JP4765711B2 - Engine intake / exhaust system - Google Patents

Description

  The present invention relates to an intake / exhaust system for an engine, and in particular, a high temperature exhaust gas is taken into an outer periphery of a catalyst carrier of an exhaust purification device provided in an exhaust system of an engine equipped with an exhaust turbine-driven supercharger to improve a regeneration capability. It is about technology to improve.

  In recent years, with the tightening of exhaust gas regulations, exhaust purification systems with particulate filters that can be regenerated by collecting particulate matter (particulate matter) discharged from engines such as diesel engines and incineration and removal. It is beginning to become mandatory. Furthermore, in the European market where passenger cars equipped with diesel engines are highly utilized, a single closed with a catalytic function that can be directly attached to the engine, enabling a small, compact and simple layout, ensuring a high exhaust gas temperature.・ A couple-type exhaust gas purification device has been devised. As an exhaust purification device, for example, as shown in FIG. 10, a cylindrical catalyst carrier 14 is held in a cylindrical casing 28 via a ceramic carrier holding material such as alumina fiber 34, or a patent document. As described in No. 1, there is known one in which a casing is provided with a return flow path that folds at least a part of exhaust gas that has passed through a catalyst carrier to flow around the catalyst carrier.

  On the other hand, in a diesel engine, research on premixed compression ignition combustion that enables simultaneous reduction of low NOx and low smoke has been actively conducted in recent years. This premixed compression ignition combustion generates and burns a uniform and lean mixture at an early stage, and as a technical problem, if the engine load is increased, pre-ignition occurs and it becomes difficult to control the ignition timing. There is a problem that it is limited to a low load region. As a method of expanding the operating range by this premixed compression ignition combustion, a part of the exhaust gas is taken out from the exhaust system and returned to the intake system, and the EGR rate of EGR (Exhaust Gas Recirculation) added to the mixture is increased. It is effective to suppress the combustion by increasing the oxygen concentration of the air-fuel mixture and to secure the air-fuel ratio. As a specific countermeasure, a high boost is obtained from a low-speed and low-load region by using a multi-stage turbocharger, for example, a high-pressure small turbocharger, and a high EGR rate and a high air-fuel ratio are secured. Conceivable. The two-stage turbocharger is also an effective means as a means for achieving both a reduction in fuel consumption and a high output at the rated point in urban areas (low / medium speed / low / medium load).

JP 2003-120260 A

  However, in the above engine, when a single exhaust purification device with a catalytic function is mounted, there is a concern that the regeneration capacity may be lowered because there is no sufficient capacity of an oxidation catalyst or the like in the previous stage. In particular, when an exhaust purification device is installed downstream of the exhaust system of the engine with multistage supercharging, the inlet temperature of the exhaust purification device is lowered, so that the regeneration capacity is further reduced as compared with the single-stage supercharging device. Is concerned.

  Further, when focusing on the catalyst carrier holding structure, the conventional holding structure cannot sufficiently reduce the heat transfer coefficient at the boundary between the outer periphery of the catalyst carrier and the casing, and the heat transfer rate from the catalyst carrier to the outer periphery of the casing is reduced. There was room for reduction, that is, improvement in the heat insulation and heat retention characteristics of the carrier.

  The present invention solves the above-described problems of the prior art, can increase the temperature rise effect and the heat insulating heat retaining characteristic in the outer peripheral portion of the catalyst carrier of the exhaust purification device, and can improve the regeneration capability of the exhaust purification device An object of the present invention is to provide an intake / exhaust system.

The present invention relates to an EGR gas passage that extracts a part of exhaust gas from the exhaust system and returns it to the intake system of the engine again, an EGR gas cooler provided in the EGR gas passage, and a supercharging provided in the intake system. An exhaust turbine provided in the exhaust system to drive the engine, and an exhaust purification device having a catalyst carrier provided downstream from the exhaust turbine, the upstream of the EGR gas cooler in the EGR gas flow path A catalyst carrier outer peripheral gas flow path is provided along the outer periphery of the catalyst carrier, and exhaust gas is introduced directly into the catalyst carrier outer gas flow path from upstream of the exhaust turbine of the exhaust system. The present invention is characterized in that a bypass flow path having a bypass valve for connecting the front side of the carrier on the exhaust gas inlet side and the upstream portion of the EGR gas flow path with respect to the catalyst carrier outer peripheral gas flow path is provided.

The exhaust gas outlet side rear of the catalyst carrier in the exhaust system, Rukoto provided a temperature sensor for controlling the bypass valve is preferably detects the exhaust gas temperature.

It is preferable to provide a nozzle that opens toward the exhaust gas inlet side end face of the catalyst carrier in the exhaust system at the outlet of the bypass flow path .

According to the present invention, the upstream side of the EGR cooler of the EGR gas passage, a catalyst carrier outer peripheral gas flow path along the outer circumference of the catalyst carrier provided, the exhaust turbine of the exhaust system to the catalyst carrier outer peripheral gas flow path The exhaust gas is directly introduced from the upstream side, and the bypass for connecting the front side of the exhaust gas inlet side of the catalyst carrier in the exhaust system and the upstream portion of the EGR gas channel with respect to the outer peripheral gas channel of the catalyst carrier. is provided with the bypass flow passage having a valve, can also you to heating from the center not only the outer peripheral portion of the catalyst carrier of the exhaust purification device, playing efficiently catalyst support from inside and outside to effectively heat And the regeneration capability of the exhaust emission control device can be improved.

  The best mode for carrying out the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a diagram schematically showing an intake / exhaust system for an engine according to an embodiment of the present invention, FIG. 2 is a diagram showing a flow of EGR gas when the bypass valve is closed, and FIG. 3 is a diagram when the bypass valve is opened. 4 is a diagram showing the flow of EGR gas, FIG. 4 is a sectional view showing the structure of the exhaust purification device, and FIG. 5 is a sectional view taken along line AA of FIG.

  In these drawings, reference numeral 1 denotes an engine, for example, a diesel engine. The engine 1 is provided with an intake / exhaust system 2 including an intake system and an exhaust system thereof. The intake / exhaust system 2 is configured as described below. . The engine body 1a of the engine 1 is provided with an intake manifold 3 constituting a part of the intake system and an exhaust manifold 4 constituting a part of the exhaust system. The intake manifold 3 is connected to an intake flow path 5 that is an intake system pipe, and the exhaust manifold 4 is connected to an exhaust gas flow path 6 that is an exhaust system pipe.

  A throttle valve 7, an intercooler 8, a high-pressure stage supercharger 9, a low-pressure stage supercharger 10, and an air flow sensor 11 are provided in the intake passage 5 in order from the downstream. That is, in the present embodiment, multistage, for example, two-stage superchargers 9 and 10 are provided in the intake system of the engine 1. The superchargers 9 and 10 are of an exhaust turbine drive type and include compressors 9a and 10a and exhaust turbines 9b and 10b. The intake passage 5 is provided with a bypass passage 13 having a bypass valve 12 connecting the upstream and downstream of the compressor 9 a of the high-pressure supercharger 9.

  The exhaust gas passage 6 has an exhaust turbine 9b for driving the high-pressure stage turbocharger 9 in order from the upstream, an exhaust turbine 10b for driving the low-pressure stage turbocharger 10, and a catalyst carrier 14 that is a particulate filter. A purification device (also referred to as an exhaust aftertreatment device) 15 is provided. The exhaust gas passage 6 is provided with a bypass passage 17 having a bypass valve 16 that connects the upstream and downstream of the exhaust turbine 9 b of the high-pressure supercharger 9. The exhaust gas passage 6 is provided with a bypass passage 19 having a bypass valve 18 connecting the upstream and downstream of the exhaust turbine 10 b of the low-pressure supercharger 10.

  Further, the engine 1 is provided with an EGR gas flow path 20 that extracts a part of the exhaust gas from the exhaust system and returns it to the intake system of the engine 1 again. One end of the EGR gas flow path 20 is connected to the exhaust manifold 4, and the other end of the EGR gas flow path 20 is connected downstream of the throttle valve 7 in the intake flow path 5. The EGR gas flow path 20 is provided with an EGR valve 21 and an EGR cooler 22 in order from the downstream side. These EGR valve 21 and EGR cooler 22 are preferably provided in the vicinity of intake manifold 3.

  On the upstream side of the EGR gas cooler 22 of the EGR gas channel 20, a catalyst carrier outer gas channel 23 is provided along the outer periphery of the catalyst carrier 14 of the exhaust purification device 15. Exhaust gas is introduced directly from upstream of the exhaust turbines 9b and 10b of the exhaust system. In other words, the catalyst carrier outer peripheral gas flow path 23 is provided on the outer periphery of the catalyst carrier 14, and the pipe (EGR gas flow path upstream portion) 20 a connecting the catalyst carrier outer peripheral gas flow path 23 and the exhaust manifold 4 has a high temperature. Exhaust gas is introduced directly into the catalyst carrier peripheral gas flow path 23.

  The bypass having a bypass valve 24 for connecting the exhaust gas inlet side front side of the catalyst carrier 14 in the exhaust gas passage 6 and the upstream portion 20a of the catalyst carrier outer peripheral gas passage 23 of the EGR gas passage 20 is provided. A flow path 25 is provided. A temperature sensor 26 for detecting the exhaust gas temperature and controlling the bypass valve 24 is provided at the exhaust gas outlet side rear side of the catalyst carrier 14 in the exhaust gas passage 6. In the intake / exhaust system 2, when a detection signal from the temperature sensor 26 is input and the detected value exceeds a set value (set temperature), the bypass valve 24 is closed, and when the detected value falls below the set value. A controller 27 is provided for controlling the bypass valve 24 to open.

  As shown in FIGS. 4 to 6, the exhaust purification device 15 has a cylindrical casing 28, and a cylindrical catalyst carrier 14 is provided in the casing 28, and the outer periphery of the catalyst carrier 14 and the casing 28 are provided. A catalyst carrier outer peripheral gas flow path 23 is provided between the inner periphery and the inner periphery of the catalyst carrier. The catalyst carrier 14 has a porous honeycomb structure made of a ceramic such as cordierite, and the inlets and outlets of each flow path partitioned in a lattice shape are alternately plugged, so that the porous supports partition each flow path. Only the exhaust gas that has permeated through the porous partition is discharged downstream, and the particulates are collected on the inner wall surface of the porous partition. Since the particulates are collected and accumulated, they are removed by incineration as appropriate so that the exhaust resistance does not increase due to clogging, and the particulate filter is regenerated, but in normal diesel engine operating conditions, the particulates There are few opportunities to obtain exhaust temperatures that are high enough to cause natural combustion. For this reason, the above particulate filter is a catalyst regeneration type particulate filter (catalyst carrier) in which an oxidation catalyst made by adding rare earth elements such as cerium is supported on a material in which platinum is supported on alumina, for example. ), And the improvement of the reproduction ability is attempted.

  One end of the casing 28 is provided with an inlet pipe portion 28a having a diameter gradually reduced in a funnel shape as a connection port for introducing exhaust gas from the downstream side of the low-pressure turbine 10b of the exhaust gas passage 6. The other end is provided with an outlet pipe portion 28b whose diameter is gradually reduced in a funnel shape as a connection port for discharging exhaust gas that has passed through the catalyst carrier 14 to the exhaust gas passage 6. On one side of the casing 28 (upper portion in the illustrated example), an introduction pipe portion 28c that is a connection port for introducing exhaust gas from the upstream portion 20a of the EGR gas passage into the catalyst carrier outer peripheral gas passage 23 is provided. On the other side (the lower side) of the casing 28, an exhaust pipe portion 28d is provided as a connection port for discharging exhaust gas from the catalyst carrier outer peripheral gas flow channel 23 to the EGR gas flow channel 20.

  As shown in FIG. 6, the bypass flow path 25 is preferably provided so as to connect the introduction pipe portion 28c and the inlet pipe portion 28a in order to simplify the structure. The outlet 25a of the bypass channel 25 is preferably open to face the inlet side end face of the catalyst carrier 14. The bypass valve 24 provided in the bypass flow path 25 is not an ON / OFF control valve, and it is preferable that stepless lift control driven by an electric motor can be performed similarly to the EGR valve 21.

  In the casing 28, both ends of the outer periphery of the catalyst carrier 14 are held, and the outer periphery of the ends of the catalyst carrier 14 is sealed with a substantially Z-shaped cross section to seal the gap between the casing 28. A plate 29 is disposed, and an annular gasket 31 having a substantially U-shaped cross section is interposed between the outer end of the end plate 29 and the annular corners 30 on both ends of the casing 28. The gasket 31 can follow the thermal expansion of the catalyst carrier 14 and the casing 28 by the spring property due to the material and the cross-sectional shape, and can ensure the sealing property. The gasket 31 is made of a heat-resistant alloy having excellent high temperature strength, for example, incoloy. Note that a holding material 32 may be provided between the outer periphery of the catalyst carrier 14 and the inner periphery of the casing 28 as necessary in terms of the strength of the catalyst carrier 14.

  In the intake / exhaust system 2 of the engine 1 having the above configuration, when the engine 1 is started, the exhaust gas discharged from the combustion chamber of the engine 1 flows from the exhaust manifold 4 to the exhaust gas flow path 6 as shown in FIG. It is introduced, passes through the exhaust turbines 9b, 10b or the bypass flow passages 17, 19 of the two-stage turbochargers 9, 10, and further passes through the catalyst carrier 14 of the exhaust purification device 15, and is then discharged to the atmosphere. The intake air passes through the compressor 10a of the low pressure supercharger 10 in the intake flow passage 5 and the compressor 9a or the bypass flow passage 13 of the high pressure supercharger 9, and further passes through the intercooler 8, the throttle valve 7, and the intake manifold 3. It is introduced into the combustion chamber of the engine 1.

  On the other hand, when the EGR valve 21 is opened, as shown in FIG. 2, a part of the exhaust gas discharged from the engine 1 is introduced from the exhaust manifold 4 to the EGR gas flow path upstream portion 20 a and the outer periphery of the exhaust purification device 15. After passing through the gas flow path 23, the gas is again returned to the intake manifold 3 of the engine 1 through the EGR cooler 22 and the EGR valve 21. At this time, the temperature of the exhaust gas downstream of the exhaust gas purification device 15 in the exhaust gas flow path 6 is detected by the temperature sensor 26, and the downstream of the exhaust gas purification device 15 of the exhaust gas flow path 6 detected by the temperature sensor 26. When the exhaust gas temperature exceeds the predetermined set value, the bypass valve 24 is closed by the controller 27. In this case, the catalyst carrier 14 of the exhaust purification device 15 is sufficiently heated by the exhaust gas flowing through the catalyst carrier outer peripheral gas flow path 23, and the catalyst carrier 14 is sufficiently regenerated.

  By the way, when the engine 1 is started, the temperature of the catalyst carrier 14 is decreased, and the exhaust gas temperature downstream of the exhaust gas purification device 15 in the exhaust gas flow path 6 detected by the temperature sensor 26 has a predetermined set value. If it falls below, the controller 27 opens the bypass valve 24. In this case, the exhaust gas introduced into the inlet side of the catalyst carrier 14 of the exhaust gas purification device 15 through the exhaust gas through which the catalyst carrier 14 of the exhaust gas purification device 15 flows through the catalyst carrier outer peripheral gas flow channel 23 and the bypass flow channel 25, The catalyst carrier 14 of the exhaust gas purification device 15 can be heated not only from the outer peripheral side but also from the center part, and the catalyst carrier 14 can be effectively regenerated by efficiently heating from the inside and outside. As a result, when the exhaust gas temperature downstream of the exhaust gas purification device 15 in the exhaust gas passage 6 exceeds the set value, the bypass valve 24 is closed, and the catalyst carrier 14 is only exhaust gas flowing through the catalyst carrier outer peripheral gas passage 23. Playback is performed by.

  Thus, according to the intake / exhaust system 2 of the engine 1, the catalyst carrier outer peripheral gas flow path 23 along the outer periphery of the catalyst carrier 14 is provided on the upstream side of the EGR gas cooler 22 of the EGR gas flow path 20. Since the exhaust gas is directly introduced into the catalyst carrier peripheral gas flow path 23 from the exhaust manifold 4 upstream of the exhaust turbines 9b and 10b of the exhaust system, the catalyst carrier 14 of the exhaust purification device 15 is provided. The temperature rise effect and heat insulation and heat retention characteristics in the outer peripheral portion can be enhanced, and the regeneration capability of the exhaust purification device 15 can be improved. In this case, the adiabatic heat retention characteristic is improved by forming a high-temperature exhaust gas layer on the outer periphery of the catalyst carrier 14 by the catalyst carrier outer periphery gas flow path 23.

  Further, a bypass passage 25 having a bypass valve 24 for connecting the front side of the exhaust gas inlet of the catalyst carrier 14 in the exhaust system and the upstream portion 20a of the catalyst carrier outer gas passage 23 of the EGR gas passage 20 is connected. Therefore, the catalyst carrier 14 can be heated not only from the outer peripheral side but also from the central part, and the catalyst carrier 14 can be effectively regenerated by being effectively heated from the inside and outside.

  Further, since a temperature sensor 26 for detecting the exhaust gas temperature and controlling the bypass valve 24 is provided behind the exhaust gas outlet side of the catalyst carrier 14 in the exhaust system, the temperature of the catalyst carrier 14 is managed. And the reproduction ability can be improved. Further, since the exhaust gas upstream of the EGR cooler 22 in the EGR gas flow path 20 is used for heat exchange for regeneration of the catalyst carrier 14, the exhaust gas temperature can be lowered before the EGR cooler 22, and the EGR cooler can be reduced. The capacity (size) of 22 can be reduced, and the structure can be simplified and the cost can be reduced.

  As mentioned above, although embodiment thru | or example of this invention has been explained in full detail with drawing, this invention is not limited to the said embodiment thru | or example, Various in the range which does not deviate from the summary of this invention. Design changes are possible. 7 to 9 are sectional views showing modifications of the exhaust purification device. In the present embodiment, the same parts as those in the above embodiment are denoted by the same reference numerals and description thereof is omitted. In the exhaust purification device 15 according to the present embodiment, a nozzle 33 that opens toward the exhaust gas inlet side end surface of the catalyst carrier 14 in the exhaust system is provided at the outlet 25a of the bypass passage 25. As shown in FIG. 8, the nozzle 33 opens to face the central portion (center portion) of the end surface on the exhaust gas inlet side of the catalyst carrier 14, and discharges hot exhaust gas when the central portion of the catalyst carrier 14 is cold. The catalyst carrier 14 may be configured to be sprayed to the center portion, or as shown in FIG. 9, the catalyst carrier 14 is opened so as to face an intermediate portion between the center portion of the exhaust gas inlet side end surface and the outer peripheral portion. The high temperature exhaust gas may be blown onto the intermediate portion of the catalyst carrier 14 when the intermediate portion of the catalyst carrier 14 is at a low temperature.

  Further, in the above embodiment, the upstream portion 20 a of the EGR gas flow path 20 is directly connected to the exhaust manifold 4, but the upstream portion 20 a of the EGR gas flow path 20 is supercharged on the high pressure stage side of the exhaust gas flow path 6. It may be connected upstream of the exhaust turbine 9 b of the machine 9.

1 is a diagram schematically showing an engine intake / exhaust system according to an embodiment of the present invention. It is a figure which shows the flow of EGR gas when a bypass valve is closed. It is a figure which shows the flow of EGR gas when a bypass valve is open. It is sectional drawing which shows the structure of an exhaust gas purification apparatus. It is the sectional view on the AA line of FIG. It is a principal part expanded sectional view of an exhaust gas purification apparatus. It is sectional drawing which shows the modification of an exhaust gas purification apparatus. It is sectional drawing which shows the modification of an exhaust gas purification apparatus. It is sectional drawing which shows the modification of an exhaust gas purification apparatus. It is sectional drawing which shows an example of the conventional exhaust gas purification apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 2 Intake / exhaust system 9,10 Supercharger 9b, 10b Exhaust turbine 14 Catalyst carrier 15 Exhaust purification device 20 EGR gas channel 20a EGR gas channel upstream part 23 Catalyst carrier outer periphery gas channel 24 Bypass valve 25 Bypass channel 26 Temperature sensor 33 Nozzle

Claims (3)

Drives an EGR gas passage that extracts a part of the exhaust gas from the exhaust system and returns it to the intake system of the engine again, an EGR gas cooler provided in the EGR gas passage, and a supercharger provided in the intake system to an exhaust turbine provided in the exhaust system, and an exhaust purification device having a catalyst support which is provided downstream of the exhaust turbine, upstream of EGR gas cooler of the EGR gas passage, the catalyst carrier An exhaust gas of the catalyst carrier in the exhaust system is provided so that an exhaust gas is provided directly from the upstream of the exhaust turbine of the exhaust system to the catalyst carrier outer gas channel. Engine intake / exhaust having a bypass flow path having a bypass valve for connecting the front side of the inlet side and the upstream portion of the EGR gas flow path from the catalyst carrier outer peripheral gas flow path Stem.   2. The intake / exhaust system for an engine according to claim 1, wherein a temperature sensor for detecting the exhaust gas temperature and controlling the bypass valve is provided behind the exhaust gas outlet side of the catalyst carrier in the exhaust system. .   The intake / exhaust system for an engine according to claim 1 or 2, wherein a nozzle that opens toward an exhaust gas inlet side end face of the catalyst carrier in the exhaust system is provided at an outlet portion of the bypass passage.

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