JP2003120383A - Method of setting fuel/air mixture for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of compensating a fresh catalyst for the shift of air-fuel ratio in lean direction during the control of the air-fuel ratio for an internal combustion engine having a catalyst and tow-sensor control. SOLUTION: The method of setting a fuel/air mixture for the internal combustion engine 2 having the catalyst 8 and at least one exhaust gas sensor 12 positioned behind the catalyst for providing first information about the oxygen content of exhaust gas, which adjusts the setting of the fuel/air mixture, forms second information about hydrogen existing in the exhaust gas behind the catalyst, which adjusts the fuel/air mixture. The method compensates the undesirable influence of hydrogen on the setting of the fuel/air mixture which causes the hydrogen cross detectability of the exhaust gas sensor in relation to the detection of hydrogen and the generation of hydrogen behind the catalyst.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides, to some extent, a first sensor in front of a catalyst and a first sensor in which an internal combustion engine has a catalyst and which controls the air-fuel ratio (fuel / air mixture ratio). It relates to a method and a device for controlling the air-fuel ratio for such an internal combustion engine, which has a so-called two-sensor control using a second exhaust gas sensor behind the catalyst.

[0002]

2. Description of the Related Art Such a method has already been disclosed in US Pat.
Known from No. 307,625. In such control, there was a problem in the fresh catalyst that the air-fuel ratio shifts toward a lean value. This shift naturally disappears as the deterioration of the catalyst progresses.

Shifting the air-fuel ratio towards lean values has the undesirable consequence of increasing nitrogen oxide emissions.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of compensating for such an unfavorable effect of increasing nitrogen oxide emissions by shifting the air-fuel ratio toward a lean value. It is an issue.

[0005]

According to the present invention, there is provided a first information relating to a catalyst and an oxygen content of an exhaust gas, the first information adjusting a setting of a fuel / air mixture, A method for setting up a fuel / air mixture for an internal combustion engine, comprising at least one exhaust gas sensor arranged behind the catalyst, wherein a second information on hydrogen present in the exhaust gas behind the catalyst is formed. , And the second information adjusts the fuel / air mixture settings.

In particular, according to the invention, an internal combustion engine is
A catalyst and at least one exhaust gas sensor located behind the catalyst, which provides first information regarding the oxygen content of the exhaust gas, the first information adjusting the setting of the fuel / air mixture. However, such a method for adjusting a fuel / air mixture for an internal combustion engine comprises the following steps: forming a second information on the hydrogen present in the exhaust gas behind the catalyst, and using the second information on the fuel / air mixture. The step of supplementally adjusting the mixture.

Other means are designed such that the second information is produced by a hydrogen sensor. As an alternative to this, the second information is formed from a comparison of the results of different evaluation methods of the deterioration state of the catalyst.

To this end, another means consists in the following steps:
That is, the step of forming a first variable for the deteriorated state of the catalyst by the first method, the step of forming a second variable for the deteriorated state of the catalyst by the second method, and the second variable of the first variable Forming a third variable giving a deviation from, a step of comparing the third variable with a predetermined threshold value, and a step of evaluating the exceeding of the threshold value as an indication of hydrogen generation. ,have.

A preferred alternative embodiment is designed such that the method of forming variables for the depletion state is based on measuring the oxygen storage capacity of the catalyst using an oxygen sensing exhaust gas sensor behind the catalyst.

Another measure is that the method of forming variables with respect to the deterioration state is designed to respond to the evolution of hydrogen behind the catalyst with different sensitivities. The preferred means for forming the first variable are the following steps: completely filling the catalyst with oxygen by operating the internal combustion engine with an excess of air, and the internal combustion engine with the fuel required for theoretical combustion. The exhaust of oxygen from the catalyst by operating with excess fuel compared to the amount of the exhaust gas and the step of identifying that the catalyst has been completely emptied of oxygen by the oxygen deficiency signal of the exhaust gas sensor. A step of determining an excess fuel amount at which the internal combustion engine is operated by the internal combustion engine until the oxygen deficiency signal is generated after the catalyst is started to be depleted, and a first variable for the deterioration state is determined based on the determined excess fuel amount. Forming.

The preferred means for forming the second variable is to take the following steps: completely emptying the catalyst of oxygen by operating the internal combustion engine with excess fuel; The step of filling the catalyst with oxygen by operating in excess of air compared to the amount of air needed for the exhaust, and the oxygen excess signal of the exhaust gas sensor identifies that the catalyst has been completely filled with oxygen. A second variable for the deterioration condition based on the determined excess oxygen, the internal combustion engine determining the excess oxygen with which the internal combustion engine has been operated, until the excess oxygen signal is generated. And forming a.

In another embodiment, when the first method evaluates the catalyst as deteriorated and the second method evaluates the catalyst as fresh, the second method generates hydrogen. Is designed to signal you.

The present invention also relates to an electronic control device for carrying out the means, sequence of steps and embodiments described above. In the present invention, the cause of the shift of the air-fuel ratio toward the lean value is that the hydrogen generation of the catalyst as a function of deterioration,
It is based on the finding that there is an interaction between the oxygen sensing exhaust gas sensor and the hydrogen crossing detectability. In this case, the term “cross-sensitivity” is a paraphrase of shifting the characteristic curve of the output signal of the exhaust gas sensor with respect to the oxygen concentration when hydrogen is generated. When hydrogen is generated, the characteristic curve shifts in the direction of increasing oxygen concentration. Therefore, the effect of hydrogen shifts the profile of the characteristic curve so that when the hydrogen is present, the sensor indicates less oxygen than is actually present. Therefore, the controller associated with the sensor is
Set up a very lean fuel / air mixture. For this reason, it is not preferable that the nitrogen oxide conversion rate, which has a high dependency on λ, is reduced.

The fresh catalyst has a property of generating hydrogen. This property becomes weaker as the deterioration progresses, but it is noticeable at first.

[0015]

1 shows a control device 1, which includes an internal combustion engine 2, a rotational speed sensor 3, a fuel supply device 4,
A means for measuring the intake air amount ml in the intake pipe 6, for example, a hot-film type air mass flowmeter 5, and an exhaust gas sensor 9 arranged in front of the catalyst 8 and behind the catalyst It has an exhaust pipe 7 with an exhaust gas sensor 12 arranged and a control unit 10. Reference numeral 11 represents a hydrogen sensor that may be present in some embodiments. In a preferred embodiment, the use of the signal of the rear oxygen sensing exhaust gas sensor 12 in certain operating conditions of the internal combustion engine eliminates the need for a hydrogen sensor. Blocks 10.1 to 10.4 represent the injection timing control function within the control unit 10. In this case, block 10.1 corresponds to the characteristic curve group memory, block 10.2 corresponds to the multiplication combination, and block 10.3
Corresponds to the primary control algorithm and block 10.4 corresponds to the complementary operating control algorithm. Block 10.5 represents a setpoint / actual value comparison on which the complementary working control algorithm is based.

The basic function of the control device 1 is the control unit 1
0, rotation speed n, air amount m, and mixture composition
λ = f (USonde_v, USonde_h) A signal relating to the fuel supply amount signal ti to operate the fuel supply device 4, for example the injection valve device. For this purpose, the provisional fuel supply signal rl, which is formed in block 10.1 as a function of the amount of air and the rotational speed, is corrected in block 10.2 by a correction factor which takes into account the deviation of the mixture composition λ from the desired value. Multiply and combine with FR.

First, in the block (primary control algorithm) 10.3, the signal USo of the front exhaust gas sensor is
A control coefficient is formed from nde_v. The signal of the first exhaust gas sensor responds to the change of the air-fuel ratio earlier in advance than the signal of the second exhaust gas sensor, based on its arrangement in the exhaust gas flow, because the internal combustion engine The exhaust gas from the first exhaust gas to the second exhaust gas sensor
This is because the sensor travels a shorter distance. This effect is further increased by the oxygen storage capacity of the catalyst. Due to the high speed of response of the control unit to the mixture error adaptation, the air-fuel ratio is initially controlled by the first exhaust gas sensor. In contrast, the signal USonde_h of the second exhaust gas sensor is generally more accurate because the catalyst located in front of the second exhaust gas sensor balances the exhaust gas components. This is because the exhaust gas is adjusted in the direction. Furthermore, the signal of the second sensor is less susceptible to aging, because the temperature load behind the catalyst is smaller than in the first exhaust gas sensor, which is built closer to the engine. Therefore, the signal of the second exhaust gas sensor is used to supplementarily correct the control. For example, the deviation of the signal of the second exhaust gas sensor can be used to correct the target value for the control by the first exhaust gas sensor.
In this case, corrective engagement is formed in block 10.4.

A sensor placed in front of the catalyst controls the mixture to a target value, in most cases λ = 1. To control. The sensor located behind the catalyst compensates for errors due to the aging of the front sensor within the upper guide control. If the front sensor indicates a very rich mixture, eg based on aging, eg λ = 1 Wrongly in the actual λ value of λ = 0.95
Control responds by leaning. The rear sensor and block 10.4 records this undesired leaning (greater than 1) of the actual λ value of the target value 1 obtained from this, and on the basis of the signal of the rear sensor, a complementary control engagement. However, for example, the target value for the front sensor is, for example, λ = 0.95. Shift to
This actually λ = 1 Is controlled.

FIG. 2 shows a diagram of the concentration of various harmful substances in the exhaust gas with respect to the air ratio λ. The dashed line represents the raw emissions of the internal combustion engine. Raw emissions can be measured in front of the catalyst. The solid line represents the concentration behind the catalyst. In particular, the undesired rapid increase in the NOx concentration in the range where λ is larger than 1 represents not only the preferable action of the catalyst in the λ control range but also the unfavorable action of the rear sensor having the possibility of hydrogen cross detection. This action shifts λ from the control range to the right.

To eliminate this, the guide control is corrected when the catalyst produces hydrogen. The premise for this is that hydrogen production is detected. A way of detecting the production of hydrogen during operation of the internal combustion engine consists in placing a hydrogen sensor behind the catalyst and evaluating this signal.
A preferred alternative, which does not require a hydrogen sensor, is described below with reference to FIGS. 3 and 4.

In this case, in a preferred embodiment,
The results of different evaluation methods of the deterioration state of the catalyst are examined for validity. The invention is based on the fact that different processes lead to the production of different amounts of hydrogen. In degraded catalysts where hydrogen production is relatively small, different methods will lead to consistent results. On the other hand, if there is a large deviation between the results, this indicates that the catalyst is producing hydrogen.

FIG. 3a shows the air ratio λvorKa in front of the catalyst.
The chronological diagram of t is shown in combination with the coasting operation process in which the fuel is cut off. Process 1 corresponds to normal control operation,
That is, the air ratio λ oscillates with a small amplitude around the value 1, to be exact, with a value slightly smaller than 1. Step 2 corresponds to fuel cutoff during coasting. At this time, only air flows through the internal combustion engine. The associated λ value is shown here as the final value from the illustrated relationship, but is infinite in principle. In the process, the catalyst is filled with oxygen to the limit of its oxygen storage capacity. In step 3, the rich mixture is temporarily operated after the coasting has ended, because it has a positive effect on the conversion capacity of the catalyst. This enrichment corresponds to the term "empty catalyst" used in FIG. The term thus paraphrases the intentional elimination of oxygen stored in the catalyst after a coasting process with excess oxygen. This enrichment can be performed until the signal from the rear sensor responds to the enrichment (time interval t).

FIG. 3b shows the corresponding signal USonde_h of the rear exhaust gas sensor for a healthy catalyst, "line 1" for hydrogen production on the one hand and "hydrogen production on the other hand". Line 2 "is shown.

First consider "Line 2" in the absence of hydrogen production. In process 1, the signal US having about 600 mV
onde_h indicates a slightly rich mixture. In process 2 of shutting off the fuel, the sensor voltage drops to a low value as shown. When the catalyst is already storing a large amount of oxygen, this reduction takes place rapidly, i.e. as in this case, practically without delay.

When the rich mixture composition is then used again for fueling, the excess fuel is compensated by the stored oxygen until the oxygen storage region of the catalyst is empty. In fresh catalysts, the amounts used in the rich mixture are much higher than in degraded catalysts. Therefore, the time t shown in FIG. 3 is, on the one hand, proportional to the oxygen storage capacity forming a measure for the state of deterioration of the catalyst. As shown in the figure, the relatively long time t corresponds to a healthy catalyst that does not generate hydrogen.

However, the use of rich mixtures increases hydrogen production. Thus, the hydrogen produced gives the rear sensor signal an action (rich shift) that is a function of the hydrogen produced. Here, as a result of the rich shift, the signal rises more rapidly in the presence of hydrogen than in the absence of hydrogen. In the fresh catalyst, due to the significant hydrogen production, the sensor signal rises much faster than in the aged catalyst. As a result, the time t is significantly reduced, during which the sensor signal remains at a low level.

This situation is represented by the "line 1" progression diagram, in which "time 1" is such that, in fact, this time t is virtually nonexistent. The result is the inadequate result that the oxygen storage capacity of the catalyst is very low, so that the catalyst is falsely evaluated as already severely degraded.

FIG. 4a shows a curve of the air ratio λvorKat in front of the catalyst, which is relevant to the diagnosis of the catalyst (determination of the state of deterioration) by measuring and evaluating the oxygen storage capacity of the catalyst. Stage 1 corresponds to normal control operation as before, the air ratio λ oscillating around a value of 1, precisely around a value slightly smaller than 1, with a small amplitude. Process 2 is fuel /
Corresponding to enriching the air mixture to a value less than 1. Due to the lack of oxygen in the exhaust gas obtained from this,
Oxygen is completely emptied from the catalyst during step 2 which is long enough. After the enrichment of the fuel is completed, the process with excess air is carried out in process 3. This causes the catalyst to be refilled with oxygen until the exhaust gas sensor signal behind the catalyst again responds to excess oxygen. Relative air excess (λ-
1) Amount of air sucked in while filling the catalyst with oxygen and m
integral of product with l ∫ [(λ-1) · ml] dt Shows a measure for the oxygen storage capacity of the catalyst.

FIG. 4b shows the corresponding signal USonde during diagnosis.
_H (signal of the rear exhaust gas sensor) is shown. In this way, the abrupt direction of the rear exhaust gas sensor signal is unaffected by any hydrogen present and the catalyst does not produce hydrogen if there is excess oxygen in the exhaust gas, thus The deterioration state can be evaluated independently of hydrogen production.

From the comparison of the results of the different methods of determining the oxygen storage capacity, it is possible to form the above second information which gives whether the catalyst is producing hydrogen. In one embodiment, in order to determine the oxygen storage capacity, the intake air volume ml and the actual λ value between the change in oxygen content in front of the catalyst and the response of the exhaust gas sensor in the back of the catalyst to it are determined. At least one integral of the product with the deviation from the value 1 may be evaluated. In particular, in the first method, when the oxygen content in front of the catalyst changes due to switching from excess oxygen to insufficient oxygen, the first product of the intake air amount ml and the deviation of the actual value λ from 1 The second method can provide an integral of 1, and the second method can provide a second integral when the oxygen content in front of the catalyst changes due to switching from oxygen deficiency to oxygen excess.

When the first integral signals the deteriorated catalyst and the second integral signals the fresh catalyst, the second information signals the generation of hydrogen. Become.

FIG. 5 shows a flow chart which is clear from the description itself as an embodiment of the method according to the invention. Step 5.1 corresponds to the method described with respect to FIG. Similarly, step 5.2 corresponds to the method described with respect to FIG. An example for the means shown in step 5.3 is further described above in the correction of the target value for the front exhaust gas sensor.

[Brief description of drawings]

FIG. 1 is a technical peripheral view showing the operation of the present invention.

FIG. 2 shows the concentration of various harmful substances in exhaust gas,
It is a chronological diagram with respect to air ratio (lambda).

FIG. 3 shows the corresponding λ in the preferred embodiment of the invention.
A curve diagram of the signal of the oxygen-sensing exhaust gas sensor behind the catalyst, ie the air ratio λ (FIG. 3a) and the corresponding signal USonde_h, at a given oxygen concentration in front of the catalyst, as set in the combustion of a mixture with values. Is.

FIG. 4 is the corresponding λ in the preferred embodiment of the invention.
In the course diagram of the signal of the oxygen sensing exhaust gas sensor behind the catalyst at a given oxygen concentration in front of the catalyst, ie the air ratio λ (FIG. 4a) and the corresponding signal USonde_h, as set in the combustion of a mixture having a value. is there.

FIG. 5 is a flow chart clear from the description of itself as an embodiment of the method according to the invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Control device 2 Internal combustion engine 3 Rotational speed sensor 4 Fuel supply device 5 Suction air amount measuring means 6 Intake pipe 7 Exhaust pipe 8 Catalyst 9 Exhaust gas sensor (front of catalyst) 10 Control unit 10.1 Characteristic curve group memory 10.2 Multiplying combination 10.3 Primary control algorithm 10.4 Control algorithm 10.5 which works complementarily Target value / actual value comparison 11 Hydrogen sensor 12 Exhaust gas sensor (catalyst rear) ml Suction air amount n Rotational speed Usoll target value USonde_h Exhaust gas sensor (catalyst rear) signal USonde_v Exhaust gas sensor (catalyst front) signal λ Air ratio

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI Theme Coat (reference) F02D 45/00 368 F02D 45/00 368F 370 370B (72) Inventor Andreas Blumenstock Stock Federation of Germany 71638 Ludwigsburg , Jagerhof Alley 79 (72) Inventor Klaus Hirschmann, Federal Republic of Germany 71701 Schwieberdingen, Stuttgarter Schutlasse 94 F-term (reference) 3G084 BA13 BA15 BA24 DA00 DA10 DA22 DA27 EB12 EC04 FA00 FA07 FA29 FA30 FA33 3G091 AB01 AB04 AB06 BA01 BA14 BA33 CB02 CB03 DB10 DB13 DC01 DC03 EA01 EA05 EA33 EA34 EA36 FB10 FB12 FC01 HA36 HA37 3G301 HA01 JA21 JA25 JA33 JB09 LB01 MA01 MA11 MA12 MA18 NA09 ND01 ND02 NE13 NE15 PA01Z PD00Z PD02 ND02 PD09A PD09Z PE01Z

Claims (10)

[Claims] 1. At least a catalyst and first information regarding the oxygen content of the exhaust gas, the first information being provided behind the catalyst, the first information adjusting the setting of a fuel / air mixture. A method of setting a fuel / air mixture for an internal combustion engine having an exhaust gas sensor, wherein a second information regarding hydrogen present in the exhaust gas behind the catalyst is formed; Information adjusts the setting of the fuel / air mixture, the method of setting the fuel / air mixture for an internal combustion engine. 2. The setting method according to claim 1, wherein the second information is formed by a hydrogen sensor. 3. The setting method according to claim 1, wherein the second information is formed by comparing results of evaluation methods of different deterioration states of the catalyst. 4. A method of forming a first variable for the deteriorated state of the catalyst by a first method; a step of forming a second variable for the deteriorated state of the catalyst by a second method; Forming a third variable that provides a deviation of the first variable from the second variable; comparing the third variable with a predetermined threshold; and having exceeded the threshold. Is evaluated as a symptom of hydrogen evolution.
Setting method described in. 5. The method of forming the variable for the degradation condition is based on measuring the oxygen storage capacity of the catalyst using an oxygen sensing exhaust gas sensor behind the catalyst. Setting method described in. 6. The method of forming the variable for the degraded state responds to hydrogen evolution behind the catalyst with different sensitivities.
Setting method described in. 7. The method according to claim 1, wherein the catalyst is completely filled with oxygen by operating the internal combustion engine with excess air, and the internal combustion engine is compared with an amount of fuel required for theoretical combustion. And exhausting oxygen from the catalyst by operating with excess fuel, and identifying that the catalyst has been completely emptied of oxygen by the oxygen shortage signal from the exhaust gas sensor, From when you start emptying until the oxygen deficiency signal occurs
The method according to claim 1, further comprising: determining an excess fuel amount at which the internal combustion engine is operated; and forming the first variable for the deterioration state based on the determined excess fuel amount. The setting method described in 6. 8. A method of completely emptying oxygen from a catalyst by operating the internal combustion engine in excess of fuel, the second method comparing the internal combustion engine with an air amount required for theoretical combustion. And then operating in excess air to fill the catalyst with oxygen, and to identify that the catalyst has been completely filled with oxygen by the oxygen excess signal of the exhaust gas sensor, and to fill the catalyst. From the beginning until the oxygen excess signal occurs,
The setting method according to claim 6, further comprising: determining an excess oxygen amount at which the internal combustion engine is operated; and forming the second variable for the deterioration state based on the determined excess oxygen amount. . 9. The second method, when the first method evaluates that the catalyst has deteriorated and the second method evaluates that the catalyst is fresh, causes the second method to generate hydrogen. 9. The setting method according to claim 6, further comprising a signal. 10. Electronic control device for carrying out at least one method according to claim 1.