JP4134398B2 - Internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an internal combustion engine provided with a NOx catalyst, and more particularly, to an internal combustion engine capable of releasing or reducing NOx stored in the NOx catalyst.
[0002]
[Prior art]
Currently, NOx catalysts that can purify NOx even in an oxygen-excess atmosphere in which oxygen in the exhaust gas becomes excessive have been developed. In an internal combustion engine capable of lean combustion, this NOx catalyst is provided to purify NOx during lean combustion. I am doing so.
As one of the NOx catalysts, a storage-type NOx catalyst (hereinafter simply referred to as NOx catalyst) that purifies NOx in exhaust gas by storing NOx on the catalyst has been developed. The NOx catalyst oxidizes NOx in the exhaust gas to generate nitrate in an oxygen-excess atmosphere, and stores NOx in this manner, while the NOx catalyst stores NOx in the exhaust gas and CO in the exhaust gas. It reacts to produce carbonate, thereby releasing and decomposing NOx. Of course, the NOx storage amount of the NOx catalyst has a limit. Therefore, before the NOx occlusion amount exceeds the limit, the exhaust air-fuel ratio is made rich so that the atmosphere surrounding the NOx catalyst is reduced to an oxygen concentration-reducing atmosphere, and NOx occluded on the catalyst is released.
[0003]
As such a technique, there is one disclosed in JP-A-7-166851. In this technique, a NOx sensor is provided downstream of the NOx catalyst, and a decrease in the purification efficiency of the NOx catalyst is detected based on the output of the NOx sensor in an oxygen-excess atmosphere. When the purification efficiency of the NOx catalyst is reduced, the NOx occluded in the NOx catalyst is released by setting the atmosphere in which the oxygen concentration is lowered for a predetermined time, and the NOx occlusion performance by the NOx catalyst is ensured again during lean combustion operation. The function of purifying NOx in exhaust gas is maintained.
[0004]
[Problems to be solved by the invention]
However, the NOx release characteristics of the NOx catalyst include changes in operating conditions such as A / F (air-fuel ratio), exhaust temperature, S / V (ratio of combustion chamber total surface area to combustion chamber volume), and deterioration of the catalyst itself. It changes by etc. Therefore, as in the above-described prior art, there is a problem that it is impossible to cope with the change in the NOx release characteristics when the time for the oxygen concentration lowering atmosphere is fixed at a preset time.
[0005]
In other words, if the time for the oxygen concentration lowering atmosphere does not correspond to the NOx release characteristics of the NOx catalyst and is insufficient, the NOx catalyst is not completely released, so the purification efficiency of the NOx catalyst is reduced and NOx into the atmosphere is reduced. The amount of emissions will increase. On the other hand, if the time for setting the atmosphere for reducing the oxygen concentration is excessive, useless fuel injection is performed, resulting in deterioration of fuel consumption.
[0006]
The present invention was devised in view of such a problem, and it was made possible to release and reduce NOx occluded in the NOx catalyst without causing deterioration in fuel consumption, regardless of changes in the NOx release characteristics of the NOx catalyst. An object of the present invention is to provide an internal combustion engine.
[0007]
[Means for Solving the Problems]
  For this reason, in the internal combustion engine of the present invention, NOx occluded in the NOx catalyst provided in the exhaust passage of the internal combustion engine is released or reduced by setting the exhaust air-fuel ratio to an atmosphere with reduced oxygen concentration. NOx release state detected by state detection means provided downstream(NOx concentration β) is the NOx concentration β in the operating state in which the NOx release amount stored in advance is substantially zero. ₀ Corrected NOx concentration γ (= β−β) ₀ )When, Judgment concentration γ ₂ Based on the comparison result, the exhaust air / fuel ratio is changed from the oxygen concentration lowering atmosphere to the oxygen excess atmosphere by the atmosphere changing means.
In another internal combustion engine according to the present invention, the NOx occluded in the NOx catalyst provided in the exhaust passage of the internal combustion engine is released or reduced by setting the exhaust air-fuel ratio to an atmosphere with a reduced oxygen concentration. The NOx release state (NOx concentration β) detected by the state detection means provided downstream of the catalyst is replaced with the NOx concentration β in the operation state in which the NOx release amount stored in advance is substantially zero. ₀ And the NOx concentration β that flows into the NOx catalyst ₁ Corrected NOx concentration γ (= β−β ₀ -Β ₁ ) And determination density γ ₂ Based on the comparison result, the exhaust air / fuel ratio is changed from the oxygen concentration lowering atmosphere to the oxygen excess atmosphere by the atmosphere changing means.
Further, the NOx concentration β in the operation state where the NOx release amount is almost zero. ₀ Is preferably updated every time the set condition that the stoichiometric feedback mode is entered and the low load and low rotation state is established immediately after the additional fuel injection control is satisfied.
[0008]
As a result, the NOx release operation can be performed without excess or deficiency in accordance with the change in the NOx release characteristics of the NOx catalyst, and the NOx stored in the NOx catalyst can be reliably released or reduced without causing deterioration in fuel consumption. .
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, the outline of the configuration of an internal combustion engine according to an embodiment of the present invention will be described. As shown in FIG. 2A, the internal combustion engine is a four-cycle engine, is a spark ignition type, and burns. This is configured as a cylinder injection type internal combustion engine (cylinder injection engine) that directly injects fuel into the room.
[0010]
An intake passage 2 and an exhaust passage 3 are connected to the combustion chamber 1 so as to communicate with each other. The intake passage 2 and the combustion chamber 1 are controlled to communicate with each other by an intake valve 4, and the exhaust passage 3 and the combustion chamber 1 are connected. The communication is controlled by the exhaust valve 5.
The intake passage 2 is provided with an air cleaner and a throttle valve (not shown), and the exhaust passage 3 is provided with an exhaust purification device 6 and a muffler (silencer) not shown. In addition, 9 is a high temperature sensor and 10 is a NOx sensor.
[0011]
An ignition plug 7 is provided at the upper center of the combustion chamber 1, and an injector 8 is provided at the upper side edge of the combustion chamber 1. This injector (fuel injection valve) 8 is arranged so that its opening faces the combustion chamber 1.
With such a configuration, air sucked in according to the opening of a throttle valve (not shown) is sucked into the combustion chamber 1 by opening the intake valve 4 and is injected based on a signal from an electronic control unit (ECU) 20. 8 is mixed with the fuel directly injected. Then, it is burned by ignition at an appropriate timing of the spark plug 7 to generate engine torque, and then exhausted from the combustion chamber 1 to the exhaust passage 3 as exhaust gas, and the exhaust purification device 6 emits CO, HC, NO_xAfter these three harmful components are purified, they are silenced by a muffler and desorbed to the atmosphere side.
[0012]
The exhaust purification device 6 is a storage type NO._xCatalyst (hereinafter simply NO_x6A) and two three-way catalysts 6B and 6C. That is, when the air-fuel ratio is lean, the exhaust gas contains almost no CO or HC, while NO._xIn the case of an oxygen-excess atmosphere, the concentration increases rapidly, but NO with a three-way catalyst_xBecause this cannot be purified, this NO_xFor NO functioning in an oxygen-rich atmosphere_xIt is occluded by the catalyst 6A, and under the stoichiometric air-fuel ratio, the three-way functions of the three-way catalysts 6B and 6C make CO, HC, NO in exhaust gas_xIt is to purify.
[0013]
One of the three-way catalysts 6C is NO_xIt arrange | positions upstream from the catalyst 6A and functions as a front catalyst. The front catalyst receives a higher temperature exhaust gas when the engine starts cold, and is activated early to purify exhaust gas components such as HC. Note that the arrangement of the three-way catalyst 6C is NO, as shown in FIG._xThe catalyst 6A and the three-way catalyst 6B may be arranged close to the engine main body, and as shown in FIG._xThe catalyst 6A and the three-way catalyst 6B may be arranged side by side.
[0014]
The three-way catalyst 6B is NO_xIt may be integrated with the catalyst 6A. That is, NO_xThe catalyst 6A may have a three-way function. In this case, NO_xThe sensor 10 is disposed downstream of the integrated catalyst.
By the way, NO_xCatalyst 6A is NO_xNO will no longer be occluded until it reaches saturation and continues to occlude_xWill be released into the atmosphere. So NO_xWhen the catalyst 6A reaches saturation, the stored NO_xNeeds to be released once, but this NO_xRelease of NO_xNO stored by making the ambient atmosphere of the catalyst 6A into an oxygen concentration decreasing atmosphere (reducing atmosphere)_xNO₂Further, NO is supplied by supplying HC and CO (reducing agent).₂Reduced to N₂It is supposed to be done by discharging as.
[0015]
Here, NO in this internal combustion engine_xNO from catalyst 6A_xThis will be described in more detail.
In a cylinder injection engine such as the present internal combustion engine, as a mode of fuel injection, a late injection mode (compression lean) in which fuel injection is performed during a compression stroke in order to realize the lean operation by the above-described stratified super lean combustion and improve fuel efficiency. Mode) and lean operation by premixed combustion, to achieve fuel injection during the intake stroke in order to obtain a slow acceleration output (intake lean mode) and stoichiometric operation by premixed combustion, A stoichiometric mode that injects fuel during the intake stroke to improve the output compared to the previous injection mode and an enrichment mode that realizes rich operation by premixed combustion and improves output over the stoichiometric operation mode are provided. And can be switched according to the operating state of the engine.
[0016]
And under each lean operation as mentioned above, NO_xSince the atmosphere around the catalyst 6A is in an oxygen-excess atmosphere, NO_xThe catalyst 6A has NO generated by lean combustion._xNOx occluded in this way is released and reduced in an atmosphere with a reduced oxygen concentration._xIn order to release NOx occluded in the catalyst 6A, an atmosphere changing means 23 for making the exhaust passage an atmosphere having a reduced oxygen concentration is provided. The atmosphere changing means 23 is configured to create an oxygen concentration lowering atmosphere using fuel injection control.
[0017]
That is, the ECU 20 of the internal combustion engine is provided with mode selection means 24 and fuel injection control means 25 as shown in the functional block diagram of FIG.
The mode selection means 24 selects one of the above modes according to the engine speed Ne and the average effective pressure Pe.
Further, the fuel injection control means 25 includes a normal fuel injection control means 26 for injecting fuel to perform normal combustion for obtaining engine output, and an additional fuel injection control means 27 for creating an atmosphere with a reduced oxygen concentration. It is provided.
[0018]
The normal fuel injection control means 26 selects a fuel injection control map corresponding to the mode set by the mode selection means 24, and uses the selected fuel injection control map to set the engine speed Ne and the average effective pressure Pe. Accordingly, a fuel injection amount and injection timing for performing normal combustion (that is, fuel injection end timing and fuel injection start timing) are set.
[0019]
Note that detection information (or calculation information) of the engine speed sensor 13 is used for the engine speed Ne, and calculation information of the effective pressure calculation means 28 is used for the average effective pressure Pe. In this effective pressure calculation means 28, the engine speed Ne and the accelerator opening θ detected by the accelerator position sensor (APS) 14 (if the throttle opening always corresponds to the accelerator opening, the throttle opening instead of the accelerator opening is used. The average effective pressure Pe is calculated from each information of the opening degree).
[0020]
The additional fuel injection control means 27 controls additional fuel injection (rich spike) performed for NOx release reduction from the NOx catalyst 6A. This additional fuel injection is performed within the expansion stroke of each cylinder (preferably the timing close to the end of the expansion stroke is preferable) in consideration of securing HC and CO in the exhaust gas and the influence on the engine output torque. I am doing so. As a result, the total air-fuel ratio (total A / F) of the normal fuel injection (main injection) and the additional fuel injection is made rich. Further, as a method of making the atmosphere around the NOx catalyst 6A the oxygen concentration lowering atmosphere, a method of enriching the air-fuel ratio only by normal fuel injection without using additional fuel injection may be used. Since the engine output fluctuates, it is necessary to perform processing that suppresses fluctuations in the engine output by ignition timing control, intake air amount control, and the like.
[0021]
The atmosphere changing means 23 has a function of making the surroundings of the NOx catalyst 6A into an oxygen concentration reducing atmosphere (reducing atmosphere) by such additional fuel injection. The additional fuel injection control means 27 and the additional fuel injection control means 27, an injector (fuel injection valve) 8 that is driven through an injector driver (not shown) to perform additional fuel injection.
[0022]
And this additional fuel injection is performed based on the determination of the determination means 21, and the determination means 21 determines the start time and end time of additional fuel injection control.
First, the determination of the start time is performed by evaluating the NOx concentration β detected by the NOx sensor 10 corresponding to the state detecting means provided on the downstream side of the NOx catalyst 6A, that is, the NOx release state from the NOx catalyst 6A. To do. That is, when an operation in the lean mode such as the intake lean mode or the compression lean mode is performed, the NOx catalyst 6A becomes an oxygen-excess atmosphere in the vicinity of the NOx catalyst 6A, and NOx is occluded in the NOx catalyst 6A. Efficiency will gradually decline. As a result, the NOx discharged downstream without being stored in the NOx catalyst 6A gradually increases, and the NOx concentration β detected by the NOx sensor 10 becomes higher. Therefore, a decrease in the purification efficiency of the NOx catalyst 6A can be determined by evaluating the NOx concentration β.
[0023]
In evaluating the NOx concentration β, first, the NOx concentration β is corrected. In other words, NO_XThe sensor 10 may have an error in detection accuracy due to individual variations or changes over time._XNO detected by sensor 10_XThe concentration β also includes NO corresponding to the detection error._XConcentration β₀Is included. Therefore, NO for this detection error_XConcentration β₀Needs to be determined and corrected in advance._XNO when operating with almost zero release_XConcentration β₀Seeking. For example, NO_XImmediately after the additional fuel injection control for releasing, the mode is the stoichiometric feedback operation, and the NO detected in the low load low rotation operation state during idling_XConcentration is detected as NO_XConcentration (NO_XSensor correction amount) β₀And stored in the storage means in the determination means 21.
[0024]
In other words, during stoichiometric feedback operation at low load and low rotation, NO_XIf the catalyst 6A is fully functional, NO_XSince the concentration is essentially zero, NO_XIf the sensor 10 is normal (if there is no error in the output value), NO_XNO detected by sensor 10_XThe concentration should also be zero. Therefore, at this time NO_XSensor 10 is constant NO_XConcentration β₀If this is detected, this is NO for the detection error._XConcentration, ie NO_XSensor correction amount β₀It becomes. And this NO_XSensor correction amount β₀Is set every time the setting condition (that is, immediately after the additional fuel injection control, stoichiometric feedback mode, low load and low rotation state) is established, and the storage in the storage means in the determination means 21 is updated. Yes.
[0025]
Thus, NO_XSensor correction amount β₀By NO_XNO detected by sensor 10_XBy correcting the concentration β, NO_XIndividual variation of the sensor 10 is compensated, and further NO_XSensor correction amount β₀Is set every time the setting conditions are met, so the detected NO_XThe influence of the change with time is also eliminated from the concentration β.
NO set in this way_XSensor correction amount β₀Detected NO_XTrue NO by correcting (subtracting) the concentration β_XConcentration (corrected NO_XConcentration) γ (γ = β-β₀) Is calculated.
[0026]
And this corrected NO_XConcentration (hereinafter simply NO_XΓ) is the NO during lean operation such as intake lean mode and compression lean mode._XNO detected downstream of catalyst 6A_XConcentration, NO_XAs the purification efficiency of the catalyst 6A decreases, that is, NO._XThe amount of occlusion increases as it approaches saturation. So this NO_XConcentration γ is NO_XNO when the purification efficiency of the catalyst 6A falls below the allowable level_XPredetermined start determination concentration γ corresponding to the concentration₁Compared to γ₁≦ γ if NO_XIt can be determined that the purification efficiency of the catalyst 6A has fallen below the allowable level.
[0027]
And the determination means 21 is NO_XWhen it is determined that the purification efficiency of the catalyst 6A has fallen below the allowable level, it is determined that it is necessary to perform additional fuel injection for releasing and reducing NOx from the NOx catalyst 6A, and an additional fuel injection start signal is transmitted. It outputs to the control means 27. The additional fuel injection control means 27 drives the injector 8 through an injector driver (not shown) in response to the input of the start signal, and performs additional fuel injection so that the air-fuel ratio is slightly smaller than the theoretical air-fuel ratio (for example, about 13). ing.
[0028]
On the other hand, the determination of the end time of the additional fuel injection control is obtained during the period during which the additional fuel injection is performed based on the output from the NOx sensor 10 and the information from the engine speed sensor 13 and the effective pressure calculation means 28. This is done by evaluating the NOx concentration β.
That is, as shown in FIG. 3, the determination means 21 outputs a start signal for additional fuel injection to the additional fuel injection control means 27 and simultaneously starts counting of the timer 12 (time t₀), Predetermined time tt₀₁Elapsed time (time t₁), The NOx concentration β input from the NOx sensor 10 is evaluated. However, as with the start time determination, NO_XConcentration β is NO_XSensor correction amount β₀Corrected by NO_XTrue NO by eliminating the effect of individual variations in sensor 10 and changes over time_XConcentration γ (γ = β-β₀) Is calculated.
[0029]
NO obtained here_XThe concentration γ is NO_XNO during additional fuel injection control for release_XNO detected downstream of catalyst 6A_XConcentration, this NO_XConcentration is NO_XNO from catalyst 6A_XThe release state is shown. That is, NO_XNO from catalyst 6A_XNO as the release of NO progresses_XNO stored in catalyst 6A_XNO, NO_XNO detected downstream of catalyst 6A_XConcentration gradually decreases. So this NO_XConcentration γ is NO_XNO at completion of discharge_XEnd determination concentration corresponding to concentration (predetermined state) γ₂(Γ₂≦ γ₁) ≦ γ₂Then NO_XNO from catalyst 6A_XIt can be determined that the release is complete.
[0030]
End determination concentration γ₂Is determined in consideration of the response delay due to the influence of exhaust gas speed, catalyst reaction speed, sensor response delay, and the like. In other words, due to the time lag due to these response delays, even if the NOx sensor 10 determines the completion of NOx release and terminates the additional fuel injection, the NOx catalyst 6A will have a rich atmosphere despite the NOx release being completed for a while. The state continues, and excessive fuel injection leads to deterioration of fuel consumption, and CO and HC are discharged, leading to deterioration of exhaust gas. Therefore, the end determination concentration γ₂Is set slightly higher than the true end determination concentration so as to finish the additional fuel injection earlier than the response delay.
[0031]
NO_XFor concentration γ, NO_XNO stored in catalyst 6A_XIn addition, NO during additional fuel injection control_XNO flowing into the catalyst 6A_XThe end determination concentration γ₂To decide. That is, inflow NO_XEnd determination concentration γ₂Is set slightly higher than the true end determination density. Further, instead of considering each of the above effects individually, the map is determined by the effective pressure (load information) Pe input from the effective pressure calculating means 28 and the engine speed Ne input from the rotation speed sensor 13. End determination concentration γ based on₂May be set.
[0032]
The above time tt₀₁Is NO_XThis is a margin time for preventing erroneous determination immediately after the start of additional fuel injection control due to the vibration of the concentration β. That is, even if additional fuel injection is started by a signal from the ECU because of a response delay due to the influence of the exhaust gas speed, catalyst reaction speed, sensor response delay, etc. described above, NO_XNO detected by sensor 10_XConcentration does not change immediately and NO_XNO detected by sensor 10_XThe density β does not change smoothly but involves some vibration, and the end determination density γ₂And start determination concentration γ₁Since the difference between the two may be small depending on the operation region, NO immediately after the start of additional fuel injection control_XConcentration γ (γ = β-β₀) Is the end determination concentration γ₂It is because it may become below.
[0033]
Therefore, time tt₀₁As NO to such an extent that erroneous determination can be prevented._XIt is necessary to secure the time until the concentration β increases, and it is determined in consideration of response delay due to exhaust gas speed, catalyst reaction speed, sensor response delay, and the like. Alternatively, it may be determined based on a map determined by the effective pressure (load information) Pe input from the effective pressure calculation means 28 and the engine speed Ne input from the rotation speed sensor 13.
[0034]
Thus, a predetermined time (time tt from the start of additional fuel injection control)₀₁) NO after elapse_XBy appropriately evaluating the concentration β, NO_XNO from catalyst 6A_XIt can be determined whether the release is complete. And NO_XNO from catalyst 6A_XWhen it is determined that the release is complete, that is, the corrected NO_XCatalyst γ is the end determination concentration γ₂When it becomes below, the determination means 21 outputs the completion | finish signal of additional fuel injection to the additional fuel injection control means 27. FIG. The additional fuel injection control means 27 stops driving the injector 8 when an end signal is input.
[0035]
As a result, the operating state of the engine becomes a lean mode such as a normal intake lean mode or a compression lean mode, and the exhaust air-fuel ratio is changed again to an oxygen-excess atmosphere, and NO_XNO at catalyst 6A_XOcclusion is resumed.
Since the internal combustion engine according to one embodiment of the present invention is configured as described above, additional fuel injection control for releasing NOx stored in the NOx catalyst 6A is performed, for example, as shown in the flowchart of FIG. It is.
[0036]
First, in the determination means 21, NO_XNOx detected by the sensor 10 NO downstream of the catalyst 6A_XDetect concentration β, NO_XSensor correction amount β₀Corrected NO corrected by_XConcentration γ and predetermined start determination concentration γ₁Are compared (step S10).
And NO_XConcentration γ is start determination concentration γ₁NO_XIt is determined that the purification efficiency of the catalyst 6A has fallen below an allowable level, and it is determined that NOx must be released from the NOx catalyst 6A. The additional fuel injection control means 27 performs additional fuel injection control for releasing NOx from the NOx catalyst 6A based on this determination, and is added so that the total air-fuel ratio is slightly smaller (for example, about 13) than the stoichiometric air-fuel ratio. The fuel is injected so that the ambient atmosphere of the NOx catalyst 6A becomes an oxygen concentration decreasing atmosphere. As a result, the NOx catalyst 6A starts releasing the stored NOx (step S20).
[0037]
Predetermined time tt from the start of additional fuel injection₀₁After the elapse (step S30), the determination means 21 next corrects NO._XConcentration γ and end determination concentration γ₂And compare. However, end determination concentration γ₂The response delay due to the effects of exhaust gas speed, catalyst reaction speed, sensor response delay, etc. and NO during additional fuel injection control_XNO flowing into the catalyst 6A_XThis is determined in consideration of the influence of (step S40).
[0038]
And NO_XConcentration γ is the end determination concentration γ₂When it becomes below, judgment means 21 is NO_XNO from catalyst 6A_XDetermine that release is complete. The additional fuel injection control means 27 ends the additional fuel injection control based on this determination, and if the engine operating state is the compression lean mode or the intake lean mode, NO_XThe ambient atmosphere around the catalyst 6A is changed again to an oxygen-excess atmosphere. Thereby, the NOx catalyst 6A starts storing NOx again (step S50).
[0039]
Thus, according to the present internal combustion engine, the end timing of the additional fuel injection is determined based on the NOx concentration β detected by the NOx sensor 10, so that the NOx release from the NOx catalyst 6A is completed. Therefore, it is possible to accurately determine NOx stored in the NOx catalyst 6A without causing deterioration in fuel consumption due to wasteful additional fuel injection, regardless of changes in the NOx release characteristics of the NOx catalyst 6A. Release reduction is possible.
[0040]
In this embodiment, the injection start timing of the additional fuel is also determined based on the NOx concentration β detected by the NOx sensor 10, but in this case, the state of reduction in the purification efficiency of the NOx catalyst is accurately determined. Therefore, it is possible to further reduce the amount of released NOx and prevent deterioration of fuel consumption.
In this way, by setting the additional fuel injection period to the minimum necessary, excessive additional fuel injection is avoided, and fuel efficiency can be improved. In addition, since NOx can be reliably released and reduced, the amount of NOx emission can always be accurately reduced, and as a result, the lean operation range can be expanded, thereby further improving fuel consumption.
[0041]
In the present embodiment, NO is determined in the determination of the end timing of the additional fuel injection._XNO contained in concentration β_XNO flowing into the catalyst 6A_XEnd determination density γ considering density₂Is determined, but NO_XWhen correcting the concentration β, this inflow_XYou may make it consider a density | concentration. That is, NO_XNO detected by sensor 10_XCorrection amount β for individual differences and changes over time from concentration β₀And inflow NO_XCorrection amount for₁And subtract true NO_XConcentration γ (γ = β-β₀-Β₁) Is calculated.
[0042]
This inflow NO_XCorrection amount for₁May be determined based on, for example, a map determined by the effective pressure (load information) Pe input from the effective pressure calculating means 28 and the engine speed Ne input from the rotation speed sensor 13. Of course NO_XNO on the upstream side of the catalyst 6A_XA sensor is installed and this upstream NO_XNO by sensor_XNO flowing into the catalyst 6A_XThe concentration may be detected and determined. In this case, more accurate determination is possible.
[0043]
In this embodiment, the NOx concentration in the exhaust gas is detected by the NOx sensor 10, and the end determination of the additional fuel injection control, that is, the completion determination of NOx release from the NOx catalyst 6A is performed based on the detected NOx concentration. However, depending on the catalyst, a part of the NOx released from the NOx catalyst in an atmosphere with a reduced oxygen concentration may be converted into NH by reaction on the catalyst._ThreeIt may become. This NH_ThreeIs a change in the NOx originally stored in the NOx catalyst._ThreeThe concentration can also be detected and used to determine NOx release completion.
[0044]
In that case, in general, many of the NOx sensors are NH in addition to the NOx concentration._ThreeSince the concentration can also be detected, in the case of such a NOx sensor, the NOx release completion determination may be performed based on the NOx sensor output value output as the sum of both. Conversely, if the NOx sensor detects only the NOx concentration, a new NH_ThreeNH in exhaust gas by providing a sensor_ThreeConcentration is detected, NOx sensor output value and NH_ThreeThe determination may be made based on both the sensor output value. NH_ThreeThe determination may be made only by the sensor.
[0045]
In the present embodiment, when the lean operation is continued, the NOx purification efficiency of the NOx catalyst is reduced due to NOx occlusion, so that enrichment is performed (that is, the atmosphere is reduced in oxygen concentration), and again when NOx release is completed. The case of returning to the lean operation state is explained, but this method is also used when NOx is released by temporarily enriching when switching from lean operation to stoichiometric operation due to acceleration by the driver's accelerator operation etc. May be used to determine the completion of NOx release, thereby end the enrichment and return to the stoichiometric operation.
[0046]
In this embodiment, the case of a cylinder injection engine which is one of the lean combustion internal combustion engines has been described. However, the internal combustion engine of the present invention is not limited to this cylinder injection engine, and an internal combustion engine capable of lean combustion. It can be widely applied to any institution.
[0047]
【The invention's effect】
As described in detail above, according to the internal combustion engine of the present invention, NOx occluded in the NOx catalyst is surely released without causing deterioration of fuel consumption due to wasteful fuel injection, regardless of changes in the NOx release characteristics of the NOx catalyst. Alternatively, it can be reduced. Further, by minimizing the oxygen concentration lowering atmosphere period, it is possible to further improve fuel efficiency by expanding the lean operation region.
[Brief description of the drawings]
FIG. 1 is a block diagram schematically showing a main configuration of a control system for additional fuel injection control of an internal combustion engine according to an embodiment of the present invention.
2A and 2B are schematic views showing the configuration of an internal combustion engine according to an embodiment of the present invention, where FIG. 2A is an overall configuration diagram, and FIG. 2B is a diagram showing a modification of the installation position of the catalyst in FIG. FIG.
FIG. 3 is a diagram for explaining the timing of starting and ending injection of additional fuel for releasing NOx from a NOx catalyst.
FIG. 4 is a flowchart showing a flow of additional fuel injection control of the internal combustion engine according to the embodiment of the present invention.
[Explanation of symbols]
3 Exhaust passage
6 Exhaust gas purification device
6A NOx catalyst
6B Three-way catalyst
6C Three-way catalyst (front catalyst)
8 Injection (fuel injection valve)
10 NOx sensor (state detection means)
20 ECU
21 judgment means
23 Atmosphere change means
25 Fuel injection control means
27 Additional fuel injection control means

Claims (3)

A NOx catalyst provided in an exhaust passage of the internal combustion engine, storing NOx in exhaust gas in an oxygen-excess atmosphere, and releasing or reducing NOx stored in an oxygen concentration-reduced atmosphere;
State detecting means provided downstream of the NOx catalyst and detecting a NOx concentration β indicating a NOx release state released from the NOx catalyst;
When NOx is released from the NOx catalyst, the exhaust air-fuel ratio is set to an atmosphere with a reduced oxygen concentration, and then the NOx concentration β output from the state detecting means is changed to an operating state in which the NOx release amount stored in advance is substantially zero. And an atmosphere changing means for changing the exhaust air / fuel ratio to an oxygen-excess atmosphere when the corrected NOx concentration γ (= β−β ₀ ) subtracted and corrected by the NOx concentration β _{0 at the} time becomes equal to or less than the determination concentration γ _2. An internal combustion engine characterized by that. A NOx catalyst provided in an exhaust passage of the internal combustion engine, storing NOx in exhaust gas in an oxygen-excess atmosphere, and releasing or reducing NOx stored in an oxygen concentration-reduced atmosphere;
State detecting means provided downstream of the NOx catalyst and detecting a NOx concentration β indicating a NOx release state released from the NOx catalyst;
When NOx is released from the NOx catalyst, the exhaust air-fuel ratio is set to an atmosphere with a reduced oxygen concentration, and then the NOx concentration β output from the state detecting means is changed to an operating state in which the NOx release amount stored in advance is substantially zero. the NOx concentration beta ₀ when, the NOx catalyst corrected NOx concentration obtained by subtracting corrected by the amount of NOx concentration beta ₁ flowing into _{γ (= β-β 0 -β} 1) is, when determining the concentration gamma ₂ or less since An internal combustion engine comprising: atmosphere changing means for changing the exhaust air-fuel ratio to an oxygen-excess atmosphere. The NOx concentration β in the operating state where the NOx release amount is almost zero. ₀ Is updated every time the setting condition that the stoichiometric feedback mode is entered and the low load and low rotation state is established immediately after the additional fuel injection control is established.
The internal combustion engine according to claim 1 or 2, characterized by the above.

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