JP3528698B2 - Fuel sulfur concentration estimation device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for estimating sulfur concentration in fuel for estimating the concentration of sulfur (S) in fuel of an internal combustion engine.

[0002]

2. Description of the Related Art Conventionally, a catalyst (NOx trap catalyst) having a function of trapping and purging NOx (nitrogen oxide) according to the air-fuel ratio of exhaust gas flowing in is provided in an exhaust passage of an internal combustion engine, It is known that NOx is trapped (absorbed) during lean operation and that NOx is purged (released) during stoichiometric or rich operation for reduction purification.

Such a NOx trap catalyst has a property that when the fuel contains a sulfur component, it is easier to trap SOx (sulfur oxide) in the exhaust than to trap NOx in the exhaust. , The NOx trap catalyst poisoned by the SOx traps has a significantly reduced NOx trap performance and cannot perform its original function. Moreover, SOx has a stricter purging condition than NOx, is in a considerably rich state, and the poisoning state cannot be released unless the catalyst temperature rises considerably.

Therefore, in a direct-injection spark-ignition internal combustion engine, additional fuel is injected during the exhaust stroke as poisoning removal processing under predetermined engine operating conditions (conditions for releasing SOx trapped in the catalyst). Then, by burning this additional fuel in the exhaust passage to raise the exhaust temperature, the catalyst temperature is raised and sulfur poisoning is released (Japanese Patent Application Laid-Open No. 9-32).
No. 619), the fuel in the combustion chamber is dividedly injected into the intake stroke and the compression stroke to increase CO in the exhaust gas,
SOx is desorbed by supplying the CO to the catalyst (see JP-A-11-107740).

[0005]

However, conventionally, there was no means for estimating the sulfur concentration in the fuel, so even if a fuel containing a large amount of sulfur components is used,
Even if a fuel containing almost no sulfur component is used, the poisoning removal processing is performed under predetermined operating conditions.
If a fuel containing a large amount of sulfur components is used, the poisoning release process will be delayed, resulting in deterioration of exhaust emissions.If a fuel containing almost no sulfur components is used, the poisoning release process will be performed regardless of necessity. Is frequently performed, which may cause deterioration of fuel efficiency and thermal deterioration of the catalyst.

In view of such conventional problems, the present invention provides a sulfur concentration in fuel estimation apparatus capable of estimating the sulfur concentration in fuel, thereby making it possible to predict catalyst poisoning and When a fuel containing a large amount of components is used, it is possible to prohibit or limit lean operation or to enable poisoning removal processing according to sulfur concentration.

[0007]

Therefore, in the invention according to claim 1, an exhaust gas purifying catalyst having an action of trapping and purging NOx according to the air-fuel ratio of the exhaust gas flowing into the exhaust passage is provided. In an internal combustion engine equipped with the same, as shown in FIG. 1, a catalyst downstream N for detecting the NOx concentration downstream of the catalyst.
Ox concentration detection means and NOx downstream of the catalyst during lean operation
The NOx trapping amount of the catalyst is calculated from the concentration, and the N
There is provided a sulfur concentration in fuel estimation device configured to include a sulfur concentration in fuel estimation unit that estimates the sulfur concentration in fuel from the change with time of the Ox trappable amount.

That is, during lean operation, N
The NOx trappable amount of the catalyst is calculated based on the Ox concentration. Since the NOx trap catalyst has the characteristic that the rate of decrease of the NOx trappable amount with time increases as the sulfur concentration in the fuel increases, the NOx trappable amount The sulfur concentration in the fuel is estimated by obtaining the change over time, that is, the rate of decrease (rate of change).

In the invention according to claim 2, the sulfur concentration in fuel estimating means estimates the sulfur poisoning amount of the catalyst based on the history of engine operating conditions, as shown in FIG. And NOx purge end state estimation means for estimating the NOx purge end state of the catalyst based on the history of engine operating conditions, and NOx when the sulfur poisoning amount is at or below a small first predetermined value during lean operation. Pre-poisoning NOx that estimates the NOx trappable amount of the catalyst before sulfur poisoning based on the rate of change in the NOx concentration downstream of the catalyst from the purge end state
The trappable amount estimation means and the lean poisoning amount based on the change rate of the catalyst downstream NOx concentration from the NOx purge end state when the sulfur poisoning amount is equal to or larger than the second predetermined value on the large side during lean operation. A post-poisoning NOx trappable amount estimating means for estimating the NOx trappable amount of the catalyst, and sulfur in the fuel based on the ratio of the NOx trappable amount after poisoning to the NOx trappable amount before poisoning. It is characterized by estimating the concentration.

That is, when the amount of sulfur poisoning based on the history of engine operating conditions is small (before poisoning), the NOx of the catalyst before sulfur poisoning is calculated based on the rate of change in the NOx concentration downstream of the catalyst from the NOx purge end state. While estimating the trappable amount,
NO downstream of catalyst from NOx purge end state when sulfur poisoning amount based on history of engine operating conditions is large (after poisoning)
NOx of catalyst after sulfur poisoning based on rate of change of x concentration
The trappable amount is estimated, the NOx trappable amount before poisoning is used as a reference, and the sulfur concentration in the fuel is estimated based on the change in the NOx trappable amount after poisoning.

According to a third aspect of the present invention, the sulfur poisoning amount estimation means calculates the sulfur poisoning amount by integrating the condition values based on the catalyst temperature and the air-fuel ratio.

According to a fourth aspect of the present invention, the NOx purge end state estimating means is configured to perform the NOx purge when the duration of the operating state in the rich or stoichiometric operation and the catalyst temperature is equal to or higher than a predetermined value for a predetermined time or longer. It is characterized in that it is estimated to be the end state.

In the invention according to claim 5, the NO before poisoning
The x trappable amount estimation means and the post-poisoning NOx trappable amount estimation means estimate the NOx concentration in the exhaust gas discharged from the engine based on the engine operating conditions.
An NOx trapping amount of the catalyst is calculated based on the time until the NOx concentration downstream of the catalyst reaches a predetermined ratio with respect to the NOx concentration discharged from the engine from the NOx purge end state. .

In the invention according to claim 6, the means for estimating sulfur concentration in fuel has a refueling presence / absence detecting means for detecting the presence / absence of refueling of the fuel tank (see FIG. 1). The latest estimated concentration value is used as the final sulfur concentration, and when there is no refueling, the latest estimated sulfur concentration value is weighted averaged to obtain the final sulfur concentration.

The invention according to claim 7 is characterized in that the refueling presence / absence detecting means detects the presence or absence of refueling based on whether the filler cap of the fuel tank is opened or not.

The invention according to claim 8 is characterized in that the refueling presence / absence detecting means detects the presence / absence of refueling based on the output of the fuel level gauge of the fuel tank.

[0017]

According to the first aspect of the present invention, during lean operation, the NOx trappable amount is calculated based on the NOx concentration downstream of the catalyst, and the fuel consumption is calculated from the change with time (decrease speed) of the NOx trappable amount. It is possible to accurately estimate the sulfur concentration inside. Therefore, by knowing the sulfur concentration in the fuel, poisoning of the catalyst can be predicted, and when fuel containing a large amount of sulfur components is used, prohibition or restriction of lean operation and prompt removal of poisoning can be performed. It is possible to deal with it by executing such a simple operation.

According to the second aspect of the present invention, based on the rate of change of the NOx concentration downstream of the catalyst from the NOx purge end state when the sulfur poisoning amount based on the history of engine operating conditions is small (before poisoning). While estimating the NOx trappable amount of the catalyst before poisoning, based on the rate of change of the NOx concentration downstream of the catalyst from the NOx purge end state when the sulfur poisoning amount based on the history of engine operating conditions is large (after poisoning) NOx after poisoning the catalyst
By estimating the trappable amount and estimating the sulfur concentration in the fuel from the ratio of the NOx trappable amount after poisoning to the NOx trappable amount before poisoning, more accurate estimation can be performed.

According to the third aspect of the present invention, the sulfur poisoning amount based on the history of engine operating conditions can be accurately calculated by integrating the condition values based on the catalyst temperature and the air-fuel ratio.

According to the fourth aspect of the present invention, the NOx purge end state of the catalyst is accurately determined by determining whether the duration of the rich or stoichiometric operation and the operating state of the high catalyst temperature has exceeded the predetermined time. Can be estimated.

According to the fifth aspect of the present invention, when estimating the NOx trappable amount before or after poisoning, the catalyst downstream NOx concentration from the NOx purge end state is the engine exhausted NOx.
The estimation accuracy of the NOx trappable amount can be increased by calculating the NOx trappable amount of the catalyst based on the time until it reaches a predetermined ratio with respect to the x concentration.

According to the sixth aspect of the present invention, the presence or absence of refueling of the fuel tank is detected, and the update speed based on the latest estimated sulfur concentration is changed in accordance with the detected refueling. The sudden change of can be dealt with reliably.

According to the invention of claim 7, the presence or absence of refueling can be accurately detected based on the presence or absence of the opening of the filler cap of the fuel tank. According to the invention of claim 8, the presence or absence of refueling can be accurately detected based on the output of the fuel level gauge of the fuel tank.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. FIG. 2 is a system diagram of an internal combustion engine showing an embodiment of the present invention.

Air from the air cleaner 3 is sucked into the combustion chamber 2 of each cylinder of the internal combustion engine (main body) 1 under the control of the throttle valve 5 provided in the intake passage 4. A fuel injection valve 6 is provided for each cylinder in a manifold portion (or intake port) downstream of the throttle valve 5 in the intake passage 4.

The fuel injection valve 6 is the control unit 1
The solenoid is energized to open the valve by an injection pulse signal output from 1 in synchronism with the engine rotation, and the fuel whose pressure is adjusted to a predetermined pressure is injected. Therefore, the fuel injection amount is controlled by the pulse width of the injection pulse signal.

Then, the injected fuel is sucked into the combustion chamber 2 together with the intake air to form an air-fuel mixture, which is ignited by the ignition plug 7 and burned based on an ignition signal from the control unit 11.

Exhaust gas from the internal combustion engine 1 is discharged from the exhaust passage 8, and the exhaust passage 8 has a three-way catalyst 9 and N for purifying exhaust gas.
The Ox trap catalyst 10 is interposed. The three-way catalyst 9 on the upstream side can purify the exhaust gas by oxidizing CO and HC in the exhaust gas and reducing NOx in the vicinity of stoichiometry (theoretical air-fuel ratio).

The NOx trap catalyst 10 on the downstream side can purify the exhaust gas by oxidizing CO and HC in the exhaust gas and reducing the NOx gas in the vicinity of the stoichiometry, and at the same time, depending on the air-fuel ratio of the inflowing exhaust gas. Of the NOx trapping agent capable of trapping NOx in a lean atmosphere in combination with a three-way catalyst.

The control unit 11 includes a CPU and R
A microcomputer including an OM, a RAM, an A / D converter, an input / output interface, etc.,
It receives input signals from various sensors and performs arithmetic processing based on these signals.

As the various sensors, a crank angle sensor 12 capable of detecting a crankshaft rotation of the internal combustion engine 1 and thereby detecting an engine speed Ne, and an intake air amount Qa upstream of the throttle valve 5 in the intake passage 4 are detected. The hot wire type air flow meter 13, the throttle sensor 14 for detecting the opening TVO of the throttle valve 5, the oxygen concentration in the exhaust gas upstream of the three-way catalyst 9 in the exhaust passage 8 to detect the exhaust gas, and thus the intake air mixture. An air-fuel ratio sensor 15 that can detect the fuel ratio is provided. In the following, the air-fuel ratio is treated as the excess air ratio (λ), and λ = 1.0 is stoichiometric.

A catalyst temperature sensor 16 for detecting the catalyst temperature Tcat of the NOx trap catalyst 10 and a NOx sensor 17 as a catalyst downstream NOx concentration detecting means for detecting the NOx concentration in the exhaust gas downstream of the NOx trap catalyst 10 are provided. ing.

Further, a filler cap open sensor 20 for detecting the opening (opening) of the filler cap 19 of the fuel tank 18, and a fuel level gauge 21 for detecting the amount of fuel remaining in the fuel tank 18 are provided. The signal is also input to the control unit 11.

Here, the control unit 11 controls the fuel injection amount of the fuel injection valve 6 in accordance with the operating state detected based on the signals from the various sensors, and the ignition of the spark plug 7 is performed. Control the timing.

Particularly, regarding the control of the fuel injection amount, from the intake air amount Qa detected by the air flow meter 13 and the engine speed Ne detected by the crank angle sensor 12, the basic fuel injection amount Tp = KCONS equivalent to the stoichiometric condition is obtained.
While calculating T × Qa / Ne (KCONST is a constant), the target air-fuel ratio tλ (stoichiometric, lean or rich) is set according to the engine operating conditions (engine speed and load),
In order to obtain this target air-fuel ratio tλ, the final fuel injection amount Ti = Tp × (1 / tλ) × COEF (COEF is various correction coefficients) is calculated, and an injection pulse signal having a pulse width corresponding to this Ti is calculated. The fuel is injected to the fuel injection valve 6 for fuel injection.

Next, in the internal combustion engine as described above, the calculation processing performed by the microcomputer in the control unit 11 for estimating the sulfur concentration in the fuel (gasoline) will be described in detail with reference to a flowchart.

FIG. 3 is a flowchart of the main routine. This routine corresponds to the sulfur concentration in fuel estimation means. In step 1 (denoted as S1 in the figure, the same applies hereinafter),
In accordance with the subroutine (step 101 to FIG. 4) of FIG. 4, the poisoning condition counter SC corresponding to the sulfur poisoning amount of the NOx trap catalyst (hereinafter simply referred to as catalyst) is calculated based on the history of engine operating conditions. This part corresponds to the sulfur poisoning amount estimation means.

In step 101, the catalyst temperature Tcat,
The air-fuel ratio λ and the intake air amount Qa are read. In step 102, the poisoning condition value SCC is calculated from the catalyst temperature Tcat and the air-fuel ratio λ with reference to the map of FIG. 11. here,
In the map of FIG. 11, the catalyst temperature Tcat is low and the air-fuel ratio λ
The leaner is the poisoning condition value SCC on the plus side (in the direction of increasing poisoning), the catalyst temperature Tcat is high, and the air-fuel ratio λ is richer, the poisoning condition value SCC is on the minus side (poisoning). Release direction).

At step 103, the latest poisoning condition value SC is added to the poisoning condition counter SC up to the last time as shown in the following equation.
The product of C, the intake air amount Qa, and the equivalence ratio (1 / λ) is added to update the poisoning condition counter SC. Qa x (1
/ Λ) corresponds to the fuel flow rate.

SC = SC + SCC × Qa × (1 / λ) However, when SC <0, SC = 0. The poisoning condition counter SC corresponds to the amount of sulfur poisoning based on the history of engine operating conditions and serves as a parameter indicating the degree of poisoning of the catalyst based on engine operating conditions.

As a result, the subroutine (poisoning condition counter calculation) of FIG. 4 is completed, and the process returns to the main routine of FIG. In step 2 of FIG. 3, in accordance with the subroutine (step 201 to FIG. 5) of FIG.
Perform NOXPG processing. This portion corresponds to the NOx purge end state estimating means.

In step 201, the air-fuel ratio λ and the catalyst temperature Tcat are read. In step 202, it is determined whether or not λ ≦ 1 (rich or stoichiometric), and in step 20
In 3, it is determined whether the catalyst temperature Tcat ≧ a predetermined value.

As a result of these judgments, λ> 1 (lean),
Or, if Tcat <predetermined value (low temperature), step 2
At 04, the timer RCC is set to 0, and at step 205 N
Ox purge end flag FNOXPG = 0 (N from the catalyst
This subroutine is finished assuming that the purge of Ox is not finished).

Λ ≦ 1 (rich or stoichiometric), and T
If cat ≧ predetermined value (high temperature), it is regarded as the NOx purge state, and the timer RCC indicating the duration of the NOx purge state is incremented by 1 in step 206 (RCC = RCC +
1) In step 207, it is determined whether the timer RCC (duration of the NOx purge state) is equal to or greater than a predetermined value (predetermined time).

As a result, if RCC <predetermined value, the present subroutine is finished as it is, and if RCC ≧ predetermined value, it is considered that the NOx purge from the catalyst is finished, and the NOx purge end flag FNOXPG is judged at step 208.
= 1 (NOx purge end state), the present subroutine ends.

From the above, the subroutine (NOx of FIG.
The purge end flag process) is ended, and the process returns to the main routine of FIG. In step 3 of FIG. 3, the refueling presence / absence flag FGC is processed according to the subroutine of FIG. 6 (step 301 to) or the subroutine of FIG. 7 (step 311). This portion corresponds to the refueling presence / absence detecting means.

In the case of the subroutine of FIG. 6, step 3
In 01, it is determined whether or not the filler cap of the fuel tank is opened based on the signal from the filler cap open sensor, and if it is opened, the refueling presence / absence flag FGC = 1 (with refueling) is set in step 302. If it is not open, step 30
In 3, the refueling presence / absence flag FGC is set to 0 (no refueling).

In the case of the subroutine of FIG. 7, step 3
At step 11, the timer C is incremented by 1 (C = C + 1), and at step 312, it is determined whether or not the timer C is equal to or more than a predetermined value. When C <a predetermined value, this subroutine is terminated, and C
When ≧ predetermined value, the process proceeds to step 313 and thereafter. This is because refueling determination is performed at predetermined time intervals.

At step 313, the output (fuel remaining amount) VRFL of the fuel tank fuel gauge is read, and step 31
At 4, the fuel remaining amount VRFL is the previous fuel remaining amount VRFLold.
More than a predetermined value α (VRFL ≧ VRFLold
+ Α) is determined.

As a result, when VRFL ≧ VRFLold + α, it is determined that there is refueling, and the refueling presence / absence flag FGC = 1 (refueling) is set in step 315, and VRFL <
When VRFLold + α, it is determined that there is no refueling, and the refueling presence / absence flag FGC = 0 (no refueling) is set in step 316.

Then, as post-processing, VRFLold = VRFL is set in step 317, and the timer C = 0 is set in step 318. As a result, the subroutine (refueling presence / absence flag processing) of FIG. 6 or 7 is terminated, and the process returns to the main routine of FIG.

In step 4 of FIG. 3, it is determined whether or not lean operation is being performed (lean operation permission condition). If lean operation is not being performed, this main routine is terminated. Although omitted in the flow chart, in order to improve the estimation accuracy of the NOx trappable amount of the catalyst, which will be described later, a predetermined estimable condition (for example, the air-fuel ratio λ is in a lean range, a catalyst temperature Tcat is in a predetermined range, The intake air amount Qa is within a predetermined range,
Even when the NOx concentration downstream of the catalyst is not within the predetermined range), this main routine may be ended.

During lean operation (and predetermined estimable condition)
If, then go to step 5. In step 5, it is determined whether or not the poisoning condition counter SC ≦ the first predetermined value A1, that is,
It is determined whether the poisoning is released (before poisoning).

As a result, step 6 is executed only when SC≤A1, that is, in the poisoning release state (before poisoning).
In step 6, the subroutine of FIG. 8 (step 401
~)), The amount of NOx trappable before the poisoning of the catalyst BS
Estimate the CAPN. That is, NOx of the present catalyst
The trappable amount CAPNM is calculated, and this is calculated as the NOx trappable amount (base NOx trappable amount) BSCAPN = CAPNM in the catalyst poisoning release state (before poisoning).
And This portion corresponds to the pre-poisoning NOx trappable amount estimating means.

In step 401, the NOx purge end flag FNOXPG = 1 or its delay flag FNOX.
It is determined whether PGD = 1. This is because the estimation is started from the NOx purge end state of the catalyst.

FNOXPG = 0 and FNOXPGD = 0
In the case of, this subroutine is terminated and FNOXPG = 1
Alternatively, if FNOXPGD = 1, the process proceeds to step 402 and subsequent steps.

In step 402, the delay flag FN
Set OXPGD = 1. In step 403, the timer TNC for counting the time from the NOx purge end state of the catalyst is incremented by 1 (TNC = TNC + 1).

In step 404, the output (NOx concentration downstream of the catalyst) VNOx of the NOx sensor is read. In step 405, referring to the map from the engine speed and load, NOx in the exhaust gas discharged from the engine and flowing into the catalyst.
The concentration (NOx concentration of engine exhaust; NOx concentration of engine out) EON is calculated. This part corresponds to the engine exhausted NOx concentration estimation means.

In step 406, the engine exhaust NOx concentration EON, the intake air amount Qa, and the equivalent ratio (1 /
From NO, the NOx mass EONM is calculated. EONM = EON × Qa × (1 / λ) Here, Qa × (1 / λ) corresponds to the fuel flow rate.

In step 407, the slice level SEON is set by multiplying the engine exhausted NOx concentration EON by a predetermined coefficient (predetermined ratio) K as in the following equation. SEON = EON × K However, K is 0 <K <1 and, for example, K = 0.1.

In step 408, the NOx concentration VNOx downstream of the catalyst has become equal to or higher than a predetermined ratio of the engine exhausted NOx concentration EON, that is, VNOx ≧ slice level SE.
It is determined whether it is ON.

When VNOx <SEON, this subroutine is finished as it is. If VNOx ≧ SEON, the process proceeds to step 409 and thereafter. In step 409,
At this time, the timer (time measurement value from the NOx purge end state) TNC is read and CAPNT = TNC is set. In this CAPNT, as shown in FIG. 12, the NOx concentration downstream of the catalyst from the NOx purge end state of the catalyst is NOx discharged from the engine.
This is the time until the concentration reaches a predetermined ratio, and corresponds to the rate of change of the NOx concentration downstream of the catalyst.

Thereafter, as post-processing, the timer TNC = 0 is set in step 410, and the NOx purge end flag FNO is set.
XPG = 0 and the delay flag FNOXPGD = 0.

Next, at step 411, the temporary NOx trap of the catalyst is referred from the time (change rate of NOx concentration downstream of the catalyst) CAPNT and the NOx mass EONM discharged from the engine with reference to the map of FIG. Possible amount CAPN
Calculate M0. In the map of FIG. 13, the time CAP
It is estimated that the longer the NT is and the larger the NOx mass EONM is, the larger the NOx trappable amount of the catalyst (temporary NOx trappable amount CAPNM0) is.

Next, at step 412, the NOx trappable amount of the catalyst (provisional NOx trappable amount CAPNM0).
NOx trappable amount at a certain reference catalyst temperature (CAP
To convert to NM), refer to the table of FIG.
After the temperature correction coefficient KTN is calculated from the catalyst temperature Tcat, the provisional NOx trappable amount CAPNM is calculated by the following equation.
The NOx trappable amount CAPNM is calculated by multiplying 0 by the temperature correction coefficient KTN.

CAPNM = CAPNM0 × KTN Finally, in step 413, the poisoning release state (before poisoning; S
Since C ≦ A1), the NOx trappable amount CAPNM is set to the pre-poisoning (base) NOx trappable amount BSCAPN as in the following equation.

BSCAPN = CAPNM As described above, the subroutine of FIG. 8 (estimation of NOx trapping amount before poisoning) is completed and the process returns to the main routine of FIG.

In step 7 of FIG. 3, it is determined whether or not the poisoning condition counter SC ≧ the second predetermined value A2, that is, whether or not after the poisoning. Of course, A2> A1. As a result, steps 8 and 9 are executed only when SC ≧ A2, that is, after poisoning.

In step 8, the NOx trappable amount ASCAPN after poisoning of the catalyst is estimated in accordance with the subroutine of FIG. 9 (steps 501 to). That is, the present NOx trappable amount CAPNM of the catalyst is calculated, and this is calculated and the NOx trappable amount ASCA after poisoning of the catalyst is calculated.
Let PN = CAPNM. This portion corresponds to the post-poisoning NOx trappable amount estimation means.

The processing of steps 501 to 512 is the same as the processing of steps 401 to 412 of FIG. 8, and as a result, the present NOx trappable amount C of the catalyst is obtained.
The APNM is calculated and the process proceeds to step 513.

In step 513, after poisoning (SC ≧ A
2), the NOx trappable amount CAPNM is converted to the post-poisoning NOx trappable amount ASC by the following equation.
APN.

ASCAPN = CAPNM As described above, the subroutine of FIG. 9 (estimation of NOx trappable amount after poisoning) is completed, and the process returns to the main routine of FIG.

In step 9 of FIG. 3, the sulfur concentration in the fuel is estimated according to the subroutine of FIG. 10 (steps 601-). However, the pre-poisoning (base) NOx trappable amount BSCAPN in the step 6 and the post-poisoning NOx trappable amount ASCAPN in the step 8 are estimated.
It is assumed that the estimation of and has been completed. This portion corresponds to the sulfur concentration in fuel estimating means.

At step 601, a poisoning condition counter (a sulfur poisoning amount based on the history of engine operating conditions) SC is read. In step 602, before poisoning (base) NOx trappable amount BSCAPN calculated in step 6 (subroutine in FIG. 8) in the poisoning release state (before poisoning).
And the post-poisoning NOx trappable amount ASCAPN calculated in step 8 (routine of FIG. 9) after the poisoning.

In step 603, the ratio AD of the post-poisoning NOx trappable amount ASCAPN to the pre-poisoning (base) NOx trappable amount BSCAPN is expressed by the following equation.
Calculate S.

ADS = ASCAPN / BSCAPN This ratio ADS indicates the fraction of the NOx trappable amount after poisoning in the poisoning release state (before poisoning).

In step 604, referring to the map of FIG. 15 from the ratio ADS and the poisoning condition counter SC,
The sulfur concentration GasS0 (ppm) in the fuel is calculated. In the map of FIG. 15, the smaller the ratio ADS is,
It is estimated that the smaller the poisoning condition counter SC is, the higher the fuel sulfur concentration GasS0 is.

The smaller the ratio ADS, the more NO after poisoning.
This is because the x trappable amount is smaller than the NOx trappable amount before poisoning (base), and it can be estimated that the sulfur concentration in the fuel is high. Further, as the poisoning condition counter SC is smaller, the amount of sulfur poisoning based on the history of engine operating conditions is smaller, and it can be estimated that poisoning has occurred because the sulfur concentration in the fuel is high.

In step 605, the refueling presence / absence flag FG
Determine the value of C. As a result, the refueling presence / absence flag FGC =
When the value is 1 (with refueling), the routine proceeds to step 606, where the latest estimated value GasS0 of the sulfur concentration at step 604 is directly determined as the sulfur concentration in fuel GasS = GasS0.

When the refueling presence / absence flag FGC = 0 (no refueling), the routine proceeds to step 607, where the sulfur concentration in the fuel GasS up to the previous time and the latest estimated sulfur concentration GasS0 in step 604 are calculated by the following equation. The sulfur concentration GasS in the fuel is updated by the weighted average process.

GasS = GasS × (1−M) + GasS0 × M M is a weighted average constant, and 0 <M <1. In this way, the update speed of the sulfur concentration GasS is changed depending on the presence or absence of refueling.

From the above, the sulfur concentration in the fuel GasS
The estimation of (ppm) is completed. The sulfur concentration in fuel GasS thus estimated can be used as follows, for example.

FIG. 16 is a flowchart of the fail-safe processing routine. In step 701, the sulfur concentration in fuel GasS estimated as described above is read.

In step 702, the sulfur concentration in fuel G
AsS is compared with a predetermined value to determine whether GasS ≧ predetermined value (high sulfur concentration). As a result, if GasS ≧ predetermined value, that is, if fuel with a considerably high sulfur concentration is used, the routine proceeds to step 703, where a predetermined fail-safe processing is performed.

As the fail-safe processing, for example, lean operation that causes sulfur poisoning is prohibited. Alternatively, the lean operation is restricted by changing the lean operation area to the reduction side. As a result, deterioration of exhaust gas can be suppressed.

Alternatively, the interval of the poisoning release processing for releasing SOx from the catalyst is changed to the reduction side. Examples of the catalyst poisoning removal processing include enrichment of the air-fuel ratio and increase of exhaust temperature due to retard of ignition timing.
In the case of a direct injection spark ignition type internal combustion engine, the processing described in the above-mentioned publication, which is presented as a conventional technique, can be performed.

Furthermore, a warning light or the like is used to warn the driver that the poor fuel having a high sulfur concentration is being used.
Needless to say, stepwise or continuous fail-safe processing may be performed according to the magnitude of the sulfur concentration GasS in the fuel.

[Brief description of drawings]

FIG. 1 is a functional block diagram showing the configuration of the present invention.

FIG. 2 is a system diagram of an internal combustion engine showing an embodiment of the present invention.

FIG. 3 is a flowchart of a main routine for estimating sulfur concentration in fuel.

FIG. 4 is a flowchart of a poisoning condition counter calculation subroutine.

FIG. 5 is a flowchart of a NOx purge end flag processing subroutine.

FIG. 6 is a flowchart of a refueling presence / absence flag processing subroutine (1).

FIG. 7 is a flowchart of a refueling presence / absence flag processing subroutine (2).

FIG. 8 is a flowchart of a pre-poisoning NOx trappable amount estimation subroutine.

FIG. 9 is a flowchart of a post-poisoning NOx trappable amount estimation subroutine.

FIG. 10 is a flowchart of a subroutine for estimating sulfur concentration in fuel.

FIG. 11 is a diagram showing a map for calculating a poisoning condition value.

FIG. 12 is a diagram showing how the NOx concentration downstream of the catalyst changes.

FIG. 13 is a diagram showing a map for calculating a provisional NOx trappable amount.

FIG. 14 is a diagram showing a temperature correction coefficient calculation table.

FIG. 15 is a diagram showing a map for calculating sulfur concentration in fuel.

FIG. 16 is a flowchart of a fail-safe processing routine.

[Explanation of symbols]

1 Internal combustion engine 4 Intake passage 5 Throttle valve 6 Fuel injection valve 7 Spark plug 8 exhaust passage 9 three-way catalyst 10 NOx trap catalyst 11 Control unit 12 crank angle sensor 13 Air flow meter 15 Air-fuel ratio sensor 16 Catalyst temperature sensor 17 NOx sensor 18 Fuel tank 20 Filler cap open sensor 21 Fuel Fuel Gauge

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP 2001-20726 (JP, A) JP 2000-274229 (JP, A) JP 11-247650 (JP, A) JP 11-107840 ( JP, A) JP 11-81987 (JP, A) JP 7-217474 (JP, A) JP 7-318556 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01N F01N 3/20

Claims (8)

(57) [Claims] 1. An internal combustion engine equipped with an exhaust gas purification catalyst having an action of trapping and purging NOx according to an air-fuel ratio of an inflowing exhaust gas in an exhaust passage, the catalyst detecting a NOx concentration downstream of the catalyst. The NOx concentration of the catalyst is detected from the downstream NOx concentration detection means and the NOx concentration of the catalyst downstream during lean operation.
An apparatus for estimating sulfur concentration in fuel, comprising: means for estimating sulfur concentration in fuel, which calculates a trappable amount and estimates the sulfur concentration in fuel from the change over time of the NOx trappable amount. 2. The sulfur concentration in fuel estimating means estimates the sulfur poisoning amount of the catalyst based on the history of engine operating conditions, and the NOx of the catalyst based on the history of engine operating conditions. NOx purge end state estimation means for estimating the purge end state, and catalyst downstream N from the NOx purge end state when the sulfur poisoning amount is equal to or smaller than the first predetermined small value during lean operation.
NO of catalyst before sulfur poisoning based on change rate of Ox concentration
Pre-poisoning NOx trapping amount estimation means for estimating x trapping amount, and catalyst downstream N from the NOx purge end state when the sulfur poisoning amount is equal to or larger than the second predetermined value on the large side during lean operation.
NO of catalyst after sulfur poisoning based on change rate of Ox concentration
and a post-poisoning NOx trappable amount estimating means for estimating a trappable amount of NOx, and a NOx after poisoning with respect to the NOx trappable amount before poisoning.
The sulfur concentration in fuel estimating apparatus according to claim 1, wherein the sulfur concentration in the fuel is estimated based on the ratio of the trappable amount. 3. The fuel poisoning amount according to claim 2, wherein the sulfur poisoning amount estimating means calculates a sulfur poisoning amount by integrating a condition value based on a catalyst temperature and an air-fuel ratio. Sulfur concentration estimation device. 4. The NOx purge end state estimating means is NO when rich or stoichiometric operation is performed and a duration of an operating state in which the catalyst temperature is a predetermined value or more is a predetermined time or more.
3. It is estimated that the x purge has ended.
Alternatively, the device for estimating sulfur concentration in fuel according to claim 3. 5. The NOx trappable amount estimation means before poisoning and the NOx trappable amount estimation means after poisoning are NOx in exhaust gas discharged from an engine based on engine operating conditions.
The engine exhaust NOx concentration estimating means for estimating the concentration is provided.
The NOx trappable amount of the catalyst is calculated based on the time until the NOx concentration downstream of the catalyst reaches a predetermined ratio with respect to the NOx concentration discharged from the engine from the Ox purge end state. The device for estimating sulfur concentration in fuel according to any one of claims. 6. The sulfur concentration in fuel estimating means has a refueling presence / absence detecting means for detecting the presence / absence of refueling of the fuel tank. When refueling is present, the latest estimated sulfur concentration value is used as the final sulfur value. The fuel according to any one of claims 1 to 5, characterized in that when the fuel concentration is not supplied, the latest estimated value of the sulfur concentration is weighted and averaged to obtain a final sulfur concentration. Medium sulfur concentration estimation device. 7. An apparatus for estimating sulfur concentration in fuel according to claim 6, wherein said refueling presence / absence detecting means detects presence / absence of refueling based on presence / absence of opening of a filler cap of the fuel tank. 8. An apparatus for estimating sulfur concentration in fuel according to claim 6, wherein said refueling presence / absence detecting means detects the presence / absence of refueling based on the output of the fuel level gauge of the fuel tank.