JP2001074727A - Device for estimating concentration of sulfur in fuel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To predict catalyst poisoning by calculating the amount of NOx of a catalyst being trapped based on the concentration of the NOx at the downstream of the catalyst in lean operation, obtaining the aging, and estimating the concentration of ions in fuel. SOLUTION: The estimation of ion concentration is subjected to arithmetic processing by a microcomputer in a control unit. First, a poisoning condition counter (SC) corresponding to the amount of sulfur poisoning of an NOx trap catalyst (catalyst) based on the history of engine operation conditions is calculated based on a catalyst temperature, an air/fuel ratio, and the amount of suction air. Then, only when it is judged to be before poisoning according to the SC value during lean operation, the amount of NOx being trapped of the current catalyst is calculated and is set to the amount of NOx being trapped before poisoning. Then, only when it is judged to be after poisoning according to the SC value, the current amount of NOx being trapped is calculated as the amount of NOx being trapped after poisoning. Then, the ratio of amount being trapped after poisoning to the amount being trapped before poisoning is obtained. The concentration of sulfur in fuel is calculated according to the ratio and the poisoning condition counter.

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 (S) concentration 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) in accordance with an air-fuel ratio of inflowing exhaust gas is provided in an exhaust passage of an internal combustion engine. It is known that NOx is trapped (absorbed) during a lean operation, and the NOx is purged (discharged) during a stoichiometric or rich operation to perform reduction and purification.

[0003] Such a NOx trap catalyst has a property that when a sulfur component is contained in the fuel, SOx (sulfur oxide) in the exhaust gas is trapped more easily than trapping NOx in the exhaust gas. In addition, the NOx trap catalyst poisoned by the SOx trap has a greatly reduced NOx trap performance, and cannot perform its original function. In addition, SOx has a stricter purge condition than NOx, is considerably rich, and the poisoning state is not released unless the catalyst temperature rises considerably.

Therefore, in a direct injection spark ignition type internal combustion engine, additional fuel is injected during an exhaust stroke as a poisoning release process under predetermined engine operating conditions (conditions for releasing SOx trapped in the catalyst). Then, by burning the additional fuel in the exhaust passage to increase the exhaust gas temperature, the catalyst temperature is raised to eliminate sulfur poisoning (Japanese Unexamined Patent Publication No. 9-32).
No. 619), the CO in the exhaust gas is increased by dividingly injecting fuel into the combustion chamber into an intake stroke and a compression stroke,
SOx is desorbed by supplying the CO to the catalyst (see JP-A-11-107740).

[0005]

However, conventionally, there has been no means for estimating the sulfur concentration in the fuel. Therefore, even if a fuel containing a large amount of a sulfur component is used,
Even if a fuel containing almost no sulfur component is used, the poisoning release process 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, causing deterioration of exhaust gas.If a fuel containing little sulfur component is used, the poisoning removal process will be performed regardless of necessity. Is frequently performed, which may cause deterioration of fuel efficiency and thermal deterioration of the catalyst.

The present invention has been made in view of the above-mentioned conventional problems, and provides a fuel sulfur concentration estimating apparatus capable of estimating a sulfur concentration in a fuel so that poisoning of a catalyst can be predicted. When a fuel containing a large amount of components is used, it is an object of the present invention to enable the prohibition or restriction of the lean operation, and to enable the poisoning release processing according to the sulfur concentration.

[0007]

According to the present invention, there is provided an exhaust gas purifying catalyst having a function of trapping and purging NOx in an exhaust passage according to an air-fuel ratio of exhaust gas flowing into the exhaust passage. As shown in FIG. 1, in the internal combustion engine provided with
Ox concentration detecting means and NOx downstream of the catalyst during lean operation
Calculate the NOx trappable amount of the catalyst from the concentration.
A fuel sulfur concentration estimating device comprising: a fuel sulfur concentration estimating means for estimating a sulfur concentration in the fuel from a 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. The NOx trappable amount is determined because the NOx trappable catalyst has a characteristic that the higher the sulfur concentration in the fuel, the more the rate of decrease of the NOx trappable amount with time increases. Then, the sulfur concentration in the fuel is estimated by calculating the time-dependent change, that is, the rate of decrease (rate of change).

In the invention according to claim 2, the sulfur concentration estimating means in the fuel, as shown in FIG. 1, estimates the sulfur poisoning amount of the catalyst based on the history of the engine operating conditions. NOx purge end state estimating means for estimating the end state of NOx purge of the catalyst based on the history of the engine operating conditions; and NOx when the sulfur poisoning amount is equal to or less than a first small predetermined value during lean operation. Pre-poisoning NOx for estimating the possible amount of NOx trapping of the catalyst before sulfur poisoning based on the rate of change of the catalyst downstream NOx concentration from the purge end state
Means for estimating the trappable amount and, based on the rate of change of the NOx concentration downstream of the catalyst from the end of the NOx purge when the sulfur poisoning amount is equal to or more than the second predetermined value on the large side during the lean operation, after the sulfur poisoning. Means for estimating the NOx trappable amount after poisoning for estimating the NOx trappable amount of the catalyst, and determining the amount of 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 sulfur poisoning amount based on the history of the engine operating conditions is small (before poisoning), the NOx of the catalyst before sulfur poisoning is determined based on the change rate of the NOx concentration downstream of the catalyst from the end state of the NOx purge. While estimating the trappable capacity,
When the sulfur poisoning amount based on the history of the engine operating conditions is large (after poisoning), the catalyst downstream NO from the NOx purge end state
NOx of catalyst after sulfur poisoning based on rate of change of x concentration
The trapping amount is estimated, the NOx trapping amount before poisoning is set as a reference, and the sulfur concentration in the fuel is estimated based on the change in the NOx trapping amount after poisoning.

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

In the invention according to claim 4, the NOx purge end state estimating means is configured to perform the NOx purge when the operation state in the rich or stoichiometric operation and the catalyst temperature is equal to or higher than a predetermined value is equal to or longer than a predetermined time. It is characterized as an end state.

[0013] In the invention according to claim 5, the NO before poisoning is selected.
The x-trappable amount estimating means and the post-poisoning NOx trappable-amount estimating means estimate the NOx concentration in the exhaust gas discharged from the engine based on the engine operating conditions.
x concentration estimating means for calculating a NOx trappable amount of the catalyst based on a period of time from when the NOx purge is completed to when the catalyst downstream NOx concentration becomes a predetermined ratio with respect to the engine exhaust NOx concentration. .

In the invention according to claim 6, the means for estimating the sulfur concentration in fuel has a means for detecting whether or not fuel is supplied to the fuel tank (see FIG. 1). It is characterized in that the latest estimated value of the concentration is the final sulfur concentration, and when there is no refueling, the latest estimated value of the sulfur concentration is weighted and 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 / absence of refueling based on the presence / absence of opening of a filler cap of a fuel tank.

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 a fuel level gauge of a fuel tank.

[0017]

According to the first aspect of the present invention, during lean operation, the amount of NOx trappable is calculated based on the NOx concentration downstream of the catalyst, and the change over time (decrease speed) of the amount of NOx trappable is used as the fuel. The sulfur concentration in the water can be accurately estimated. Therefore, by knowing the sulfur concentration in the fuel, it is possible to predict the poisoning of the catalyst, and when a fuel containing a large amount of sulfur components is used, the prohibition or restriction of the lean operation and the prompt processing of the poisoning release process are performed. It is possible to cope with it by performing it properly.

According to the second aspect of the present invention, when the sulfur poisoning amount based on the history of the engine operating conditions is small (before poisoning), the change rate of the NOx concentration downstream of the catalyst from the end state of the NOx purge is determined. While the possible amount of NOx trap before the poisoning of the catalyst is estimated, the amount of sulfur poisoning based on the history of the operating conditions of the engine is large (after the poisoning). NOx after poisoning of 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 invention, by integrating the condition values based on the catalyst temperature and the air-fuel ratio, it is possible to accurately calculate the sulfur poisoning amount based on the history of the engine operating conditions.

According to the fourth aspect of the present invention, the end state of the NOx purge of the catalyst is accurately determined by determining whether or not the duration of the operation state in the rich or stoichiometric operation and in which the catalyst temperature is high has exceeded a predetermined time. Can be estimated.

According to the fifth aspect of the invention, when estimating the possible amount of NOx trapping before or after poisoning, the concentration of NOx downstream of the catalyst from the end state of NOx purge is determined by the NOx emission from the engine.
By calculating the NOx trappable amount of the catalyst based on the time until the x concentration becomes a predetermined ratio, the estimation accuracy of the NOx trappable amount can be improved.

According to the present invention, the presence or absence of refueling of the fuel tank is detected, and the renewal speed based on the latest estimated value of the sulfur concentration is changed in accordance with the detection, whereby the fuel property by refueling is changed. Sudden changes can be dealt with reliably.

According to the present invention, the presence or absence of refueling can be accurately detected based on whether or not the filler cap of the fuel tank has been opened. According to the invention according to claim 8, the presence or absence of refueling can be accurately detected based on the output of the fuel gauge of the fuel tank.

[0024]

Embodiments of the present invention will be described below. FIG. 2 is a system diagram of an internal combustion engine showing one embodiment of the present invention.

The 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 section (or an intake port) downstream of the throttle valve 5 in the intake passage 4.

The fuel injection valve 6 is connected to the control unit 1
The solenoid is energized by an injection pulse signal output in synchronism with the engine rotation from 1 to open the valve to inject fuel adjusted to a predetermined pressure. 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, and is ignited by the ignition plug 7 based on an ignition signal from the control unit 11 and burns.

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

The NOx trap catalyst 10 on the downstream side can oxidize CO and HC in the exhaust gas and reduce NOx in the vicinity of the stoichiometric gas to purify the exhaust gas, and can also convert the NOx gas according to the air-fuel ratio of the exhaust gas flowing in. That is, the three-way catalyst is combined with a NOx trapping agent capable of trapping NOx in a lean atmosphere.

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

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

Further, 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 downstream of the NOx trap catalyst 10 are provided. ing.

Further, a filler cap open sensor 20 for detecting the opening of the filler cap 19 of the fuel tank 18 and a fuel gauge 21 for detecting the remaining fuel 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 signals from the various sensors, and controls the ignition of the ignition plug 7. Control the time.

In particular, the control of the fuel injection amount is based on the intake air amount Qa detected by the air flow meter 13 and the engine speed Ne detected by the crank angle sensor 12, and the basic fuel injection amount Tp = KCONS corresponding to stoichiometry.
While calculating T × Qa / Ne (KCONST is a constant), a target air-fuel ratio tλ (stoichiometric, lean or rich) is set according to the engine operating conditions (engine speed and load),
A final fuel injection amount Ti = Tp × (1 / tλ) × COEF (COEF is various correction coefficients) is calculated so as to obtain the target air-fuel ratio tλ, and an injection pulse signal having a pulse width corresponding to the Ti is calculated. Output to the fuel injection valve 6 to perform fuel injection.

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

FIG. 3 is a flowchart of the main routine. This routine corresponds to fuel sulfur concentration estimating means. In step 1 (referred to as S1 in the figure, the same applies hereinafter),
According to the subroutine (step 101 to FIG. 4) of FIG. 4, a poisoning condition counter SC corresponding to the sulfur poisoning amount of the NOx trap catalyst (hereinafter simply referred to as catalyst) based on the history of the engine operating conditions is calculated. This part corresponds to the sulfur poisoning amount estimating 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 in FIG. here,
The map of FIG. 11 shows that the catalyst temperature Tcat is low and the air-fuel ratio λ
The leaner the poisoning condition value SCC is to the positive side (poisoning increasing direction), the higher the catalyst temperature Tcat, and the richer the air-fuel ratio λ, the larger the poisoning condition value SCC to the negative side (poisoning). Release direction).

In step 103, the latest poisoning condition value SC is added to the poisoning condition counter SC up to the previous time as expressed by the following equation.
The product of C, the intake air amount Qa, and the equivalent ratio (1 / λ) is added to update the poisoning condition counter SC. In addition, Qa × (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 sulfur poisoning amount based on the history of the engine operating conditions, and is a parameter indicating the degree of catalyst poisoning based on the engine operating conditions.

Thus, the subroutine (poisoning condition counter calculation) in FIG. 4 is completed, and the process returns to the main routine in FIG. In step 2 of FIG. 3, according to the subroutine (step 201) of FIG.
NOXPG processing is performed. This part corresponds to 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).
In 3, it is determined whether or not the catalyst temperature Tcat ≧ a predetermined value.

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

Λ ≦ 1 (rich or stoichiometric) and T
If cat ≧ predetermined value (high temperature), the NOx purge state is considered, 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 or not the timer RCC (the duration of the NOx purge state) has become equal to or greater than a predetermined value (a predetermined time).

As a result, if RCC <predetermined value, this subroutine is terminated as it is. If RCC ≧ predetermined value, it is considered that purging of NOx from the catalyst has been completed.
= 1 (NOx purge end state), and this subroutine ends.

As described above, the subroutine (NOx
(Purge end flag process), and returns to the main routine of FIG. In step 3 of FIG. 3, the refueling presence / absence flag FGC is processed in accordance with the subroutine of FIG. 6 (steps 301 to 31) or the subroutine of FIG. This part corresponds to a refueling presence / absence detecting means.

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

In the case of the subroutine of FIG.
In step 11, the timer C is incremented by 1 (C = C + 1), and in step 312, it is determined whether or not the timer C has exceeded a predetermined value.
When ≧ predetermined value, the process proceeds to step 313 and subsequent steps. This is because the refueling determination is performed at predetermined time intervals.

At step 313, the output (remaining fuel amount) VRFL of the fuel remaining meter of the fuel tank is read, and at step 31
At 4 the fuel remaining VRFL is changed to the previous fuel remaining VRFLold
(VRFL ≧ VRFLold)
+ Α) is determined.

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

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

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

During a lean operation (and under certain presumable conditions)
If, go to step 5. In step 5, whether or not the poisoning condition counter SC ≦ the first predetermined value A1 is satisfied, that is,
It is determined whether or not the poisoning is released (before poisoning).

As a result, only when SC ≦ A1, that is, when the poisoning is released (before poisoning), step 6 is executed.
In step 6, the subroutine of FIG.
), The possible amount of NOx trap BS before poisoning of the catalyst
Estimate the CAPN. That is, the current catalyst NOx
The trappable amount CAPNM is calculated, and the calculated trappable amount CAPNM is used as the NOx trappable amount (base NOx trappable amount) in the catalyst poisoning released state (before poisoning). BSCAPN = CAPNM
And This portion corresponds to the pre-poisoning NOx trap possible amount estimating means.

In step 401, the NOx purge end flag FNOXPG = 1 or its delay flag FNOX
It is determined whether or not PGD = 1. This is for starting the estimation from the end state of the NOx purge of the catalyst.

FNOXPG = 0 and FNOXPGD = 0
In the case of, this subroutine ends, 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 measuring the time from the end state of the NOx purge of the catalyst is increased by 1 (TNC = TNC + 1).

At step 404, the output of the NOx sensor (NOx concentration downstream of the catalyst) VNOx is read. In step 405, the NOx in the exhaust gas discharged from the engine and flowing into the catalyst is referred to based on the engine speed and the load with reference to a map.
The concentration (engine exhaust NOx concentration; engine-out NOx concentration) EON is calculated. This part corresponds to the engine exhaust NOx concentration estimating means.

In step 406, as shown in the following equation, the equivalent ratio (1/1 / the engine exhaust NOx concentration EON) and the intake air amount Qa is calculated.
From λ), 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 exhaust NOx concentration EON by a predetermined coefficient (predetermined ratio) K as in the following equation. SEON = EON × K Here, K is 0 <K <1, for example, K = 0.1.

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

If VNOx <SEON, this subroutine ends. If VNOx ≧ SEON, the process proceeds to step 409 and subsequent steps. In step 409,
At this time, the timer (time value from the end state of the NOx purge) TNC is read, and CAPNT = TNC. As shown in FIG. 12, the CAPNT is such that the NOx concentration downstream of the catalyst from the end state of the NOx purge of the catalyst decreases the engine exhaust NOx.
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, at step 410, the timer TNC is set to 0, and the NOx purge end flag FNO
It is assumed that XPG = 0 and the delay flag FNOXPGD = 0.

Next, in step 411, the temporary NOx trap of the catalyst is determined based on 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 shown in FIG. Capable amount CAPN
Calculate M0. In the map of FIG. 13, the time CAP
It is estimated that the longer the NT and the larger the NOx mass EONM, the larger the NOx trappable amount (temporary NOx trappable amount CAPNM0) of the catalyst is.

Next, at step 412, the NOx trappable amount of the catalyst (temporary NOx trappable amount CAPNM0)
Is the NOx trapping amount (CAP) at a certain reference catalyst temperature.
NM), refer to the table of FIG.
After calculating the temperature correction coefficient KTN 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 as the pre-poisoning (base) NOx trappable amount BSCAPN as in the following equation.

BSCAPN = CAPNM With the above, the subroutine of FIG. 8 (estimation of the possible amount of NOx trap 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 poisoning condition counter SC ≧ second predetermined value A2, that is, whether or not poisoning has occurred. Of course, A2> A1. As a result, only when SC ≧ A2, that is, after poisoning, steps 8 and 9 are executed.

In step 8, the possible NOx trapping amount ASCAPN after the poisoning of the catalyst is estimated in accordance with the subroutine (steps 501 to 501) of FIG. That is, the current NOx trappable amount CAPNM of the catalyst is calculated, and this is calculated as the NOx trappable amount ASCA after poisoning of the catalyst.
PN = CAPNM. This part corresponds to the post-poisoning NOx trappable amount estimating means.

The processing in steps 501 to 512 is the same as the processing in steps 401 to 412 in FIG.
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 according to the following equation.
APN.

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

In step 9 in FIG. 3, the sulfur concentration in the fuel is estimated in accordance with the subroutine (steps 601 to 601) in FIG. 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 has been completed. This part corresponds to a sulfur concentration in fuel estimating means.

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

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

ADS = ASCAPN / BSCAPN This ratio ADS indicates what percentage of the NOx trappable amount has become after poisoning with respect to the poisoning released state (before poisoning).

In step 604, the ratio ADS and the poisoning condition counter SC are referred to with reference to the map shown in FIG.
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, the higher the fuel sulfur concentration GasS0.

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), so that it can be estimated that the sulfur concentration in the fuel is high. Further, the smaller the poisoning condition counter SC is, the smaller the sulfur poisoning amount based on the history of the engine operating conditions is. Therefore, it can be estimated that poisoning has occurred because the sulfur concentration in the fuel is high.

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

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

GasS = GasS × (1−M) + Gas0 × MM M is a weighted average constant, and 0 <M <1. In this way, the renewal speed of the sulfur concentration GasS is changed depending on the presence or absence of refueling.

As described above, the sulfur concentration in the fuel GasS
(Ppm) estimation ends. The sulfur concentration GasS in the fuel estimated in this way can be used, for example, as follows.

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

In step 702, the sulfur concentration G in the fuel
AsS is compared with a predetermined value to determine whether or not GasS ≧ predetermined value (high sulfur concentration). As a result, if GasS ≧ predetermined value, that is, if a fuel having a considerably high sulfur concentration is used, the routine proceeds to step 703, where a predetermined fail-safe process is performed.

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

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

Further, the driver is warned by a warning light or the like that a poor fuel having a high sulfur concentration is used.
It goes without saying that the fail-safe process may be performed stepwise or continuously according to the magnitude of the sulfur concentration GasS in the fuel.

[Brief description of the drawings]

FIG. 1 is a functional block diagram showing a 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 trapping amount estimation subroutine.

FIG. 9 is a flowchart of a subroutine for estimating a possible NOx trapping amount after poisoning;

FIG. 10 is a flowchart of a fuel sulfur concentration estimation subroutine.

FIG. 11 is a diagram showing a poisoning condition value calculation map;

FIG. 12 is a diagram showing a state of a change in NOx concentration downstream of a catalyst.

FIG. 13 is a diagram showing a map for calculating a tentative 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 the sulfur concentration in fuel.

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

[Explanation of symbols]

 Reference Signs List 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 gauge

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G01N 31/10 G01N 31/10 F term (Reference) 2G042 AA01 AA04 BA08 BB07 CA01 CB01 3G091 AA12 AA17 AA23 AA24 AA28 AB03 AB06 AB09 BA11 BA14 BA15 BA19 BA33 CB02 CB05 DB06 DB10 DB13 DC01 DC06 EA00 EA01 EA05 EA07 EA18 EA30 EA31 EA33 EA34 FA06 FB10 FB11 FB12 FC02 HA08 HA18 HA36 HA37 HA39

Claims (8)

[Claims] 1. An internal combustion engine provided with an exhaust gas purifying catalyst having a function of trapping and purging NOx in accordance with an air-fuel ratio of exhaust gas flowing into an exhaust passage, wherein the catalyst detects NOx concentration downstream of the catalyst. Downstream NOx concentration detecting means, and NOx of the catalyst based on NOx concentration downstream of the catalyst during lean operation.
And a fuel sulfur concentration estimating means for calculating a trappable amount and estimating a sulfur concentration in the fuel from a temporal change of the NOx trappable amount. And a sulfur poisoning amount estimating means for estimating a sulfur poisoning amount of the catalyst based on a history of engine operating conditions, and a NOx amount of the catalyst based on a history of the engine operating conditions. NOx purge end state estimating means for estimating the purge end state; and a catalyst downstream N from the NOx purge end state when the sulfur poisoning amount is equal to or smaller than a small first predetermined value during lean operation.
Based on the rate of change of the Ox concentration, the NO of the catalyst before sulfur poisoning was determined.
means for estimating the possible amount of NOx trap before poisoning for estimating the possible amount of x-trapping, and a catalyst downstream N from the end state of NOx purge when the sulfur poisoning amount is equal to or more than a second predetermined value on the large side during lean operation.
NO of the catalyst after sulfur poisoning is determined based on the rate of change of the Ox concentration.
NOx trap possible amount estimating means for estimating the x trappable amount, and NOx after poisoning with respect to the NOx trappable amount before poisoning.
2. The apparatus for estimating sulfur concentration in fuel according to claim 1, wherein the sulfur concentration in fuel is estimated based on the ratio of the trappable amounts. 3. The fuel in accordance with claim 2, wherein said 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 configured to execute a NO or a stoichiometric operation when the duration of the operating state in which the catalyst temperature is equal to or higher than a predetermined value is equal to or longer than a predetermined time.
3. The system according to claim 2, wherein the x purge end state is estimated.
4. An apparatus for estimating sulfur concentration in fuel according to claim 3. 5. The NOx trapping amount estimation means before poisoning and the NOx trapping amount estimation means after poisoning comprise NOx in exhaust gas discharged from the engine based on engine operating conditions.
An engine exhaust NOx concentration estimating means for estimating the concentration;
5. The NOx trapping possible amount of the catalyst is calculated based on a time until the NOx concentration downstream of the catalyst from the Ox purge end state becomes a predetermined ratio to the NOx concentration discharged from the engine. An apparatus for estimating a sulfur concentration in fuel according to any one of the above. 6. The fuel sulfur concentration estimating means includes fueling presence / absence detecting means for detecting the presence / absence of fueling to the fuel tank. When fueling is present, the latest estimated sulfur concentration is used as the final sulfur content. The fuel according to any one of claims 1 to 5, wherein when the fuel 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. A fuel sulfur concentration estimating apparatus according to claim 6, wherein said refueling presence / absence detecting means detects the presence / absence of refueling based on the presence / absence of opening of a filler cap of a fuel tank. 8. A fuel sulfur concentration estimating apparatus according to claim 6, wherein said refueling presence / absence detecting means detects the presence / absence of refueling based on an output of a fuel level gauge of a fuel tank.