JP2011032932A - Internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably provide a desired exhaust gas air-fuel ratio regardless of a change in the operating condition of an internal combustion engine. <P>SOLUTION: This internal combustion engine 1 includes: a fuel injection valve 21 provided in an exhaust passage 12; an exhaust gas cleaning element 19 arranged downstream of the fuel injection valve; a bypass passage 40 branched upstream of the fuel injection valve 21 and merged downstream of the exhaust gas cleaning element 19; and an operating valve 24 changing the opening ratio between a main passage 12M leading from a branch to a confluent portion and the bypass passage 40. Since an exhaust gas flow rate in the main passage can be changed, even if the operating condition of the engine is changed, the desired exhaust gas flow rate in the main passage is easily provided. When regenerating the exhaust gas purifying element 19, the desired exhaust gas air-fuel ratio is stably provided. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an internal combustion engine, and more particularly, to an internal combustion engine provided with a fuel injection valve provided in an exhaust passage.

  For example, an exhaust purification element such as an NOx storage reduction catalyst is provided in an exhaust passage of an internal combustion engine such as a diesel engine. In order to periodically regenerate the exhaust purification element, fuel is injected and supplied into the exhaust passage from a fuel injection valve provided in the exhaust passage (see, for example, Patent Document 1).

JP 2008-112455 A

  However, the flow rate and oxygen concentration of the exhaust gas flowing in the exhaust passage vary depending on the operating state of the internal combustion engine. Therefore, it may be difficult to control the exhaust gas air-fuel ratio to a desired rich air-fuel ratio suitable for regeneration by injecting fuel from the fuel injection valve. For example, when the load on the internal combustion engine increases during vehicle acceleration or the like, the intake air amount increases, and the flow rate and oxygen concentration of the exhaust gas increase. Therefore, it is necessary to increase the fuel injection amount accordingly. However, when the exhaust gas flow rate and the oxygen concentration are remarkably increased, desired enrichment may be difficult, and fuel consumption may be deteriorated by injecting a large amount of fuel.

  Accordingly, the present invention has been made in view of such circumstances, and an object thereof is to provide an internal combustion engine that can stably obtain a desired exhaust air-fuel ratio regardless of changes in the operating state of the internal combustion engine. There is.

According to one aspect of the invention,
A fuel injection valve provided in the exhaust passage;
An exhaust purification element provided in the exhaust passage downstream of the fuel injection valve;
A bypass passage branched from the exhaust passage upstream of the fuel injection valve and joined to the exhaust passage downstream of the exhaust purification element;
An on-off valve for changing an opening ratio between the main passage, which is the exhaust passage between the branch portion and the junction portion, and the bypass passage;
An internal combustion engine is provided.

  According to this, the flow rate ratio of each exhaust gas flowing through the main passage and the bypass passage can be changed by the opening / closing valve, and the flow rate of the exhaust gas flowing through the main passage can be changed. Therefore, even when the operating state of the engine changes, a desired exhaust gas flow rate in the main passage can be easily obtained, and a desired exhaust air-fuel ratio can be stably obtained.

  Preferably, the internal combustion engine has at least a first position in which the on-off valve is at least fully opened and the bypass passage is fully closed, and a second position in which both the main passage and the bypass passage are partially opened. It further has valve control means for controlling any of the above.

  In this case, if the on-off valve is in the second position, the exhaust gas flow rate in the main passage can be reduced as compared with the case where the on-off valve is in the first position.

  Preferably, the valve control means controls the on-off valve to either the first position or the second position according to a load state of the internal combustion engine when fuel is injected from the fuel injection valve.

  Thereby, the exhaust gas flow rate in the main passage can be controlled to a desired flow rate regardless of the change in the load state of the internal combustion engine.

  Preferably, the valve control means controls the open / close valve to the second position when fuel is injected from the fuel injection valve during high load operation of the internal combustion engine.

  According to this, the exhaust gas flow rate in the main passage can be reduced during high load operation of the internal combustion engine, and a desired rich air-fuel ratio can be easily realized.

  Preferably, the internal combustion engine further includes an air nozzle for injecting air to a nozzle part of the fuel injection valve exposed in the main passage, and the valve control means is configured to inject the main nozzle when injecting air from the air nozzle. The on-off valve is controlled to a third position where the passage is fully closed and the bypass passage is fully open.

  Thereby, the deposit production | generation in a nozzle part can be prevented beforehand.

  Preferably, the exhaust purification element includes an NOx storage reduction catalyst.

  Preferably, the internal combustion engine further includes another exhaust purification element provided in the exhaust passage on the downstream side of the merging portion.

  The present invention exhibits an excellent effect that a desired exhaust air-fuel ratio can be stably obtained regardless of changes in the operating state of the internal combustion engine.

1 is a schematic view showing an internal combustion engine according to an embodiment of the present invention. It is the schematic which shows the principal part of an internal combustion engine. It is the schematic which shows the on-off valve in a 1st position. It is the schematic which shows the on-off valve in a 2nd position. It is the schematic which shows the on-off valve in a 3rd position. It is a flowchart which shows an example of control of this embodiment. The map for determining the fuel injection quantity of a main injector is shown. The map for determining a target torque is shown.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 shows an internal combustion engine (engine) according to an embodiment of the present invention. The engine 1 of this embodiment is an automobile and multi-cylinder compression ignition internal combustion engine, that is, a diesel engine. The engine 1 includes a common rail fuel injection device. That is, the fuel stored in the fuel tank 2 is sent to the high-pressure pump 5 by the feed pump 3 and the supply pump 4, and the high-pressure pump 5 pressurizes the sent fuel to a high pressure and pumps it to the common rail 6. The supply pump 4 and the high-pressure pump 5 are driven by a crankshaft 8 of the engine 1 via a power transmission member 7 such as a belt.

  The high-pressure fuel stored in the common rail 6 is directly injected and supplied from the main injector 9 into the combustion chamber 10 when the main injector 9 as the main fuel injection valve is opened.

  The fuel tank communicates with the additive tank via an additive supply pipe having an additive pump. The additive pump is controlled by a controller (not shown) and configured to supply an appropriate amount of fuel additive to the fuel tank in accordance with the amount of fuel. The exhaust gas discharged from the combustion chamber 10 passes through the turbine 11t of the turbocharger 11, then flows through the exhaust passage 12 on the downstream side thereof, is purified as described later, and is discharged to the atmosphere. The engine 1 also includes an EGR device 13. The EGR device includes an EGR passage 15 for recirculating exhaust gas in the exhaust passage 12 (particularly in the exhaust manifold on the upstream side of the turbine) to the intake passage 14, an EGR cooler 16 that cools the EGR gas flowing through the EGR passage 15, And an EGR valve 17 for adjusting the flow rate of the EGR gas. An electronically controlled intake throttle valve 49 is provided in the intake passage 14.

  The exhaust passage 12 includes an oxidation catalyst 18 that oxidizes and purifies unburned components (hydrocarbon HC and carbon monoxide CO) in the exhaust gas, and an NOx storage reduction catalyst that purifies nitrogen oxide NOx in the exhaust gas. 19 and a particulate filter (hereinafter referred to as DPF) 20 that collects and incinerates particulate matter (fine particles PM) in exhaust gas are provided in series in order from the upstream side. The oxidation catalyst 18, the NOx catalyst 19 and the DPF 20 form first, second and third exhaust purification elements, respectively.

  The exhaust passage 12 is provided with a fuel injection valve 21 that injects fuel into the exhaust passage 12 in order to mainly regenerate the NOx catalyst 19 and the DPF 20. Hereinafter, the fuel injection valve 21 is referred to as an exhaust injector. The exhaust injector 21 is disposed in the exhaust passage 12 upstream of the oxidation catalyst 18 and downstream of the turbine 11t. A front end portion of the exhaust injector 21 is formed with a spout portion 21A (see FIG. 2) having one or a plurality of spouts (not shown) serving as a fuel outlet, and this spout portion 21A is disposed in the exhaust passage 12. And is exposed in the exhaust passage 12. Fuel is supplied to the exhaust injector 21 from the supply pump 4 through the fuel pipe 22.

  The engine 1 is provided with an electronic control unit (hereinafter referred to as ECU) 50 as a control means. The ECU 50 includes a CPU, a ROM, a RAM, an input / output port, a storage device, and the like (not shown). The main injector 9, the high pressure pump 5, the EGR valve 17, the intake throttle valve 49 and the exhaust injector 21 are controlled by the ECU 50. The ECU 50 receives detection signals for the accelerator opening, the engine rotation speed, and the intake air amount from an accelerator opening sensor, an engine rotation speed sensor, and an air amount sensor (not shown).

  In particular, in the present embodiment, a bypass passage 40 is provided. The bypass passage 40 branches from the exhaust passage 12 on the upstream side of the exhaust injector 21 and joins the exhaust passage 12 on the downstream side of the NOx catalyst 19 and the upstream side of the DPF 20. Hereinafter, the exhaust passage 12 from the branch portion C to the junction portion D is referred to as a main passage 12M. An opening / closing valve 24 for changing the opening ratio between the main passage 12M and the bypass passage 40 is provided.

  As shown in detail in FIG. 2, a bent pipe portion 12A as a bent portion is formed in the middle of the exhaust passage 12 due to the convenience of in-vehicle layout, etc., and the exhaust injector 21 and the open / close are opened in the bent pipe portion 12A. A valve 24 is provided. The on-off valve 24 is disposed in the curved pipe portion 12A. In the present embodiment, the bending angle of the curved pipe portion 12A is about 90 °, but this bending angle can be arbitrarily set. The inlet part of the bypass passage 40 is connected to the inlet part and the in-corner side of the curved pipe part 12A.

  A straight pipe portion 12B is connected to the downstream side of the curved pipe portion 12A as a straight portion, and an oxidation catalyst 18, a NOx catalyst 19 and a DPF 20 are provided in the straight pipe portion 12B. The space between the NOx catalyst 19 and the DPF 20 is widened, and the outlet of the bypass passage 40 is connected thereto. The exhaust injector 21 is attached to the outer corner portion of the curved pipe portion 12A substantially parallel to the central axis of the straight pipe portion 12B, and is arranged so that the nozzle portion 21A at the tip of the exhaust injector 21 faces the oxidation catalyst 18. The fuel injected from the injection port of the exhaust injector 21 can reach the oxidation catalyst 18 without hitting the inner wall of the exhaust passage 12 as much as possible.

  The on-off valve 24 has a rotating shaft 25 and is of a butterfly type that is rotationally driven by an actuator 26 such as a servo motor. The rotary shaft 25 is disposed on the in-corner side of the curved pipe portion 12A immediately after the bypass passage is branched, and the on-off valve 24 is rotatable around this position. The on-off valve 24 can alternately open and close the inlet portion of the main passage 12M and the inlet portion of the bypass passage 40. The actuator 26 is connected to the ECU 50, and the angular position of the on-off valve 24 is controlled by the ECU 50 and the actuator 26.

  The on-off valve 24 is operated by the ECU 50 at least in the first position as shown in FIG. 3 where the main passage 12M is fully opened and the bypass passage 40 is fully closed, and in FIG. 4 where both the main passage 12M and the bypass passage 40 are partially opened. It is controlled to one of the second positions as shown. In this embodiment, the on-off valve 24 is also controlled by the ECU 50 to the third position as shown in FIG. 5 where the main passage 12M is fully closed and the bypass passage 40 is fully opened.

  As shown in FIGS. 3 to 5, when the reference position is an angular position passing through the center of the rotation shaft 25 and parallel to the axial direction of the straight pipe portion 12B, the first position is defined by the angle θ1, and the second position The position is defined by the angle θ2, and the third position is defined by the angle θ3. However, θ1> θ2> θ3. When the opening degree of the main passage 12M is A and the opening degree B of the bypass passage 40 (where 0 ≦ A, B ≦ 100), the opening ratio A: B is obtained when the on-off valve 24 is at the first position θ1. When the opening / closing valve 24 is in the third position θ3, 0: 100, and when the opening / closing valve 24 is in the second position θ2, for example, 20:80 is set. The opening ratio when the on-off valve 24 is in the second position θ2 can be arbitrarily set. In accordance with these opening ratios, the flow rate ratio between the exhaust gas flow rate in the main passage 12M and the exhaust gas flow rate in the bypass passage 40 is changed in substantially the same manner.

  The actuator 26 is provided with an angle sensor such as a rotary encoder, a magnetic sensor, or an optical sensor in order to detect the angular position of the on-off valve 24 and perform feedback control of the angular position.

  In addition, the curved pipe portion 12A is provided with an air nozzle 28 for injecting air for cleaning and cooling (air) into the nozzle portion 21A at the tip of the exhaust injector 21 exposed in the main passage 12M. The air nozzle 28 has an air outlet at the tip thereof directed to the nozzle part 21 </ b> A of the exhaust injector 21, preferably to the nozzle hole. The air nozzle 28 is disposed at a position immediately after the nozzle part 21 </ b> A, and is disposed obliquely with respect to the axial direction of the exhaust injector 21. The air nozzle 28 is supplied with pressurized air from an air tank 30 serving as a pressurized air supply source via an air pipe 29. The air nozzle 28 is controlled by the ECU 50.

  As shown in FIG. 2, the exhaust injector 21 is provided with a temperature sensor 31 for detecting the temperature of the nozzle part 21A. The ECU 50 controls the air nozzle 28 based on the nozzle part temperature detected by the temperature sensor 31, as will be described in detail later.

  As shown in FIG. 1, an auxiliary valve 41 is provided in the main passage 12 </ b> M downstream of the NOx catalyst 19 and upstream of the joining position of the bypass passage 40. Like the on-off valve 24, the auxiliary valve 41 is a butterfly type driven by an actuator 42, and its angular position is controlled by the ECU 50 and the actuator 26. The auxiliary valve 41 can change the opening degree of the main passage 12M from the fully open position to the fully closed position at the installation position.

  A first exhaust temperature sensor 23 is provided in the exhaust passage 12 upstream from the branch position of the bypass passage 40. A second exhaust temperature sensor 43 is provided in the exhaust passage 12 downstream from the joining position of the bypass passage 40 and upstream of the DPF 20. An exhaust gas temperature detection signal from these sensors is input to the ECU 50.

  Now, with respect to each exhaust purification element, the oxidation catalyst 18 has a large number of noble metals such as platinum dispersed in the coating material on the surface of the base material, and oxidizes and purifies HC and CO in the exhaust. However, in the case of a diesel engine, the air-fuel ratio A / F of the exhaust gas is significantly leaner than the stoichiometric air-fuel ratio (for example, 14.6), and the excess air ratio λ is greater than 1. Therefore, the amount of HC and CO contained in the exhaust is relatively small. In the case of a diesel engine, the exhaust temperature is relatively low, and the main NOx catalyst 19 and DPF 20 catalyst are difficult to activate. Therefore, the exhaust gas is heated by the oxidation heat of HC and CO in the oxidation catalyst 18, and the NOx catalyst 19 and the DPF 20 are heated by the heated exhaust gas to promote their activation.

Next, the NOx storage reduction catalyst (LNT: Lean NOx Trap) 19 is configured by supporting a noble metal such as platinum Pt and a NOx absorbing component on the surface of a base material made of an oxide such as alumina Al ₂ O _3. ing. The NOx absorption component is composed of at least one selected from alkali metals such as potassium K, sodium Na, lithium Li, and cesium Cs, alkaline earths such as barium Ba and calcium Ca, and rare earths such as lanthanum La and yttrium Y. .

The NOx catalyst 19 has a NOx absorption / release action. That is, when the air-fuel ratio of the exhaust gas supplied to the catalyst is leaner than the stoichiometric air-fuel ratio (when the catalyst is in an oxygen-excess atmosphere and the excess air ratio λ is greater than 1), the catalyst converts NOx in the exhaust gas to the nitrate content. Occlude in shape. On the other hand, when the air-fuel ratio of the exhaust gas supplied to the catalyst is the stoichiometric air-fuel ratio or richer (when the catalyst is in an oxygen-deficient atmosphere and the excess air ratio λ is 1 or less), the catalyst releases the stored NOx. . The released NOx reacts with the reducing agent (mainly HC) contained in the atmospheric gas in the catalyst and is reduced to N ₂ . This prevents NOx from being discharged into the atmosphere.

  When the NOx catalyst 19 occludes NOx until it is saturated (full), it cannot occlude NOx. Therefore, in order to recover or maintain the NOx storage capacity of the NOx catalyst 19, NOx regeneration for releasing the stored NOx from the NOx catalyst is periodically executed. At this time, rich spike is executed by injecting fuel from the exhaust injector 21 to enrich the air-fuel ratio of the exhaust gas (that is, making the air-fuel ratio of the exhaust gas smaller than the stoichiometric air-fuel ratio).

On the other hand, due to the sulfur (S) content contained in the fuel, the NOx catalyst 19 may occlude the sulfur component in the exhaust gas as a sulfate such as BaSO ₄ and poison (S poison). . When S poisoning occurs, the NOx occlusion ability decreases. Therefore, S poisoning regeneration or S purge for desorbing sulfate from the NOx catalyst is performed. Also at this time, fuel is injected from the exhaust injector 21 to enrich the air-fuel ratio of the exhaust gas. However, since sulfate is more stable than nitrate, it is not detached from the catalyst only by enriching the exhaust air-fuel ratio. In order to desorb the sulfate, it is necessary to place the NOx catalyst at a high temperature (for example, 400 ° C. or higher) and then put it in a rich atmosphere. Therefore, a rich spike intended for high temperature enrichment is referred to as a high temperature rich spike. The released sulfate is decomposed into sulfur oxide (SOx) in the catalyst. Since NOx regeneration can be performed at a lower temperature than S poisoning regeneration (for example, about 200 to 300 ° C.), NOx regeneration is simultaneously performed when S poisoning regeneration is performed.

  Next, the DPF 20 collects and removes particulate matter (PM) contained in the exhaust, and is a so-called wall flow type in which both ends of the honeycomb-shaped heat-resistant substrate are alternately closed in a checkered pattern. Any type of filter that physically collects PM can be used, such as a filter having a mesh shape or a foam shape. In the present embodiment, a so-called continuous regeneration type DPF with a catalyst in which a noble metal such as Pt is supported inside the DPF is used. In this case, HC in the exhaust gas supplied to the DPF is oxidized and burned by the catalytic action, and at this time, PM accumulated in the DPF is burned and removed.

  The DPF can operate even at a relatively low temperature. However, when the amount of accumulated PM exceeds a predetermined amount, it is necessary to perform filter regeneration for forcibly removing the PM to recover the PM collecting ability. When performing this filter regeneration, fuel is injected from the exhaust injector 21 to enrich the air-fuel ratio of the exhaust gas. The amount of PM accumulated in the DPF 20 is estimated by the ECU 50 based on the detection value of the differential pressure sensor 32 shown in FIG.

  Now, the operation of the present embodiment will be described briefly. During normal operation of the engine, as shown in FIG. 3, the on-off valve 24 is controlled to the first position θ1, and the auxiliary valve 41 is controlled to the fully open position. Then, as if there is no bypass passage 40, the entire amount of the exhaust gas flows in the exhaust passage 12 (particularly in the main passage 12M). At this time, the oxidation catalyst 18 oxidizes HC and CO in the exhaust, and simultaneously heats and raises the temperature of the exhaust gas. The NOx catalyst 19 stores NOx in the exhaust, and the DPF 20 collects PM in the exhaust.

  Similarly, at the time of NOx regeneration and filter regeneration, the on-off valve 24 is controlled to the first position θ1, and the auxiliary valve 41 is controlled to the fully open position. Then, fuel is injected from the exhaust injector 21.

  During NOx regeneration, fuel is injected from the exhaust injector 21 for a relatively short time (for example, about several tens of seconds). On the other hand, during regeneration of the filter, fuel is intermittently injected from the exhaust injector 21 for a longer time. When fuel injection is performed, a part of HC in the exhaust is first oxidized and burned by the oxidation catalyst 18, and rich high-temperature exhaust gas containing the remaining HC is discharged from the oxidation catalyst 18. After this rich high-temperature exhaust gas passes through the NOx catalyst 19, it reaches the DPF 20, whereby the DPF 20 is heated, and the HC supplied to the DPF 20 is combusted in the DPF 20, and the deposited PM is combusted. Since a certain amount of oxygen is required for burning the deposited PM, fuel is intermittently injected from the exhaust injector 21. The exhaust air-fuel ratio during fuel injection is rich, but the exhaust air-fuel ratio is lean (λ> 1, for example, about 2) when viewed on the average over the entire filter regeneration execution time.

  On the other hand, at the time of S poison regeneration or S purge execution, the on-off valve 24 is controlled to either the first position θ1 or the second position θ2 according to the engine load, and the auxiliary valve 41 is operated in this manner. In conjunction with this, either the fully open position as shown in FIG. 3 or the partially open position as shown in FIG. 4 is controlled. Then, fuel is injected from the exhaust injector 21.

  During this S poisoning regeneration, the fuel is intermittently injected from the exhaust injector 21 for a relatively long time (for example, about several tens of minutes). Then, the NOx catalyst 19 is heated by the same principle as that at the time of filter regeneration, and becomes high temperature, and the sulfate stored in the NOx catalyst 19 is desorbed and decomposed by HC. At the time of this S poisoning regeneration, it is necessary to make the exhaust gas richer than at the time of filter regeneration. The exhaust air-fuel ratio is rich (λ <1, for example, about 0.95) even when viewed on average over the entire S poisoning regeneration time. However, it is preferable to intermittently supply the fuel because the catalyst temperature may decrease if the NOx catalyst is continuously placed in a rich atmosphere (reducing atmosphere). S poisoning can also occur in the oxidation catalyst 18 in the preceding stage, but the oxidation catalyst 18 is also regenerated in S poisoning simultaneously with the S poisoning regeneration in the NOx catalyst 19 in the subsequent stage.

  At the time of filter regeneration and S poisoning regeneration, air may be injected from the air nozzle 28 in order to achieve a desired exhaust air-fuel ratio or supply necessary oxygen.

  The opening / closing valve 24 is controlled to the first position θ1 during low-load operation of the engine (for example, during idling) and during medium-load operation. At this time, the amount of intake air is relatively small, and therefore the flow rate and oxygen concentration of the exhaust gas exhausted from the engine are also relatively low, and the desired catalyst temperature and exhaust air / fuel ratio suitable for regeneration can be obtained only by fuel injection from the exhaust injector 21. This is because it can be easily realized. On the other hand, the open / close valve 24 is controlled to the second position θ2 during high-load operation of the engine. At this time, the amount of intake air is relatively large, and therefore the flow rate and oxygen concentration of the exhaust gas discharged from the engine are also relatively high, and the desired catalyst temperature and exhaust air / fuel ratio can be realized only by fuel injection from the exhaust injector 21. Because it is difficult.

  As shown in FIG. 4, when the on-off valve 24 is controlled to the second position θ2, only a part of the exhaust gas passes through the on-off valve 24 and flows through the main passage 12M, and then flows through the oxidation catalyst 18 and the NOx catalyst 19. The flow rate of exhaust gas and the passage speed thereof are reduced compared to the case of the first position θ1. Therefore, the desired catalyst temperature and exhaust air / fuel ratio can be easily realized only by fuel injection from the exhaust injector 21. Further, since it is not necessary to perform a large amount of fuel injection, it is possible to prevent deterioration of fuel consumption. Since the auxiliary valve 41 is also controlled to the partially open position, this also promotes reduction of the exhaust gas flow rate.

  The position itself when the on-off valve 24 is at the second position θ2 and the aforementioned opening ratio A: B are preferably set so as to obtain such a desired catalyst temperature and exhaust air-fuel ratio.

  The remainder of the exhaust gas flows through the bypass passage 40 and bypasses the oxidation catalyst 18 and the NOx catalyst 19. A part of the exhaust gas and the remaining part merge at the junction D and are supplied to the DPF 20.

  Thus, a desired exhaust air-fuel ratio can be stably obtained regardless of changes in the operating state of the engine.

  By the way, immediately after the regeneration, the on-off valve 24 is controlled to the third position θ3 as shown in FIG. Then, pressurized air is injected and supplied from the air nozzle 28 to the nozzle part 21 </ b> A of the exhaust injector 21. By this pressurized air, the fuel adhering to the nozzle part 21A is blown off and the nozzle part 21A is cooled. Thereby, the production | generation of the solid carbide | carbonized_material, ie, a deposit resulting from the residual fuel of 21 A of nozzle parts can be suppressed. The auxiliary valve 41 is controlled to a partially opened position or a fully opened position as shown in FIG.

  Since the nozzle part 21A is exposed to the exhaust gas at normal times, the fuel remaining in the nozzle part 21A or on the outer wall of the nozzle part may be heated and carbonized by the exhaust gas to become solid carbide, that is, deposit. This deposit can be a cause of hindering fuel injection by clogging the nozzle hole or preventing movement of the needle valve or the like.

  Therefore, if the residual fuel in the nozzle part 21A is blown off as described above, deposit generation when the nozzle part 21A is subsequently exposed to exhaust gas can be suppressed. In order to further suppress deposit generation, the exhaust injector 21 is preferably provided with a water cooling mechanism.

  In particular, it is preferable to operate the air nozzle 28 when the temperature sensor 31 detects a nozzle portion temperature of a predetermined value or more. Thereby, the nozzle part 21A can always be controlled to a temperature lower than a predetermined value, and the heating of the nozzle part 21A and thus the generation of deposits can be further suppressed.

  Hereinafter, a procedure of an example of control in the present embodiment will be described with reference to FIG. This control is executed by the ECU 50. Here, a case where S poison regeneration, that is, S purge is executed continuously after filter regeneration will be described. In this case, the NOx catalyst 19 can be preheated by the previous filter regeneration, and at the same time, the deposited PM can be burned and removed, and the DPF 20 can be prevented from becoming hot due to the subsequent S purge and burning the DPM 20 at a high temperature. There are benefits.

  This control is started simultaneously with the engine start. In the first step S10, the on-off valve 24 is controlled to the first position θ1.

  In step S12, it is determined whether or not the temperature Te of any exhaust purification element (for example, the NOx catalyst 19) estimated by the ECU 50 based on the detected value of the exhaust temperature sensor 23 exceeds a predetermined temperature Tes. The predetermined temperature Tes is set near the lowest temperature among the temperatures at which all of the oxidation catalyst 18, the NOx catalyst 19, and the DPF 20 are activated. If Te ≦ Tes, the process returns to step S10. If Te> Tes, the process proceeds to step S14.

  In step S14, it is determined whether or not the control mode preset or programmed in the ECU 50 has shifted to the DPF regeneration / S purge mode in which the regeneration of the DPF 20 and the S purge of the NOx catalyst 19 are continuously performed. This transition is made when a predetermined condition is satisfied. If the control mode has not shifted to the DPF regeneration / S purge mode, the process returns to step S10, and if the control mode has shifted to the DPF regeneration / S purge mode, the process proceeds to step S16.

  In step S16, DPF regeneration is executed, and fuel is injected from the exhaust injector 21 as described above.

  In step S18, it is determined whether or not the elapsed time td measured by the ECU 50 from the start of DPF regeneration is equal to or longer than a predetermined time tds. If the elapsed time td is not equal to or longer than the predetermined time tds, the process returns to step S16. On the other hand, if the elapsed time td is equal to or longer than the predetermined time tds, the process proceeds to step S20, and the S purge is started at the same time as the DPF regeneration is terminated. As a result, the fuel is injected from the exhaust injector 21 as described above.

  Next, in step S22, it is determined whether or not the engine load is high, specifically, whether or not a parameter value representing the engine load is a predetermined value or more. That is, the ECU 50 determines the fuel injection amount Q to be injected from the main injector 9 from a map as shown in FIG. 7 based on, for example, the detected values of the engine rotational speed Ne and the accelerator opening Ac. If the determined fuel injection amount Q is equal to or higher than the injection amount threshold value Qs corresponding to the high load corresponding to the current engine speed Ne, it is determined that the engine load is high. In this case, the parameter representing the engine load is the fuel injection amount Q, and the predetermined value is the injection amount threshold value Qs.

  Alternatively, when performing so-called torque control, the ECU 50 determines a target torque trq to be output by the engine from a map as shown in FIG. 8 based on the detected value of the engine rotational speed Ne and the determined fuel injection amount Q, for example. To do. If the determined target torque trq is equal to or higher than the torque threshold trqs corresponding to the high load corresponding to the current engine speed Ne, it is determined that the engine load is high. In this case, the parameter representing the engine load is the target torque trq, and the predetermined value is the torque threshold trqs.

  If it is determined in step S22 that the engine load is not high, that is, if it is determined that the engine load is low or medium load, the routine proceeds to step S24, where the on-off valve 24 is controlled to the first position θ1. On the other hand, when it is determined in step S22 that the engine load is high, the routine proceeds to step S26, where the on-off valve 24 is controlled to the second position θ2.

  Next, in step S28, it is determined whether or not the elapsed time tp measured by the ECU 50 from the start of the S purge is equal to or longer than the predetermined time tps. If the elapsed time tp is not equal to or longer than the predetermined time tps, the process returns to step S20. On the other hand, if the elapsed time tp is equal to or longer than the predetermined time tps, the process proceeds to step S30 and the S purge is terminated.

  Next, in step S32, the on-off valve 24 is controlled to the third position θ3. In step S34, the air nozzle 28 is operated for a predetermined time. Then, the fuel adhering to the nozzle part 21A is blown off by the pressurized air injected from the air nozzle 28, and the nozzle part 21A is cooled at the same time. The air nozzle 28 may be operated continuously or intermittently.

  Next, in step S36, it is determined whether or not the temperature Ti of the nozzle portion 21A of the exhaust injector 21 detected by the temperature sensor 31 is less than a predetermined temperature Tis. The predetermined temperature Tis is set near the lowest temperature at which deposits may occur in the nozzle portion 21A.

  When the nozzle part temperature Ti is equal to or higher than the predetermined temperature Tis, the process returns to step S32. On the other hand, when the nozzle part temperature Ti is lower than the predetermined temperature Tis, the on-off valve 24 is returned to the first position θ1, and the control is terminated.

  As described above, according to the present embodiment, since the on-off valve 24 for changing the opening ratio of the main passage 12M and the bypass passage 40 is provided, the flow rate of the exhaust gas flowing through the main passage 12M is changed or reduced. be able to. Therefore, even when the engine operating state changes, particularly when the engine load increases, the desired exhaust gas flow rate can be easily obtained, and the desired exhaust air-fuel ratio can be stably obtained.

  By the way, when the exhaust injector 21, the on-off valve 24, and the air nozzle 28 are provided in the curved pipe portion 12A, there are the following advantages. That is, when attaching these separate parts to the exhaust passage, the attachment portion is preferably made of cast iron from the viewpoint of ensuring rigidity and attachment accuracy. At this time, if the attachment portion is a straight pipe portion, the attachment portion itself becomes large and heavy, which is disadvantageous in terms of cost. However, if the attachment portion is a curved pipe portion as in this embodiment, the attachment portion can be reduced in size and weight, which is advantageous in terms of cost.

  In the above control, the air nozzle 28 is operated after the on-off valve 24 is moved to the third position. Therefore, the supply air can be rebounded by the on-off valve 24 and hit the exhaust injector 21, and air can be supplied to the semi-closed space from the on-off valve 24 to the air nozzle 28. Therefore, pressurized air can be used efficiently and cooling efficiency and cleaning efficiency can be improved.

  As mentioned above, although embodiment of this invention was described in detail, this invention can also employ | adopt other embodiment. For example, the internal combustion engine may be a spark ignition internal combustion engine, in particular a direct injection lean burn gasoline engine. The position of the on-off valve may be continuously variable. In this case, it is preferable to continuously variably control the position of the on-off valve according to the engine load state. The on-off valve may be composed of a plurality of valves, for example, two valves respectively disposed in the main passage and the bypass passage.

1 Internal combustion engine 12 Exhaust passage 12M Main passage 18 Oxidation catalyst 19 NOx catalyst 20 Particulate filter (DPF)
21 Fuel injection valve (exhaust injector)
21A nozzle part 24 on-off valve 28 air nozzle 40 bypass passage 50 electronic control unit (ECU)

Claims (7)

A fuel injection valve provided in the exhaust passage;
An exhaust purification element provided in the exhaust passage downstream of the fuel injection valve;
A bypass passage branched from the exhaust passage upstream of the fuel injection valve and joined to the exhaust passage downstream of the exhaust purification element;
An on-off valve for changing an opening ratio between the main passage, which is the exhaust passage between the branch portion and the junction portion, and the bypass passage;
An internal combustion engine comprising: A valve that controls the on-off valve to at least one of a first position in which the main passage is fully opened and the bypass passage is fully closed, and a second position in which both the main passage and the bypass passage are partially opened. The internal combustion engine according to claim 1, further comprising a control unit. When the fuel is injected from the fuel injection valve, the valve control means controls the open / close valve to either the first position or the second position according to a load state of the internal combustion engine. The internal combustion engine according to claim 2. The internal combustion engine according to claim 2, wherein the valve control means controls the open / close valve to a second position when fuel is injected from the fuel injection valve during high load operation of the internal combustion engine. An air nozzle for injecting air to a nozzle portion of the fuel injection valve exposed in the main passage; The internal combustion engine according to any one of claims 2 to 4, wherein the on-off valve is controlled to a third position in which the valve is fully opened. The internal combustion engine according to any one of claims 1 to 5, wherein the exhaust purification element includes an NOx storage reduction catalyst. The internal combustion engine according to any one of claims 1 to 6, further comprising another exhaust purification element provided in the exhaust passage on the downstream side of the merging portion.

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