DE19549649B4 - Control for catalyst in exhaust system of IC engine - Google Patents

Abstract

The IC engine has a catalyst (13) in the exhaust system as well as a sensing system for exhaust quality. When the engine is operating in lean burn the catalyst eventually becomes saturated with nitrous oxide. This saturation is detected and a recycling of part of the exhaust gasses into the inlet manifold produces a slight reduction in the burn providing some unburnt gasses in the exhaust. This enables the adsorbed nitrous oxide to be oxidised and disposed off safely. Two levels of saturation detectors are provided. The level of recycling is such as not to affect the fuel efficiency unduly an does not affect the motor running characteristics greatly. No change in the airflow intake, throttle setting etc. are required.

Description

The invention relates to a device for one Internal combustion engine with a catalytic converter with which the emission can be suppressed into the atmosphere by nitrogen oxide.

It is a process for improvement fuel economy or other performance criteria an internal combustion engine is known in which the air-fuel ratio regulating a target value (e.g. 22) that is leaner than the theoretical air-fuel ratio (14.7) to thereby perform lean burn in the engine if the engine is in a predetermined drive state is driven. However, will Three way catalyst converter for uses the engine to which the aforementioned method is applied, can nitric oxide (NOx) during the lean burn is not enough be cleaned because the three-way catalyst converter in the lean Air fuel ratio range doesn't work at its full potential. Are in this regard Experiments carried out the emission of NOx also in the lean combustion engine reduce by using a so-called NOx catalyst, the NOx absorbed by the engine in an oxygen enriched Condition (oxidizing atmosphere) is released, and the adsorbed NOx in a hydrocarbon (HC) excess state deoxidized (reducing atmosphere).

The amount of NOx from the NOx catalyst can be absorbed, however, is limited. The engine becomes continuous driven in the lean-burn state, the catalyst is with NOx saturated. In this case, the largest part of NOx gas emitted by the engine is emitted into the atmosphere. To counteract this before or when the NOx catalyst with adsorbed NOx saturated is a transition to control the grease mixture, which determines the air-fuel ratio a theoretical relationship or controls a near value to thereby operate in theoretical relationship or to start the engine's fat-burning operation. The resulting Exhaust gas containing a lot of unburned gases is generated a reducing atmosphere for the Deoxidation of NOx around the catalyst.

With regard to the time at that the lean-burn operation on the operation in the theoretical relationship or switching the fat burning operation is a procedure from Japanese patent application KOKEI publication number H5-133260 known in which the elapsed time from the start of the lean fuel ratio control is measured and the transition to rich air fuel control is increasingly performed when a predetermined time has passed. With this procedure the lean air-fuel ratio control after the completion of the Deoxidation of NOx started again by the catalyst during the bold air-fuel ratio control is adsorbed. In this way, the lean burn and alternatively, the rich combustion is carried out to increase the emission of NOx reduce.

If the predetermined time from the start lean air-fuel ratio control has elapsed, however, after that in the aforementioned publication disclosed control always determines that the amount of adsorbed NOx the saturated Has reached value. At this moment, the lean burn condition reinforced changed to the rich combustion state. The improvement of Lean-burn fuel consumption cannot therefore be used in sufficient Ways can be achieved and fuel economy will be appropriate reduced. About that also varies at the time of changing the air-fuel ratio the engine torque and has a bad impact on the Motor operation. In a vehicle that uses the engine as its primary drive used can be a change of the engine torque a shock similar to one Cause acceleration shock, so that drive feeling deteriorates when the engine torque variation occurs frequently, during that Vehicle is running at a constant speed. It also increases the emission of HC when the air-fuel ratio is enriched. From the point of view of improving the driving experience and reducing the Emission of HC is therefore not preferable to increase the air-fuel ratio and frequently to change.

In international patent publication no. WO93 / 08383 discloses a method for deoxidizing NOx, that of the exhaust gas purification device during the lean-burn drive of the Motors is adsorbed. In this process, the amount of adsorption of NOx from the exhaust gas purifying catalyst and the drive state in changes the rich combustion state when based on the Result of the estimate it is determined that the Adsorption amount of NOx is the saturation amount has reached.

In this procedure, in which the base of the estimated Adsorption amount of NOx is determined whether the catalyst with NOx saturated is, however, is sometimes when NOx adsorption properties Catalysts, which are attached to the individual engines, from each other deviate, sometimes impossible, to correctly determine that the Catalyst the saturated Has reached state.

The EP 0598917 A1 discloses a control system for an internal combustion engine which is provided with a NOx-adsorbing agent which is arranged within an exhaust pipe of the engine and which adsorbs NOx when the air / force substance ratio of exhaust gas flowing in there is lean and releases NOx, which it has adsorbed when the air / fuel ratio of exhaust gas flowing in becomes rich.

In the system disclosed, the Amount of NOx that is in the NOx absorbing agent from the engine load and the engine speed is estimated, and if this is the estimated amount of NOx the maximum NOx adsorbing capacity of the NOx adsorbing agent reached, the air / fuel ratio of the adsorbing into the NOx Agent flowing Exhaust made fat.

In the present invention a release amount of nitrogen oxide from an exhaust gas catalyst estimated, and whether the estimated Dispensed amount of nitrogen oxide exceeds a predetermined amount or not is determined. When it is determined that the release amount of nitrogen oxide exceeds a predetermined amount, an air-fuel ratio becomes one Air-fuel mixture changed, to change lean burn to fat burn when it is determined that the released amount of nitrogen oxide exceeds the predetermined amount.

According to the present invention the release amount of nitric oxide, i.e. H. the amount of nitric oxide, which leaves the catalytic converter determines and when the release amount of nitrogen oxide is not the predetermined one When the quantity is reached, the change from lean combustion process to Fat burning process, d. H. Driving to achieve NOx reduction not done as long as less NOx released into the atmosphere is as a prescribed value even if the exhaust gas purification device in a saturated State is where it is saturated with NOx which has adsorbed the device. As a result the smoothness in machine operation and fuel consumption did not deteriorate.

The system, which in the EP 0598917 A1 discloses determines the amount of NOx that the NOx adsorbing agent has adsorbed, but does not determine an amount of NOx that originates from the NOx adsorbing agent without being adsorbed by the NOx adsorbing agent.

In contrast, the present invention Task based on a lot of NOx also soften the catalytic converter includes determining a NOx catalyst; d. H. a Amount of NOx released into the atmosphere.

This task is due to the characteristics of claim 1 solved.

Preferred embodiments of the invention are in the dependent claims 2 to 8 disclosed.

According to the system in the EP 0598917 A1 an amount of NOx emanating from the NOx adsorbing agent is not determined. This makes it impossible to perform precisely control for suppressing an amount of NOx released into the atmosphere up to a prescribed amount.

Even in the system in the EP 0598917 A1 is disclosed, an attempt to control an amount of NOx released into the atmosphere up to a prescribed amount can be made based on the determined amount of NOx adsorbed by the NOx adsorbing agent. However, the system is required to perform control by considering the following requirement, for example:
There is a relationship that the larger an amount of NOx adsorbed becomes, the larger the ratio of an amount of NOx released into the atmosphere to an amount of NOx released from the engine becomes.

Thus, an engine operating condition where a big Amount of NOx released from the machine should be considered. Specifically, it has to Air / fuel ratio enriched (i.e., NOx reducing operation must be made). To release and reducing NOx generated by the NOx adsorbing agent is adsorbed before the amount of adsorbed NOx becomes large. As a result, there is a high probability that unnecessary fat operations carried out resulting in deteriorated fuel consumption. This is counteracted according to the present invention made a determination regarding the amount of nitrogen oxide released by the catalytic converter and driving to achieve NOx reduction is performed by changing the lean-burn method for fat burning driving, is not executed until the amount of NOx, which in the atmosphere is released exceeds a predetermined amount.

As a result, the present makes Invention, unlike the prior art, no change from lean combustion processes to fat burning drives, d. i.e., driving to achieve NOx reduction as long as a lot of NOx released into the atmosphere becomes less than a prescribed value even if the Emission control device in a saturated state is where it is saturated with NOx which has adsorbed the device so that smoothness in machine operation and Fuel consumption will not deteriorate.

For the state where a lot of NOx is released into the atmosphere is less than a prescribed amount, such condition can z. B. can be achieved when NOx purification by a three-way catalyst other than done by a NOx catalyst or when the combustion temperature is so low that a lot of NOx released by the machine is reduced.

The invention is explained in more detail below with reference to the drawing, for example. In this demonstrate:

1 1 shows a schematic view of a combustion control device according to an embodiment of the invention together with an engine,

2 a functional block diagram of the in 1 combustion control device shown,

3 a portion of a flowchart of the combustion control routine used by the in 2 shown electronic control unit is executed,

4 the remaining part of the flow chart of the combustion control routine that corresponds to the flow chart of 3 follows

5 part of a flow chart of the in 4 shown subroutine for calculating the NOx release amount Q _NT ,

6 the remaining part of the flow chart of the subroutine for calculating the NOx release amount Q _NT , which is the flow chart of 5 follows

7 2 shows a graphical representation of an exemplary diagram of the excess air ratio λ-estimated amount D _{N of} the concentration of the engine output NOx,

8th 2 shows a graphical representation of an exemplary diagram of the ignition timing correction coefficient K _{I g} ,

9 a graphical illustration of an exemplary graph of the accumulated value SQ _{N (i + 1)} the amount of the engine output estimated NOx adsorption ratio K _NOX of the NOx catalyst,

10 2 shows a graphical representation of an exemplary diagram of the excess air ratio λ-estimated value K _{CAT of} the NOx purification ratio of a three-way catalytic converter,

11 6 is a flowchart of the misfire control routine executed in a combustion control method for an internal combustion engine according to a second embodiment of the present invention;

12 6 is a flowchart of the ignition control routine executed in a combustion control method for an internal combustion engine according to a third embodiment of the present invention;

13 1 is a functional block diagram of an electronic control unit of a combustion control device for an internal combustion engine according to a fourth embodiment of the present invention;

14 a flowchart of the air-fuel ratio control routine performed by the in 13 shown electronic control unit is executed,

15 the remaining part of the flowchart of the subroutine for calculating the estimated NOx release amount corresponding to the flowchart of 5 follows

16 a graphical representation of the changes in the amount Q _{NO of} the engine output NOx and the amount Q _{NT of} the catalyst output NOx over time,

17 an exemplary graphical representation of an EGR quantity diagram for the normal lean-burn engine, which is in the in the 3 and 4 combustion control routine shown is used, and

18 an exemplary graphical representation of an ignition timing diagram for the normal lean-burn engine used in the combustion control routine.

It now becomes a combustion control method and a device for an internal combustion engine according to various embodiments the invention described with reference to the accompanying drawings.

In 1 denotes the reference symbol 1 the car engine operated under the control of a combustion control device described below. The engine, ie, for example, a six-cylinder in-line gasoline engine, has combustion chambers, a supply system, an ignition system and the like, which are designed for the lean combustion drive.

The motor 1 has feed openings 2 on that with a feed manifold 4 are connected in which fuel injectors 3 are provided for the corresponding cylinders. A supply line 9 that is connected to the intake manifold is with an air purifier 5 and a throttle valve 7 provided (more generally speaking, with an output operating device for adjusting the motor output). The throttle valve 7 is with the accelerator pedal 7a connected. An idle engine speed control valve 8th (ISC) is provided in a bypass line, which is the throttle valve 7 bridged. An exhaust manifold 11 is with exhaust ports 10 of the motor 1 connected. There is also a silencer (not shown) with the exhaust manifold 11 via an exhaust pipe 14 and an exhaust gas purifying catalyst 13 connected.

The exhaust gas purification catalyst 13 has a NOx catalyst 13a and a three-way catalyst converter 13b on that on the downstream side of the NOx catalyst 13a is arranged. The NOx catalyst 13a contains Pt (platinum) and an alkali precious earth metal such as lanthanum and cerium as a catalytic substance, and functions to adsorb NOx in the oxidizing atmosphere and deoxidize NOx in N ₂ (nitrogen) and the like in the reducing atmosphere containing HC. The three-way catalyst converter 13b works by oxidizing HC and CO (carbon monoxide) and deoxidizing NOx. The NOx deoxidation ability is maximum in or near the theoretical (stoichiometric) air-fuel ratio.

There is also a circulation line 26 For exhaust gas recirculation (EGR) between the exhaust manifold 11 and the feed manifold 4 connected so that part of the exhaust gases in the exhaust manifold 11 to the intake manifold 4 via the circulation line 26 returned and the combustion chamber 15 is fed when one in the line 26 arranged EGR valve 27 is open. When the exhaust gas is recirculated to the supply side in this manner, the combustion temperature is lowered to suppress the generation of NOx.

The motor 1 is also with a spark plug 16 to ignite a mixture of air and fuel provided by the supply opening 2 to the combustion chamber 5 is directed.

The combustion control device according to a first embodiment of the invention for controlling combustion in the engine 1 has an electronic control unit 23 (ECU) as the main component. The ECU 23 comprises an input / output device, a memory device (ROM, RAM, non-volatile RAM or the like) with a multiplicity of control programs stored therein, a central processing unit (CPU), a time counter and the like (these are not shown in the drawing). Various sensors used in 1 are shown with the input side of the ECU 23 connected.

In 1 denotes the reference symbol 6 an airflow sensor attached to the supply line 9 is attached and the supply air quantity A _f detected. A Karman vortex airflow sensor or the like is appropriately used as an airflow sensor 6 used. Furthermore, the reference symbol denotes 12 an air-fuel ratio sensor (linear air-fuel ratio sensor or the like) that is attached to the exhaust pipe 14 is arranged to detect the excess air ratio λ (more generally, an air-fuel ratio information variable); 18 denotes a crank angle sensor with an encoder that is connected to the camshaft of the engine 1 is connected and generates a crank angle _{synchronization} signal θ _CR ; and 19 denotes a throttle sensor for detecting the opening θ _{TH of} the throttle valve 7 , Furthermore, the reference symbol denotes 20 a water temperature sensor for detecting the engine cooling temperature T _W ; 21 denotes an atmospheric pressure sensor for detecting the atmospheric pressure P _a ; and 22 denotes a supply air temperature sensor for detecting the supply air temperature T _a . The engine speed N _e is determined by the ECU 23 calculated according to the time interval between the crank angle synchronization signals θ _CR by the crank angle sensor 18 to be delivered. The engine load L _e is calculated according to the engine revolution speed N _e or the throttle opening θ _TH by the throttle sensor 19 is detected.

The ECU 23 calculates the optimal values of the fuel injection amount, the ignition timing and the like based on parts of the information detected by various sensors. The ECU 23 drives the fuel injectors 23 and the ignition unit 24 according to the results of the calculation. These elements 3 and 24 are with the output side of the ECU 23 connected. The ignition unit 24 supplies a high voltage to the spark plug 16 of each cylinder in response to the command from the ECU 23 ,

The ECU 23 This embodiment has various functions from a functional point of view 2 are shown.

Specifically, the ECU 23 a drive state determination unit 30 to determine if the engine 1 is to be operated in the lean-burn state or the theoretical air-fuel ratio drive state (hereinafter referred to as the theoretical ratio drive state) in accordance with the engine speed N _e , the cooling temperature T _W , the engine load L _e and the presence / absence of the acceleration determination signal. The ECU also contains 23 an air-fuel ratio changing unit 31 to switch the air-fuel ratio of the engine 1 supplied air-fuel mixture between the lean air-fuel ratio and the theoretical air-fuel ratio according to the result of the determination of the drive state determination unit 30 , The ECU also has an adsorption saturation determination unit 32 to determine whether the NOx catalyst 13a is saturated with NOx. The adsorption saturation determination unit 32 outputs a NOx reducing signal when it is determined that the NOx catalyst 13a is saturated with NOx. In a broad sense, the adsorption saturation determination unit estimates 32 the state of adsorption of NOx of the NOx catalyst 13a ,

The adsorption saturation determination unit 32 has a catalyst delivery NOx amount estimator (nitrogen oxide delivery amount estimator) 33 for deriving an estimated value Q _{NT of} the amount of NOx discharged from the NOx catalyst 13a from parts of the information which is detected by the corresponding sensors; and a comparator 34 to compare the estimated value Q _NT with the threshold value Q _NTO . The comparator 34 provides the NOx reducing signal to a flip-flop circuit 35 to be set if the estimated value Q _{NT is} greater than the threshold value Q _NTO . The flip-flop circuit 35 is reset when the theoretical air-fuel ratio is changed from the air-fuel ratio changing unit 31 is selected.

The ECU 23 has a combustion temperature lowering unit 36 to lower the combustion temperature in the engine 1 in the required manner. The temperature reduction unit 36 sets the EGR amount and the ignition timing in the engine 1 according to the presence / absence of the NOx reducing signal and increases the EGR amount and retards the ignition timing to lower the combustion temperature to reduce NOx. In a broad sense, the temperature lowering unit deteriorates 36 the state of combustion in the engine.

Furthermore, the ECU 23 an acceleration determination / threshold change unit 37 on. The threshold change unit 37 compares the valve opening speed of the throttle valve 7 with an acceleration determination threshold A _th . If the throttle valve opening speed exceeds the threshold value A _th , the threshold value change unit determines 37 that the acceleration drive request is issued and outputs an acceleration determination signal. In response to this signal, the drive state determination unit determines 30 that the engine 1 should be operated in the theoretical ratio drive state. The threshold A _th that of the threshold change unit 37 used for the determination takes a different value according to the presence or absence of the NOx reducing signal. That is, when the NOx reducing drive is applied in response to the NOx reducing signal, the threshold value A _th becomes small; this makes it easier to change the drive state from the lean-burn state to the theoretical ratio drive state. The operation of the combustion control device having the above configuration will now be explained.

Determines the drive state determination unit 30 that the engine is to run in the lean-burn state, the lean air-fuel ratio becomes from the air-fuel ratio changing unit 31 selected. In this case the throttle valve 7 and / or the ISC valve 8th opened to increase the amount of supply air, the fuel injection amount from the fuel injection valve 3 is kept substantially constant. It follows that an air-fuel mixture with an air-fuel ratio larger than the theoretical air-fuel ratio is the engine 1 is fed, causing the engine 1 is driven in the lean combustion state. During the fat-burning drive, a reducing atmosphere is created around the NOx catalyst 13a generated around so that NOx that is in the exhaust gases from the engine 1 is contained on the NOx catalyst 13a can be adsorbed.

However, in the lean-burn state, the estimated value Q _{NT of} the NOx discharge amount becomes from the NOx estimation unit 33 is estimated, and the estimated value Q _NT is compared with the threshold value Q _NTO from the comparator 34 compared. If the estimated value Q _{NT is} larger than the threshold value Q _NTO , it is determined that the NOx adsorbing ability of the NOx catalyst 13a has substantially reached the saturated state, and the NOx reducing signal is from the comparator 34 output. Thereupon, the EGR amount and the ignition timing from the temperature lowering unit 36 is set, which responds to the NOx reducing signal, and the NOx reducing drive is applied to deteriorate the combustion condition or the combustion in the engine 1 mitigate. As a result, the combustion temperature is lowered to reduce the amount of NOx discharged.

If the acceleration determination signal from the threshold value changing unit 37 to the drive state determination unit 30 is supplied, the drive state determining unit determines 30 further that the engine 1 is to be driven in the theoretical ratio driving state, and the theoretical air-fuel ratio is changed from the air-fuel ratio changing unit 31 selected. In this case, a theoretical or stoichiometric air-fuel mixture is added to the engine 1 fed so that the engine 1 in the theoretical ratio drive state is driven to the output of the engine 1 to increase. During the drive in the theoretical ratio contain those from the engine 1 exhaust gases emitted a larger amount of HC and CO than in the lean-burn state. There is therefore a reducing atmosphere around the NOx catalyst 13a witnessed to cause deoxidation (reduction) of the adsorbed NOx.

Furthermore, at the time of the NOx reducing drive the acceleration determination threshold set to a smaller value so that the change in the drive state in the theoretical ratio drive state is facilitated. It follows that the response of the acceleration drive request can be improved in the NOx-reduced drive, in which the Motor output reduced compared to the drive that is not reduced in NOx is.

Next is the operation of the Combustion control device explained in detail.

While driving the engine 1 becomes a crank angle synchronization signal θ _CR from the crank angle sensor 18 generated at every crank angle CA, for example at 120 °. Every time the crank angle synchronization signal θ _{CR of} the ECU 23 is entered as an interrupt signal, the combustion control routine included in the 3 and 4 is shown by the ECU 23 executed.

First, in step S10 from the drive state determination unit 30 the ECU 23 according to the engine speed N _e , the cooling temperature T _W , the engine load L _e, and the presence / absence of the acceleration determination signal from the threshold value changing unit 37 determines whether the theoretical ratio drive condition applies. For example, the theoretical ratio drive condition applies when the engine speed N _e and the cooling temperature T _{W are} equal to or greater than the corresponding predetermined values and the engine load L _{e is} equal to or less than a predetermined value. This condition is also given when the acceleration determination signal is generated.

If the theoretical ratio driving condition is not given and therefore the result of the determination in step S10 is "NO", the air-fuel ratio is changed by the air-fuel ratio changing unit 31 set to the lean air-fuel ratio (step S11). At the next step S12, a determination is made as to whether the value of a flag f (NR) is "1", thereby indicating the execution of the NOx reducing engine. Is the NOx catalyst 13a not yet saturated with adsorbed NOx, the result of the determination in step S12 becomes "NO", and control proceeds to step S14.

In step S14, the estimated value Q _{NT of} a discharge amount of NOx from the exhaust gas purification device 13 through the NOx estimation unit 33 calculated. For the calculation of the estimated value Q _NT , a subroutine is executed which uses a method ( 5 ) Of the votes for calculating the amount of NOx from the engine Q _NO 1 and a process ( 6 ) for calculating the estimated value Q _NT , which is based on the value Q _NO , which is in the calculation method of 5 was derived.

In step S60 of 5 according to the excess air ratio λ (more generally, the air-fuel ratio information variable), the estimated value D _{N of} the concentration of the engine output NOx (NOx output from the engine) is obtained from a graph ( 7 ), which is determined empirically and previously in the ECU 23 was saved. The excess air ratio λ is either that of the air-fuel ratio sensor 12 measured value or a target value set according to the motor drive condition. Furthermore, the estimated NOx concentration D _{N may be determined} according to the air-fuel ratio or the equivalent ratio (which is reciprocal to the excess air ratio) instead of the excess air ratio λ.

In the diagram of 7 the estimated value D _{N of} the concentration of the engine output NOx is set to have a maximum value when the excess air ratio λ is slightly larger than 1.0, that is, when the air-fuel ratio is slightly leaner than the theoretical air-fuel ratio. The estimated value D _N decreases substantially at a constant rate with a decrease in the excess air ratio λ in an area (lean air-fuel ratio range) where the excess air ratio λ is small, and decreases significantly at a constant rate with an increase in the excess air ratio λ in an area (rich air-fuel ratio range) where the excess air ratio λ is large.

When the readout of the estimated engine output NOx concentration D _N is completed, control proceeds to step S62. In step S62, a correction coefficient K _{I g} for the ignition timing is obtained from a diagram of 8th taken. The correction coefficients K _Ig were previously in the ECU 23 saved. In the in 8th In the diagram shown, the correction coefficient K _{Ig is} set so that it takes a reference value 1.0 when the ignition timing is set at a predetermined value on the leading side, and decreases when the ignition timing is changed toward the delay side.

As will be described later, the correction coefficient K _{Ig is} used to correct the estimated value D _{N of} the concentration of the engine output NOx read in step S60. The correction is made to properly deduce the amount of engine output NOx from the fact that the combustion is weakened and the combustion temperature is lowered to decrease the amount of engine output NOx when the ignition timing is changed toward the retard side.

In step S62, various correction coefficients for the EGR amount, the supply air temperature, the humidity and the like can be calculated and used to correct the estimated value D _{N of} the concentration of the engine output NOx, which is extracted in step S60.

In the next step S64, a supply air amount Q _a for each cylinder, that is, a supply air amount Q _a from the previous measurement time (before the current measurement time by the crank angle 120 ° CA) to the current measurement time based on the detection value A _f from the airflow sensor 6 and the machine speed N _e . The influence of atmospheric pressure and the supply air temperature on the detection value A _{f of} the air flow sensor 6 switch off, the detection value A _f according to the detection signals P _a and T _a from the atmospheric pressure sensor 21 and the supply air temperature sensor 22 corrected. The supply air quantity Q _a can also depend on the motor speed N _e , the supply air pressure P _b ect. are derived, and the calculation method for this is not limiting.

In step S66, the amount Q _NO of NOx discharged from the engine is calculated for each detection of the crank angle synchronization signal θ _CR with the following equation (1) according to the estimated value D _{N of} the concentration of the engine discharge NOx, the supply air amount Q _a, and the correction coefficient K _Ig derived as described above. Q N0 = k 1 × K Ig × Q a × D N , (1) where k _{1 is} a correction coefficient related to the amount of EGR, humidity and the like other than the correction coefficient K _Ig .

After calculating the amount Q _{N0 of} the engine output NOx, control proceeds to step S68. In step S68, the accumulated value SQ _{N (i + 1) of} the amount Q _N0 of NOx released from the engine and the exhaust gas purifying catalyst 13 happened up to the present time, calculated by the following equation (2), the value expressing the integrated value ∫Q _N0 dt of the amount Q _N0 of NOx emitted by the engine up to the present time: ∫Q N0 dt = SQ N (i + 1) = SQ N (i) + Q N0 , (2) where ∫SQ _{N (i)} indicates an integrated or accumulated value calculated in the previous cycle of the control routine, and Q _N0 indicates the amount of engine output NOx calculated in step S66 in the current cycle of the control routine.

In the next step S70, an estimated value K _NOX is the adsorption of NOx on the NOx catalyst 13a when the engine output NOx the exhaust gas purifying catalyst 13 happens based on the accumulated value SQ _{N (i + 1) of} the amount of the engine output NOx derived in step S68. For this purpose, an estimated adsorption ratio K _NOX , which corresponds to the accumulated value SQ _{N (i + 1)} , is taken from the diagram of 9 taken from that previously in the ECU 23 was saved.

In the diagram of 9 the estimated adsorption ratio K _{NOX is} set to take a maximum value of 1.0 when the accumulated value SQ _{N (i + 1) is} "0" and gradually decreases to a predetermined value K _N1 (e.g., a value of 0, 1) with an increase in the accumulated value SQ _{N (i + 1)} . One in 9 curve shown accumulated value SQ _{N (i + 1)} -estimated adsorption ratio K _NOX is expressed by the following equation (3): K N OX = (1 - K N1 ) × exp [(- k 2 ) × SQ N (i + 1) ] + K N1 , (3) where k _{2 is} a correction coefficient (constant).

The estimated adsorption ratio K _NOX can be derived by performing a calculation based on equation (3) instead of estimating the adsorption ratio K _NOX using the graph of 9 is carried out.

In the next step S72, the estimated value K _{CAT of} the ratio of the NOx purification by the three-way catalyst converter 13b of the exhaust gas purification catalyst 13 from the diagram of 10 taken on the basis of the excess air ratio λ. In view of the fact that the NOx purifying ability of the three-way catalyst converter 13b only in a narrow excess air ratio range where the excess air ratio λ is 1.0 or a near value thereof, the estimated cleaning ratio K _CAT according to the diagram of FIG 10 set such that it very quickly reaches a maximum value K _C2 (for example a value of 0.95) from a predetermined value K _C1 (for example a value of 0 to 0.1) when the excess air ratio λ increases from a value, which is slightly less than 1.0 up to a value of 1.0, increases and decreases very quickly from the maximum value K _C2 to the predetermined value K _C1 with a further increase in the excess air ratio λ. Since the excess air ratio λ during the lean-burn engine is a value (for example, 1.5) that is considerably larger than 1.0, the estimated cleaning ratio (K _CAT ) during the lean-burn engine becomes equal to the predetermined value K _C1 .

Instead of estimating the cleaning ratio K _CAT using the diagram of 10 The estimated cleaning ratio K _CAT can be easily derived by assuming that the cleaning ratio K _{CAT has} a value of 0 for the excess air ratio λ that falls within the narrow excess air ratio range (e.g. 0.95 ≤ λ ≤ 1.05) , 95, and that the cleaning ratio K _{CAT has} a value of "0" for the excess air ratio λ falling within a range (e.g., λ <0.95, 1.05 <λ) outside the narrow excess air ratio range.

In the next step S74, the NOx _discharge ratio is calculated according to the equation (NOx discharge ratio = (1 - K _NOX ) × (1 - K _CAT )) based on the engine discharge NOx amount Q _N0 , the estimated value K _NOX of Adsorption ratio of NOx by the NOx catalyst 13a and the estimated value K _{CAT of} the NOx purification ratio by the three-way catalyst converter 13b , Furthermore, the estimated value Q _{NT of} the catalyst output NOx amount for each detection of the crank angle synchronization signal θ _CR is calculated by using the following equation (4), which is based on the NOx output ratio and the engine output NOx amount Q _N0 in step S66 is calculated. The estimated value Q _NT is substantially equal to the actually measured value of the amount of NOx released by the exhaust gas purification device 13 is released into the atmosphere. Q NT = Q N0 × {(1 - K NOX ) × (1 - K CAT )} (4)

Equation (4) indicates that if the adsorption of NOx by the NOx catalyst 13a is continued under such a condition that the purification ratio K _CAT by the three-way catalyst converter 13b has the predetermined value K _C1 , such as in the lean-burn state, the NOx cleanability of the exhaust gas purification device 13 is reduced and therefore the catalyst discharge NOx amount Q _NT increases, so that the NOx adsorption ratio K _{NOX is} reduced.

After the estimated value Q _{NT of} the amount of catalyst discharge NOx is calculated, that goes Control of step S16 from 3 further. The comparator determines in step S16 34 whether the estimated value Q _{NT of} the amount of catalyst discharge NOx derived as described above is larger than the predetermined threshold value Q _{NT 0} . For example, a legal limit of NOx emission is used as the basis for setting the threshold value Q _{NT 0} . If the result of the determination in step S16 is "NO", that is, if the NOx adsorption amount has not reached the saturated state, it is determined that the amount of NOx released into the atmosphere is equal to or less than the maximum allowable value , and control goes to step S40 4 further.

In step S40, the amount of recirculation electricity (hereinafter referred to as EGR amount) E _{gr of} the EGR gas in the normal lean-burn state is set. In detail, an EGR quantity E _{LN is determined} as an EGR quantity E _gr for the normal lean-burn combustion drive from an EGR quantity diagram ( 17 ) for the normal lean-burn engine, which was previously in the ECU 23 was stored according to the engine speed N _e and the charge efficiency η _{v of} the air-fuel mixture. In the EGR quantity diagram, the EGR quantity E _{LN is expressed} as a function of the engine speed N _e and the charging efficiency η _{v of} the air / fuel mixture (E _gr = E _LN (N _e , η _v ).

Unlike the NOx-reduced drive state or the theoretical ratio drive state, a large amount of EGR is not required in the normal lean-burn state. The EGR quantity E _LN in the diagram is therefore set smaller than the EGR quantities E _N0 , E _ST for the same N _e , η _v in the EGR setting diagram for the NOx-reduced drive state or the theoretical ratio drive state.

In the next step S42, an ignition timing θ _{LN is determined} from an ignition timing diagram ( 18 ) which was previously in the ECU 23 was stored for the normal lean-burn engine, as the ignition timing θ _Ig for the normal lean-burn engine according to the engine speed N _e and the charge efficiency η _{v of} the air / fuel mixture. In the diagram, the ignition timing θ _{LN is expressed} as a function of the engine speed N _e and the charge efficiency η _{v of} the air-fuel mixture (θ _Ig = θ _LN (N _e , η _v )). Since the ignition timing needs to be advanced to improve the combustion efficiency at the time of the normal lean-burn engine, the ignition timing θ _LN in this ignition timing diagram becomes a value on the advanced side from the ignition timings θ _N0 , θ _ST for the same N _e , η _v for the NOx-reduced drive and the theoretical ratio drive.

After setting the ignition timing θ _Ig , control proceeds to step S44. In step S44, the acceleration determination threshold value A _{th is set} to a reference threshold value A ₀ , which is greater than the threshold value A _{N 0} for the NOx-reduced drive (A ₀ > A _{N 0} ). Therefore, during the normal lean burn drive, there is no shift to the theoretical ratio drive state without the throttle valve 7 is opened faster than in the NOx-reduced drive state. This is because the engine output is higher in the normal lean-burn state than in the NOx-reduced drive state, and it is therefore possible to consider a fairly substantial acceleration drive requirement even if the theoretical ratio drive is not performed. Another reason is to prevent the drive state from being changed frequently to the theoretical ratio drive state in order to avoid reducing the fuel consumption.

Next, control proceeds to step S36, in which the fuel amount is accurately calculated based on the supply air amount and the air-fuel ratio in a usual manner. After this, the execution of the combustion control routine in the current cycle is completed. A next crank angle synchronization signal θ _{CR of} the ECU 23 is supplied, the combustion control routine is then started again from step S10.

If it is determined in step S10 that the theoretical ratio driving condition is not given, and if it is determined in step S16 that the estimated value Q _{NT of} the catalyst _discharge NOx amount has not reached the threshold value Q _NT0 , a sequence of the steps becomes S10, S11, S12, S14, S16, S40, S42, S44 and S36 performed repeatedly to operate the engine 1 in the normal lean-burn state. During this time, NOx is in the exhaust gases on the NOx catalytic converter 13a adsorbed.

Thereafter, if it is determined in step S16 that the estimated value Q _{NT of} the catalyst discharge NOx amount has exceeded the threshold value Q _NTO during the lean-burn drive and the result of the determination in step S16 therefore becomes "YES", it is determined that the NOx adsorbing ability of the NOx catalyst 13a is saturated. In this case, control proceeds to step S18. In step S18, the value of a flag f (NR) is set to "1", indicating that the NOx-reduced drive is being carried out.

Next, control goes to step S30 4 further. In step S30, according to the engine speed N _e and the charge efficiency η _{v of} the air-fuel mixture, an EGR amount E _{N0 is used} as the EGR amount E _gr for the NOx-reduced drive by the temperature reduction unit 36 of 1 taken from an EGR setting diagram (not shown) for the NOx-reduced drive. This diagram was determined empirically and in the ECU 23 saved.

In the diagram for the NOx-reduced drive, the EGR quantity E _{N0 is expressed} as a function of the engine speed N _e and the charge effectiveness η _{v of} the air / fuel mixture (E _gr = E _N0 (N _e , η _v )) and set to a value that is greater than the EGR amount E _gr for the same N _e , η _v in the EGR setting diagram ( 17 ) for the normal lean-burn drive. The EGR amount E _gr that from the exhaust manifold 11 to the intake manifold 4 is circulated becomes larger than in the case of the normal lean-burn engine, thereby lowering the combustion temperature and reducing the NOx release amount.

After the EGR amount E _gr is set, control proceeds to step S32. In step S32, in accordance with the engine speed N _e and the charge effectiveness η _{v of} the air / fuel mixture, an ignition timing θ _N0 as the ignition timing θ _Ig for the NOx-reduced drive is read from an ignition timing diagram (not shown) for the NOx-reduced drive, this diagram being determined empirically and previously in the ECU 23 was saved.

In the (not shown) ignition timing setting diagram for the NOx-reduced drive, the ignition timing θ _{N0 is expressed} as a function of the engine speed N _e and the charge efficiency η _{v of} the air-fuel mixture (θ _Ig = θ _N0 (N _e , η _v )) and to a value on the delay side from the ignition timing θ _Ig for the same N _e , η _v in the ignition timing diagram ( 18 ) set for the normal lean-burn drive. The time for the spark plug 16 therefore, the ignition of the air-fuel mixture is delayed so that the exhaust stroke is started before the combustion is completed. Therefore, the combustion temperature does not rise so high and the NOx release amount is reduced.

After setting the ignition timing θ _Ig , control proceeds to step S34. In step S34, according to an acceleration determination threshold setting diagram (not shown) for the NOx-reduced drive, the valve opening speed threshold (acceleration determination threshold) A _{th of} the throttle valve 7 to the NOx-reduced acceleration determination threshold value A _N0 by the threshold value change unit 38 changed. In this diagram, the threshold value A _N0 , which is expressed as a function of the vehicle speed, is set to a value that is smaller than the normal threshold value A ₀ . The transition from the lean-burn engine to the theoretical ratio engine is therefore carried out on the low throttle valve opening speed side. As a result, when an acceleration drive request is issued during the NOx-reduced drive, the engine output, which has been reduced by lowering the combustion efficiency by the NOx-reduced drive, is rapidly increased, thereby making the acceleration drive smooth.

After setting the acceleration determination threshold A _th , control proceeds to step S36. In step S36, the amount of fuel from the fuel injection valve 3 must be supplied, calculated in the usual manner based on the supply air amount and the air-fuel ratio according to a predetermined equation. The amount of fuel supplied during the NOx-reduced drive is kept at a constant value when the air-fuel ratio is kept at a predetermined value. On the other hand, if the air-fuel ratio is changed within the lean air-fuel ratio range to thereby lower the combustion temperature, the fuel supply amount is variably set according to the EGR amount E _N0 and the ignition timing θ _N0 .

When the calculation of the fuel supply amount is completed in step S36, the execution of the combustion control routine in the current cycle is completed. After that, when the next crank angle synchronization signal θ _{CR of} the ECU 23 is supplied, the combustion control routine is started again from step S10.

Since the flag f (NR) is already at "1" after the start of the NOx-reduced drive is set, a sequence of steps S10, S11, S12, S30, S32, S34 and S36 are repeatedly executed to reduce the NOx Drive, when it is determined in step S10 that the theoretical ratio driving condition is not given.

As described above, according to the engine combustion control of this embodiment, even when the catalyst _discharge NOx estimated amount Q _{NT reaches} the predetermined value Q _NT0 at which the NOx adsorption amount can be regarded as substantially saturated during the lean-burn drive, there is no possibility that the drive state is increasingly changed from the lean-burn drive to the theoretical ratio drive in order to deoxidize the adsorbed NOx. Rather, in the engine combustion control of this embodiment, when the NOx catalyst 13a is saturated, the NOx-reduced drive, in which the EGR amount is increased and the ignition timing is delayed, is exercised. As a result, the amount of NOx released into the atmosphere can always be kept at a value equal to or less than the constant value Q _NT0 without _causing a torque _variation due to the transition to the theoretical ratio driving state.

Further, since the acceleration determination threshold A _{th is set} to a small value in the NOx-reduced driving state, the driving state tends to be changed to the theoretical ratio driving state which, usually the NOx-reduced drive, does not last for a long period of time. Therefore, a reduction in fuel economy caused by the NOx-reduced engine can be suppressed within an allowable range.

While the normal lean-burn drive or the lean-burn drive for NOx reduction Control proceeds to step S20 if it is determined in step S10 that the theoretical ratio drive condition is given and therefore the result of the determination in step S10 becomes "YES". In step S20 becomes the air-fuel ratio from the lean air-fuel ratio changed to the theoretical Luftkraftstoffver ratio, whereby the drive state from Lean combustion state is changed to the theoretical ratio drive state.

In the next step S22, the flag f (NR) is set to "0", which indicates that the NOx-reduced drive is not being applied. This is because the NOx-reduced drive is inhibited in the theoretical ratio drive state, as will be described later. Furthermore, in step S22, a time counter for counting the elapsed time from the moment at which the theoretical ratio drive starts is started. In the next step S24, it is checked by referring to the content of the time counter whether a predetermined time t _R (for example, 3 seconds) has elapsed from the start of the theoretical ratio drive. If the result of the determination in step S24 is "NO", control proceeds to step S50 4 further.

In step S50, an EGR amount E _ST as an EGR amount E _gr for the theoretical ratio drive is read out from the (not shown) EGR amount setting diagram for the theoretical ratio drive in accordance with the engine speed N _e and the charging efficiency η _{v of} the air / fuel mixture that was previously in the ECU 23 was saved. In this diagram, the theoretical air-fuel ratio EGR amount E _{ST is expressed} as a function of the engine speed N _e and the charging efficiency η _{v of} the air-fuel mixture (E _gr = E _ST (N _e , η _v )), and is set to a value that is larger is the EGR quantity E _gr for the same N _e , η _v in the EGR quantity law diagram ( 17 ) for the normal lean-burn drive. The EGR amount E _gr in the theoretical ratio drive therefore becomes larger than the EGR amount in the normal lean-burn engine, which lowers the combustion temperature and reduces the NOx release amount.

After the EGR amount E _gr is set, control proceeds to step S52. In step S52, an ignition timing θ _ST as the ignition timing θ _Ig for the theoretical ratio drive is read out from an ignition timing diagram (not shown) for the theoretical ratio drive that was previously in the ECU 23 was stored according to the engine speed N _e and the charge effectiveness η _{v of} the air-fuel mixture. In the above diagram, the ignition timing θ _{ST is expressed} as a function of the engine speed N _e and the charge efficiency η _{v of} the air-fuel mixture (θ _Ig = θ _ST (N _e , η _v )), and to a value on the retard side from the ignition timing θ _Ig for that same N _e , η _v in the ignition timing diagram ( 18 ) for the normal lean-burn engine or the one for the NOx-reduced engine. Because the time for the spark plug 16 is delayed to ignite the air-fuel mixture, therefore, the exhaust stroke is started before the combustion is completely completed, whereby the NOx release amount is reduced. Furthermore, knocking in the theoretical ratio drive can also be prevented.

In the next step S44, the acceleration determination threshold value A _{th is reset} from the threshold value A _N0 for the NOx-reduced drive to the reference threshold value A ₀ , which is greater than the threshold value A _N0 . In the next step S36, the fuel quantity to be delivered is then calculated. After the fuel delivery amount is fully calculated in step S36, the execution of the combustion control routine in the current cycle is ended. A next crank angle synchronization signal θ _{CR of} the ECU 23 is supplied, the combustion control routine is then started again from step S10.

After the start of the theoretical ratio drive, a sequence of steps S10, S20, S22, S24, S50, S52, S44 and S36 is repeatedly executed to perform the theoretical ratio drive until the predetermined time t _{R has} passed. In the theoretical ratio drive, the exhaust gas contains a lot of HC, so that around the NOx catalyst 13a the reducing atmosphere is created. It follows from this that the NOx catalyst 13a absorbed NOx is reduced or deoxidized.

If the predetermined time t _{R has passed} from the start of the theoretical ratio drive, and therefore the result of the determination in step S24 becomes "YES", control proceeds to step S26. In step S26, it is determined that the reduction or deoxidation of the adsorbed NOx is sufficiently exerted, and the accumulated value SQ _{N (i + 1) of} the engine output NOx amount is reset to a value "0". Steps S50, S52, S44 and S36 are then carried out in succession.

In the next and the following The theoretical ratio drive is executed as long as control cycles the theoretical ratio drive condition given is. If the condition is not met, there will be a transition to the lean-burn drive.

A combustion control device for an internal combustion engine will now be described explained according to a second embodiment of the invention.

The device of this embodiment is constructed essentially the same as the device of FIG 1 , so that an explanation for common components of both devices is unnecessary. In this embodiment, the EGR circulation line 26 and the EGR valve 27 , in the 1 shown are not required.

The ECU 23 this embodiment has various functions, in 13 components shown.

In detail, the ECU 23 an engine delivery NOx quantity estimator 130 for estimating the amount of NOx released from the engine 1 to the exhaust pipe 14 , The NOx estimation unit 130 has an engine output NOx concentration estimation unit 131 to estimate the concentration D _{N of} the NOx from the engine 1 to the exhaust pipe 14 is delivered according to the excess air ratio λ; a delay correction unit 132 deriving a correction coefficient K _Ig , which is used to correct the estimated NOx concentration D _N according to the ignition timing; and a supply air amount calculation unit 133 to calculate the amount Q _a of supply air supplied to the engine 1 is fed. In the NOx estimation unit 130 becomes the product of the supply air quantity Q _a , the estimated NOx concentration D _N and the correction coefficient K _Ig by multipliers 200 is calculated as the estimated value Q _{NO of} the engine output NOx amount.

The ECU 23 also includes an adsorption ratio estimator 135 for deriving the estimated value K _{NOX of} the adsorption ratio of NOx by the NOx catalyst 13a according to the accumulated value SQ _{N (i + 1) of} the engine output NOx amount; a cleaning ratio estimator 136 for deriving the estimated value K _{CAT of} the purification ratio of NOx by the three-way catalyst converter 13b according to the excess oxygen ratio λ; a catalyst delivery NOx quantity estimator 137 for deriving the NOx discharge ratio based on the estimated NOx adsorption ratio K _NOX and the estimated NOx purification ratio K _CAT , and for deriving the product of the NOx discharge ratio and the estimated engine discharge NOx amount Q _N0 as the estimated catalyst discharge NOx -Quantity Q _NT ; and a comparator 138 to compare the estimated amount of catalyst _delivery NOx Q _NT with the threshold Q _NT0 . If the estimated _{discharge amount} Q _{NT is} larger than the threshold value Q _NT0 , a fat burning drive _signal from the comparator 138 output. When the fat burning drive signal is output for a predetermined period of time t _R , a reset signal becomes the adsorption ratio estimator 135 is output so that the accumulated value SQ _{N (i + 1) of} the engine output NOx amount is reset to "0".

The above combustion control device is configured to change the driving state to the fat burning state when the NOx adsorbing ability of the NOx catalyst 13a is substantially saturated during the lean burn drive and maintains the fat burn drive for a predetermined period of time around the NOx catalyst 13a in a reducing atmosphere to increase the adsorbability of the NOx catalyst 13a regain. The fat-burning state contains a drive state in which the air-fuel ratio is feedback-controlled (regulated) essentially in relation to the theoretical air-fuel ratio.

Operation of the above combustion control device is explained below.

Every time the crank angle synchronization signal θ _{CR of} the ECU 23 while the engine is running 1 is fed, the in 14 shown combustion control routine executed.

First, it is determined in step S210 whether the lean-burn driving condition is given. For example, the lean burn drive condition is given when the following requirements and the like are satisfied at the same time: the engine 1 is operated in the warm-up state; the motor 1 is operated in a predetermined drive range, which is determined by the engine speed N _e and the engine load; and the engine 1 is not operated in a drive state in which the motor should be accelerated or decelerated.

Is the result of the determination in Step S210 is "NO", that is, the lean-burn driving condition not fulfilled, Control proceeds to step S212 and the fat burning drive control is carried out.

On the other hand, if the lean-burn driving condition is satisfied and the result of the determination in step S210 is "YES", control proceeds to step S214 and the estimated value Q _{NT of} the NOx amount from the exhaust gas purifying catalyst device 13 delivered is derived. In step S214, the subroutine that executes the in 5 calculation method shown and a in 15 contains the calculation method shown. Since the calculation method of 5 has already been explained and most of the in 15 the calculation method shown in that 6 , the subroutine is briefly explained below.

In this subroutine, the estimated value D _{N of} the engine output NOx concentration is obtained from the graph of FIG 7 (Step S60 from 5 ) according to the excess air ratio λ by the concentration estimation unit 131 , in the 13 is read out. Furthermore, the correction coefficient K _Ig from the diagram of 8th according to the ignition timing by the delay correction unit 132 of 13 (Step S62) read out. As next, the supply air amount Q _a for each cylinder according to the engine speed N _e and the detection value A _f from the air flow sensor 6 through the supply air amount calculation unit 133 of 13 (Step S64). Then, the engine output NOx amount Q _{N0 is determined} for each detection of the crank angle synchronization signal θ _CR by using the equation (1) according to the estimated NOx concentration D _N , the correction coefficient K _Ig, and the supply air amount Q _a by the NOx amount estimator 130 of 13 (Step S66).

After the calculation of the engine output NOx amount Q _N0 , control proceeds to step S367 15 further. In step S367, it is determined whether a predetermined time period t _R (for example, 3 seconds) has passed from the start of the combustion engine. During the lean-burn drive, the result of the determination in step S367 becomes "NO", and control proceeds to step S368, which goes to step S68 6 equivalent. In step S368, the accumulated value SQ _{N (i + 1) of} the engine output NOx amount Q _N0 is calculated using the equation (2).

In the next step S370, which corresponds to step S70 of 6 corresponds to, the estimated value K _{NOX of} the adsorption ratio of NOx, that of the NOx catalyst 13a at the time when the NOx discharged from the engine is the exhaust gas purifying catalyst device 13 happens, derived in accordance with the accumulated value SQ _{N (i + 1) of} the engine output NOx amount Q _N0 calculated in step S368. The diagram of 9 is used to estimate the adsorption ratio K _NOX . Alternatively, the calculation is performed using equation (3) or the following regression equation: K NOX (i + 1) = 1 - (1 - K N1 ) × k 2 × {(1 - α) × SQ N (i) + α × Q N (i) } where α is a constant.

In the next step S372, which corresponds to step S72 of 6 corresponds to, the estimated value K _{CAT of} the purification ratio of NOx by the three-way catalyst converter 13b from the diagram of 10 on the basis of the excess air ratio λ by the cleaning ratio estimation unit 136 of the 13 taken. Instead of estimating the cleaning ratio K _CAT using the diagram of 10 The cleaning ratio K _CAT can be determined briefly by determining whether the excess air ratio λ is within or outside a narrow excess air ratio range, as is the case with the first embodiment.

Further, in step S374, the step S74 of 6 corresponds to the NOx discharge ratio by the catalyst discharge NOx quantity estimation unit 137 of 13 based on the estimated value K _{NOX of} the adsorption ratio of NOx by the NOx catalyst 13a and the estimated value K _{CAT of} the NOx purification ratio by the three-way catalyst converter 13b calculated. Further, the estimated value Q _{NT of} the catalyst output NOx amount for each detection of the crank angle synchronization signal θ _{CR is} calculated according to the aforementioned equation (4) based on the NOx output ratio and the engine output NOx amount Q _N0 , which are performed in step S66 the engine output NOx quantity estimation unit 130 the 13 is calculated.

After calculating the estimated value Q _NT , control goes to step S216 14 further. In step S216, the comparator 138 of 13 determines whether the estimated value Q _{NT of} the catalyst _discharge NOx amount is larger than a predetermined threshold value Q _NT0 . If the result of the determination in step S216 is "NO", it is determined that the amount of NOx released into the atmosphere is equal to or less than a maximum allowable value, and control proceeds to step S218 to execute the lean-burn drive control.

On the other hand, if the result of the determination in step S216 is "YES", that is, if the catalyst discharge NOx amount Q _{NT is} larger than the predetermined threshold value Q _NT0 , the _{adsorbability of} the NOx catalyst becomes 13a considered saturated. In this case, control proceeds to step S212 to execute the fat burning drive control.

If a change is made from the lean burn engine to the fat burn engine when the NOx amount Q _NT becomes larger than the threshold value Q _NT0 , the amount of HC released by the engine 1 is released, larger than in the lean-burn state. The HC then reacts with NOx to that of the NOx catalyst 13a deoxidize adsorbed NOx. It follows that the amount of NOx released into the atmosphere is reduced and the NOx catalyst 13a can adsorb NOx again.

If it is determined in step S216 for the first time that the amount of NOx Q _{NT is} larger than the threshold value Q _NT0 and a change is made in the fat-burning drive control as described above, the time counter of the ECU becomes 23 started at this time to start counting the elapsed time from the start of the fat burning drive control.

As described above, if the NOx catalyst 13a is saturated with adsorbed NOx even if the lean burn drive condition is not satisfied, the fat burn drive is executed to deoxidize NOx. During this time, a sequence of steps S210, S214, S216 and S212 is carried out repeatedly. If the result of the determination in step S367 is that in FIGS 5 and 15 Subroutine "NO" shown and corresponding to step S214, that is, if a predetermined time t _R does not pass after the start of the rich combustion drive control, the accumulated value SQ _{N (i + 1) of} the engine output NOx amount is also updated in S368. It is therefore determined in step S216 that the catalyst discharge NOx amount Q _{NT is} still larger than the threshold value Q _NT0 . As a result, the fat-burning driving state is maintained for the predetermined time t _R so that the NOx is completely deoxidized.

If the predetermined time t _{R has passed} after the start of the fat burning drive control and the result of the determination in step S367 is "YES", control proceeds to step S376. In step S376, it is assumed that all of the NOx on the NOx catalyst 13a has been adsorbed, deoxidized, and a reset signal becomes the adsorption ratio estimation unit 135 of 13 is output, whereby the accumulated value SQ _{N (i + 1) of} the engine output NOx amount is reset to "0". As a result, the estimated value of the NOx adsorption ratio K _NOX derived in the next step S370 becomes 1.0, and the estimated value Q _{NT of} the catalyst discharge NOx amount calculated in step S374 becomes "0". In this case, control proceeds to step S218 to restart the lean burn drive control. This means that the fat burning drive control for deoxidizing NOx has ended.

Thereafter, when the estimated NOx adsorption ratio K _{NOX is decreased} again as the accumulated value SQ _{N (i + 1) of} the engine output NOx amount increases, the estimated value Q _{NT of} the catalyst output NOx amount increases again.

Will the drive state of the engine 1 Changes between the lean-burn state and the fat-burn state, the engine discharge NOx amount Q _N0 and the catalyst discharge NOx amount Q _{NT change} with the elapsed time as in FIG 16 shown. In 16 the one- _dot chain line indicates the engine output NOx amount Q _N0 , the solid line indicates the catalyst output NOx amount Q _NT , and the dashed area indicates the NOx adsorption amount or the cleaning amount by the exhaust gas purifying catalyst device 13 on.

As in 16 shown, the NOx purification amount is reduced by the exhaust gas purifying catalyst device 13 with the elapsed time during the lean-burn drive. Then, when the estimated value Q _{NT of} the catalyst _discharge NOx amount reaches the predetermined value Q _NT0 , when a time of, for example, t _{L1 has} elapsed from the start of the lean-burn engine, the engine drive state is changed from the lean-burn state (A) to the fat-burning state. Thereafter, the fat burning drive is maintained for the predetermined period of time t _R. During the fat-burning drive, all of it is from the NOx catalyst 13a adsorbed NOx deoxidizes. If the predetermined time t _{R has passed} after the start of the fat-burning drive and the lean-burn state (B) has been set again, the NOx adsorption capacity of the NOx catalytic converter becomes 13a restored.

Further, since a change from the lean-burn state to the fat-burn state is made immediately after the catalyst discharge NOx amount Q _{NT reaches} the predetermined value Q _NT0 , the amount of NOx released into the atmosphere can always be equal to or less than the predetermined value Q _{NT0 be} pressed. As indicated, for example, by the time period t _{L1 of} the lean-burn combustion engine (A) and the time period t _L2 (≠ t _L1 ) of the lean-burn combustion engine (B), the time period t of the lean-burn combustion state is not always constant. That is, in the driving state in which the NOx discharge amount is small, the lean-burn drive is maintained for a relatively long period of time. The frequency of transition to the fat-burning engine is therefore small, making it possible to suppress deterioration in fuel economy and variation in torque. Further, in the case that the engine drive is carried out in such a manner that the engine drive range frequently changes between drive ranges with different target air-fuel ratios, a transition between the lean-burn engine and the rich-combustion engine is performed according to the drive state thus changed. Therefore, no problem arises even if the present invention is applied to such a motor drive.

The present invention is not to the aforementioned first and second embodiment limited and it can various modifications can be made.

For example, in the first embodiment the engine drive condition from the lean burn condition to the theoretical Ratio driving state changed where the air-fuel ratio is set to the theoretical air-fuel ratio, for example at the time of the accelerator drive or a heavy duty drive. Alternatively, a transition from the lean burn condition to the fat burn condition where that Air-fuel ratio is set smaller than the theoretical air-fuel ratio.

Furthermore, in the first embodiment, the determination as to whether the transition to the NOx-reduced drive should be made is made according to the result of a comparison of the estimated value Q _NT and the amount of catalyst discharge NOx (g / sec) with the threshold value Q _NT0 . However, the determination as to whether the transition to the NOx-reduced drive should be made can also be made according to the result of a comparison between one actual measured value or estimated value of that from the NOx catalyst 13a adsorbed amount of NOx and the saturated amount of adsorption, or according to the result of a determination associated with the release NOx concentration (PPM).

It is also possible to determine that the amount of adsorption of NOx by the NOx catalyst 13a has reached the saturated value, and perform the NOx-reduced drive when a predetermined period of time has passed from the start of the lean-burn drive. Preferably, the predetermined period of time is set so that the output NOx amount Q _NT does not exceed the predetermined value Q _NT0 .

Furthermore, the NOx-reduced drive the EGR amount increases and the ignition timing delayed to lower the combustion temperature. However, it is not necessary both processes simultaneously perform, and only one of these operations can be performed.

In the NOx discharge amount calculation subroutine the first embodiment are valued Values used, which are taken from different diagrams. It can however, actually measured values are used instead of the estimated values, the parts of the information correspond to that of different sensors is delivered.

Furthermore, in the first embodiment Acceleration determination (i.e., determining whether there is an acceleration drive request or does not exist) based on the opening speed of the Throttle valve performed. Alternatively, the acceleration determination can be based on a Feed information variables are performed, for example a variation in the supply air amount or a variation in the negative pressure of the supply air.

In the first embodiment, it is determined that the NOx catalyst 13a is saturated with adsorbed NOx when the catalyst _delivery NOx amount Q _N has exceeded the threshold value Q _NT0 . Instead, it is possible to include parts of the engine's load information (for example, amounts of fuel that the engine 1 to be accumulated) during the lean-burn drive, to derive the accumulated value therefrom and to determine that the NOx catalyst 13a is saturated with adsorbed NOx when the accumulated value exceeds a predetermined value. In this modification, the ECU 23 the lean burn accumulation through.

In the third embodiment, the air-fuel ratio is set to the super-lean air-fuel ratio AF _T and a predetermined amount of exhaust gases are recirculated by EGR to cause ignition failure. A sufficient effect can, however, only be achieved by setting the air-fuel ratio to the super-lean air-fuel ratio AF _T. Furthermore, an ignition failure can reasonably be caused simply by recirculating the exhaust gases from EGR. In this case, it is advantageous to set the recirculation amount of the exhaust gases to a larger value.

In the second embodiment, the air-fuel ratio is substantially set to the theoretical air-fuel ratio in the fat-burning drive control for deoxidizing adsorbed NOx. However, it is only necessary to have a reducing atmosphere around the NOx catalyst 13a to create around that contains HC. Therefore, the air-fuel ratio can be set to a value that is on the rich side in terms of the theoretical air-fuel ratio.

Further, in the second embodiment, the determination of whether a transition between the lean-burn engine and the fat-burn engine should be made is made according to the result of comparing the catalyst _discharge NOx amount Q _NT with the threshold value Q _NT0 . Alternatively, the need for a transition may be determined according to the result of a determination associated with the emission NOx concentration (PPM), etc. In each of the above embodiments, estimated values are used which are derived from various diagrams. However, actually measured values can also be used instead of the estimated values.

Furthermore, in each embodiment a six-cylinder in-line petrol engine used. The combustion control device however, the present invention can be applied to any type of internal combustion engine independently of the number of cylinders and type are applied. Furthermore, the feature of the first to fourth embodiments in the required Ways can be combined.

From the embodiments described above of the present invention, it will be appreciated that the invention will occur to those skilled in the art amended can be made without departing from the spirit and scope of the invention. Such modifications are within the scope of the following claims.

Claims (8)

Control device for an internal combustion engine ( 1 ) with a catalytic converter ( 13 ) and a nitrogen oxide emission control device, the exhaust gas catalytic converter in an exhaust line ( 14 ) of the internal combustion engine is arranged and is operable to absorb nitrogen oxide when in the exhaust gas catalytic converter ( 13 ) flowing exhaust gases have a lean air / fuel ratio, and to deoxidize absorbing nitrogen oxide when the oxygen concentration of the incoming exhaust gases is reduced, wherein the nitrogen oxide emission control device can be operated, and the concentration of the exhaust gas catalytic converter ( 13 ) to reduce flowing gases, thereby forming a reducing atmosphere, with: a nitrogen oxide emission estimation device ( 130 . 135 . 136 . 137 ) to estimate an emission (Q _{N T} ) of a nitrogen oxide from the catalytic converter ( 13 ); a facility ( 138 ) to determine whether the emission (Q _{N T} ) of nitrogen oxide by the nitrogen oxide emission estimator ( 130 . 135 . 136 . 137 ) is estimated to exceed a predetermined amount (Q _{N TO} ); and a combustion state changing device ( 138 ) to change the air-fuel ratio of the air-fuel mixture to make a change from the lean-burn state to the fat-burn state when the device ( 138 ) determines that the emission (Q _{N T} ) of nitrogen oxide exceeds the predetermined amount (Q _{N TO} ) in the lean-burn state. A control device according to claim 1, wherein the nitrogen oxide emission estimation means ( 130 . 135 . 136 . 137 ) an engine nitrogen oxide emission estimator ( 130 ) for estimating an emission quantity (Q _{N O} ) of nitrogen oxide from the internal combustion engine ( 1 ) to the exhaust pipe ( 14 ) and an adsorption ratio estimator ( 135 ) to estimate an adsorption ratio (KN _Ox ) of nitrogen oxide, which is generated by the exhaust gas catalytic converter ( 13a ) is adsorbed; and the nitrogen oxide emission estimator ( 130 . 135 . 136 . 137 ) the amount of emissions (Q _{N T} ) of nitrogen oxide from the catalytic converter ( 13 ) estimates the amount of emissions (Q _{N O} ) of nitrogen oxide from the internal combustion engine ( 1 ) based on the engine nitrogen oxide emission estimator ( 130 ) is estimated, and the adsorption ratio (K _NOX ) of nitrogen oxide, which is generated by the catalytic converter ( 13b ) which is adsorbed by the adsorption ratio estimator ( 135 ) is estimated. A control device according to claim 2, wherein the nitrogen oxide emission estimation means ( 130 . 135 . 136 . 137 ) a cleaning ratio estimator ( 136 ) for estimating a cleaning ratio (K _CAT ) of the nitrogen oxide which is generated by the catalytic converter ( 13b ) is cleaned; and the nitrogen oxide emission estimator ( 130 . 135 . 136 . 137 ) the emission (Q _{N T} ) of nitrogen oxide from the catalytic converter ( 13 ), which is based on the emission (Q _NO ) of nitrogen oxide from the internal combustion engine, which is generated by the engine nitrogen oxide emission estimator ( 130 ) is estimated, and the adsorption ratio (K _NOX ) of nitrogen oxide, which is generated by the catalytic converter ( 13b ) which is adsorbed by the adsorption ratio estimator ( 136 ) is estimated, and the cleaning ratio (KC _AT ) of nitrogen oxide, which is cleaned by the exhaust gas catalytic converter (), which is determined by the cleaning ratio estimating device ( 136 ) is estimated. A control device according to claim 2, wherein the engine emission estimator ( 130 ) the emission (Q _NO ) of nitrogen oxide from the internal combustion engine ( 1 ) to the exhaust pipe ( 14 ) estimates the concentration (D _N ) of nitrogen oxide from the internal combustion engine ( 1 ) to the exhaust pipe ( 14 ) and a supply information variable representing an amount (Qa) of supply air that the internal combustion engine ( 1 ) is supplied. A control device according to claim 4, wherein the engine emission estimator ( 130 ) the concentration (D _N ) of nitrogen oxide from the internal combustion engine ( 1 ) to the exhaust pipe, which is based on the air-fuel ratio variable (λ), which represents the air-fuel ratio of the air-fuel mixture that the internal combustion engine ( 1 ) is supplied. A control device according to claim 2, wherein the engine emission estimator ( 130 ) the amount of exhaust gas (Q _{N O} ) of nitrogen oxide from the internal combustion engine ( 1 ) to the exhaust pipe ( 14 ) corrected by the engine nitrogen oxide emission estimator ( 130 ) according to the ignition timing (T _Ig ) of the internal combustion engine ( 1 ) is estimated. A control device according to claim 2, wherein the engine nitrogen oxide emission estimator ( 130 ) the amount (Q _NO ) of nitrogen oxide released by the internal combustion engine ( 1 ) to the exhaust pipe ( 14 ) corrected by the engine nitrogen oxide emission estimator ( 130 ) is estimated according to an amount of exhaust gases that are sent to the internal combustion engine ( 1 ) is recirculated. A control device according to claim 2, wherein the adsorption ratio estimator ( 135 ) estimates the adsorption ratio (K _NOX ) of nitrogen oxide from the catalytic converter ( 13a ) is adsorbed, which on the total emission (∫Q _NO dt) of nitrogen oxide from the internal combustion engine ( 1 ) to the catalytic converter ( 13 ) based on a period of time that begins when the lean burn condition starts and ends when the fat burn condition changes.