JP2005113775A - INTERNAL COMBUSTION ENGINE WITH OCCLUSION TYPE NOx CATALYST - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently perform NOx purge with good fuel economy in relation to an internal combustion engine with occlusion type NOx catalyst performing NOx purge with rich spike. <P>SOLUTION: This engine is provided with occlusion type NOx catalyst 25, a NOx purge control means 28b performing NOx purge by making air fuel ratio rich, and an intake air flow rate condition determination means 28c determining whether intake air flow rate is in a low flow rate condition or not. The NOx purge control means 28b performs NOx purge under conditions where NOx occlusion state of the occlusion type NOx purification catalyst 25 reaches NOx purge state and the intake air flow rate condition determination means 28d determines that intake air flow rate is in the low flow rate condition. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an internal combustion engine that includes a storage-type NOx purification catalyst and performs NOx purge when the NOx storage amount of the storage-type NOx purification catalyst increases, and more particularly to an internal combustion engine with a storage-type NOx catalyst that is suitable for use in automobiles. .

  In recent years, lean burn internal combustion engines (lean burn engines) in which an internal combustion engine is operated at a lean air-fuel ratio to improve fuel efficiency have been put into practical use in the field of automobile engines and the like. In such a lean burn engine, when operating at a lean air-fuel ratio, the three-way catalyst cannot sufficiently purify NOx (nitrogen oxides) in the exhaust gas due to its purification characteristics. Exhaust purification catalyst device comprising an occlusion-type NOx catalyst that occludes or adsorbs NOx (hereinafter simply referred to as occlusion) to release and reduce NOx occluded during operation at a stoichiometric or rich air-fuel ratio Is equipped.

Such a storage-type NOx catalyst stores NOx in exhaust gas as nitrate (X—NO ₃ ) in an excess state of oxygen in an internal combustion engine, and stores the stored NOx mainly in an excess state of carbon monoxide (CO). It is a catalyst having the property of being released at a reduced pressure to nitrogen (N ₂ ) (at the same time, carbonate X-CO ₃ is produced).
Therefore, in practice, when the lean air-fuel ratio operation continues for a predetermined time, the exhaust air-fuel ratio is controlled to the stoichiometric air-fuel ratio or the rich air-fuel ratio by switching the air-fuel ratio in the combustion chamber or supplying the reducing agent to the exhaust pipe. Switching to rich air-fuel ratio operation periodically (this is called rich spike), thereby creating a reducing atmosphere with a lot of CO in the oxygen concentration-reducing atmosphere, releasing the stored NOx, and purifying and reducing (NOx purge). The type NOx catalyst can be regenerated (see, for example, Patent Document 1).

Further, as a technique related to a diesel engine, a technique for performing an air-fuel ratio enrichment process (NOx purge) for a predetermined period only when the engine is in a decelerating state and the catalyst (storage NOx catalyst) is in an active state has been proposed. (For example, refer to Patent Document 2). Here, the condition that the vehicle is in a decelerating condition is that there is little influence on drivability during deceleration. In this case, the fuel cut condition may or may not be satisfied in the deceleration state. Therefore, when the fuel cut condition is satisfied, the fuel cut is stopped and fuel injection is performed to realize the air-fuel ratio enrichment process. On the other hand, when the fuel cut condition is not satisfied (that is, during fuel injection), the air-fuel ratio enrichment process is realized by increasing the fuel amount or reducing the air amount while leaving the fuel amount unchanged. By realizing the air-fuel ratio enrichment process in this way, a wide range of opportunities for performing the air-fuel ratio enrichment process is prepared, and the air-fuel ratio enrichment process is performed under the condition that the catalyst is in an active state. By preventing wasteful operation, deterioration of fuel consumption and increase in HC emissions are prevented.
Japanese Patent No. 2,586,738 JP 2002-371889 A

By the way, in the first conventional technique (the technique described in Patent Document 1), when the lean air-fuel ratio operation is continued until a predetermined time set in advance, the NOx purge is set to be performed. Since no consideration is given to the running state of the vehicle, the NOx purge may be during acceleration of the vehicle or during steady running.
However, for example, during vehicle acceleration, engine output is required and the intake air flow rate is increased accordingly. However, when the intake air flow rate is large as during acceleration of the vehicle, a rich air-fuel ratio for performing NOx purge is performed. In order to drive, it is necessary to supply a large amount of fuel according to the intake flow rate, which is disadvantageous in terms of fuel consumption. Further, when the intake air flow rate is large, the exhaust gas flow rate is also increased, the contact time between the catalyst and the exhaust gas is shortened, and the reaction of the exhaust gas by the catalyst becomes insufficient. Therefore, a substitution reaction between CO used for NOx purge and occluded NOx and a reduction reaction of NOx are not easily caused, which is disadvantageous in exhaust gas purification.

  For example, FIG. 4 is a time chart showing A / F (air-fuel ratio), lean duration, mode flag (operation mode), and vehicle speed. As shown in FIG. 4, when the vehicle is stopped, the lean operation is used to make the air-fuel ratio lean, and the intake flow rate is increased by switching to the stoichiometric operation that makes the air-fuel ratio stoichiometric in response to a start request (depressing the accelerator pedal). When it is determined that the lean continuation time has reached the predetermined time when the lean operation is switched to the stoichiometric operation, the NOx purge is performed during the stoichiometric operation with the intake air flow rate increased. It will be. In this case, the above problem occurs.

  On the other hand, in the above-described second conventional technique (the technique described in Patent Document 2), the NOx purge by the air-fuel ratio enrichment process for a predetermined period is performed only when the engine is in the decelerating state and the catalyst is in the active state. Therefore, it is possible to avoid performing NOx purge during the acceleration described above, and there is no disadvantage in terms of fuel consumption and exhaust gas purification, but it is not possible to reliably avoid NOx purge when the intake air flow rate is large. .

  The present invention has been devised in view of the above-described problems, and in an internal combustion engine that has a NOx purging catalyst and performs NOx purging with a rich spike, the NOx purging can be efficiently performed with good fuel consumption. An object of the present invention is to provide an internal combustion engine with a type NOx catalyst.

  Therefore, an internal combustion engine with a storage-type NOx catalyst according to the present invention (Claim 1) is a vehicle internal-combustion engine provided with a storage-type NOx catalyst and NOx purge control means for enriching the air-fuel ratio and performing NOx purge. Intake flow rate state determining means for determining whether or not the intake flow rate is in a low flow rate state, the NOx purge control means, the NOx occlusion state of the storage type NOx purification catalyst has reached the NOx purge state, The NOx purge is performed on condition that the intake flow rate determination means determines that the intake flow rate is in a low flow rate state.

Preferably, the intake flow rate state determining means determines that the intake flow rate is in a low flow rate state when there is no acceleration request to the vehicle and the engine speed is equal to or lower than a preset upper limit value (claim). Item 2).
The intake flow rate state determining means is configured to determine whether or not the intake flow rate is in a low flow rate state by comparing a parameter value corresponding to the intake flow rate with a determination reference value, and the NOx of the storage type NOx purification catalyst. Even if the occlusion state reaches the NOx purge state, if the intake flow rate determination means does not determine that the intake flow rate is a low flow rate, the time is set so that the low flow rate determination is made even if the flow rate is relatively high. It is preferable to change the determination reference value according to the progress (Claim 3).

The vehicular internal combustion engine is configured to be able to perform a lean operation in which the air-fuel ratio is made leaner than the stoichiometric air-fuel ratio and combustion is performed, and in the NOx purge control means, the lean operation is continued for a preset predetermined time or more. Then, it is preferable to determine that the NOx occlusion state of the storage type NOx purification catalyst has reached the NOx purge state (Claim 4).
In this case, the NOx purge state is a state in which the estimated value of the NOx storage amount of the storage type NOx purification catalyst has reached the storage saturation amount or a state in which the storage saturation amount has approached a predetermined range. Preferred (claim 5).

  According to the internal combustion engine with a storage type NOx catalyst of the present invention, when the NOx storage state of the storage type NOx purification catalyst reaches the NOx purge state, it is determined by the intake flow rate state determination means that the intake flow rate is in a low flow rate state. Therefore, since the NOx purge is performed, the increase in fuel accompanying the enrichment of the air-fuel ratio during the NOx purge can be suppressed, and the deterioration of fuel consumption due to the NOx purge can be suppressed. Further, since the exhaust gas flow rate is also suppressed, a long contact time between the catalyst and the exhaust gas can be secured, and the substitution reaction and reduction reaction for the NOx purge can be sufficiently performed, so that the NOx purge can be performed efficiently. In addition, it is advantageous in terms of exhaust gas purification (claim 1).

When there is no acceleration request to the vehicle and the engine rotation speed is less than or equal to the preset upper limit value, it is determined that the intake flow rate is in the low flow rate state, so that the intake flow rate is in the low flow state easily and appropriately. (Claim 2).
By comparing the parameter value corresponding to the intake flow rate with the determination reference value, it is determined whether or not the intake flow rate is in a low flow rate state, and the NOx occlusion state of the storage type NOx purification catalyst reaches the NOx purge state. However, if it is not determined that the intake flow rate is in the low flow rate state, the NOx is changed by changing the determination reference value over time so that the low flow rate determination is made even if the flow rate is relatively high. A problem that the purge is not performed for a long time can be avoided (claim 3).

  If the lean operation is continued for a predetermined time or more, it is determined that the NOx storage state of the storage type NOx purification catalyst has reached the NOx purge state, thereby easily and appropriately determining that the NOx purge state has been reached. (Claim 4).

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIGS. 1 to 3 show an internal combustion engine with an occlusion-type NOx catalyst as one embodiment of the present invention. FIG. Is a flowchart for explaining the control, and FIG. 3 is a time chart for explaining the control.
First, an internal combustion engine (hereinafter also referred to as an engine) according to the present invention will be described. This engine is a lean burn internal combustion engine (lean burn engine) in which the internal combustion engine is operated at a lean air-fuel ratio to improve fuel efficiency. In order to purify NOx that is likely to be generated during lean burn, a storage-type NOx catalyst 25 is provided.

The engine also performs fuel cut control (fuel supply stop / restart control) that stops fuel injection under predetermined operating conditions such as when the vehicle is decelerated, and then resumes fuel injection when the predetermined operating conditions are met. By doing so, fuel consumption can be reduced.
The lean burn engine will be further described. The engine switches the fuel injection mode (operation mode) so that the fuel injection in the intake stroke (intake stroke injection mode) or the fuel injection in the compression stroke (compression stroke injection mode). ) Can be implemented as an in-cylinder spark-ignition gasoline engine (hereinafter referred to as an in-cylinder injection engine). The in-cylinder injection engine 11 can be easily operated at a theoretical air-fuel ratio (stoichiometric), an operation at a rich air-fuel ratio (rich air-fuel ratio operation), or an operation at a lean air-fuel ratio (lean air-fuel ratio operation). In particular, in the compression stroke injection mode, it is possible to operate at a super lean air-fuel ratio.

  Specifically, as shown in FIG. 1, an electromagnetic fuel injection valve 14 is attached to a cylinder head 12 of the engine 11 together with a spark plug 13 for each cylinder. The fuel can be directly injected into 15. A fuel supply device (fuel pump) (not shown) is connected to the fuel injection valve 14 via a fuel pipe (not shown). The fuel in the fuel tank is supplied at a high fuel pressure, and this fuel is supplied from the fuel injection valve 14. The fuel is injected into the combustion chamber 15 at a desired fuel pressure. At this time, the fuel injection amount is determined from the fuel discharge pressure of the fuel pump and the valve opening time (fuel injection time) of the fuel injection valve 14.

  An intake port is formed in the cylinder head 12 in a substantially upright direction for each cylinder, and one end of an intake manifold 16 is connected so as to communicate with each intake port. A drive-by-wire (DBW) type electric throttle valve 17 is connected to the other end of the intake manifold 16, and the throttle valve 17 is provided with a throttle sensor 18 for detecting a throttle opening θth. Further, an exhaust port is formed in the cylinder head 12 in a substantially horizontal direction for each cylinder, and one end of an exhaust manifold 19 is connected to communicate with each exhaust port.

The engine 11 is provided with a crank angle sensor 20 that detects a crank angle. The crank angle sensor 20 can detect an engine rotational speed (engine speed) Ne.
An exhaust pipe (exhaust passage) 21 is connected to the exhaust manifold 19 of the engine 11, and the exhaust pipe 21 is illustrated via a small three-way catalyst 22 and an exhaust purification catalyst device 23 close to the engine 11. No muffler is connected.

  This exhaust purification catalyst device 23 has a NOx reduction function for storing NOx in the exhaust gas when the exhaust air-fuel ratio is a lean air-fuel ratio, and a harmful substance (HC) in the exhaust gas when the exhaust air-fuel ratio is close to the theoretical air-fuel ratio. , CO, NOx) in order to have a redox function for purifying the catalyst, the storage NOx catalyst 25 and the three-way catalyst 26 are provided, and the three-way catalyst 26 is the storage type. It is disposed downstream of the NOx catalyst 25. The three-way catalyst 26 also serves to reduce NOx that cannot be reduced by the storage NOx catalyst 25 itself when the NOx stored from the storage NOx catalyst 25 is released.

When the occlusion-type NOx catalyst 25 has a function of not only reducing NOx but also a three-way catalyst that oxidizes HC and CO (herein referred to as a three-way function), exhaust purification is performed. The catalyst device 23 may be composed of only this storage-type NOx catalyst 25.
This storage-type NOx catalyst 25 has a reduction function of temporarily storing NOx in an oxidizing atmosphere (NOx reduction function) and releasing NOx in a reducing atmosphere mainly containing CO to reduce it to N ₂ (nitrogen) or the like. It is. Specifically, the storage-type NOx catalyst 25 is configured as a catalyst having platinum (Pt), rhodium (Rh) or the like as a noble metal, and the storage material is made of an alkali metal such as barium (Ba) or an alkaline earth metal. It has been adopted.

In order to control such an engine 11, an ECU (electronic control unit) 28 having an input / output device, a storage device (ROM, RAM, nonvolatile RAM, etc.), a central processing unit (CPU), a timer counter, etc. The ECU 28 performs overall control of the exhaust emission control device of the present embodiment including the engine 11.
For this reason, various sensors are connected to the input side of the ECU 28, and detection information from these sensors is input. On the other hand, the ignition plug 13 and the fuel injection valve 14 described above are connected to the output side of the ECU 28 via an ignition coil. The ignition coil, the fuel injection valve 14 and the like are detected information from various sensors. The optimum values such as the fuel injection amount and ignition timing calculated based on the above are output. Accordingly, an appropriate amount of fuel is injected from the fuel injection valve 14 at an appropriate timing, and ignition is performed at an appropriate timing by the spark plug 13.

  In order to perform such engine control, the ECU 28 sets the target in-cylinder pressure corresponding to the engine load based on the accelerator opening information from the accelerator opening sensor (APS) 24 and the engine rotational speed information Ne from the crank angle sensor 20. That is, the target average effective pressure Pe is obtained, and a function (operation) for setting the fuel injection mode from a map (not shown) according to the target average effective pressure Pe and the engine speed information Ne. Mode setting means) 28a.

  In the operation mode setting means 28a, for example, when both the target average effective pressure Pe and the engine speed Ne are small, the compression stroke injection mode is selected as the fuel injection mode, and fuel is injected into the compression stroke, while the target average effective When the pressure Pe increases or the engine speed Ne increases, the intake stroke injection mode is selected as the fuel injection mode, and fuel is injected into the intake stroke.

  In particular, in the compression stroke injection mode, the operation mode setting means 28a sets a super lean combustion operation mode (which is also simply referred to as a lean operation mode) in which the air-fuel ratio is extremely lean and is set in the intake stroke injection mode. In some cases, a lean combustion operation mode (simply referred to as a lean operation mode) in which the air-fuel ratio is slightly leaned, and a stoichiometric combustion mode (stoichiometric mode) in which the air-fuel ratio is operated with the stoichiometric air-fuel ratio (stoichiometric). One of the rich combustion operation modes (rich operation modes) in which the air-fuel ratio is operated slightly rich is set. In any operation mode, the operation mode setting means 28a sets a target air-fuel ratio (target A / F) as a control target from the target average effective pressure Pe and the engine speed Ne corresponding to the operation mode ( This function is an air-fuel ratio control means), and an appropriate amount of fuel injection is determined based on this target A / F.

By the way, in the storage type NOx catalyst 25, NOx in the exhaust gas is stored as nitrate in an oxygen concentration excess atmosphere as in the super lean combustion operation in the lean mode, and the exhaust gas is purified. On the other hand, in an atmosphere where the oxygen concentration is lowered, the nitrate stored in the NOx storage catalyst 25 reacts with the CO in the exhaust to produce carbonate, and NOx is released, and NO ₂ is harmlessly reduced and discharged. Is done. When NOx occlusion proceeds to the NOx storage catalyst 25 and the NOx saturation state is reached, NOx cannot be occluded. Therefore, when approaching the saturation state, the exhaust air / fuel ratio is set to the stoichiometric or rich air / fuel ratio (this is the rich spike). The storage NOx catalyst 25 atmosphere is in a state where the oxygen concentration is lowered, and control (NOx purge control or NOx release control) for releasing NOx stored in the storage NOx catalyst 25 is performed.

  A rich spike mode is provided as a special operation mode of the engine, and the ECU 28 is provided with a function (NOx purge control means) 28b for performing NOx purge control. Further, in order to determine whether or not NOx purge is required by the NOx purge control means 28b, the ECU 28 indicates that the NOx occlusion state of the occlusion-type NOx catalyst 25 is in a saturated state region (region where the predetermined ratio of saturated state has been reached). A function (NOx occlusion state determination means) 28c for determining whether or not the engine pressure has reached a function, and a function (intake flow rate state determination means) 28d for determining whether or not the intake flow rate of the engine is a low flow rate state below a reference level. Is provided.

  In the NOx purge control means 28b, the NOx occlusion state determination means 28c determines that the NOx occlusion state has reached the saturated state region, and the intake flow rate state determination means 28d determines that the intake flow rate of the engine is in a low flow rate state below the reference level. If it is determined that NOx purge is required, the operation mode setting means 28a causes the rich spike mode to be selected as the operation mode.

  By the way, in the NOx occlusion state determination unit 28c of the present embodiment, when the super lean mode for discharging NOx is performed by the setting of the operation mode setting unit 28a, the duration time is counted, and the duration time is determined in advance. When the set predetermined time is reached, it is determined that the NOx occlusion state of the occlusion-type NOx catalyst 25 has reached the saturation state region. That is, when the super lean mode is continuously performed, the NOx occlusion amount increases according to the duration time, and therefore the NOx occlusion amount can be estimated from the duration time of the super lean mode.

Therefore, the above-described predetermined time is set to a time that is appropriately shorter than the time for the NOx occlusion amount to reach the saturated state (a time of a predetermined ratio with respect to the time to reach the saturated state) by continuing the super lean mode. Thus, before the NOx occlusion amount reaches the complete saturation state, it is determined that the NOx purge amount has been reached and a NOx purge request is issued.
In this NOx purge control, as described above, the fact that the engine intake flow rate is in a low flow rate state below the reference level is added to the NOx purge execution condition, so NOx purge is not performed even if there is a NOx purge request. Therefore, before the NOx occlusion amount reaches a fully saturated state, the NOx purge execution condition is satisfied by leaving the NOx purge request while leaving an appropriate occlusion margin in the occlusion-type NOx catalyst 25. During this time, a certain amount of NOx treatment is possible.

Note that the NOx occlusion state determination unit 28c may perform the above determination by estimating the NOx occlusion amount based on the accumulated time of the super lean mode instead of the duration of the super lean mode.
Further, in the intake air flow state determination means 28d of this embodiment, (i) there is no request for acceleration to the vehicle, (ii) the vehicle speed is less than or equal to a preset upper limit value, and (iii) the engine speed is preset. It is determined that the intake flow rate is in a low flow rate state when three conditions that are equal to or less than the upper limit value are met. It should be noted that there is no acceleration request to the vehicle under the condition (i) that the accelerator pedal is not depressed from the accelerator opening information from the APS 24 (or information on the idle switch that detects whether or not the accelerator pedal is depressed). It can be judged from.

  The conditions are set in this way because (i) if there is a request for acceleration to the vehicle, the throttle opening will naturally increase, so that the intake flow rate does not become low, (ii) the vehicle speed is high, (Iii) This is based on the fact that when the engine rotational speed is high, the intake air flow rate is secured to some extent and the low flow rate state does not occur even if the accelerator pedal is not depressed. Of the vehicle speed condition (ii) and the engine speed condition (iii), the engine speed condition (iii) is relatively strong as a condition that the intake flow rate does not become a low flow rate state. Since the vehicle speed condition is relatively weak as a condition that the intake flow rate does not become a low flow rate state, only the conditions (i) and (iii) may be adopted.

Of course, the intake flow rate state determining means 28d may compare the intake flow rate measured by the air flow sensor with a preset reference intake flow rate to determine whether or not it is in a low flow rate state. The intake flow rate state may be determined based on the throttle valve opening (throttle opening).
Since the internal combustion engine with an occlusion-type NOx catalyst as one embodiment of the present invention is configured as described above, control is performed when the fuel is cut, for example, as shown in FIG.

  First, it is determined whether or not the lean continuation time (super-lean mode continuation time) is equal to or greater than a predetermined time set in advance (step S10). Is equal to or longer than a predetermined time, it is determined whether or not there is an acceleration request to the vehicle based on whether or not the idle switch is on (step S20). If there is no acceleration request to the vehicle, it is determined whether or not the vehicle speed is less than or equal to a preset upper limit value (step S30). If the vehicle speed is less than or equal to the upper limit value, is the engine speed less than or equal to a preset upper limit value? It is determined whether or not (step S40). Here, if the engine speed is equal to or lower than the upper limit value, NOx purge is performed (step S50). Even if the lean duration time exceeds the predetermined time, there is a request for acceleration to the vehicle, the vehicle speed is higher than the upper limit value, or the engine speed is higher than the upper limit value. Then, the operation mode is changed to the stoichiometric mode to avoid the NOx occlusion burden on the catalyst (step S60).

  When the vehicle travels, for example, as shown in the time chart of FIG. 3, each parameter [A / F (air / fuel ratio), lean duration, mode flag (operation mode), Ne (engine speed), idle switch, The NOx purge is performed according to the state of the vehicle speed. In other words, when the lean operation is performed and the lean continuation time increases and the lean continuation time reaches the predetermined time at time t1, the NOx purge is not performed immediately when the acceleration request to the vehicle is generated. Then, the operation mode is changed to stoichiometric and waits for the NOx purge condition to be satisfied. After that, at time t2, (i) there is no acceleration request to the vehicle (idle switch is on), (ii) the vehicle speed is low (below the upper limit value), and (iii) the engine speed is low (below the upper limit value). When the NOx purge condition is satisfied, the NOx purge is performed. In this example, there is no acceleration request to the vehicle even after completion of the NOx purge, so the lean continuation time is counted again after returning to the lean mode.

  In this way, when the lean continuation time becomes equal to or longer than the predetermined time (NOx occlusion amount reaches the saturation state), (i) there is no acceleration request to the vehicle, and (ii) the vehicle speed is low (upper limit value) (Iii) (iii) If the engine speed is low (below the upper limit value), it can be determined that the intake flow rate is in the low flow state, and the intake flow rate is in the low flow state. Since the NOx purge is performed as a condition, the NOx purge is not performed when the engine output is required and the intake air flow rate is increased accordingly, for example, during acceleration of the vehicle.

  Therefore, when the intake air flow rate is large, a large amount of fuel is supplied along with this, so a large amount of fuel supply is required during a rich spike for NOx purge, which is disadvantageous in terms of fuel consumption. Is done. In addition, when the intake air flow rate is large, the exhaust gas flow rate also increases, the contact time between the catalyst and the exhaust gas becomes short, the reaction of the exhaust gas by the catalyst becomes insufficient, and the NOx occluded with CO used in the NOx purge. However, such a situation is also avoided, although the substitution reaction with NOx and the reduction reaction of NOx are less likely to occur and the exhaust gas purification is disadvantageous.

  As a result, it is possible to suppress the fuel increase accompanying the rich spike (rich air-fuel ratio) during the NOx purge, and to suppress the deterioration of fuel consumption due to the NOx purge. In addition, the exhaust gas flow rate can be suppressed, the contact time between the catalyst and the exhaust gas can be ensured for a long time, and the substitution reaction and the reduction reaction for the NOx purge can be sufficiently performed, so that the NOx purge can be performed efficiently. Also, the exhaust gas purification is advantageous.

Although the embodiments of the present invention have been described above, the present invention is not limited to such embodiments, and various modifications can be made without departing from the spirit of the present invention.
For example, in the present embodiment, the vehicle speed and the engine rotational speed conditions are set to be equal to or less than the respective upper limit values. However, the vehicle speed and the engine rotational speed condition are added to the vehicle speed and the engine rotational speed condition, respectively. May be set to be between each lower limit value and each upper limit value. In this case, NOx purge during idle idling is avoided, and shortening of the lean operation time during idling can be avoided, so that deterioration of fuel consumption can be prevented.

  Further, even if the lean continuation time is equal to or longer than the predetermined time (the NOx occlusion amount has reached the saturation state region), the NOx purge is not performed unless it is determined that the intake flow rate is in the low flow state. In consideration of the case where the NOx purge is greatly delayed, the condition for determining whether or not the intake flow rate is in a low flow rate state is gradually reduced with the passage of time after the lean continuation time exceeds a predetermined time. Also good. This relaxation of conditions is, for example, by increasing the upper limit value of the vehicle speed or engine speed by changing the criterion for determining whether or not the intake flow rate is low to a relatively high value (a larger flow rate). Can be implemented.

  In this case, a method of changing the upper limit value of the vehicle speed or the engine rotational speed to a larger value if the intake air flow rate does not become a low flow state for a predetermined time or longer after the lean continuation time exceeds the predetermined time. Or, when the lean continuation time exceeds a predetermined time, the upper limit value of the vehicle speed or engine speed is gradually changed to a larger one (either continuous or stepwise) as time elapses. Techniques can be considered.

1 is a configuration diagram showing an internal combustion engine with a storage-type NOx catalyst as one embodiment of the present invention. FIG. It is a flowchart explaining the control by the internal combustion engine with an occlusion type NOx catalyst as one embodiment of the present invention. It is a time chart explaining the control by the internal combustion engine with a storage type NOx catalyst as one embodiment of the present invention. It is a time chart explaining the subject of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Engine 23 Exhaust purification catalyst apparatus 25 Occlusion type NOx catalyst 28 ECU (electronic control unit)
28a Operation mode setting means 28b NOx purge control means 28c NOx occlusion state determination means 28d Intake flow rate state determination means

Claims (5)

In an internal combustion engine for a vehicle comprising an NOx storage type catalyst and NOx purge control means for performing NOx purge by enriching the air-fuel ratio,
Intake flow rate state determining means for determining whether or not the intake flow rate is in a low flow rate state,
The NOx purge control means is provided on the condition that the NOx occlusion state of the storage type NOx purification catalyst has reached the NOx purge state, and that the intake flow rate determination means has determined that the intake flow rate is a low flow rate state. An internal combustion engine for a vehicle with an occlusion-type NOx catalyst, wherein the NOx purge is performed. The intake flow rate state determining means determines that the intake flow rate is in a low flow rate state when there is no acceleration request to the vehicle and the engine speed is equal to or lower than a preset upper limit value. An internal combustion engine for a vehicle with an occlusion type NOx catalyst according to claim 1. The intake flow rate state determining means is configured to determine whether or not the intake flow rate is in a low flow rate state by comparing a parameter value corresponding to the intake flow rate with a determination reference value,
Even if the NOx occlusion state of the storage type NOx purification catalyst reaches the NOx purge state, if the intake flow rate state determining means does not determine that the intake air flow rate is in the low flow rate state, the low flow rate determination is made even if the flow rate is relatively high. The internal combustion engine for a vehicle with an occlusion-type NOx catalyst according to claim 1 or 2, wherein the determination reference value is changed as time elapses. The vehicle internal combustion engine is configured to be able to perform a lean operation in which combustion is performed with the air-fuel ratio leaner than the stoichiometric air-fuel ratio,
The NOx purge control means determines that the NOx occlusion state of the occlusion-type NOx purification catalyst has reached a NOx purge state when the lean operation is continued for a preset predetermined time or more. The internal combustion engine for vehicles with an occlusion type NOx catalyst of any one of 1-3. The NOx purge state is a state in which the estimated value of the NOx storage amount of the storage-type NOx purification catalyst has reached the storage saturation amount or a state close to a predetermined range with respect to the storage saturation amount. An internal combustion engine for a vehicle with a storage type NOx catalyst according to claim 4.

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