovery device. Can be suppressed. Therefore, it is possible to contribute to early activation of the catalyst in the catalyst device, maintenance of the activation temperature, and increase in the amount of heat recovered from the exhaust gas in the exhaust heat recovery device.

An exhaust system for an engine according to another aspect of the present invention is an exhaust system for an engine including a cylinder in which a mixture of fuel and air is combusted, and includes an exhaust passage through which exhaust discharged from the cylinder passes. Further, in at least a part of the exhaust passage, the exhaust passage inner wall surface defining the exhaust passage is a grooved inner wall surface in which a plurality of fine grooves extending in the flow direction of the exhaust gas are densely arranged. The fine groove has a groove width of 100 μm to 700 μm, is incorporated in the exhaust passage and purifies the exhaust, and the exhaust gas is disposed downstream of the catalyst device in the exhaust circulation direction. A waste heat recovery device that is incorporated in the passage and recovers the thermal energy held by the exhaust, and is connected to the catalyst device from the outlet of the cylinder in the exhaust passage. The exhaust passage inner wall surface in at least a part of the exhaust passage, and the exhaust passage inner wall surface in at least a part of the second exhaust passage connecting the catalyst device to the exhaust heat recovery device are the grooved inner wall surface. It is a, each of the plurality of fine grooves formed in the exhaust passage wall surface of the first exhaust passage has a first groove width, is formed in the exhaust passage wall surface of the second exhaust passage each of the plurality of fine grooves that have a said wider than the first groove width second groove width.

  The flow rate of the exhaust flow decreases as it goes downstream of the exhaust passage. In particular, before and after the exhaust gas passes through the catalyst device, the flow rate varies greatly. For this reason, since the exhaust flow passing through the first exhaust passage is relatively fast, the vortex flow is relatively small, whereas the exhaust flow passing through the second exhaust passage is relatively slow, The eddy current is relatively large. According to the exhaust device described above, the fine groove corresponding to the change in the flow velocity of the exhaust flow in the exhaust passage can be set on the inner wall surface of the exhaust passage. That is, the fine groove has a groove width corresponding to the diameter change of the vortex flow of the exhaust flow as it goes downstream of the exhaust passage, and the vortex flow is caused in each of the first and second exhaust passages. It can be appropriately separated from the inner wall surface of the exhaust passage. Therefore, exhaust loss can be effectively reduced.

  According to the exhaust system for an engine of the present invention, it is possible to suppress the heat radiation of the exhaust heat in the exhaust passage without greatly increasing the cost and the number of manufacturing steps.

FIG. 1 is a schematic view showing an engine exhaust device according to a first embodiment of the present invention. 2A is a perspective view of a state where the exhaust pipe is divided in half in the axial direction, FIG. 2B is a sectional view of the exhaust pipe, and FIG. 2C is a partially enlarged view of FIG. 2B. It is. FIG. 3 is a schematic diagram showing an aspect of the exhaust flow. 4A is a diagram showing the positional relationship between the vortex flow of the exhaust flow and the inner wall surface when the inner wall surface of the exhaust pipe is flat, and FIG. 4B is a diagram in which fine grooves are formed on the inner wall surface of the exhaust gas. It is a figure which shows the positional relationship of the said eddy current and the said inner wall surface in the case. FIG. 5 is a schematic cross-sectional view showing an engine exhaust device according to a second embodiment of the present invention. FIG. 6 is a schematic diagram for explaining the groove width of the fine groove formed on the inner wall surface of the exhaust pipe in the second embodiment. FIG. 7 is a block diagram illustrating an example of the exhaust heat recovery apparatus. FIG. 8 is a schematic cross-sectional view showing an engine exhaust device according to a modified embodiment of the present invention. FIG. 9 is a schematic diagram for explaining a modification of the fine groove.

[First Embodiment]
<Engine structure>
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram showing an engine exhaust device according to a first embodiment of the present invention, and shows a schematic configuration of an engine body 1 and an exhaust device 20 of the engine body 1. First, the engine body 1 will be described. The engine main body 1 shown here is a reciprocating piston type multi-cylinder gasoline engine mounted on the vehicle as a power source for driving the vehicle such as an automobile. In the present embodiment, the fuel supplied to the engine body 1 is mainly composed of gasoline.

  The engine body 1 includes a cylinder block 3, a cylinder head 4, and a piston 5. The cylinder block 3 has a plurality of cylinders 2 (only one of them is shown in the figure) arranged in a direction perpendicular to the paper surface of FIG. In the cylinder 2, the fuel / air mixture burns. The cylinder head 4 is attached to the upper surface of the cylinder block 3 and closes the upper opening of the cylinder 2. The piston 5 is accommodated in each cylinder 2 so as to be reciprocally slidable, and is connected to the crankshaft 7 via a connecting rod 8. In response to the reciprocating motion of the piston 5, the crankshaft 7 rotates about its central axis.

  A combustion chamber 6 is formed above the piston 5. An intake port 9 and an exhaust port 10 communicating with the combustion chamber 6 are formed in the cylinder head 4. On the bottom surface of the cylinder head 4, an intake side opening 4 </ b> A that is a downstream end of the intake port 9 and an exhaust side opening 4 </ b> B (cylinder outlet) that is an upstream end of the exhaust port 10 are formed. The cylinder head 4 is assembled with an intake valve 11 for opening / closing the intake side opening 4A and an exhaust valve 12 for opening / closing the exhaust side opening 4B. The engine of this embodiment is a double overhead camshaft (DOHC) engine. Two intake side openings 4A and two exhaust side openings 4B are provided for each cylinder 2, and two intake valves 11 and two exhaust valves 12 are also provided.

  The intake valve 11 and the exhaust valve 12 are so-called poppet valves, and each include an umbrella-shaped valve body that opens and closes the openings 4A and 4B, and a stem that extends vertically from the valve body. The valve body has a valve surface facing the combustion chamber 6. In the present embodiment, the combustion chamber 6 is defined by the inner wall surface of the cylinder 2, the crown surface of the piston 5, the bottom surface of the cylinder head 4, and the valve surfaces of the intake valve 11 and the exhaust valve 12.

  The cylinder head 4 is provided with an intake side valve mechanism 13 and an exhaust side valve mechanism 14 for driving the intake valve 11 and the exhaust valve 12, respectively. The valve mechanisms 13 and 14 drive the stems of the intake valve 11 and the exhaust valve 12 in conjunction with the rotation of the crankshaft 7. By driving these stems, the valve body of the intake valve 11 opens and closes the intake side opening 4A, and the valve body of the exhaust valve 12 opens and closes the exhaust side opening 4B.

  An intake side variable valve timing mechanism (intake side VVT) 15 is incorporated in the intake side valve mechanism 13. The intake side VVT 15 is an electric VVT provided on the intake camshaft, and the intake valve 11 is opened and closed by continuously changing the rotation phase of the intake camshaft with respect to the crankshaft 7 within a predetermined angle range. To change. Similarly, an exhaust side variable valve timing mechanism (exhaust side VVT) 16 is incorporated in the exhaust side valve mechanism 14. The exhaust side VVT 16 is an electric VVT provided on the exhaust camshaft, and the exhaust valve 12 is opened and closed by continuously changing the rotational phase of the exhaust camshaft with respect to the crankshaft 7 within a predetermined angular range. To change.

  One ignition plug 17 for supplying ignition energy to the air-fuel mixture in the combustion chamber 6 is attached to the cylinder head 4, one for each cylinder 2. The spark plug 17 is attached to the cylinder head 4 so that the ignition point faces the combustion chamber 6. The spark plug 17 discharges a spark from its tip in response to power supply from an ignition circuit (not shown), and ignites the air-fuel mixture in the combustion chamber 6.

  The cylinder head 4 is provided with one injector 18 for each cylinder 2 for injecting fuel mainly composed of gasoline into the combustion chamber 6 from the tip. The injector 18 injects fuel supplied through a fuel supply pipe (not shown). Connected to the upstream side of the fuel supply pipe is a high-pressure fuel pump (not shown) composed of a plunger-type pump or the like interlocked with the crankshaft 7. A common rail (not shown) for accumulating pressure common to all the cylinders 2 is provided between the high-pressure fuel pump and the fuel supply pipe. The fuel accumulated in the common rail is supplied to the injectors 18 of the respective cylinders 2, whereby high pressure fuel is injected from the injectors 18 into the combustion chamber 6.

  FIG. 1 exemplifies a spark ignition combustion type engine body 1 using a spark plug 17 that is generally employed in a gasoline engine. The engine body 1 may be an HCCI combustion (premixed compression ignition combustion) type engine. In this case, the injector 18 injects at least part of the amount of fuel to be injected during one cycle into the combustion chamber 6 before the compression top dead center. The injected fuel is mixed with air (intake air) introduced into the combustion chamber 6 and then self-ignited, for example, near the compression top dead center. That is, the fuel / air mixture is self-ignited as the piston 5 compresses it. When the HCCI combustion method is employed, the spark plug 17 can be omitted, but the spark plug 17 may be provided for spark assist during cold start of the engine. In the HCCI combustion method, combustion with high thermal efficiency can be performed in the combustion chamber 6, but therefore, the exhaust heat tends to become small (the exhaust temperature becomes low).

<Exhaust device structure>
The exhaust device 20 is a device that discharges combustion gas (exhaust gas) discharged from the cylinder 2 of the engine body 1 to the outside. The exhaust manifold 21, the catalyst device 22, and the silencer 23 are sequentially arranged from the upstream side of the exhaust flow. And a common exhaust pipe 30 connecting them. In the present embodiment, the exhaust port 10, the exhaust manifold 21 and the common exhaust pipe 30 of each cylinder 2 are exhaust passages through which the exhaust discharged from each cylinder 2 passes. The common exhaust pipe 30 includes an upstream exhaust pipe 31 that connects the exhaust manifold 21 and the catalyst device 22, and a downstream exhaust pipe 32 that connects the catalyst device 22 and the silencer 23. A turbocharger may be incorporated between the exhaust manifold 21 and the catalyst device 22.

  The exhaust manifold 21 collects exhaust discharged from the exhaust port 10 of each cylinder 2 in one flow path and sends it to the common exhaust pipe 30. The inlet side of the exhaust manifold 21 is connected to the cylinder head 4, and the outlet side is connected to the upstream end 311 of the upstream exhaust pipe 31. Inside the exhaust manifold 21, there is provided an exhaust passage composed of a branch passage connected to the exhaust port 10 of each cylinder 2 and a collecting passage that collects them together. The exhaust passage is defined by an inner wall surface 211 in the exhaust manifold 21.

  The catalyst device 22 is a device that is incorporated in an exhaust passage and purifies exhaust gas, and removes harmful components such as NOx, CO, and HC contained in the exhaust gas. The catalytic device 22 includes a catalytic converter 221 in which, for example, a three-way catalyst is attached to the surface of a lattice-shaped carrier. In order to make the catalytic converter 221 function, it is necessary to heat the catalyst converter 221 to a temperature higher than a predetermined temperature (activation temperature) at which the catalyst is activated. The downstream end 312 of the upstream exhaust pipe 31 is connected to the inlet side of the catalyst device 22, and the upstream end 321 of the downstream exhaust pipe 32 is connected to the outlet side.

  The silencer 23 is disposed at the end of the exhaust passage and is a device for reducing exhaust noise and exhaust temperature. Inside the silencer 23, a silencing space (expansion chamber), an exhaust introduction pipe, an exhaust lead pipe, a silencing material, and the like are provided. A downstream end 322 of a downstream exhaust pipe 32 is connected to the exhaust introduction pipe. The downstream end of the exhaust outlet pipe is a tail pipe 231 drawn from the silencer 23. From the tail pipe 231, exhaust gas is discharged to the outside.

<Internal structure of exhaust pipe>
As described above, in order to activate the catalyst included in the catalyst device 22 early when the engine body 1 is started, and to maintain the activation temperature of the catalyst during operation, the heat held by the exhaust discharged from the engine body 1 is retained. It is desirable to guide the exhaust to the catalytic device 22 without escaping as much as possible. In particular, when the HCCI combustion method is adopted for the engine body 1, the exhaust temperature is inherently low, so that the demand for not letting exhaust heat escape naturally increases.

  In view of this point, the first embodiment shows an example in which the upstream exhaust pipe 31 is provided with a structure for reducing exhaust loss caused by exhaust heat escaping to the outside. 2A is a perspective view of a state in which the upstream exhaust pipe 31 is divided in half in the axial direction, FIG. 2B is a cross-sectional view of the upstream exhaust pipe 31, and FIG. 2C is FIG. 2B. FIG.

  The upstream exhaust pipe 31 has an inner wall surface 31A (exhaust passage inner wall surface) that partitions the exhaust passage. The inner wall surface 31A is a grooved inner wall surface in which a plurality of fine grooves 40 are densely arranged. The fine groove 40 extends linearly in the flow direction of the exhaust flow 50 flowing in the upstream exhaust pipe 31 indicated by an arrow in FIG. The fine groove 40 is a groove having a V-shaped cross section having a groove width S of a predetermined length, and a pair of top portions 401 that are opening edges of the V-shaped groove, a trough portion 402 that is the deepest portion of the V-shaped groove, and a pair And a pair of inclined surfaces existing between the top portion 401 and the trough portion 402.

  The shape of the fine groove 40 can be selected as appropriate. For example, the fine groove 40 having a U-shaped section or a rectangular section may be used. In addition, it is desirable that the extending direction of the fine groove 40 coincides with the tube axis direction of the upstream exhaust pipe 31 that is the flow direction of the exhaust flow 50, but the direction having a slight angle with respect to the tube axis direction extends. It may be a direction. The fine groove 40 is preferably provided over the entire circumference in the circumferential direction of the inner wall surface 31A of the upstream exhaust pipe 31 and the entire length in the axial direction, but a part of the circumferential region or a part of the axial section is provided. The formation of the fine groove 40 may be omitted.

  In the present embodiment, the groove width S of the fine grooves 40 and the arrangement pitch P of the plurality of fine grooves 40 are substantially the same. That is, the adjacent fine grooves 40 are arranged in the circumferential direction of the upstream exhaust pipe 31 so that the top portions 401 are adjacent (joined). For this reason, in a cross-sectional view orthogonal to the extending direction of the fine groove 40 (FIGS. 2A and 2B), there is a structure in which a sharp peak portion formed by a joint portion between the top portions 401 exists between the adjacent fine grooves 40. In other words, the structure is such that there is substantially no planar portion between the fine grooves 40. Here, the groove width S and the arrangement pitch are assumed to be “substantially” the same between the top portions 401 of the adjacent fine grooves 40 and a flat portion having a fine width inevitably generated during processing, or the peak portion. This is because a case in which a flat portion having a slight width is positively formed so as not to be too sharp is assumed.

  Here, an example is shown in which the inner wall surface 31 </ b> A of the upstream exhaust pipe 31 is a grooved inner wall surface including the fine grooves 40. The grooved inner wall surface may be applied to the inner wall surface of the exhaust passage that divides the exhaust passage in at least a part or all of the exhaust passage between the cylinder 2 and the catalyst device 22. In the present embodiment, the exhaust passage that connects the exhaust side opening 4 </ b> B (cylinder outlet) of the cylinder head 4 and the catalyst device 22 includes the exhaust port 10, the exhaust manifold 21, and the upstream exhaust pipe 31. The fine groove 40 should just be provided in the exhaust passage inner wall surface which divides the exhaust passage of at least one part or all the sections among these exhaust passages. For example, in addition to the inner wall surface 31 </ b> A of the upstream exhaust pipe 31, fine grooves may be provided on the inner wall surface of the exhaust port 10, or fine grooves may be provided at appropriate positions on the inner wall surface of the exhaust manifold 21.

  Various existing methods can be employed as a method for forming the fine groove 40. For example, a method of forming a fine groove 40 linearly extending in one direction on one side of a rectangular metal flat plate and forming the metal flat plate into a cylindrical shape with the engraved surface of the fine groove 40 inside. it can. A pair of edges of the metal flat plates that are overlapped with each other by cylindrical molding are joined by seam welding. In addition, a method of inserting a core having a fine protrusion corresponding to the fine groove 40 into the metal tube can be employed.

<Advantages of fine grooves>
The advantage of the grooved inner wall surface provided with the fine groove 40 will be described. FIG. 3 is a schematic diagram showing an aspect of the exhaust flow 50. The exhaust flow 50 includes a main flow 51 and a vortex flow 52 that is a side flow accompanying the main flow 51. The main flow 51 is a gas flow toward the exhaust direction, that is, the downstream side in the extending direction of the upstream exhaust pipe 31. The vortex flow 52 is a vortex swirling around the axis of travel of the main flow 51.

  For example, in an ordinary passenger car, the exhaust flow 50 has a flow rate of about 10 to 70 m / s when the diameter of the exhaust pipe is about 30 mmφ and the engine speed is about 1000 to 6000 rpm. According to the knowledge of the present inventors, such an exhaust flow 50 includes the main flow 51 and the vortex flow 52 described above. Further, the vortex flow 52 has a characteristic that it has a strong property of transporting heat. Furthermore, the diameter (scale) of the vortex flow 52 tends to decrease as the flow velocity of the exhaust flow 50 increases.

  FIG. 4A is a diagram showing a positional relationship between the vortex flow 52 of the exhaust flow 50 and the inner wall surface when the inner wall surface of the exhaust passage (the inner wall surface 31A of the upstream exhaust pipe 31) is flat. If the inner wall surface of the exhaust passage is flat, the vortex flow 52 can approach the inner wall surface of the exhaust passage, and accordingly heat transfer is easily performed between the two. For this reason, the heat of the exhaust flow 50 passing through the upstream exhaust pipe 31 is easily radiated to the outside through the pipe wall of the upstream exhaust pipe 31. That is, the transfer (heat transfer) of thermal energy between the vortex 52 and the inner wall surface 31A becomes active, and the heat dissipation loss of the exhaust heat increases. Due to this heat dissipation, there may occur a case where the exhaust gas having a temperature necessary for the activation of the catalyst cannot be supplied to the catalyst device 22 through the exhaust passage.

  On the other hand, FIG. 4B is a diagram showing the positional relationship between the vortex 52 and the inner wall surface when the fine groove 40 is formed on the inner wall surface of the exhaust passage. The groove width S of the fine groove 40 is set smaller than the vortex scale D (diameter) of the vortex 52 of the exhaust flow 50. When such a fine groove 40 is provided in the inner wall surface 31 </ b> A, the vortex flow 52 (turbulent flow) cannot enter the fine groove 40 and remains at the top of the fine groove 40. That is, as compared with the case of a flat inner wall surface as shown in FIG. 4A, the vortex 52 is separated from the inner wall surface 31A. Therefore, heat transfer is difficult to be performed between the vortex flow 52 and the inner wall surface 31 </ b> A, and heat radiation through the pipe wall of the upstream exhaust pipe 31 is suppressed.

  When the upstream exhaust pipe 31 is assumed to have a diameter of about 30 mmφ and the flow velocity of the exhaust flow 50 is about 10 to 70 m / s as in the above example, the preferable groove width S of the fine groove 40 is about 100 μm to 700 μm. is there. In order to separate the vortex 52 from the inner wall surface 31A as much as possible with respect to the groove height h of the fine groove 40, it is only necessary to increase the groove height h. However, if the groove height h is excessively increased, the surface area of the inner wall surface 31A increases. Too much. In this case, the heat dissipation improvement accompanying the increase in the surface area is superior to the effect of separating the vortex 52 from the inner wall surface 31A. Therefore, it is desirable that the groove width S of the fine groove 40 and the groove height h satisfy the relationship of S ≧ h. Here, if the groove height h is too low, the effect of separating the vortex 52 from the inner wall surface 31A becomes relatively small. Therefore, it is particularly desirable to set the groove width S and the groove height h of the fine groove 40 so that h / S is in the range of 0.5 to 1.0. Thereby, it is possible to balance the increase in the surface area of the inner wall surface 31A due to the formation of the fine grooves 40 and the effect of suppressing heat transfer by separating the vortex flow 52 from the inner wall surface 31A.

  By making the inner wall surface 31A into a grooved inner wall surface in which many of the fine grooves 40 having the groove width S and the groove height h as described above are densely arranged, the exhaust flow accompanied by the vortex flow 52 having a high heat transfer property 50 can be separated from the inner wall surface 31A, and the heat release of the exhaust heat is suppressed. Accordingly, it is possible to introduce the exhaust flow 50 into the catalyst device 22 connected to the downstream end 312 of the upstream exhaust pipe 31 while keeping the exhaust heat warm. This contributes to early activation of the catalyst and maintenance of the activation temperature. Further, it is possible to obtain the heat insulation effect of the exhaust gas simply by forming the fine groove 40 on the inner wall surface 31A, and the cost and the number of manufacturing steps are reduced as compared with the case where a coating layer for keeping the heat is separately provided on the inner wall surface 31A. be able to.

  In particular, when the HCCI combustion method is adopted for the engine body 1, the advantage of providing the fine groove 40 becomes significant. As described above, in the HCCI combustion method, combustion with high thermal efficiency can be performed in the combustion chamber 6, but the exhaust heat tends to be small. For this reason, conventionally, in order to maintain the activation temperature of the catalyst, control for reducing the thermal efficiency of the engine, for example, control such as changing the fuel injection timing to slow down the combustion is performed. However, according to the present embodiment, the loss of exhaust heat can be suppressed to a low level, so that control for intentionally reducing the thermal efficiency of the engine in order to maintain the activation temperature of the catalyst can be minimized. Therefore, the thermal efficiency of the engine can be improved.

[Second Embodiment]
FIG. 5 is a schematic sectional view showing an engine exhaust device 20A according to the second embodiment of the present invention, and shows a schematic configuration of the engine body 1 and the exhaust device 20A of the engine body 1. As shown in FIG. Since the structure of the engine body 1 is as described in the first embodiment, the description thereof is omitted here. The exhaust device 20A includes an exhaust heat recovery device 24 in addition to the exhaust manifold 21, the catalyst device 22, and the silencer 23 shown in the first embodiment, and includes a common exhaust pipe 30A that connects them. The exhaust heat recovery device 24 is incorporated in an exhaust passage downstream of the catalyst device 22 (upstream of the silencer 23) in the exhaust circulation direction.

  A specific example of the exhaust heat recovery device 24 will be described later (FIG. 7), and is a device that recovers thermal energy held by the exhaust gas flowing through the exhaust passage. The recovered thermal energy is used for improving the operation efficiency of the engine body 1. As a matter of course, in order to increase the recovery amount of thermal energy, it is desirable to introduce exhaust gas as hot as possible into the exhaust heat recovery device 24.

  The common exhaust pipe 30 </ b> A is a first downstream exhaust that connects the upstream exhaust pipe 31 (same as in the first embodiment) that connects the exhaust manifold 21 and the catalyst device 22 and the catalyst device 22 and the exhaust heat recovery device 24. A pipe 33 and a second downstream exhaust pipe 34 connecting the exhaust heat recovery device 24 and the silencer 23. The upstream end 331 of the first downstream exhaust pipe 33 is connected to the outlet side of the catalyst device 22, and the downstream end 332 is connected to the inlet side of the exhaust heat recovery device 24. The upstream end 341 of the second downstream exhaust pipe 34 is connected to the exhaust side of the exhaust heat recovery device 24, and the downstream end 342 is connected to the exhaust introduction pipe included in the silencer 23.

  In the exhaust passage of the second embodiment, it is the exhaust passage that connects the exhaust side opening 4B (cylinder outlet) to the exhaust heat recovery device 24 that needs to be kept warm. Specifically, the exhaust passage is composed of the exhaust port 10, the exhaust manifold 21, the upstream exhaust pipe 31, and the first downstream exhaust pipe 33. The grooved inner wall surface described in the first embodiment is applied to an exhaust passage inner wall surface that divides the exhaust passage in at least some or all of the exhaust passages.

  As a preferable example, an inner wall surface 31A of the upstream exhaust pipe 31 (a part of the first exhaust passage) and an inner wall surface 33A of the first downstream exhaust pipe 33 (a part of the second exhaust passage) are respectively provided. The example which forms the fine groove | channel 40 extended in the flow direction of exhaust can be given. As the fine groove 40 formed in the first downstream exhaust pipe 33, the same structure as that shown in FIGS. 2A to 2C can be adopted. The fine groove 40 is preferably provided over the entire circumference in the circumferential direction and the entire length in the axial direction of the inner wall surfaces 31A and 33A of the upstream exhaust pipe 31 and the first downstream exhaust pipe 33. The formation of the fine groove 40 in the directional region or a part of the axial direction may be omitted.

  According to the exhaust device 20A of the second embodiment, the heat radiation of the exhaust heat in the upstream exhaust pipe 31 disposed between the exhaust side opening 4B and the catalyst device 22, and the catalyst device 22 and the exhaust heat recovery device 24 The heat radiation of the exhaust heat in the first downstream exhaust pipe 33 disposed between the two can be suppressed. Therefore, it is possible to contribute to the early activation of the catalyst in the catalyst device 22, the maintenance of the activation temperature, and the increase in the amount of heat recovered from the exhaust in the exhaust heat recovery device 24.

  Although the fine groove 40 having the same groove width S may be provided in the upstream exhaust pipe 31 and the first downstream exhaust pipe 33, the groove width S may be varied according to the flow velocity of the exhaust flow 50. FIG. 6 is a schematic diagram for explaining a preferred arrangement of fine grooves in the second embodiment. In FIG. 6, the inner wall surface 31A of the upstream exhaust pipe 31 and the inner wall surface 33A of the first downstream exhaust pipe 33 are shown in a flatly developed state.

  A first fine groove 41 is formed in the inner wall surface 31 </ b> A of the upstream exhaust pipe 31. A second fine groove 42 is formed on the inner wall surface 33A of the first downstream exhaust pipe 33 located on the downstream side of the upstream exhaust pipe 31 in the exhaust flow direction. Each of the first fine grooves 41 has a predetermined first groove width S1. Each of the second fine grooves 42 has a second groove width S2 that is wider than the first groove width S1.

  The flow velocity of the exhaust flow 50 decreases as it goes downstream of the exhaust passage. In particular, before and after the exhaust gas passes through the catalyst device 22, the flow velocity changes greatly. For this reason, since the exhaust flow 50 passing through the upstream exhaust pipe 31 is relatively fast, the vortex flow 52 is relatively small, whereas the exhaust flow 50 passing through the first downstream exhaust pipe 33 is relatively slow. Therefore, the vortex 52 becomes relatively large. Therefore, in the state shown in FIG. 4B, that is, the optimum groove width S of the fine groove 40 for preventing the vortex 52 from entering the upstream exhaust pipe 31 and the first downstream exhaust pipe 33. Will be different.

  According to the example of FIG. 6, fine grooves corresponding to changes in the flow velocity of the exhaust flow in the exhaust passage can be set on the inner wall surfaces 31A and 33A, respectively. That is, the first and second fine grooves 41 and 42 have a groove width corresponding to the diameter change of the vortex 52 of the exhaust flow 50 toward the downstream side of the exhaust passage. Accordingly, in each of the exhaust pipes 31 and 33, the vortex flow 52 can be appropriately separated from the inner wall surfaces 31A and 33A, and exhaust heat radiation can be effectively reduced.

  Here, a specific example of the exhaust heat recovery device 24 will be illustrated. FIG. 7 is a block diagram showing an example of the exhaust heat recovery device 24 for a water injection device that injects high temperature water into the cylinder 2. The exhaust heat recovery device 24 has a function of generating high-temperature water to be supplied to the cylinder 2 and a function of raising the intake air temperature, and includes a condenser 241, a water tank 242, a heat exchanger 243, and an intake air temperature raising device 244. Further, for injection of the high-temperature water into the cylinder 2, the engine body 1 is provided with a pressure accumulation rail 248 and a water injection nozzle 24N.

  The condenser 241 is a thermal device that condenses water vapor contained in the exhaust gas flowing through the common exhaust pipe 30A. The condenser 241 condenses water vapor contained in the exhaust gas by cooling the exhaust gas by heat exchange with a refrigerant such as engine cooling water. The water tank 242 is a tank that stores condensed water, and the condensed water generated by the condenser 241 is introduced through the first pipe 245. The heat exchanger 243 is a heat exchanger that is arranged upstream of the condenser 241 and raises the temperature of the condensed water stored in the water tank 242 by heat exchange with the exhaust before flowing into the condenser 241. The intake air temperature raising device 244 is a thermal device that receives heat energy from the exhaust gas flowing through the common exhaust pipe 30 </ b> A and performs heat exchange that gives the heat energy to the intake air flowing through the intake passage 91.

  Condensed water is sent from the water tank 242 to the heat exchanger 243 through the second pipe 246 by operation of a low-pressure pump (not shown). The heat exchanger 243 includes a meandering pipe disposed so as to be able to exchange heat with the common exhaust pipe 30A. The condensed water that has passed through the heat exchanger 243 is heated to about 150 to 250 ° C. This high-temperature condensed water is sent to the pressure accumulation rail 248 through the third pipe 247. At this time, the high-temperature condensed water is pumped by a high-pressure pump (not shown) and stored in the pressure accumulation rail 248 in a pressure accumulation state. Water injection nozzles 24N are attached to the four branch pipes extending from the pressure accumulation rail 248. From the water injection nozzle 24N, high-temperature condensed water generated by using the exhaust heat by the exhaust heat recovery device 24 is injected into the cylinder 2.

  When the high-temperature condensed water is injected into the cylinder 2, the high-temperature condensed water expands in the cylinder 2 and increases the pressure in the cylinder 2. Thus, the thermal efficiency of an engine can be improved by converting the energy of high-temperature condensed water into pressure (work). Moreover, since the intake air flowing through the intake passage 91 is also heated, the combustion temperature in the combustion chamber 6 can be increased. In the present embodiment, the inner wall surfaces 31A and 33A of the upstream exhaust pipe 31 and the first downstream exhaust pipe 33 that guide the exhaust to the exhaust heat recovery device 24 are formed into the fine grooves 40 (first and second fine grooves 41 and 42). An inner wall surface with a groove is provided. Therefore, the exhaust heat can be introduced into the exhaust heat recovery device 24 with the exhaust heat loss at a low level, so that the functions of high-temperature condensed water generation and intake air heating by the exhaust heat recovery device 24 can be further enhanced.

[Third Embodiment]
FIG. 8 is a schematic cross-sectional view showing an engine exhaust device 20B according to a third embodiment of the present invention, and shows a schematic configuration of the engine main body 1 and the exhaust device 20B of the engine main body 1. The structure of the engine body 1 is the same as that of the first embodiment. The exhaust device 20B is a catalyst-less exhaust system, and includes the exhaust manifold 21 and the silencer 23 shown in the first embodiment, and the exhaust heat recovery device 24 shown in the second embodiment, and a common exhaust pipe that connects them. 30B.

  The common exhaust pipe 30 </ b> B includes an upstream exhaust pipe 35 that connects the exhaust manifold 21 and the exhaust heat recovery device 24, and a downstream exhaust pipe 36 that connects the exhaust heat recovery device 24 and the silencer 23. The upstream end 351 of the upstream exhaust pipe 35 is connected to the outlet side of the exhaust manifold 21, and the downstream end 352 is connected to the inlet side of the exhaust heat recovery device 24. The upstream end 361 of the downstream exhaust pipe 36 is connected to the exhaust side of the exhaust heat recovery device 24, and the downstream end 362 is connected to the exhaust introduction pipe included in the silencer 23.

  In the engine body 1, it is possible to prevent harmful components such as NOx, CO, and HC from being generated in the exhaust gas by adopting a lean combustion or compression ignition method. In this case, it is possible to omit the catalyst device 22 shown in the first and second embodiments from the exhaust system (catalyst-less). In the exhaust device 20B of the third embodiment, the catalyst device 22 is omitted, while the exhaust heat recovery device 24 is incorporated in the common exhaust pipe 30B.

  In the exhaust passage of the third embodiment, it is the exhaust passage that connects the exhaust side opening 4B (cylinder outlet) to the exhaust heat recovery device 24 that needs to be kept warm. Specifically, the exhaust passage is composed of the exhaust port 10, the exhaust manifold 21, and the upstream exhaust pipe 35. The grooved inner wall surface described in the first embodiment is applied to an exhaust passage inner wall surface that divides the exhaust passage in at least some or all of the exhaust passages.

  As a preferred example, an example in which a fine groove 40 extending in the exhaust flow direction is formed on the inner wall surface of the upstream exhaust pipe 35 can be cited. As the fine groove 40 formed in the upstream exhaust pipe 35, the same structure as that shown in FIGS. 2A to 2C can be adopted. The fine groove 40 is desirably provided over the entire circumference in the circumferential direction and the entire length in the axial direction of the inner wall surface of the upstream exhaust pipe 35, but to some circumferential regions or some axial sections. The formation of the fine groove 40 may be omitted.

  According to the exhaust device 20B of the third embodiment, it is possible to suppress heat dissipation of the exhaust heat in the upstream exhaust pipe 35 disposed between the exhaust side opening 4B and the exhaust heat recovery device 24. Therefore, it is possible to contribute to an increase in the amount of heat recovered from the exhaust in the exhaust heat recovery device 24.

[Description of Modified Embodiment]
As mentioned above, although embodiment of this invention was described, this invention is not limited to this, For example, the following modified embodiment can be taken.

  (1) In the above embodiment, the example in which the heat release of the exhaust heat is suppressed by forming the fine groove 40 in the upstream exhaust pipe 31 or the like has been described. In addition to the fine groove 40, another heat dissipation prevention structure may be provided. For example, the outer periphery of the exhaust pipe in which the fine groove 40 is engraved on the inner wall surface may be covered with another heat insulating pipe to further suppress the heat dissipation of the exhaust heat.

  (2) In the first embodiment, the example in which the fine groove 40 having the predetermined groove width S is formed on the inner wall surface 31A of the upstream exhaust pipe 31 is shown. In the second embodiment, the first fine groove 41 having the first groove width S1 is provided on the inner wall surface 31A of the upstream exhaust pipe 31, and the second fine groove 42 having the second groove width S2 is provided on the first downstream exhaust pipe 33. The example which forms in 33A of inner wall surfaces of this was shown. In the case where the flow velocity of the exhaust flow 50 decreases toward the downstream side of the exhaust passage, instead of the above, the groove width S of the fine groove may be made different in one exhaust pipe.

  FIG. 9 is a schematic diagram for explaining a fine groove pattern according to a modification. For example, the inner wall surface 31A of the upstream exhaust pipe 31 is divided into a first region R1 on the upstream side of the exhaust passage and a second region R2 on the downstream side. An upstream fine groove 43 having a first groove width S11 is arranged in the first region R1, and a downstream fine groove 44 having a second groove width S12 (S11 <S12) is arranged in the second region R2. When the flow velocity of the exhaust flow 50 is decelerated downstream, the vortex scale of the vortex 52 of the exhaust flow 50 increases toward the downstream. According to the modification of FIG. 9, the fine grooves 43 and 44 having groove widths S11 and S12 set according to the flow velocity of the exhaust flow 50 are arranged in the first region R1 and the second region R2, respectively. Therefore, the effect of reducing the heat dissipation loss of higher exhaust heat can be obtained.

1 Engine Body 2 Cylinder 3 Cylinder Block 4A Intake Side Opening 4B Exhaust Side Opening (Cylinder Outlet)
5 Piston 6 Combustion chamber 10 Exhaust port (part of exhaust passage)
20, 20A, 20B Exhaust device 21 Exhaust manifold (part of exhaust passage)
22 catalyst device 23 silencer 24 exhaust heat recovery device 30, 30A, 30B common exhaust pipe (part of exhaust passage)
31 Upstream exhaust pipe (first exhaust passage)
31A Inner wall surface (exhaust passage inner wall surface)
32 Downstream exhaust pipe 33 First downstream exhaust pipe (second exhaust passage)
33A Inner wall surface (exhaust passage inner wall surface)
34 Second downstream exhaust pipe 40 Fine groove 41 First fine groove 42 Second fine groove 50 Exhaust flow 51 Main flow 52 Vortex (longitudinal vortex)
S groove width S1, S2 first and second groove width h groove height

Claims (5)

An exhaust system for an engine having a cylinder in which a mixture of fuel and air burns,
An exhaust passage through which the exhaust discharged from the cylinder passes,
In at least a part of the exhaust passage, an exhaust passage inner wall surface defining the exhaust passage has a groove in which a plurality of fine grooves having a groove width of 100 μm to 700 μm extending in the flow direction of the exhaust gas are densely arranged. An exhaust system for the engine that is the inner wall. The engine exhaust system according to claim 1,
A catalyst device that is incorporated in the exhaust passage and purifies the exhaust;
An exhaust system for an engine, wherein an inner wall surface of the exhaust passage in at least a part of the exhaust passage connecting the outlet of the cylinder to the catalyst device in the exhaust passage is the inner wall surface with a groove. The engine exhaust system according to claim 1,
An exhaust heat recovery device that is incorporated in the exhaust passage and recovers thermal energy held by the exhaust;
An exhaust system for an engine, wherein an inner wall surface of the exhaust passage in at least a part of the exhaust passage connecting the outlet of the cylinder to the exhaust heat recovery device in the exhaust passage is the grooved inner wall surface. The engine exhaust system according to claim 1,
A catalyst device incorporated in the exhaust passage and purifying the exhaust;
An exhaust heat recovery device that is incorporated in the exhaust passage downstream of the catalyst device in the exhaust flow direction and recovers the thermal energy held by the exhaust, and
Of the exhaust passage, the exhaust passage inner wall surface in at least a part of the first exhaust passage that connects the outlet of the cylinder to the catalyst device, and the second exhaust that connects the catalyst device to the exhaust heat recovery device. An exhaust system for an engine, wherein an inner wall surface of the exhaust passage in at least a part of the passage is the grooved inner wall surface. An exhaust system for an engine having a cylinder in which a mixture of fuel and air burns,
An exhaust passage through which the exhaust discharged from the cylinder passes,
In at least a part of the exhaust passage, an exhaust passage inner wall surface defining the exhaust passage is a grooved inner wall surface in which a plurality of fine grooves extending in a flow direction of the exhaust gas are densely arranged. In the exhaust system,
The fine groove has a groove width of 100 μm to 700 μm,
A catalyst device incorporated in the exhaust passage and purifying the exhaust;
An exhaust heat recovery device that is incorporated in the exhaust passage downstream of the catalyst device in the exhaust flow direction and recovers the thermal energy held by the exhaust, and
Of the exhaust passage, the exhaust passage inner wall surface in at least a part of the first exhaust passage that connects the outlet of the cylinder to the catalyst device, and the second exhaust that connects the catalyst device to the exhaust heat recovery device. The exhaust passage inner wall surface in at least a part of the passage is the grooved inner wall surface,
Each of the plurality of fine grooves formed on the inner wall surface of the exhaust passage of the first exhaust passage has a first groove width,
An exhaust system for an engine, wherein each of the plurality of fine grooves formed on the inner wall surface of the second exhaust passage has a second groove width wider than the first groove width.

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