JP2010248943A - Exhaust gas temperature raising device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas temperature raising device quickly raising the temperature of exhaust gas flowing in an exhaust emission control catalyst and suppressing the consumption of fuel for raising temperature. <P>SOLUTION: The exhaust gas temperature raising device 1 supplies fuel and secondary air and raises the temperature of exhaust gas flowing in the exhaust emission control catalyst 2 through the reaction heat thereof. The exhaust gas temperature raising device 1 includes a decomposition catalyst 3 disposed in an exhaust gas passage 13 on an upstream of the exhaust emission control catalyst 2, decomposing fuel, and making the decomposed fuel react with the secondary air and oxidized, an exhaust fuel injection valve 4 for supplying fuel to the decomposition catalyst 3, a secondary air supply means 5 for supplying secondary air to the decomposition catalyst 3, an electric heater 6 for heating the decomposition catalyst 3, and a control means 7. The control means 7 starts supply of fuel by the exhaust fuel injection valve 4 and supply of secondary air by a secondary air supply means 5 after activating the decomposition catalyst 3 by heating the same by an electric heater 6 when the temperature of exhaust gas flowing in the exhaust emission control catalyst 2 is lower than a target temperature. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an exhaust gas temperature raising device for raising the temperature of exhaust gas flowing into an exhaust gas purification catalyst for purifying exhaust gas from an engine.

  In recent years, along with the tightening of exhaust gas regulations, it has become essential to raise the temperature of the exhaust gas purification catalyst provided in the exhaust passage early after the engine is started under the COLD conditions in the exhaust gas test mode.

  In order to raise the catalyst temperature, for example, it is conceivable to perform combustion control of the engine such as post-injection. However, in a diesel engine, raising the temperature by combustion control immediately after starting is a matter of improving the combustion stability of the engine. Strict from the aspect.

  Therefore, conventionally, a temperature rise by an external device such as a burner has been put into practical use (see, for example, Patent Document 1).

  Generally, the temperature rise by the burner is such that fuel is injected into the exhaust passage of the engine, the fuel and secondary air are mixed and ignited, and the exhaust heat flowing into the exhaust gas purification catalyst is warmed by the combustion heat. ing.

  There is also a system that combines exhaust fuel injection and ignites with a glow plug by mixing exhaust injection and secondary air.

JP 2008-291760 A

  However, both of those that ignite the fuel (air mixture) with the above-described burner or glow plug raise the temperature of all the engine-out exhaust gas, so that there is a lot of exhaust gas volume that must be raised, and the exhaust gas purification catalyst is activated. A large amount of fuel is required to warm the exhaust gas to a temperature (150 to 200 ° C.). In addition, the temperature rise by the glow plug is expected to have a small heat dissipation area and poor efficiency.

  Accordingly, an object of the present invention is to provide an exhaust gas temperature raising apparatus that can solve the above-mentioned problems, can quickly raise the temperature of exhaust gas flowing into the exhaust gas purification catalyst, and can suppress fuel consumed for temperature rise. It is to provide.

  In order to achieve the above object, according to the present invention, an exhaust gas purification catalyst is provided in an exhaust passage of an engine, and fuel and secondary air are supplied to and reacted with an exhaust passage upstream of the exhaust gas purification catalyst. In the exhaust gas temperature raising device that preheats the exhaust gas flowing into the exhaust gas purification catalyst, the exhaust gas is provided in an exhaust passage upstream of the exhaust gas purification catalyst, decomposes the fuel, and decomposes the decomposed fuel into the secondary A decomposition catalyst for oxidizing with air, an exhaust fuel injection valve for supplying fuel to the decomposition catalyst, a secondary air supply means for supplying secondary air to the decomposition catalyst, and the decomposition catalyst An electric heater for heating, a control means for controlling the exhaust fuel injection valve, the secondary air supply means, and the electric heater, and the control means is provided on the exhaust gas purification catalyst. When the temperature of the exhaust gas entering is lower than a predetermined target temperature, after the cracking catalyst is heated and activated by the electric heater, the fuel is supplied by the exhaust fuel injection valve and the secondary air supply means The supply of secondary air is started.

  Preferably, the cracking catalyst is accommodated in a cylindrical casing provided in the exhaust passage, and the casing has a downstream exhaust passage connected to one end and an upstream exhaust passage connected to the other end. And the upstream exhaust passage is inclined with respect to the casing so that the exhaust gas introduced from the upstream exhaust passage into the casing forms a swirl flow in the casing. .

  Preferably, the control means determines the supply amount of the secondary air by the secondary air supply means so that the excess air ratio of the mixture of the fuel and the secondary air becomes 1 or more. .

  Preferably, the exhaust fuel injection valve and the cracking catalyst are connected by an introduction path extending from the exhaust fuel injection valve to the cracking catalyst, and the secondary air supply means is connected to the introduction path and is connected to the inside of the introduction path. And a supply passage for introducing secondary air to the introduction passage so that the secondary air introduced from the supply passage to the introduction passage forms a swirl flow in the introduction passage. It is inclined with respect to it.

  According to the present invention, it is possible to quickly raise the temperature of the exhaust gas flowing into the exhaust gas purification catalyst and to exhibit an excellent effect that the fuel consumed for the temperature rise can be suppressed.

FIG. 1 is a schematic view of an exhaust gas temperature raising apparatus according to an embodiment of the present invention. FIG. 2 is a view in the direction of the arrow II in FIG. FIG. 3 is a schematic configuration diagram of the engine of the present embodiment.

  Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  The exhaust gas temperature raising apparatus of the present embodiment is applied to, for example, a diesel engine (hereinafter referred to as an engine) that is mounted on a vehicle and uses light oil as fuel.

  Based on FIG. 3, the schematic structure of the engine targeted by the present embodiment will be described.

  As shown in FIG. 3, the engine 10 includes an engine main body 11 in which a combustion chamber is formed, an intake passage 12 for supplying intake air to the engine main body 11, and an exhaust for discharging exhaust gas from the engine main body 11. A passage 13, a turbocharger 14 for pressurizing and compressing intake air to the engine body 11, an exhaust gas purification catalyst 2 for purifying exhaust gas from the engine body 11, and exhaust gas flowing into the exhaust gas purification catalyst 2 An exhaust gas temperature raising device 1 for raising the temperature is provided.

  The engine body 11 is provided with an injector (not shown) for injecting and supplying fuel (light oil fuel) to the combustion chamber, and fuel from the fuel system (fuel pump, common rail, etc.) of the engine 10 is supplied to the injector. .

  The turbocharger 14 includes a turbine 141 that is provided in the exhaust passage 13 and is rotated by exhaust gas (exhaust energy) from the engine body 11, and a compressor 142 that is provided in the intake passage 12 and is rotationally driven by the turbine 141.

  In the exhaust passage 13, a turbine 141, an exhaust gas temperature raising device 1, and an exhaust gas purification catalyst 2 are provided in order from the upstream side (engine body 11 side).

  The exhaust gas purification catalyst 2 is, for example, a NOx reduction catalyst that reduces and removes NOx in the exhaust gas, a three-way catalyst, an oxidation catalyst, or the like. The exhaust gas purification catalyst 2 has a predetermined light-off temperature at which the function as a catalyst is activated. The light-off temperature of the exhaust gas purification catalyst 2 of this embodiment is about 200 ° C.

  The exhaust gas temperature raising device 1 supplies fuel and secondary air to the exhaust passage 13 upstream of the exhaust gas purification catalyst 2 and causes the fuel and secondary air to react with each other. The temperature of the inflowing exhaust gas is raised in advance.

  In the exhaust gas temperature raising apparatus 1 of the present embodiment, a light oil decomposition catalyst 3 for performing exhaust injection is provided in an exhaust passage 13 upstream of the exhaust gas purification catalyst 2, and an electric heater 6 of a metal carrier is disposed in front of the light oil decomposition catalyst 3. Use only when cold. Exhaust injection refers to fuel injection into the exhaust passage 13, and secondary air refers to new air supplied to the exhaust passage 13.

  The exhaust gas temperature raising device 1 includes an exhaust gas temperature sensor 71 for detecting the temperature of exhaust gas flowing into the exhaust gas purification catalyst 2, and a casing 8 provided in the exhaust passage 13 between the turbine 141 and the exhaust gas purification catalyst 2. , A cracking catalyst (hereinafter referred to as a light oil cracking catalyst) 3 accommodated in the casing 8, an exhaust fuel injection valve 4 for supplying fuel (temperature raising agent) to the light oil cracking catalyst 3, and a light oil cracking catalyst 3 Secondary air supply means 5 for supplying secondary air to the fuel, an electric heater 6 for heating the light oil cracking catalyst 3, a catalyst temperature sensor 72 for detecting the temperature of the light oil cracking catalyst 3, and the exhaust An electronic control unit (hereinafter referred to as “ECU”) 7 serving as a control means for controlling the fuel injection valve 4, a later-described adjustment valve 52 of the secondary air supply means 5, and the electric heater 6 is provided.

  As shown in FIG. 1, the casing 8 is formed in a substantially cylindrical shape. More specifically, the casing 8 includes a large-diameter portion 81 that extends to the left and right, a tapered portion 82 that continuously extends rightward from the right end of the large-diameter portion 81 and is reduced in diameter toward the right. A small-diameter portion 83 continuously extending rightward from the right end of the tapered portion 82.

  An exhaust gas outflow pipe 131 forming the exhaust passage 13 on the downstream side (exhaust gas purification catalyst 2 side) is connected to one end portion (right end portion) of the casing 8. The exhaust gas outflow pipe 131 in the illustrated example is disposed concentrically with the casing 8 and joined to the right end of the small diameter portion 83.

  The other end portion of the casing 8 (the left end portion of the large-diameter portion 81) is connected to an exhaust gas inflow pipe 132 that forms the exhaust passage 13 on the upstream side (the turbine 141 side).

  The exhaust gas inflow pipe 132 is configured to decenter the exhaust gas from the inlet and place it in the casing 8 to have a swirl effect. More specifically, the exhaust gas inflow pipe 132 is radial and axial with respect to the outer peripheral surface of the casing 8 so that the exhaust gas introduced into the casing 8 from the exhaust gas inflow pipe 132 forms a swirl flow S1 in the casing 8. And is joined to the outer peripheral surface. As shown in FIG. 2, the exhaust gas inflow pipe 132 of the illustrated example has an inlet that is radially offset with respect to the center of the casing 8, and extends upward along the substantially tangential direction of the casing 8 from the inlet.

  By the swirl flow S1, the exhaust gas flows in the casing 8 around the central axis C of the casing 8 and flows to the downstream side (exhaust gas outlet pipe 131 side) to the right along the central axis C.

  The exhaust gas inflow pipe 132 is provided with the exhaust gas temperature sensor 71 (see FIG. 3), and the exhaust gas temperature sensor 71 detects the temperature of the exhaust gas flowing through the exhaust gas inflow pipe 132. The exhaust gas temperature sensor 71 is communicably connected to the ECU 7 and transmits a detection value (exhaust gas temperature) to the ECU 7.

  An end plate 84 is provided at the left end of the casing 8 (large diameter portion 81) so as to close the left end. The end plate 84 in the figure is formed in a disk shape having a larger diameter than the large diameter portion 81 and is joined to the left end of the large diameter portion 81. A through hole 92 that communicates the inside and outside of the casing 8 is formed at the center of the end plate 84.

  The light oil cracking catalyst 3 is disposed on the right side of the through hole 92 (inward of the casing 8), in close proximity to the through hole 92, and the exhaust fuel injection valve 4 and the secondary air are on the left side (outside of the casing 8). Supply means 5 are arranged.

  The light oil cracking catalyst 3 is for decomposing the fuel from the exhaust fuel injection valve 4 and oxidizing the decomposed fuel with the secondary air from the secondary air supply means 5. , CO, and H, a catalyst component for decomposing (reforming), and metal carriers 31 and 32 on which the catalyst component is supported.

  In this embodiment, the catalyst component of the light oil cracking catalyst 3 is a Pd-based catalyst component that has excellent light oil cracking characteristics. In addition, the material of the carriers 31 and 32 is a material having a small heat capacity (such as a thin film metal honeycomb), and is actively warmed by exhaust gas heat. Further, the light oil cracking catalyst 3 and the electric heater 6 are integrated, and the electric heater 6 assists in raising the temperature of the catalyst component at low temperatures. The catalyst component of the light oil cracking catalyst 3 has a predetermined light-off temperature, and in the illustrated example, is the same temperature (about 200 ° C.) as the light-off temperature of the exhaust gas purification catalyst 2.

  More specifically, the light oil cracking catalyst 3 is disposed on the left end side inside the large-diameter portion 81 slightly on the right side (downstream side) from the outlet of the exhaust gas inflow pipe 132 and aligned with the through hole 92. Arranged on the central axis C. The illustrated light oil cracking catalyst 3 is fixed to the end plate 84 via an inner introduction pipe 93 to be described later.

  The carrier of the light oil cracking catalyst 3 has a columnar base 31 (for example, a stainless steel base) that has a honeycomb cross section and extends to the left and right along the central axis C of the casing 8, and a cylindrical outer cylinder 32 that covers the outer periphery of the base 31. Have

  As will be described in detail later, a mixture of fuel and secondary air flows into the light oil cracking catalyst 3 from the left end. In this embodiment, the end of the light oil cracking catalyst 3 on the inflow side of the air fuel mixture Constitutes the electric heater 6.

  That is, in the portion extending from the left end of the light oil cracking catalyst 3 to a predetermined length (the portion on the left side of the two-dot chain line D in FIG. 1), the catalyst component is not supported on the base 31, and the portion on the right side of the non-supported portion. The catalyst component is supported only on the substrate 31. A pair of electrodes 61 for energization heating is attached to the outer cylinder 32 of the non-supporting portion. The electrodes 61 are connected to a power source (not shown) (battery battery or the like) and supplied with electric power, and are connected to the ECU 7 so as to be communicable. The ECU 7 controls energization on / off and the amount of electricity.

  In the electric heater 6, when electric power is supplied to the electrode 61 and the left end portion (non-carrying portion) of the outer cylinder 32 is resistance-heated, the heat at the left end portion is transmitted to the right outer cylinder 32 and the outer cylinder 32 and the base 31 are heated as a whole, and the catalyst component is heated.

  A catalyst temperature sensor 72 (see FIG. 3) is attached to the outer cylinder 32. The catalyst temperature sensor 72 is communicably connected to the ECU 7 and transmits a detection value (catalyst temperature) to the ECU 7.

  The exhaust fuel injection valve 4 is provided outside the casing 8 so as to be spaced leftward from the casing 8. The exhaust fuel injection valve 4 is directed on the central axis C of the casing 8 so that the fuel injection direction is directed toward the light oil cracking catalyst 3 (through hole 92 of the casing 8) and aligned with the light oil cracking catalyst 3 (through hole 92). Be placed. In the illustrated example, an outer introduction pipe 91 described later is provided between the exhaust fuel injection valve 4 and the through hole 92 of the end plate 84, and the exhaust fuel injection valve 4 is connected to the end plate via the outer introduction pipe 91. 84 is fixed. The exhaust fuel injection valve 4 is provided with a cooling jacket 41 for preventing thermal damage. The cooling jacket 41 has a cooling liquid path 411 formed so as to surround the exhaust fuel injection valve 4, and a cooling liquid such as cooling water flows through the cooling liquid path 411.

  The exhaust fuel injection valve 4 is connected to the fuel system of the engine 10 and supplied with fuel, similarly to the injector of the engine body 11. The exhaust fuel injection valve 4 is communicably connected to the ECU 7, and the injection amount and injection timing are controlled by the ECU 7.

  The exhaust fuel injection valve 4 and the light oil decomposition catalyst 3 are connected by an introduction path 9 extending from the exhaust fuel injection valve 4 to the light oil decomposition catalyst 3.

  The introduction path 9 extends rightward from the exhaust fuel injection valve 4 to the end plate 84 of the casing 8, communicates with the through hole 92 of the end plate 84, communicates with the through hole 92, and the through hole 92. The inner introduction pipe 93 extends rightward from the end plate 84 to the light oil cracking catalyst 3. The outer introduction pipe 91, the through hole 92, and the inner introduction pipe 93 are arranged side by side on the central axis C of the casing 8 concentrically with the casing 8.

  A passage extending along the central axis C of the casing 8 is formed in the outer introduction pipe 91 with a substantially circular cross section. The outer introduction pipe 91 is joined to the outer surface of the end plate 84 so that the exhaust fuel injection valve 4 is inserted at the left end and the right end surrounds the through hole 92.

  The inner introduction pipe 93 is formed in a funnel shape whose diameter is increased on the right side. The left end of the inner introduction pipe 93 surrounds the through hole 92 and a flange 811 is formed at the edge, and is joined (for example, bolted) to the inner surface of the end plate 84 by the flange 811. The inner introduction pipe 93 extends from the left end to the right while expanding in diameter to the right, and the right end is formed to have substantially the same diameter as the outer cylinder 32 of the light oil cracking catalyst 3 and is joined to the left end of the outer cylinder 32.

  The inlet of the left end of the light oil cracking catalyst 3 is covered with the inner introduction pipe 93 so that the exhaust gas in the casing 8 does not flow into the light oil cracking catalyst 3. Further, since the air-fuel mixture supplied to the light oil cracking catalyst 3 passes through the introduction passage 9, the air-fuel mixture does not mix with the exhaust gas in the casing 8.

  The secondary air supply means 5 agitates and injects the fuel injected from the exhaust fuel injection valve 4 with the secondary air. In this embodiment, the secondary air supply means 5 is discharged from the compressor 142 of the turbocharger 14 as secondary air. Supercharged air is used.

  As shown in FIG. 3, the secondary air supply means 5 is provided with a supply path 51 having an upstream end connected to the outlet of the compressor 142 and a downstream end connected to the introduction path 9, and a supply path 51 provided in the supply path 51. And an adjustment valve 52 for adjusting the flow rate of the secondary air flowing through the passage 51.

  As shown in FIG. 1, the supply path 51 in the illustrated example is branched into two branch pipes 511 on the downstream side, and these two branch pipes 511 are respectively connected to the outer introduction pipes 91 of the introduction path 9.

  The branch pipe 511 is configured so that secondary air (that is, pressurized air from the compressor 142) introduced from the branch pipe 511 to the outer introduction pipe 91 (passage) forms a swirl flow S2 in the outer introduction pipe 91. The outer introduction pipes 91 are respectively joined to the outer introduction pipes 91 while being inclined in the radial direction and the axial direction. As shown in FIG. 2, in the illustrated example, the branch pipes 511 are respectively connected to both sides of the outer introduction pipe 91 and extend vertically opposite to each other along the tangential direction of the outer introduction pipe 91.

  By this swirl flow S2, the secondary air flows in the axial direction toward the through hole 92 while turning around the central axis C in the introduction path 9.

  The adjustment valve 52 (see FIG. 3) is configured so that the valve opening degree can be continuously adjusted between fully closed and fully opened, and is, for example, a butterfly valve. The adjustment valve 52 is communicably connected to the ECU 7, and the opening degree is controlled by the ECU 7.

  The ECU 7 controls the electric heater 6, the exhaust fuel injection valve 4, and the adjustment valve 52 based on the detection values of the exhaust gas temperature sensor 71 and the catalyst temperature sensor 72.

  When the temperature of the exhaust gas detected by the exhaust gas temperature sensor 71 is lower than a predetermined target temperature, the ECU 7 of the present embodiment first heats and activates the light oil decomposition catalyst 3 with the electric heater 6, and the light oil decomposition catalyst 3. Then, the fuel supply by the exhaust fuel injection valve 4 and the secondary air supply by the secondary air supply means 5 are started. Here, as the target temperature, a temperature higher than the light-off temperature of the exhaust gas purification catalyst 2 (about 220 ° C. in the present embodiment) can be considered. The target temperature is appropriately set in consideration of the temperature drop during the period from the exhaust gas temperature sensor 71 to the exhaust gas purification catalyst 2.

  In addition, the ECU 7 supplies the secondary air supplied by the secondary air supply means 5 (opens the valve of the adjustment valve 52) so that the λ (excess air ratio) of the mixture of fuel and secondary air becomes equal to or greater than the target λ. Degree). The target λ is 1 or more, more preferably 1.1.

  Next, the operation of the exhaust gas temperature raising apparatus 1 of the present embodiment will be described based on FIGS. 1 and 2.

  As shown in FIG. 1, the exhaust gas discharged from the engine body 11 flows through the exhaust gas inflow pipe 132 into the casing 8 of the exhaust gas temperature raising device 1. The exhaust gas may be at a low temperature, for example, when the engine is started or during idling operation in a cold region. In such a case, the temperature of the exhaust gas is raised by the light oil cracking catalyst 3.

  Specifically, when the exhaust gas flowing into the casing 8 is at a low temperature, first, power is supplied to the electrode 61 of the electric heater 6 to electrically heat the light oil decomposition catalyst 3. Thereby, the temperature of the light oil cracking catalyst 3 rises and the catalyst component of the light oil cracking catalyst 3 is activated.

  Next, in order to supply fuel and secondary air to the activated light oil cracking catalyst 3, fuel is injected from the exhaust fuel injection valve 4, and the adjustment valve 52 of the secondary air supply means 5 is opened to introduce the introduction path. The secondary air is introduced into 9.

  The injected fuel and the introduced secondary air are mixed in the introduction path 9 and flow into the light oil cracking catalyst 3 through the introduction path 9. The fuel that has flowed into the light oil cracking catalyst 3 is decomposed on the upstream side of the light oil cracking catalyst 3 to become light HC and the like, and these light HC and the like undergo oxidation reaction with the secondary air that has flowed into the light oil cracking catalyst 3. The gas oil decomposition catalyst 3 is heated by the oxidation heat of the oxidation reaction, and the heated gas oil decomposition catalyst 3 exchanges heat with the exhaust gas in the casing 8 to raise the temperature of the exhaust gas.

Further, in the light oil cracking catalyst 3, a high temperature gas (CO ₂ , H ₂ O, etc.) is generated by an oxidation reaction, and the high temperature gas flows out of the light oil cracking catalyst 3 and is mixed with the exhaust gas in the casing 8. The temperature of the exhaust gas is also raised by mixing with the high temperature gas.

  The heated exhaust gas flows out from the exhaust gas outflow pipe 131 and then flows into the exhaust gas purification catalyst 2. The exhaust gas purification catalyst 2 is heated and activated by the heated exhaust gas, and the exhaust gas purification catalyst 2 purifies the exhaust gas (NOx removal, etc.).

  As described above, according to the present embodiment, the direct heating of the light oil cracking catalyst 3 by the electric heater 6 and the exhaust fuel injection are performed immediately after the engine is started, so that the exhaust gas purification catalyst 2 can be activated quickly. it can. At the same time, compared with the method of directly warming the exhaust gas such as a burner, electricity for heating the light oil cracking catalyst 3 is supplied, so that deterioration of fuel consumption can be minimized.

  Here, the light oil cracking catalyst 3 is formed in a smaller capacity than the exhaust gas purification catalyst 2. Preferably, the capacity of the light oil cracking catalyst 3 is 100 cc or more and less than 300 cc. This is because if the capacity is less than 100 cc, the amount of heat per unit time generated from the light oil cracking catalyst 3 is small and it takes time to raise the exhaust gas. If it exceeds 300 cc, the light oil cracking catalyst 3 is activated. This is because the amount of electricity necessary for the increase is increased. In addition, the capacity | capacitance of the light oil cracking catalyst 3 is not limited to this, It sets suitably by the volume (flow rate in idling operation) of exhaust gas which should be heated up, target temperature, etc.

  In the present embodiment, the exhaust gas from the exhaust gas inflow pipe 132 is converted into the swirl flow S1 in the casing 8, so that the exhaust gas can be efficiently heated.

  That is, the direction of the inlet of the exhaust gas inflow pipe 132 is shifted from the center of the casing 8, and the exhaust gas from the exhaust gas inflow pipe 132 becomes a swirl flow S <b> 1 in the casing 8.

The swirl flow S1 causes the exhaust gas to flow in the axial direction while spirally swirling around the surface of the outer cylinder 32 of the light oil cracking catalyst 3 in the circumferential direction. Therefore, the contact time and the contact area between the exhaust gas and the outer cylinder 32 become larger than when the exhaust gas does not turn around the outer cylinder 32, and the amount of heat transferred from the outer cylinder 32 to the exhaust gas increases. Further, since the swirl flow S1 is formed, the swirl flow S1 stirs the exhaust gas and the high-temperature gas (CO ₂ , H ₂ O, etc.) from the light oil cracking catalyst 3, and promotes mixing of these gases. .

  In addition, by making the secondary air flowing into the introduction path 9 into the swirl flow S2, the fuel injected into the outer introduction pipe 91 from the exhaust fuel injection valve 4 is mixed with the secondary air from the branch pipe 511. In doing so, mixing of the fuel and secondary air can be facilitated.

  Further, the swirl flow S2 is formed in the upstream introduction path 9 (outer introduction pipe 91), and the downstream end (downstream end of the inner introduction pipe 93) is expanded to the same diameter as the outer cylinder 32 of the light oil cracking catalyst 3. Thus, the air-fuel mixture can flow into the entire surface of the light oil cracking catalyst 3.

  That is, the air-fuel mixture in the outer introduction pipe 91 flows through the through-hole 92 and the inner introduction pipe 93 of the end plate 84 to the light oil cracking catalyst 3 in sequence, but when the swirl flow is not formed, the air-fuel mixture penetrates. The light oil cracking catalyst 3 is directed from the hole 92 in a substantially straight line. In that case, the air-fuel mixture may be supplied to the central portion of the light oil cracking catalyst 3 only within the same range as the diameter of the through hole 92.

  On the other hand, in this embodiment, since the air-fuel mixture is the swirl flow S2, when the air-fuel mixture passes through the inner introduction pipe 93, the air-fuel mixture circulates along the tapered inner wall surface of the inner introduction pipe 93. Swirling in the direction, spread in the radial direction and diffused. Therefore, the air-fuel mixture is supplied to the entire surface of the light oil cracking catalyst 3 in a substantially uniform state, whereby the entire light oil cracking catalyst 3 can be used effectively.

  Next, an example of the exhaust gas temperature raising control by the exhaust gas temperature raising device 1 of the present embodiment will be described. The following steps 1 to 4 are executed by the ECU 7 during operation of the engine 10.

  1. Determine if the exhaust gas temperature needs to be measured by measuring the exhaust gas temperature.

  In step 1, the ECU 7 determines whether or not the temperature of the exhaust gas detected by the exhaust gas temperature sensor 71 (hereinafter referred to as detected exhaust gas temperature) is equal to or lower than a target temperature (such as 220 ° C., the exhaust injection decomposition temperature by the exhaust gas purification catalyst 2). Judgment is made, and the process proceeds to Step 2 when:

  2. When the temperature is lower than the target temperature, heating by the electric heater 6 is started.

  In step 2, it is determined whether or not the light oil cracking catalyst 3 is activated, and is activated by the electric heater 6 when it is not activated. Specifically, in step 2, the ECU 7 determines whether or not the temperature of the light oil cracking catalyst 3 detected by the catalyst temperature sensor 72 (hereinafter referred to as a detected catalyst temperature) is equal to or lower than a predetermined cracking catalyst target temperature. Sometimes, the electrode 61 of the electric heater 6 is energized and the process proceeds to step 3, and when it exceeds, the process proceeds to step 3 without energizing.

  Here, the cracking catalyst target temperature in step 2 is a temperature higher than the light-off temperature of the light oil cracking catalyst 3, and is set to the same temperature (about 220 ° C.) as the target temperature in step 1 in this embodiment.

  3. When the light oil cracking catalyst 3 reaches the target temperature, exhaust injection starts. Since the catalyst component is activated, electricity is not needed, so electricity supply is stopped.

  In step 3, the ECU 7 determines whether or not the detected catalyst temperature of the catalyst temperature sensor 72 is equal to or lower than the target temperature, and returns to step 2 in the following case. On the other hand, when the detected catalyst temperature exceeds the target temperature, the ECU 7 ends energization of the electric heater 6, controls the exhaust fuel injection valve 4 to inject fuel, and adjusts the valve 52 of the secondary air supply means 5. Open the valve.

  In the present embodiment, the injection amount of the exhaust fuel injection valve 4 is obtained based on the difference between the detected exhaust gas temperature of the exhaust gas temperature sensor 71 and the target temperature, the exhaust gas flow rate, and the like. Specifically, the ECU 7 calculates the required heat amount from the exhaust gas temperature and the target temperature, determines an injection amount that can obtain the required heat amount, and sets the injection amount as the target injection amount of the exhaust fuel injection valve 4.

  Further, the opening degree of the adjustment valve 52 is determined so that the fuel injected from the exhaust fuel injection valve 4 is basically oxidized by the light oil decomposition catalyst 3.

  The ECU 7 calculates and determines the supply amount of the secondary air from the target injection amount of the exhaust fuel injection valve 4 and the above target λ (minimum λ = 1.1, in which the oxygen is insufficient in the example shown below). Inject the required amount. Secondary air is obtained from the compressor 142 outlet of the turbocharger 14 and is supplied only during exhaust injection.

  4). When the exhaust gas temperature of the main catalyst reaches the target temperature (such as 220 ° C), supply of fuel and secondary air is stopped.

  In step 4, the ECU 7 determines whether or not the exhaust gas temperature detected by the exhaust gas temperature sensor 71 is equal to or lower than the target temperature, and returns to step 3 in the following case. On the other hand, when the detected exhaust gas temperature exceeds the target temperature, the ECU 7 ends the fuel injection by the exhaust fuel injection valve 4 and closes the adjustment valve 52.

  As described above, according to the present embodiment, the temperature of the exhaust gas flowing into the exhaust gas purification catalyst 2 can be quickly raised, and the fuel consumed for the temperature rise can be suppressed.

  As a result, the exhaust gas purification catalyst 2 can be made to function even when the engine is started, and the exhaust gas treatment performance can be improved when the engine is started.

  Moreover, since the light oil cracking catalyst 3 itself is heated by using the electric heater 6 and the light oil cracking catalyst 3 as an integral metal carrier, the responsiveness is good. Since it is sufficient to energize only the small light oil cracking catalyst 3 itself, power consumption can be reduced. Since the light oil cracking catalyst 3 is heated by an oxidation reaction, it is not necessary to heat it by the electric heater 6 after the light is turned off.

  Since the light oil cracking catalyst 3 has a large heat radiation surface, it is possible to raise the temperature of exhaust gas efficiently, and the heat radiation area is large and efficient compared to the glow plug.

  Since only the mixture of the exhaust injection and the secondary air needs to be heated, the exhaust gas volume is small and the influence on the fuel consumption is suppressed as much as possible.

  In general, exhaust injection cannot decompose light oil at a low temperature compared to POST (post injection), and heavy HC tends to slip (outflow). In this embodiment, light oil is converted into light HC by the light oil decomposition catalyst 3. It can be used from a low temperature by decomposing it into CO, H and making it easy to use as a catalyst. As a result, it is possible to suppress the slip of HC and raise the temperature of exhaust gas by using exhaust injection immediately after the engine is started.

  In addition, this invention is not limited to the above-mentioned embodiment, Various modifications and application examples can be considered.

  For example, the fuel supplied to the cracking catalyst is not limited to light oil, and various fuels can be used. In the above-described embodiment, the same type of fuel as that injected from the injector is injected from the exhaust fuel injection valve. However, a different type of fuel may be injected. In that case, it is preferable that the cracking catalyst can decompose (reform) the fuel supplied from the exhaust fuel injection valve.

  In the above-described embodiment, the light oil cracking catalyst 3 and the electric heater 6 are integrated, but the present invention is not limited to this. For example, it is possible to provide a separate electric heater upstream (eg, at the inlet) of the light oil cracking catalyst 3.

  In the above-described embodiment, the exhaust gas temperature sensor 71 is provided in the exhaust passage 13 upstream of the casing 8, but the present invention is not limited to this, and the exhaust passage 13 between the casing 8 and the exhaust gas purification catalyst 2 and the exhaust gas purification catalyst 2. It may be provided at the entrance. Further, the temperature of the exhaust gas flowing into the exhaust gas purification catalyst 2 may be estimated from, for example, a detected value (outside temperature) of an outside temperature sensor or the like. In that case, a predetermined outside air temperature corresponding to the predetermined target temperature is obtained in advance, and the ECU 7 performs energization heating by the electric heater 6 when the detected value of the outside air temperature sensor is lower than the predetermined outside air temperature when starting the engine. After performing, it is conceivable to perform fuel injection by the exhaust fuel injection valve 4 and supply of secondary air by the secondary air supply means 5 for a predetermined time (for example, a period from engine start to warm-up end). .

  The shape of the casing 8 is not limited to a cylinder, and various shapes such as a square tube (cylinder having a rectangular cross section) are conceivable.

  The adjustment valve 52 of the secondary air supply means 5 is not limited to the above. The adjustment valve 52 may be a valve (for example, a solenoid valve) that is configured to be switched between full open and fully closed and that is controlled to open and close by the ECU 7. In that case, it is preferable to form the supply path 51 of the secondary air supply means 5 so that λ of the air-fuel mixture becomes equal to or greater than the target λ when the adjustment valve is fully opened.

  The secondary air supplied to the light oil cracking catalyst 3 is not limited to the pressurized air from the compressor 142 of the turbocharger 14. For example, in an engine without a turbocharger, it may be possible to supply pressurized air from an air tank or the like to the light oil cracking catalyst 3.

  In the above-described embodiment, the electric heater 6 is switched on and off based on the temperature detected by the catalyst temperature sensor 72, but the present invention is not limited to this. For example, on / off of the electric heater 6 may be controlled based on time. In this case, the ECU 7 starts energization of the electric heater 6 when the temperature of the exhaust gas flowing into the exhaust gas purification catalyst 2 is lower than a predetermined target temperature, and after a certain period of time after the start of energization (the light oil decomposition catalyst 3 is activated). Energization may be terminated after the elapse of time).

DESCRIPTION OF SYMBOLS 1 Exhaust gas temperature rising device 2 Exhaust gas purification catalyst 3 Light oil decomposition catalyst (decomposition catalyst)
4 Exhaust fuel injection valve 5 Secondary air supply means 6 Electric heater 7 ECU (control means)
8 Casing 9 Introduction path 13 Exhaust path

Claims (4)

An exhaust gas purification catalyst is provided in the exhaust passage of the engine, fuel and secondary air are supplied to the exhaust passage upstream of the exhaust gas purification catalyst and reacted, and the exhaust gas flowing into the exhaust gas purification catalyst by the reaction heat is preliminarily In the exhaust gas temperature raising device for raising the temperature,
A decomposition catalyst provided in an exhaust passage upstream of the exhaust gas purification catalyst, for decomposing the fuel, and for causing the decomposed fuel to undergo an oxidation reaction with the secondary air;
An exhaust fuel injection valve for supplying fuel to the cracking catalyst;
Secondary air supply means for supplying secondary air to the cracking catalyst;
An electric heater for heating the cracking catalyst;
A control means for controlling the exhaust fuel injection valve, the secondary air supply means, and the electric heater;
When the temperature of the exhaust gas flowing into the exhaust gas purification catalyst is lower than a predetermined target temperature, the control means heats the decomposition catalyst with the electric heater and activates it, and then the fuel by the exhaust fuel injection valve And the secondary air supply by the secondary air supply means are started.   The cracking catalyst is accommodated in a cylindrical casing provided in the exhaust passage, and the casing has a downstream exhaust passage connected to one end and an upstream exhaust passage connected to the other end. 2. The exhaust gas according to claim 1, wherein the upstream exhaust passage is inclined with respect to the casing so that the exhaust gas introduced into the casing from the upstream exhaust passage forms a swirl flow in the casing. Temperature rising device.   The said control means determines the supply amount of the secondary air by the said secondary air supply means so that the excess air ratio of the mixture of the said fuel and the said secondary air may become 1 or more. Exhaust gas temperature riser. The exhaust fuel injection valve and the cracking catalyst are connected by an introduction path extending from the exhaust fuel injection valve to the cracking catalyst,
The secondary air supply means has a supply path that is connected to the introduction path and introduces secondary air into the introduction path, and the supply path is secondary air introduced from the supply path into the introduction path. The exhaust gas temperature raising device according to any one of claims 1 to 3, wherein the exhaust gas temperature raising device is inclined with respect to the introduction path so as to form a swirl flow in the introduction path.

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