JP4774653B2 - Engine exhaust purification device and computer program thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to an exhaust emission control device for an engine.
[0002]
[Prior art]
  Conventionally, NO emitted from diesel engines and gasoline engines_X(Nitrogen oxide) is the NO placed in the exhaust passage of the engine_XIt is known to reduce and purify with an absorbent material. This NO_XThe absorber is NO in an oxygen-excess atmosphere with an oxygen concentration in the exhaust gas of a predetermined value (for example, 4%) or more._XNO is absorbed as the oxygen concentration decreases_XAre to be released. This NO_XAbsorber is NO_XNO increases when absorption increases_XBefore it happens, NO_XSo-called refreshing to release the slag is required. For example, NO_XNO absorbed by the absorbent_XWhen the absorption amount exceeds a predetermined amount, the air-fuel ratio supplied to the engine is made richer than the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio, so that the oxygen concentration in the exhaust gas is reduced and NO is reduced._XIs being released.
[0003]
  However, according to the above prior art, NO is initially detected when the air-fuel ratio in the exhaust gas shifts from lean to rich, that is, when the O2 concentration in the exhaust gas decreases from, for example, 4% or more to 0.5% or less._XLarge amounts of NO from the absorbent_XIs released rapidly, so this NO_XWhich leads to a shortage of HC for reducing NO._XThere is a problem that the purification rate decreases.
[0004]
  Therefore, in Japanese Patent Laid-Open No. 2001-090594, the above-described NO_XAn absorbent material is provided in the exhaust passage of the engine, and usually the main fuel is injected during the compression stroke._XNO from absorbent_XIn addition to the main fuel injection, so-called post-injection is performed in which fuel is injected in the expansion stroke or exhaust stroke, and the post-injection timing is delayed from the compression top dead center for a predetermined time from the start of post-injection. Is increased, and then the retardation angle is decreased. According to this prior art, NO_XNO from absorbent_XWhen a large amount of HC is released, a large amount of HC can be supplied by delaying the start of post-injection._XNO released from the absorbent_XIt is possible to avoid a state in which HC for reducing the amount is insufficient.
[0005]
[Problems to be solved by the invention]
  However, according to the above-described prior art, NO is initially detected when the air-fuel ratio in the exhaust gas shifts from lean to rich._XLarge amounts of NO from the absorbent_XCan be solved, but if the post-injection time is not set properly, it is effective to discharge soot made of carbon particle condensate generated in the combustion chamber of the engine into the atmosphere. There was a problem that it could not be suppressed.
[0006]
  The present invention has been made in consideration of the above problems, and the problem is NO._XNO from absorbent_XDuring release, a large amount of NO while suppressing the generation of soot_XIs to suppress the sudden release.
[0007]
[Means for Solving the Problems]
  In order to achieve the above object, the present invention provides the following solution as a solution.
[0008]
  That is, the present applicant has found and proposed that the soot discharge can be effectively suppressed by setting the post-combustion timing to be almost immediately after the end of the main combustion. (Japanese Patent Application No. 2000-352922) In the present invention, such post-injection timing control is performed with a large amount of NO._XAfter that, by adjusting the injection amount and the injection timing so that the sudden release can be suppressed, soot generation is suppressed and a large amount of NO is_XIt is intended to achieve a balance with rapid release suppression.
[0009]
  Specifically, first, in the first configuration of the present invention, the fuel injection valve that directly injects fuel into the combustion chamber and the exhaust passage are arranged in an oxygen-excess atmosphere._XAs the oxygen concentration decreases, NO_XNO release_XAn absorbent material and main combustion means for injecting main fuel by the fuel injection valve at a predetermined time up to the vicinity of compression top dead center and performing main combustion that generates a required torque at least in the first half of the expansion stroke based on the main fuel , NO above_XNO from absorbent_XWhen the release request is made, the fuel injection valve injects the rear fuel at a predetermined time in the first half of the expansion stroke after the main fuel injection so that the combustion starts almost immediately after the main combustion is finished, and the amount of the rear fuel NO_XFrom the time when the release request is established until the predetermined period elapses, post-combustion means that gradually increases with the passage of time,
  It is comprised so that it may be provided.
[0010]
  According to the first configuration of the present invention, NO_XNO from absorbent_XWhen the release request is made, the post-combustion time is set based on the approximate end time of the main combustion, so that the post-injected post-injected fuel is in a state where the carbon present in the engine combustion chamber and the surrounding oxygen are well mixed. Since it burns with the carbon, the amount of soot discharged from the carbon condensate can be effectively reduced.
[0011]
  Also, after fuel is NO_XBy gradually increasing the amount from the time when the release request is established, the decrease in oxygen concentration in the exhaust gas can be moderated, and the initial NO at which the air-fuel ratio in the exhaust gas has shifted from lean to rich_XNO from absorbent_XNO can be released slowly, so NO_XIt can suppress that a purification rate falls.
[0012]
  Further, in the second configuration of the present invention, the fuel injection valve that directly injects the fuel into the combustion chamber and the exhaust passage are disposed, and NO is generated in an oxygen-excess atmosphere._XAs the oxygen concentration decreases, NO_XNO release_XAn absorbent material and main combustion means for injecting main fuel by the fuel injection valve at a predetermined time up to the vicinity of compression top dead center and performing main combustion that generates a required torque at least in the first half of the expansion stroke based on the main fuel , NO above_XNO from absorbent_XAt the time of the release request, after the main fuel is injected, after the main fuel is injected, the fuel is injected by the fuel injection valve at a predetermined time in the first half of the expansion stroke, and the post-combustion is started. Set the combustion time to NO_XA post-combustion means for retarding the main combustion in a stepwise manner with the passage of time from the time when the release request is established until a predetermined period elapses,
  It is comprised so that it may be provided.
[0013]
  According to the second configuration of the present invention, NO_XNO from absorbent_XWhen the release request is made, the post-combustion time is set based on the approximate end time of the main combustion. Since it burns with the carbon, the amount of soot discharged from the carbon condensate can be effectively reduced.
[0014]
  The amount of reducing agent supplied into the exhaust gas depends on the amount of post fuel that is not combusted in the combustion chamber and is released into the exhaust passage, and the amount that is released increases as the post combustion timing is delayed. Therefore, according to the second configuration of the present invention, the combustion timing of the post-combustion is NO._XBy being configured to retard in stages from the time when the release request is established, the early stage when the air-fuel ratio in the exhaust gas shifts from lean to rich, the post-combustion time is early, and the post-fuel burns sufficiently in the combustion chamber. An increase in the amount of reducing agent supplied inside can be suppressed. As a result, the decrease in oxygen concentration in the exhaust gas can be moderated, so NO_XLarge amounts of NO from the absorbent_XCan be prevented from being released rapidly. After that, the combustion timing of post-combustion is retarded in stages, so that the amount of reducing agent supplied into the exhaust can be increased, and NO_XCan be reduced and purified efficiently.
[0015]
  MaThe first of the present invention3In this configuration, the engine is a diesel engine, and the main combustion means is multistage injection in which the main injection is divided into multiple injections near the top dead center of the compression stroke, and is not performed during post-combustion by the post-combustion means. With respect to the time of post-combustion, the number of injections of the multistage injection is reduced or the injection pause interval is reduced.
[0016]
  As described above, when post-combustion is performed, the fuel efficiency for the post-fuel becomes worse. On the other hand, in multistage injection of main injection, it is known that fuel efficiency is improved by appropriately setting the number of injections and the injection pause interval. (For example, refer to Japanese Patent Application Laid-Open No. 2001-055950) For example, the number of injections is large when the fuel is divided into two, and the fuel consumption rate is large compared to the three-split injection, and the injection pause interval is long when the injection pause interval is short. Fuel consumption rate is greater than time. Therefore, according to the fifth configuration of the present invention, at the time of post-combustion, the fuel consumption deterioration associated with post-combustion is reduced by reducing the number of injections of multi-stage injection or by shortening the injection pause interval compared to non-post-combustion. Can be suppressed.
[0017]
  In addition, the first of the present invention4In this configuration, a computer program incorporated in hardware resources including a computer is provided, and the computer program injects main fuel directly into the combustion chamber by the fuel injection valve at a predetermined time up to the vicinity of the compression top dead center. , A main combustion procedure for performing main combustion for generating a required torque at least in the first half of the expansion stroke based on the main fuel, and NO_XNO from absorbent_XAt the time of release request, after the main fuel is injected, the fuel injection valve directly injects the rear fuel into the combustion chamber at a predetermined timing in the first half of the expansion stroke so that the combustion is started almost immediately after the main combustion. Fuel amount is NO_XA post-combustion procedure that gradually increases as time elapses from when the release request is established until a predetermined period elapses,
  The hardware resource is configured to be executed.
[0018]
  First of the present invention4According to the configuration of NO_XNO from absorbent_XWhen the release request is made, the post-combustion time is set based on the approximate end time of the main combustion, so that the post-injected post-injected fuel is in a state where the carbon present in the engine combustion chamber and the surrounding oxygen are well mixed. Since it burns with the carbon, the amount of soot discharged from the carbon condensate can be effectively reduced.
[0019]
  Also, the amount of fuel after_XBy gradually increasing the amount from the time when the release request is established, the decrease in oxygen concentration in the exhaust gas can be moderated, and the initial NO at which the air-fuel ratio in the exhaust gas has shifted from lean to rich_XNO from absorbent_XNO can be released slowly, so NO_XIt can suppress that a purification rate falls.
[0020]
  First of the present invention5In this configuration, a computer program incorporated in hardware resources including a computer is provided, and the computer program injects main fuel directly into the combustion chamber by the fuel injection valve at a predetermined time up to the vicinity of the compression top dead center. A main combustion procedure for performing main combustion for generating a required torque at least in the first half of the expansion stroke based on the main fuel;
  NO_XNO from absorbent_XWhen the release request is made, after the main fuel is injected, the fuel injection valve directly injects the rear fuel into the combustion chamber at a predetermined timing in the first half of the expansion stroke so that the combustion is started almost immediately after the main combustion. Set the combustion timing of post-combustion to NO_XA post-combustion procedure for retarding stepwise with the passage of time from the time when the release request is established until a predetermined period elapses,
  The hardware resource is configured to be executed.
[0021]
  First of the present invention5According to the configuration of NO_XNO from absorbent_XWhen the release request is made, the post-combustion time is set based on the approximate end time of the main combustion, so that the post-injected post-injected fuel is in a state where the carbon present in the engine combustion chamber and the surrounding oxygen are well mixed. Since it burns with the carbon, the amount of soot discharged from the carbon condensate can be effectively reduced.
[0022]
  Also, the combustion timing of post-combustion is NO_XBy being configured to retard in stages from the time when the release request is established, the early stage when the air-fuel ratio in the exhaust gas shifts from lean to rich, the post-combustion time is early, and the post-fuel burns sufficiently in the combustion chamber. An increase in the amount of reducing agent supplied inside can be suppressed. As a result, the decrease in oxygen concentration in the exhaust gas can be moderated, so NO_XLarge amounts of NO from the absorbent_XCan be prevented from being released rapidly. After that, the combustion timing of post-combustion is retarded in stages, so that the amount of reducing agent supplied into the exhaust can be increased, and NO_XCan be efficiently reduced and purified.
[0023]
【The invention's effect】
  According to the present invention, NO_XNO from absorbent_XDuring release, a large amount of NO while suppressing the generation of soot_XCan be prevented from being released rapidly.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
  Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0025]
  FIG. 1 is an overall view of an automobile diesel engine according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes an engine body, which has a plurality of cylinders 2 (only one cylinder is shown in the figure), and a piston 3 is removably fitted in each cylinder 2. A combustion chamber 4 is defined in each cylinder 2. In the combustion chamber 4 of each cylinder 2, a fuel injection valve 5 is disposed substantially at the center of the upper surface, and fuel is directly injected from the fuel injection valve 5 into the combustion chamber 4 of each cylinder 2 at a predetermined timing. It has become so. Further, a water temperature sensor 18 for detecting the cooling water temperature of the engine is provided at a position facing a water jacket (not shown) of the engine body 1.
[0026]
  The fuel injection valve 5 is connected to a common common rail (stock pressure chamber) 6 for storing high-pressure fuel, and the common rail 6 is provided with a pressure sensor 6a for detecting the internal fuel pressure (common rail pressure). A high pressure supply pump 8 driven by the crankshaft 7 is connected. The high-pressure supply pump 8 controls the fuel supply pressure, so that the fuel pressure in the common rail 6 detected by the pressure sensor 6a is maintained at, for example, about 20 MPa or more during engine idle operation, and other operations are performed. Sometimes it works to keep it above 50 MPa.
[0027]
  A crank angle sensor 9 that detects the rotation angle of the crankshaft 7 is provided. The crank angle sensor 9 includes a plate to be detected (not shown) provided at the end of the crankshaft 7 and an electromagnetic pickup disposed so as to face the outer periphery of the plate. A pulse signal is output in response to the passage of protrusions formed at predetermined angles all around the outer periphery of the plate.
[0028]
  In the downstream portion of the intake passage 10 connected to the engine main body 1, a branch is provided for each cylinder 2 via a surge tank (not shown), and each of these branches is connected to each cylinder via an intake port. 2 combustion chambers 4. The intake passage 10 is provided with an intake pressure sensor 10a for detecting the intake pressure supplied to each cylinder 2.
[0029]
  In the intake passage 10, in order from the upstream side to the downstream side, a hot film type air flow sensor 11 that detects an intake flow rate sucked into the engine body 1 and intake air driven by a turbine 21 described later are compressed. A blower 12, an intercooler 13 that cools the intake air compressed by the blower 12, and an intake throttle valve 14 that restricts the cross-sectional area of the intake passage 10 are provided.
[0030]
  The intake throttle valve 14 is a butterfly valve provided with a notch so that intake air can flow even in a fully closed state, and the magnitude of the negative pressure acting on the diaphragm 15 is negative, as with the EGR valve 24 described later. The opening degree of the valve is adjusted by adjusting the electromagnetic valve 16 for pressure control. The intake throttle valve 14 is provided with a sensor (not shown) for detecting the opening degree.
[0031]
  Further, the upstream portion of the exhaust passage 20 connected to the engine body 1 is branched into branch portions for each cylinder 2, and these branch portions are respectively connected to the combustion chambers 4 of the respective cylinders 2 through exhaust ports. Yes. In the exhaust passage 20, the turbine 21 rotated by the exhaust flow in order from the upstream side to the downstream side, and NO in the exhaust gas._XNO to purify_XAbsorbent 22 and this NO_XA temperature sensor 19 for detecting the exhaust gas temperature in the vicinity of the absorbent 22 is provided. In addition, based on this temperature sensor 19, NO_XThe temperature of the absorbent 22 is estimated.
[0032]
  NO above_XThe absorbent 22 includes a cordierite carrier formed in a honeycomb structure having a large number of through holes extending in parallel to each other along the flow direction of exhaust gas, and two catalyst layers are formed on each through hole wall surface. It is. Specifically, the inner catalyst layer has a noble metal such as platinum and NO._XAbsorbent barium supports porous materials such as alumina and ceria as support materials, while the outer catalyst layer supports platinum, rhodium and barium as porous materials as support materials. is doing. This NO_XThe absorbent 22 is NO when the oxygen concentration in the exhaust gas is high, that is, when the air-fuel ratio of the combustion chamber 4 is lean._XWhile the air-fuel ratio of the combustion chamber 4 is near or higher than the stoichiometric air-fuel ratio and the oxygen concentration in the exhaust gas decreases, the absorbed NO_XIt is an absorption reduction type that releases and purifies. Where NO by barium_XThe absorption and release action of NO depends on the temperature state, and in the temperature range of about 250 ° C. to about 400 ° C., NO_XAlthough the purification rate is high, NO is higher or lower than that._XThe purification rate decreases.
[0033]
  The blower 12 disposed in the intake passage 10 and the turbine 21 disposed in the exhaust passage 20 constitute a turbocharger 25. The turbocharger 25 is a turbocharger composed of a variable geometry turbo (VGT) having a configuration in which the nozzle cross-sectional area of the exhaust passage 20 changes, and a diaphragm actuator 30 for changing the nozzle cross-sectional area; An electromagnetic valve 31 for controlling the negative pressure of the diaphragm actuator 30 is provided.
[0034]
  An exhaust gas recirculation passage (hereinafter referred to as an EGR passage) 23 that recirculates part of the exhaust gas to the intake air is connected to the exhaust passage 20 on the upstream side of the turbine 21. The EGR passage 23 has a downstream end connected to the intake passage 10 on the downstream side of the intake throttle valve 14. Further, in the EGR passage 23, a negative pressure operation type exhaust gas recirculation amount adjusting valve (hereinafter referred to as an EGR valve) 24 having a valve opening degree adjustable is disposed downstream.
[0035]
  The EGR valve 24 is urged in the closing direction by a spring (not shown) in the EGR valve 24 and driven in the opening direction by a diaphragm actuator 24a so that the opening degree of the EGR passage 23 is linearly adjusted. It is configured. That is, a negative pressure passage 27 is connected to the diaphragm actuator 24a, and the negative pressure passage 27 is connected to a vacuum pump (negative pressure source) 29 via a negative pressure control electromagnetic valve 28. . When the electromagnetic valve 28 communicates or blocks the negative pressure passage 27, the negative pressure for driving the EGR valve is adjusted and the EGR valve 24 is driven to open and close. Further, a lift sensor 26 for detecting the position of the valve body is provided at the installation position of the EGR valve 24.
[0036]
  The fuel injection valve 5, the high-pressure supply pump 8, the intake throttle valve 14, the EGR valve 24, the turbocharger 25, and the like are stored in a memory in an engine control unit (hereinafter referred to as ECU) 35 described later. It is configured to operate based on a computer program. Therefore, the ECU 35 has an output signal from the pressure sensor 6a, an output signal from the crank angle sensor 9, an output signal from the pressure sensor 10a, an output signal from the air flow sensor 11, and an output signal from the water temperature sensor 18. An output signal, an output signal from the lift sensor 26 of the EGR valve 24, and an output signal from an accelerator sensor 32 that detects an operation amount of an accelerator pedal operated by a driver are input.
[0037]
  The ECU 35 includes a main injection control means 40 for controlling the injection state of the main injection from the fuel injection valve 5 in accordance with the operating state of the engine, and the fuel injection at a predetermined timing in the first half of the expansion stroke after the main injection. There is a post-injection control means 41 for controlling the fuel to be post-injected from the valve 5, and an exhaust gas recirculation amount control means 39 for controlling the exhaust gas recirculation amount by driving the EGR valve according to the operating state of the engine. Have.
[0038]
  This embodimentIn this state, the following control is performed by the main injection control means 40 and the post injection control means 41.
The post-fuel injection timing is controlled based on the operating state so that post-combustion is started immediately after the end of main combustion.
After fuel injection timing is NO_XThe retardation is controlled step by step from the time when the release request is established.
After injection amount is NO_XIncrease control is performed step by step from the time when the release request is established.
NO_XAt the time of post-injection in response to the release request, the main injection injected in one combustion cycle in each cylinder is divided into multiple injections, and the number of main injections is reduced or the injection pause interval is reduced.
NO_XWhen the temperature of the absorbent 22 is low, the main injection injected in one combustion cycle in each cylinder is divided into multiple injections, and the number of main injections is increased or the injection pause interval is increased.
NO_XWhen absorbent 22 temperature is low, NO_XEven when the discharge is not requested, the post injection is executed and the post injection timing is NO._XIt is advanced with respect to the release request time.
[0039]
  Hereinafter, each control (1)-(6) is demonstrated.
[0040]
  (1) The injection timing of the post fuel is controlled based on the operating state so that the post combustion is started almost immediately after the main combustion is completed.
[0041]
  This diesel engine can reduce soot generated by the main injection by performing the post injection at a predetermined time after the main injection of fuel. In this case, when the engine is in an operation state in which the amount of soot discharged from the combustion chamber 4 tends to be large, for example, in an operation state in which the engine load is greater than or equal to medium load, or in an operation state in which the engine speed is greater than or equal to about 2000 rpm. Or, in an engine in which a diesel particulate filter (DPF) is installed in the exhaust passage 20, if this DPF is in a low temperature state of 300 ° C. or lower and its purification function is low, At a predetermined time set on the basis of the time when the diffusion fuel by the main injection ends (in an operation state where the engine speed is 1500 rpm or more, a time of 30 ° to 60 ° CA after the top dead center of the compression stroke) By performing the post-injection, the soot discharge can be reduced.
This is because mixing of soot and oxygen present in the combustion chamber 4 at the end of the diffusion combustion is promoted, and combustion is started by fuel after being injected in a state where it is easy to ignite. This is because it can be reduced.
[0042]
  The main injection is a fuel injection that is performed at a predetermined timing from the intake stroke to the initial stage of the expansion stroke at an injection amount corresponding to the required output of the engine or more, and one or all of the main injected fuels. Since the soot is generated when the part diffuses and burns, the fuel is post-injected to reduce the soot. In this case, if the main injection of fuel is performed at a predetermined time from the vicinity of the compression stroke dead center to the beginning of the expansion stroke, all the fuel becomes diffusion fuel except in the light load state, and both the premixed combustion and the diffusion combustion are performed in the light load state. Done.
[0043]
  In addition, if the main fuel is injected between the intake stroke and the top dead center of the compression stroke, premixed combustion is mainly performed, and no soot is generated by this combustion, but the fuel adhering to the wall of the combustion chamber is compressed. When ignition occurs near the top dead center, diffusion combustion may occur and soot may be generated. Even in such a case, soot can be reduced by performing the post-injection of the fuel.
[0044]
  The main fuel injection is divided into at least two or less of a predetermined timing from the intake stroke to the compression stroke top dead center and a predetermined timing from the vicinity of the compression stroke top dead center to the early stage of the expansion stroke. Including the case of doing.
[0045]
  Here, the end timing of diffusion combustion will be described in detail. This diffusion combustion is determined based on the heat generation rate, and according to the “Internal combustion engine lecture” (publisher Yokendo Co., Ltd., author Fujio Nagao), the heat generation rate is expressed as shown in the following formula (1). expressed.
[0046]
  dQ / dθ = [A / (K (θ) −1)] × [V (θ) · (dP (θ) / dθ)
+ K (θ) · P (θ) · (dV (θ) / dθ)] (1)
  Here, A is the work equivalent of heat, K (θ) is the specific heat ratio, V (θ) is the stroke volume, P (θ) is the in-cylinder pressure, and θ is the crank angle.
[0047]
  According to the manual of the combustion analyzer CB566 manufactured by Ono Sokki Co., Ltd., the specific heat ratio K (θ) is expressed based on the following formulas (2) to (5).
[0048]
  K (θ) = Cp / Cv (2)
  Cp = ap + b · (T (θ) / 100) + c · (T (θ) / 100) · 2 + d · (100 / T (θ)) (3)
  Cv = Cp− (A · Ro) / M (4)
  T (θ) = (P (θ) · V (θ) /29.27) · G (5)
  Here, Cp is constant pressure specific heat, Cv is constant volume specific heat, Ro is gas constant, M is the molecular weight of air, T (θ) is gas temperature, G is gas weight, ap, b, c and d are other constants. is there.
[0049]
  From the above formulas (2) to (5), the heat generation rate dQ / dθ shown in formula (1) is a function f (P (θ), which is a function of the in-cylinder pressure P (θ) and the stroke volume V (θ). V (θ)). Further, when the stroke volume V (θ) is expressed based on the bore diameter B and the stroke S, the heat generation rate dQ / dθ is expressed by the following equation (7). As shown.
[0050]
  V (θ) = (π · B 2 S / 8) · (1-cos θ) (6)
  dQ / dθ = [f (P (θ + Δθ), V (θ + Δθ)) − f (P (θ), V (θ))] / Δθ (7)
  Therefore, if there is in-cylinder pressure data for each crank angle, the heat generation rate can be calculated based on this data. The heat generation rate obtained in this way is shown in FIGS. 2A to 2C, and the heat generation rate showed a large value in the positive direction according to the combustion by the main injection of fuel. Thereafter, since the heat generation rate becomes 0 in accordance with the end of the diffusion combustion, the end point of the diffusion combustion is obtained based on the time t1 at which the heat generation rate becomes substantially zero.
[0051]
  RealProcessingIn the state, at the normal time, an ignition delay time (for example, 0.4 ms) set in advance based on the operation state so that the combustion by the post-injection is started in the vicinity of the time point t1 obtained in advance as described above. In consideration of a time of about 0.7 ms), the post-injection timing is set to be earlier than the time t1 by an amount corresponding to the ignition delay time.
[0052]
  The ignition delay time varies depending on the engine displacement and the fuel injection pressure. When the injection pressure is 50 MPa to 200 MPa in an engine of 1000 cc to 3000 cc, the ignition delay time is 0.4 ms to 0.7 ms. It will be about. The ignition delay time is longer than the ignition delay time (0.1 ms to 0.3 ms) of the main injection performed at the compression stroke top dead center. This is because the in-cylinder temperature after the compression stroke top dead center is relatively low. This is because the post-injection is performed when it is low.
[0053]
  In addition, as an output timing of the injection drive signal to the fuel injection valve, an invalid time (drive delay time) from the time when the injection valve opening / closing signal is output until the actual injection is started is also included in the above ignition delay time. What has been taken into account is stored in the ECU 35.
[0054]
  For example, when the engine speed is controlled to 2000 rpm and the average effective pressure Pe is controlled to 0.57 Mpa, the heat in the combustion chamber in the case of main injection of fuel near the top dead center at the time of compression during medium-load rotation When the occurrence rate is thermodynamically calculated and graphed based on the change in pressure in the cylinder corresponding to the crank angle and the change in volume of the cylinder, as shown in FIG. After a delay time Tm of about 0.1 ms elapses, heat generation Y due to premixed combustion of the main injected fuel and heat generation K due to diffusion combustion of approximately the same level occur, and top dead center of the compression stroke It was confirmed that the diffusion combustion ended at a time t1 which was delayed by 0.6 ms from a later time tf of about 35 ° (CA).
[0055]
  Therefore, by performing the fuel post-injection at the time tf of about 35 ° (CA) after the top dead center of the compression stroke, the fuel injected thereafter can be burned at the end time t1 of the diffusion combustion. In other words, the fuel that has been post-injected at time tf starts to combust at time t1 when the ignition delay time (Tf) of about 0.6 ms has elapsed, and the heat generation amount N increases.
[0056]
  On the other hand, when the engine speed is controlled to 2500 rpm and the average effective pressure Pe is controlled to 0.9 MPa, the engine is premixed as shown in FIG. Compared with the heat generation Y of combustion, heat generation K due to diffusion combustion occurs for a considerably long period of time, and this diffusion combustion is considerably late at 0.7 ms behind about 47 ° (CA) after the top dead center of the compression process. Since there is a tendency to end at t1, by performing post-injection of fuel at a time tf of about 47 ° (CA) after the top dead center of the compression stroke, the fuel injected thereafter is terminated at the end of the diffusion combustion. It can be burned at t1.
[0057]
  When the engine speed is controlled to 1500 rpm and the average effective pressure Pe is controlled to 0.3 MPa, when the engine is under low load and low speed, as shown in FIG. Although it is difficult to distinguish the combustion from the heat generation state, the diffusion combustion is completed at a relatively early time t1 that is about 0.5 ms later than about 30 ° (CA) after the top dead center of the compression stroke. Since the heat generation rate becomes zero, the post-injection of the fuel is performed at the time tf of about 30 ° (CA) after the top dead center of the compression stroke. It can be burned at time t1.
[0058]
  Next, the effect of reducing soot by setting the post-injection timing of the fuel based on the end timing of the diffusion combustion will be described. That is, after the main injection of the fuel, the fuel post-injection timing is changed variously at the time of low load and low rotation of the engine in which the engine speed is controlled to 1500 rpm and the average effective pressure Pe is controlled to 0.3 MPa. As shown in FIG. 3 (a), an experiment was conducted to measure the amount of soot generated, and after the main injection of fuel, the advance was made by a time corresponding to the ignition delay time from the end point t1 of diffusion combustion. It has been confirmed that the amount of soot generated is remarkably reduced when the fuel post-injection timing is set after 30 ° (CA) after the top dead center of the compression stroke, which is considered to be the time tf.
[0059]
  Similarly, after the main injection of the fuel, the fuel post-injection timing is variously changed during the middle-load medium rotation when the engine speed is controlled to 2000 rpm and the average effective pressure Pe is controlled to 0.57 MPa. As shown in FIG. 3 (b), an experiment was conducted to measure the amount of soot generated. After the main injection of fuel, the advance angle was increased by a time corresponding to the ignition delay time from the end point t1 of diffusion combustion. It was confirmed that the generation amount of soot was remarkably reduced when the fuel post-injection timing was set after 35 ° (CA) after the top dead center of the compression stroke, which is considered to be the time tf.
[0060]
  Further, after the main injection of the fuel, the post-injection timing of the fuel is variously changed at the time of high load high rotation of the engine in which the engine speed is controlled to 2500 rpm and the average effective pressure Pe is controlled to 0.9 MPa. As shown in FIG. 3 (c), an experiment was conducted to measure the amount of soot generated, and after the main injection of fuel, the fuel was advanced by a time corresponding to the ignition delay time from the vicinity of the end point t1 of diffusion combustion. It was confirmed that the amount of soot generated is significantly reduced when the fuel post-injection timing is set after 47 ° (CA) after the top dead center of the compression stroke, which is considered to be the time point tf when the angle is made. . In each of the above experimental examples, the engine load was set constant, and the ratio of the post-injection amount to the main injection amount of fuel was set to 20%.
[0061]
  In FIGS. 3A to 3C, when the post-injection timing is 0 ° (CA), data is shown when only main injection is performed without performing post-injection of fuel. .
[0062]
  Further, when the engine speed is controlled to 1500 rpm and the average effective pressure Pe is controlled to 0.3 MPa, when the engine is under low load and low speed, the ignition delay is delayed from the vicinity of the end point t1 of the diffusion combustion by the main injection of fuel. At the time of 30 ° (CA) after the top dead center (ATDC) of the compression stroke, which is considered to be a time point tf that is advanced by a time corresponding to the time, the fuel is post-injected, and the fuel after the main injection amount When an experiment was conducted to measure the amount of soot generated by changing the ratio (P / T) of the injection amount in the range of 10% to 45%, as shown by the solid line in FIG. As the post injection amount ratio (P / T) increased, soot generation decreased. On the other hand, when fuel post-injection is performed at 8 ° (CA) after the top dead center of the compression stroke (ATDC), which is considered to be before the time tf, FIG. As shown by the broken line, the amount of soot increased with the increase in the ratio of the post-injection amount (P / T).
[0063]
  Further, when the engine speed is controlled to 2000 rpm and the average effective pressure Pe is controlled to 0.57 MPa, the ignition delay is delayed from the vicinity of the end point t1 of the diffusive combustion due to the main injection of fuel at the time of medium-load rotation. Compression stroke top deadline considered to be a time point 35 ° (CA) after the compression stroke top dead center (ATDC) considered to be a time point tf advanced by a time corresponding to the time, and before the time point tf. At the time of 20 ° (CA) after the point (ATDC), an experiment was conducted to measure the amount of soot generated by post-injecting the fuel, the engine speed was controlled to 2500 rpm, and the average effective pressure Pe was 0 After a time tf advanced by a time corresponding to the ignition delay time from the end point t1 of the diffusion combustion by the main injection of fuel at the time of high load and high rotation controlled at .9 MPa. At the time of 48 ° (CA) after the compression stroke top dead center (ATDC) and 20 ° (CA) of the compression stroke top dead center (ATDC) considered to be before the time tf. Even when an experiment was conducted to measure the amount of soot generated by post-injecting fuel, as shown in FIGS. 4 (b) and 4 (c), data similar to that at the time of low load and low rotation was obtained. .
[0064]
  From the experimental data, the fuel post-injection timing is set based on the end point of the diffusion combustion generated in the combustion chamber 4 by the main injection of the fuel, and the post-injection is performed at or near the end of the diffusion combustion. By igniting the generated fuel, the carbon is effectively burned by the post-injection of the fuel in a state where the carbon and oxygen existing in the combustion chamber 4 of the engine are sufficiently mixed in accordance with the end of the diffusion combustion. It can be seen that the amount of soot discharged from the combustion chamber 4 to the exhaust passage 20 can be reduced.
[0065]
  The end point of the diffusion combustion changes so that the period from the main injection end timing becomes longer as the load increases or the rotation speed increases according to the engine load and the rotation speed. As shown in 2 (a) to (c), the time point t1 at which the heat generation rate due to diffusion combustion becomes 0 is mapped based on various experimental data performed in the engine operating state, and read out from this map. Can be set.
[0066]
  Further, the detection signal of the temperature sensor for detecting the temperature in the combustion chamber 4, the detection signal of the combustion light sensor, or the amount of highly reactive hydrogen, hydrocarbons, etc. with a biased charge existing in the combustion chamber 4 is detected. Combustion state discriminating means for discriminating the diffusion combustion state according to the detection signal of the sensor is provided. In this combustion state discriminating means, whether or not the temperature after the main injection of the fuel has become a low temperature below a predetermined temperature, combustion light The end point of the diffusion combustion is determined by determining whether or not the amount of luminescence is lost or whether or not the amount of hydrogen or hydrocarbons is rapidly decreased. Based on this point of time, the fuel in the next combustion cycle is determined. You may comprise so that a post injection timing may be set. Further, a differential value of a value obtained by subtracting the adiabatic expansion temperature from the in-cylinder temperature detected by the temperature sensor is obtained, and the end point of the diffusion combustion is determined by detecting the time point when the differential value becomes 0 from the minus value. You may make it discriminate | determine.
[0067]
  As described above, based on the end point of diffusion combustion determined based on each operating state of the engine, the time near the end point of diffusion combustion (crank angle ± 5 °), preferably the end of diffusion combustion By configuring so that the start timing of fuel post-injection is set according to each operating state so that combustion by post-injection is started immediately afterward, the fuel is discharged at the optimal time corresponding to the operating state of the engine. The amount of soot discharged by jetting can be effectively reduced.
[0068]
  Note that in a diesel engine equipped with a turbocharger 25 that is driven by exhaust gas and supercharges intake air, when a predetermined amount of fuel is post-injected after the main injection of fuel as described above, the exhaust gas pressure increases. Thus, the supercharging action of the turbocharger 25 is enhanced. As a result, the amount of fresh air introduced into the combustion chamber 4 is increased, so that the combustion of carbon remaining in the combustion chamber 4 is promoted and the generation of soot is effectively suppressed. . Then, if the intake air amount increases due to the supercharging action of the turbocharger 25, the end timing of the diffusion combustion of the main injected fuel tends to be advanced, so that it corresponds to the end timing of the diffusion combustion. By correcting the post-injection timing of the fuel, the amount of soot led out to the exhaust passage 20 can be further reduced while effectively suppressing soot generation.
[0069]
  Further, in the diesel engine equipped with the turbocharger 25, exhaust gas recirculation means 33 for recirculating part of the exhaust gas to the intake system is provided, and exhaust gas recirculation control means 39 provided in the ECU 35 provides exhaust gas recirculation. When the feedback control is performed so that the recirculation rate of the turbocharger becomes the target value, when the intake air amount increases in accordance with the supercharging action of the turbocharger 25, the recirculation is returned to the intake system accordingly. Since the exhaust gas to be increased is increased, NO that is led out from the combustion chamber 4 to the exhaust passage 20_xThere is the advantage that the amount is further effectively reduced.
[0070]
  (2) NO after fuel injection timing_XStep-by-step delay control from the time the release request is established. Regarding the relationship between the post-injection timing and the amount of HC, as shown in FIG. 5A, the post-injection timing is set to about 30 ° (CA) after the top dead center of the compression stroke when the engine is under low load and low speed. However, the amount of HC produced does not increase significantly, and during medium-load rotation, as shown in FIG. 5 (b), HC production occurs until around 35 ° (CA) after the top dead center of the compression stroke. The amount of HC does not increase significantly, and at the time of high load and high rotation, as shown in FIG. 5 (c), the amount of HC produced is significant until around 45 ° (CA) after the top dead center of the compression stroke. It was confirmed that it would not increase.
[0071]
  That is, as shown in FIG. 5, the HC generation amount decreases as the post-injection timing is advanced, centering on the post-injection timing at which the HC generation amount determined for each operation region becomes significant. If the time is delayed, the amount of HC produced increases.
[0072]
  In the present embodiment, the amount of HC as a reducing agent is adjusted using the characteristics shown in FIG.
[0073]
  Specifically, NO_XNO from absorbent_XAt the time when the release request is established, the oxygen concentration in the exhaust gas is first reduced by advancing the post-injection timing from the post-injection timing at which the HC generation amount determined for each operating region becomes significant, and reducing the HC amount. Abrupt decline can be suppressed, and thereafter the post-injection timing is reduced by increasing the amount of HC by retarding the post-injection timing step by step from the post-injection timing at which the amount of HC generated for each operating region becomes significant. NO increases due to increased dosage_XThe purification rate can be improved.
[0074]
  (3) NO after fuel_XIncrease control step by step from the time the release request is established.
[0075]
  In this embodiment, NO_XNO from absorbent_XAt the time when the release request is established, first, the rear fuel amount is set to be relatively small to reduce the reducing agent amount, thereby suppressing a rapid decrease in the oxygen concentration in the exhaust gas. By increasing the amount of reducing agent and increasing the amount of NO_XThe purification rate can be improved.
[0076]
  (4) NO_XAt the time of post-injection in response to a release request, the main injection injected in one combustion cycle in each cylinder is divided into multiple injections, and the number of main injections is reduced or the injection pause interval is reduced.
[0077]
  In multistage injection of main injection in a diesel engine, it is known that fuel efficiency is improved by appropriately setting the number of injections and the injection pause interval. For example, JP-A-2001-055950 discloses this point. It is disclosed. Specifically, with regard to the number of injections, the fuel consumption rate is greater when the injection is divided into two than when the injection is divided into three, and the fuel consumption rate is greater when the injection pause interval is short than when the injection pause interval is short. .
[0078]
  Therefore, in this embodiment, the main injection is divided into multiple stages for injection, and NO._XAt the time of post-injection accompanying the release request, NO_XDeterioration of fuel consumption can be suppressed by reducing the number of divided injections of main injection compared to when release is not required, or by reducing the injection pause interval between main injections even if the number of divided injections is the same.
[0079]
  (5) NO_XWhen the temperature of the absorbent 22 is low, the main injection injected in one combustion cycle in each cylinder is divided into multiple injections, and the number of main injections is increased or the injection pause interval is increased.
[0080]
  In multistage injection of main injection in a diesel engine, it is known that the exhaust gas temperature can be raised by appropriately setting the number of injections and the injection pause interval. For example, JP-A-2001-055950 It is disclosed in the publication. Specifically, with regard to the number of injections, the exhaust gas temperature rises in the case of the three-part injection, compared to the time of the two-part injection, and the injection pause interval has an exhaust gas temperature that is shorter than when the injection pause interval is long. Rises.
[0081]
  Therefore, in this embodiment, the main injection is divided into multiple stages for injection, and NO._XWhen the absorbent 22 temperature is low, NO_XEven when the release is not required, the post-combustion is executed and the number of divided injections of the main injection is increased, or the injection pause interval between the main injections is increased even if the number of divided injections is the same. Can raise temperature, NO_XThe effect of increasing the temperature of the absorbent 22 can be improved.
[0082]
  (6) NO_XWhen absorbent 22 temperature is low, NO_XEven when the discharge is not requested, the post injection is executed and the post injection timing is set to NO._XLead angle control with respect to release request.
[0083]
  Regarding the relationship between the post-injection timing and the exhaust gas temperature, the engine speed is controlled to 2000 rpm and the average effective pressure is controlled to 0.5 MPa. As shown in FIG. 6, an experiment was conducted in which the exhaust gas temperature was measured with various changes, and as shown in FIG. It was confirmed that the exhaust gas temperature gradually decreased when the exhaust gas temperature became the highest and became slower than the crank angle.
[0084]
  Therefore, in this embodiment, NO_XNon-NO when absorbent 22 temperature is low_XEven when the discharge is requested, the post injection is executed and the post injection timing is set to NO._XThe exhaust gas temperature is increased to a high level by advancing the exhaust gas so as to approach the end timing of the main combustion with respect to the release request._XNO can be obtained_XCan be raised to the purification temperature range, NO_XNO of absorbent 22_XDeterioration of purification rate can be suppressed.
[0085]
  Hereinafter, the present embodiment will be described with reference to FIGS.StateSpecific control will be described.
[0086]
  First, various data are input in step S1 of FIG. 7, and the target torque Tr of the engine is set in step S2. The target torque Tr is set based on, for example, a map of engine speed and accelerator opening.
[0087]
  Next, in step S3, a basic main injection amount Qmb, a basic main injection timing Imb, and a basic post-injection amount Qpb corresponding to the operating state are set. The basic main injection amount Qmb and the basic main injection timing Imb are set based on a map of the target torque Tr and the engine speed. The basic post-injection amount Qpb is set based on a basic post-injection amount supply map of the target torque Tr and the engine speed, and is a fixed amount only in a high rotation or high load region where the amount of soot is increased. For other areas where the amount of wrinkles is small, the amount is set to zero. In other areas where the amount of soot generation is small, the basic post-injection amount Qpb is set to 0 to improve fuel efficiency, but the basic post-injection amount Qpb is set to be larger than 0 to further improve the reduction of soot. You may make it show. In the high rotation or high load region where the amount of soot is increased, the basic post-injection amount Qpb is set to a fixed amount, but it is set to increase as the target torque Tr and the engine speed increase. Also good.
[0088]
  In step S4, NO_XIn the subsequent step S5, NO is estimated by estimating the absorbent 22 temperature Tcate._XNO absorbed by the absorbent 22_XThe amount NOe is estimated. NO_XThe absorbent 22 temperature Tcate is estimated based on the exhaust gas temperature detected by the temperature sensor 19 or estimated based on temperature data set experimentally based on the operating state such as the fuel injection amount and the engine speed. Is done. NO_XThe amount NOe is the fuel injection amount, engine speed, and estimated NO when the air-fuel ratio is lean._XInstantaneous absorption NO based on absorbent 22 temperature Tcate_XThe amount is calculated and its instantaneous absorption NO_XThe amount is calculated and accumulated. Further, when the air-fuel ratio is richer than the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio, the fuel injection amount, the engine speed, and the estimated NO_XInstantaneous release NO based on absorbent 22 temperature Tcate_XThe amount is determined and its instantaneous release NO_XEstimated NO when the amount was estimated during lean operation_XDecrease from amount NOe
Calculated residual NO_XAs a quantity.
[0089]
  In step S6, NO estimated in step S5._XIt is determined whether the amount NOe is equal to or greater than the allowable amount NOo. If YES is determined in the step S6, the process proceeds to a step S7 so as to determine whether or not the timer T is being counted. When it is determined NO in step S7, the estimated NO_XSince the amount NOe is in a state where the amount NOo is less than or equal to the allowable amount NOo, NO in steps S8 to S11 below._XSet the control amount for releasing. In step S8, the main injection is two-stage injection, the first main injection amount Qm1λ, the first main injection timing Im1λ, the second main injection amount Qm2λ, the second main injection timing Im2λ, and the main injection interval at the normal time ( It is set short with respect to step S26 described later. In step S8, the post-injection amount Qpλ is reset, the post-injection timing Ipλ is set, and the optimal post-injection timing Ipba is set. Here, the optimum post-injection timing Ipba is set to an advance side with respect to the post-injection timing Ipλ, and coincides with the end timing of main combustion in the two-stage injection of the first main injection amount Qm1λ and the second main injection amount Qm2λ. It is time. Since the end point of the main combustion differs depending on the engine operating state as described in FIG. 3, the optimum post-injection timing Ipba is shown in a map of the engine operating state, for example, the engine speed and the target torque. The optimum post-injection timing Ipba is increased from the compression top dead center as the engine speed and target torque are increased. The total injection amount of the first main injection amount Qm1λ, the second main injection amount Qm2λ, and the post-injection amount Qpλ is set so that the air-fuel ratio is richer than the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio.
[0090]
  In step S9, a timer T1 and an air-fuel ratio enrichment end timing Ten are set. Timer T1 is estimated NO_XIn step S8, the post-injection amount is gradually increased from the basic post-injection amount Qpb set in step S3 to the post-injection amount Qpλ set in step S8 from the time point when the amount NOe becomes equal to or less than the allowable amount NOo. It is set based on the magnitude of the difference between the set first main injection amount Qm1λ and the second main injection amount Qm2λ and the basic main injection amount Qmb set in step S3. Further, the air-fuel ratio enrichment end timing Ten is set based on a fixed predetermined time, for example, a time obtained by adding 0.5 to 5 sec to the determined timer T1.
[0091]
  In step S10, an increase rate ΔQp per time for increasing the post-injection amount Qpλ stepwise and a retard rate ΔIp per time for retarding the post-injection timing Ipλ stepwise are set. The increase rate ΔQp is set by dividing the difference between the post-injection amount Qpλ set in step S8 and the basic post-injection amount Qpb set in step S3 by the timer T1 set in step S9. The retardation rate ΔIp is set by dividing the difference between the post-injection timing Ipλ set in step S8 and the optimal post-injection timing Ipba by the timer T1 set in step S9.
[0092]
  In step S11, the basic post-injection amount Qpb set in step S3 is substituted for the previous post-injection amount Qp, and the optimal post-injection timing Ipba is substituted for the previous post-injection timing Ipa, and the flow proceeds to the subsequent step S12. If the determination in step S7 is YES, steps S8 to S11 have already been performed, and the process bypasses steps S8 to S11 and proceeds to step S12.
[0093]
  In step S12, the timer T is counted up. In step S13, it is determined whether or not the timer T is smaller than the timer T1 set in step S9. When YES is determined in step S13, the increase rate ΔQp set in step S10 is added to the previous post-injection amount Qp in step S14 to set the current post-injection amount Qpi. The current post-injection timing Ipai is set by adding the retardation rate ΔIp set in step S10 to the injection timing Qp.
[0094]
  In step S16 of FIG. 8, the first main injection amount Qm1λ set in step S8 is injected at the first main injection timing Im1λ, the second main injection amount Qm2λ is injected at the second main injection timing Im2λ, and The post-injection amount Qpi increased in steps in step S14 is injected at the post-injection timing Ipai retarded in steps in step S15.
[0095]
  When NO is determined in step S13, the process proceeds to step S17, and it is determined whether or not the timer T is larger than the timer T1 set in step S9 and smaller than the air-fuel ratio enrichment end time Ten set in step S9. To do. When YES is determined in step S14, the process proceeds to step S18, the post-injection amount Qpλ set in step S8 is set in the current post-injection amount Qpi, and the current post-injection timing Ipai is set in step S8. The post injection timing Ipλ is set.
[0096]
  In the following step S16, the first main injection amount Om1λ set in step S8 is injected at the first main injection timing Im1λ, the second main injection amount Om2λ is injected at the second main injection timing Im2λ, and step S18. The post injection amount Qpi set in step S18 is injected at the post injection timing Ipai set in step S18.
[0097]
  When it is determined NO in step S17, the timer T is cleared in step S19, and the estimated NO_XThe amount NOe is reset, and the process proceeds to step S20 in FIG. Further, when it is determined NO in step S6, the process similarly proceeds to step S20 in FIG.
[0098]
  In step S20, NO estimated in step S4_XIt is determined whether or not the absorbent material 22 temperature Tcate is equal to or lower than a predetermined temperature Tcato. Here, the predetermined temperature Tcato is NO_XAlthough the absorbent 22 temperature is higher than the activation temperature (for example, 200 ° C.), NO_XThe noble metal (for example, Pt) contained in the absorbent 22 is in an inactive state, and NO_XThe temperature is set at a low purification rate.
[0099]
  When it is determined YES in step S20, the process proceeds to step S21, and NO_XA main injection form for raising the temperature of the absorbent 22 is set. Specifically, assuming that the main injection is three-stage injection, the first main injection amount Qm1b, the first main injection timing Im1b, the second main injection amount Qm2b, the second main injection timing Im2b, the third main injection amount Qm3b, the third The main injection timing Im3b is set. Further, the injection pause interval of each main injection is set to 50 to 500 μs.
It should be noted that two-stage injection may be used instead of three-stage injection, and the injection pause interval of each main injection may be set longer than that of the three-stage injection, for example, 500 to 1000 μs.
[0100]
  In step S22, it is divided into three stages in step S21, and the timing coincident with the end timing of main combustion by the three-stage injection is changed as the optimum post-injection timing Ipbb as the injection end timing of the main injection is changed. Set. That is, here, the timing that coincides with the end timing of the main combustion when the main injection is three-stage injection and the main injection pause interval is set to 50 to 500 μs is set as the optimum post-injection timing Ipbb. Subsequently, in step S23, the main injection divided in three stages set in step S21 is injected at each injection timing, and in step S3, the basic post-injection amount Qpb set in step S3 is set in step S22. Injection is performed at the optimal post-injection timing Ipbb. This makes NO_XThe temperature of the absorbent 22 can be raised.
[0101]
  When it is determined NO in step S20, the process proceeds to step S24, in which the main injection is set as a two-stage injection, and each main injection pause interval is set to 50 to 500 μs.
[0102]
  In step S25, it is determined whether or not the post-injection amount Qpb is set to 0. If NO is determined, the process proceeds to step S26, and the two-stage injection is performed according to the two-stage injection set in step S24. Is set as the optimal post-injection timing Ipbc. That is, here, the timing that coincides with the end timing of the main combustion when the main injection is two-stage injection and the main injection pause interval is set to 50 to 500 μs is set as the optimum post-injection timing Ipbc.
[0103]
  In step S27, the main injection divided in two stages set in step S24 is injected at each injection timing, and when the post-injection amount Qpb is set, it is set in step S3 set in step S26. The basic post-injection amount Qpb is injected at the optimal post-injection timing Ipbc set in step S22.
[0104]
  Less than, RealActions and effects of the embodiment will be described with reference to FIGS.
[0105]
  First, as shown in FIG._XAbsorbent 22 temperature Tcate and estimated NO_XBased on the amount NOe, it is divided into the following four states.
NO_XThe temperature Tcate of the absorbent 22 is higher than the activation temperature Tcat, and the estimated NO_XThe amount NOe is greater than the allowable amount NOo and NO_XBetween the time T0 when the release request is established and the timer T1 (first period 1A),
NO_XThe temperature Tcate of the absorbent 22 is higher than the activation temperature Tcat, and the estimated NO_XThe amount NOe is greater than the allowable amount NOo and NO_XFrom the time point T0 to the time point T1 when the release request is established to the air-fuel ratio enrichment end time Ten (first period 1B),
NO_XThe temperature Tcate of the absorbent 22 is lower than the activation temperature Tcat, and the estimated NO_XWhen the amount NOe is less than or equal to the allowable amount NOo (second period)
NO_XThe temperature Tcate of the absorbent 22 is higher than the activation temperature Tcat,
      Estimated NO_XWhen the amount NOe is less than or equal to the allowable amount NOo (third period)
  Then, as shown in FIG. 10 according to the above states, the following main injection and post-injection control is performed.
In the first period 1A, as shown in FIG._XThe amount NOe is greater than the allowable amount NOo and NO_XBetween the time T0 when the release request is established and the timer T1, the injection timing Ipi of the post fuel Qpi is retarded stepwise with respect to the main combustion end timing Ipba (→ indicates the movement). Therefore, NO_XIn the initial stage when the air-fuel ratio is shifted from lean to rich for release, an increase in the amount of HC (reducing agent amount) can be suppressed, and the decrease in the oxygen concentration in the exhaust gas can be moderated. NO_XCan be suppressed as shown by a solid line.
In the first period 1A, as shown in FIG. 10A, the post fuel Qpi is NO._XThe amount is increased stepwise from the release request time T0 to the timer T1. (The shaded area in the figure) Therefore, the decrease in the oxygen concentration of the exhaust can be slowed down, and a large amount of NO_XCan be prevented from being released rapidly.
In the first period 1B, the post fuel is increased and the post injection timing is retarded as shown in the solid fuel line Qpi and post injection timing Ipi shown by the solid line in FIG. The amount of reducing agent supplied can be increased, NO_XThe purification rate can be improved.
In the first periods 1A and 1B, as shown in FIG. 10A, the number of main injections is set to two (Qm1λ, Qm2λ), and the number of main injections is decreased. Therefore, deterioration of fuel consumption can be suppressed.
In the second period, as shown in FIG. 10B, the number of main injections is set to three (Qm1b, Qm2b, Qm3b), and the number of main injections is increased. Therefore, the exhaust gas temperature can be raised and NO_XThe temperature of the absorbent 22 can be raised.
In the second period, as shown in FIG. 10B, the post-injection timing Ipbb is set to NO._XIt is advanced with respect to the post-injection timing Ipλ when the release is requested. Therefore, NO_XWhen absorbent 22 temperature is low, NO_XThe temperature of the absorbent 22 can be raised and NO_XThe purification rate can be improved.
In the third period, as shown in FIG. 10C, the post fuel injection timing is set based on the operating state so that the post combustion timing Ipbc based on the post fuel Qpb is almost immediately after the main combustion. Is done. Therefore, since the post-injected post-fuel burns together with the carbon in a state where carbon and oxygen present in the combustion chamber 4 of the engine are well mixed, soot emission can be suppressed.
[0106]
  (referenceForm)
  referenceThe form is, The above embodimentIn contrast, (2) post fuel injection timing control and (3) post fuel injection amount control are different, and the others are the same.
[0107]
  Specifically, the injection timing of the post fuel and the injection amount of the post fuel are controlled as follows.
(2) After fuel injection timing is NO_XAt the time when the release request is established, the control is performed so as to retard the main combustion end timing and thereafter approach the main combustion end timing.
(3) After fuel amount is NO_XWhen the release request is established, the first predetermined increase is set, and then the second predetermined increase is set to be smaller than the first predetermined increase.
[0108]
  Hereinafter, a specific description will be given based on FIGS. 11 and 12.
[0109]
  referenceIn the form, only the steps surrounded by the wavy line in the flowchart of FIG.the aboveSince this is different from the embodiment, only this difference will be described.
[0110]
  In step S109 of FIG. 11, a timer T2 for defining a period in which the post fuel injection timing is retarded with respect to the main combustion end timing, and an air-fuel ratio enrichment end timing Ten are set. Here, T2 and Ten are fixed values.
[0111]
  In steps S110 and S111, processing similar to that in steps S11 and S12 in FIG. 7 is performed. In step S112, it is determined whether or not the timer T is smaller than the timer T2 set in step S109. If it is determined YES, the current post-injection amount Qpi and the current post-fuel injection timing are determined in step S113. Ipi is set. The current post-injection amount Qpi is obtained by adding a preset fixed increase ΔQpz to the previous post-injection amount Qp set in step S110. The current post-fuel injection timing Ipi is obtained by adding a preset fixed delay correction amount ΔIpz to the previous post-fuel injection timing Ip set in step S110.
[0112]
  When it is determined NO in step S112, it is determined in step S114 whether the timer T is greater than the timer T2 set in step S109 and smaller than the air-fuel ratio rich end timing Ten. If YES is determined in step S114, the current post-injection amount Qpi and the current post-fuel injection timing Ipi are set in step S115. The current post-injection amount Qpi is the same as the post-injection amount Qpλ set in step S18 of FIG. 7, and the current post-fuel injection timing Ipi is the same as the post-fuel injection timing Ipλ set in step S18 of FIG. It is.
[0113]
  Less than,referenceThe operation and effect of the embodiment will be described with reference to FIGS. still,the aboveFruitProcessingThe description of the same effect as the state is omitted.
In the first period 1A, as shown in FIG._XThe amount NOe is greater than the allowable amount NOo and NO_XBetween the time T0 when the release request is established and the timer T2, the post fuel injection timing Ipa + ΔIp is retarded with respect to the main combustion end timing Ipba. Therefore, NO_XIn the initial stage when the air-fuel ratio is shifted from lean to rich for release, the amount of HC can be increased._XA reduction in the purification rate can be suppressed.
In the first period 1A, as shown in FIG._XThe amount NOe is greater than the allowable amount NOo and NO_XFrom the time T0 when the release request is established to the timer T2, the post fuel amount is increased (shaded area in the figure). Therefore, NO_XIn the initial stage when the air-fuel ratio is shifted from lean to rich for release, the amount of HC can be increased._XA reduction in the purification rate can be suppressed.
In the first period 1B, as shown in FIG. 12B, the rear fuel Qpb amount is decreased and the rear fuel injection timing Ipλ is advanced, so that deterioration of fuel consumption can be suppressed.
[0114]
  still,the aboveEmbodimentAnd reference formThen, although the example of the diesel engine was shown, you may apply to the cylinder direct injection type gasoline engine which injects a fuel directly in a cylinder. In that case, it may be ignited by the spark plug again at the combustion timing of the post fuel so that the post combustion is performed reliably.
[Brief description of the drawings]
FIG. 1 is an overall view showing an exhaust emission control device for a diesel engine.
FIG. 2 is a time chart showing a change in heat generation rate when there is no combustion chamber.
FIG. 3 is a graph showing a relationship between a post-injection amount and a soot generation amount.
FIG. 4 is a graph showing a relationship between a ratio of a post-injection amount to a main injection amount and a soot generation amount.
FIG. 5 is a graph showing a relationship between a ratio of a post injection amount to a main injection amount and an HC amount.
FIG. 6 is a graph showing the relationship between the post-injection amount and the exhaust gas temperature.
[Fig. 7]FruitThe flowchart which shows the fuel-injection control in embodiment.
[Fig. 8]FruitThe flowchart which shows the fuel-injection control in embodiment.
FIG. 9FruitThe time chart which concerns on embodiment.
FIG. 10FruitThe time chart which concerns on embodiment.
FIG. 11referenceThe flowchart which shows the fuel-injection control in a form.
FIG.referenceThe time chart which concerns on a form.
[Explanation of symbols]
1: Engine body
5: Fuel injection valve
22: NO_XAbsorber
40: Main injection control means
41: Sub-injection control means

Claims (5)

A fuel injection valve for injecting fuel directly into the combustion chamber, disposed in the exhaust passage, a NO _X absorbent to release the NO _X due to the absorption decreases in the oxygen concentration of NO _X in an oxygen-rich atmosphere, near the compression top dead center Main combustion means for injecting main fuel by the fuel injection valve at a predetermined time until the main combustion means for generating a required torque at least in the first half of the expansion stroke based on the main fuel, and NO NO from the NO _X absorbent _{When X} release is requested, after the main fuel is injected, after the main fuel is injected, the fuel injection valve injects the rear fuel at a predetermined timing in the first half of the expansion stroke, and the rear fuel is injected. An exhaust emission control device for an engine, comprising: a post-combustion unit that increases the amount in a stepwise manner as time elapses from when the NO _X release request is established until a predetermined period elapses. A fuel injection valve for injecting fuel directly into the combustion chamber, disposed in the exhaust passage, a NO _X absorbent to release the NO _X due to the absorption decreases in the oxygen concentration of NO _X in an oxygen-rich atmosphere, near the compression top dead center Main combustion means for injecting main fuel by the fuel injection valve at a predetermined time until the main combustion means for generating a required torque at least in the first half of the expansion stroke based on the main fuel, and NO NO from the NO _X absorbent At the time of _X release request, after the main fuel is injected, after the main fuel is injected, the fuel is injected by the fuel injection valve at a predetermined time in the first half of the expansion stroke, and the post-combustion is started. And a post-combustion means for retarding the combustion timing of the main combustion in a stepwise manner with the passage of time from the time when the NO _X release request is established until a predetermined period elapses. Characterized by Exhaust emission control device of the engine. Oite to claim 1,
The engine is a diesel engine, and the main combustion means is multistage injection in which main injection is divided into multiple injections near the top dead center of the compression stroke. The engine exhaust gas purification apparatus is configured to reduce the number of injections of the multistage injection or to reduce the injection pause interval. Embedded in hardware resources including a computer, the main fuel is injected directly into the combustion chamber by the fuel injection valve at a predetermined time up to the vicinity of compression top dead center, and the required torque is generated at least in the first half of the expansion stroke based on the main fuel A main combustion procedure for performing the main combustion, and a NO _X release request from the NO _X absorbent, so that combustion is started immediately after the main combustion is almost finished, after the injection of the main fuel, a predetermined part of the first half of the expansion stroke A post-combustion procedure in which post-fuel is injected directly into the combustion chamber by a fuel injection valve at a time, and the post-fuel amount is increased stepwise over time until a predetermined period elapses from the time when the NO _X release request is established Is executed by the hardware resource. Embedded in hardware resources including computers,
A main combustion procedure in which main fuel is directly injected into the combustion chamber by a fuel injection valve at a predetermined time up to near the compression top dead center, and main combustion is performed to generate a required torque at least in the first half of the expansion stroke based on the main fuel;
When the NO _X release request from the NO _X absorbent is requested, the fuel injection valve directly enters the combustion chamber by a fuel injection valve at a predetermined timing in the first half of the expansion stroke after the main fuel injection so that combustion is started almost immediately after the main combustion is completed. The post fuel is injected, and the combustion timing of the post combustion is gradually retarded with the passage of time from the time when the NO _X release request is established until the predetermined period elapses. And after-burning procedure,
A computer program that causes the hardware resource to execute.

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