JP2000120484A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve drivability by restraining a fluctuation in engine output in a cruise operation state by increasingly correcting a suction air quantity by a prescribed quantity when engine output by correction of an ignition timing delay is judged comparatively large. SOLUTION: A judgment is made on whether or not it is lean operation time (S10), and when it is YES, a judgment is made on whether or not SOx sticks by a prescribed quantity or more to an NOx absorber (S12). When it is YES, a judgment is made on whether or not a vehicle is put in a cruise operation state (S16), and when it is YES, a judgment is made on whether or not a crank angle speed variation ΔME is not less than a prescribed value SM (S16). When it is NO, that is, when judged that a fluctuation in engine output is comparatively small, the ignition timing is corrected so as to delay by a prescribed quantity (S18). While, when it is YES, that is, when judged that a fluctuation in engine output by correction of an ignition timing delay is comparatively large, a preset third map is searched from an engine speed and intake pipe inside absolute pressure to calculate an increasing correction quantity of a suction air quantity to open a bypass air control valve by a corresponding quantity (S20).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine.

[0002]

2. Description of the Related Art In recent years, lean air-fuel ratios such as lean-burn engines have been developed. In such engines, when exhaust gas is in a lean atmosphere, nitrogen oxides in the exhaust gas are absorbed, A NOx absorbent (NOx absorption catalyst, nitrogen oxide purifying means) for reducing (purifying) nitrogen oxides absorbed when the exhaust gas is in a rich atmosphere below the stoichiometric air-fuel ratio.
Purification of NOx (nitrogen oxide) components in a lean atmosphere is performed by using such methods.

[0003] By the way, the fuel contains sulfur S, and the sulfur is deposited on the catalyst surface or on the micropores by SOx.
When the catalyst is attached (absorbed) as (sulfur oxide), the purification efficiency of the catalyst is reduced. In particular, in the above-mentioned NOx absorbent, sulfur is easily absorbed, so-called sulfur poisoning occurs, and NO
x absorption efficiency decreases.

[0004] The temperature suitable for absorption (adsorption) or reduction (desorption) of the NOx absorbent is from 250 ° C to 550 ° C, but the temperature suitable for sulfur poisoning regeneration is higher than 600 ° C in a rich atmosphere. ℃, and 700 ℃
When the temperature is raised to the extent, the sulfur poisoning can be more effectively regenerated.

Therefore, in Japanese Patent Application Laid-Open No. Hei 8-100639, it is estimated from a traveling distance or the like whether or not the vehicle is poisoned by sulfur. By raising the temperature and burning off the attached sulfur, increasing the intake air amount by the value obtained by searching the map from the engine speed and load, correcting the increase in the intake air amount, and recovering the engine output reduced by the ignition timing retard I have.

[0006]

However, in the above prior art, the engine is actually searched only by searching for a predetermined characteristic (map) from the engine speed and the load to obtain the increased intake air amount, and actually performing the engine operation. It does not detect the fluctuation of the output and perform the increase correction of the intake air amount.

Further, in the above-described prior art, the ignition timing is corrected to be retarded and the intake air amount is increased in a medium load range to a high load range in which the engine feeling is stable and the driving feeling is not deteriorated. In a low load range such as an operation state, a change in the engine output due to the retard correction becomes large, leading to a decrease in drivability.

Therefore, an object of the present invention is to solve the above-mentioned disadvantages, and when the vehicle is in a cruise driving state,
The engine output fluctuation is monitored from the change in the crank angular velocity, and when the change in the crank angular velocity is less than a predetermined value, the ignition timing is retarded to raise the exhaust gas temperature, and when the change in the crank angular velocity is equal to or more than the predetermined value, Increase the amount of intake air and correct it.
Accordingly, it is an object of the present invention to provide an exhaust gas purifying apparatus for an internal combustion engine which suppresses fluctuations in engine output in a cruise operation state and improves drivability.

[0009]

In order to achieve the above object, according to the present invention, an exhaust system of an internal combustion engine is provided, and when the air-fuel ratio of the exhaust gas is lean, the amount of the exhaust gas is reduced. In an exhaust gas purifying apparatus for an internal combustion engine having a nitrogen oxide purifying means for absorbing nitrogen oxides and reducing the absorbed nitrogen oxides when the air-fuel ratio of the exhaust gas is a stoichiometric air-fuel ratio or rich, the cruise operation A cruise operation state detection means for detecting whether or not the engine is in a state, a comparison means for detecting a change in the crank angular velocity of the internal combustion engine and comparing the detected change with a predetermined value when the internal combustion engine is detected to be in a cruise operation state; When the detected change in the crank angular speed is less than a predetermined value, and when the nitrogen oxide purifying means is poisoned by sulfur, the ignition timing supplied to the internal combustion engine is retarded to reduce the exhaust gas temperature. Exhaust gas temperature raising means for raising the, and the time change of the detected crank angular velocity is a predetermined value or more, and composed as provided an intake air amount increasing means for increasing an intake air quantity supplied to the internal combustion engine.

Accordingly, when it is determined that the engine output (torque) due to the retard correction is relatively large, the intake air amount is increased, more specifically, the increase correction is performed by a predetermined amount.
The engine output (torque) reduced by the ignition timing retard correction can be increased (recovered), and the fluctuation of the engine output can be suppressed, so that the drivability, particularly, the drivability in a cruise driving state can be improved. it can.

Further, the increase correction of the intake air amount is performed when it is determined that the fluctuation of the engine output (torque) due to the retard correction is relatively large, so that the intake air amount is not unnecessarily increased. Therefore, the fuel injection amount is not unnecessarily increased.

[0012]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of an exhaust gas purifying apparatus for an internal combustion engine according to the present invention.

FIG. 1 is an overall view schematically showing the exhaust gas purifying apparatus.

In FIG. 1, reference numeral 10 denotes a multi-cylinder internal combustion engine such as a four-cylinder engine (hereinafter referred to as "engine").
Indicates its body.

The intake air introduced from an air cleaner (not shown) disposed at the end of the intake pipe 12 is controlled in its flow rate by a throttle valve 16 housed in a throttle body 14 while a surge tank and an intake manifold (both in FIG. (Not shown), and flows into each cylinder.

An injector (fuel injection valve) 18 is provided near an intake valve (not shown) of each cylinder to inject fuel. The air-fuel mixture injected and integrated with the intake air is ignited by an ignition plug (not shown) in each cylinder and burns to drive a piston (not shown).

The exhaust gas after combustion is sent to an exhaust pipe 22 via an exhaust valve (not shown) and an exhaust manifold (not shown). A NOx absorbent (NOx absorption catalyst or nitrogen oxide purifying means) 24 having a three-way catalyst function is disposed in the exhaust pipe 22.

The NOx absorbent 24 is the same as that described in
-66129 or a catalyst of the same type as the NOx absorbent described in JP-A-7-217474,
When the air-fuel ratio of the exhaust gas is lean, it absorbed nitrogen oxides in the exhaust gas, and when the air-fuel ratio of the exhaust gas was the stoichiometric air-fuel ratio or rich, in other words, when the oxygen concentration in the exhaust gas decreased, it was absorbed. NOx is converted to unburned HC and CO in exhaust gas.
And purify by reduction.

In the intake pipe 12, a bypass air passage 26 that connects the intake pipe 12 to the atmosphere is connected between the injector 18 and the throttle body 14. An air cleaner 28 is attached to the atmosphere opening end of the bypass air passage 26, and a bypass air control valve (EACV) 30 is arranged in the middle of the air cleaner 28.

The bypass air control valve 30 is a normally closed type, and has a valve body 30a for continuously changing the opening degree (opening area) of the bypass air passage 26;
a spring 30b for urging the valve body 30a in the closing direction, and an electromagnetic solenoid 30c for moving the valve body 30a in the opening direction against the spring force when energized.

In FIG. 1, a crank angle sensor (shown as "NE" in the figure) 34 is provided near a camshaft or a crankshaft (both not shown) of the engine body 10, and a cylinder is provided for each specific crank angle of a specific cylinder. It outputs a discrimination signal, a TDC signal at or near TDC (top dead center), and a CRK signal at every predetermined crank angle.

A throttle opening sensor (shown as "TH" in the figure) 36 is connected to the throttle valve 16, and outputs a signal proportional to the throttle opening TH. An absolute pressure sensor (indicated as “PBA” in the figure) 40 is provided at the end of the downstream branch path 38 and outputs a signal corresponding to the absolute pressure PBA in the intake pipe.

A water temperature sensor (shown as "TW" in the figure) 42 is provided at an appropriate position such as a cylinder block to output a signal corresponding to the engine cooling water temperature TW, and is provided upstream of the NOx absorbent 24 in the exhaust pipe 22. Is provided with an O ₂ sensor (shown as “O ₂ ”) 46 in the figure, and outputs a signal proportional to the oxygen concentration in the exhaust gas.

Further, NO
x Temperature sensor close to the absorber 24 (“TCAT” in the figure)
And outputs a signal corresponding to the temperature (or exhaust temperature) TCAT of the NOx absorbent 24.

Further, a vehicle speed sensor 50 is provided near a drive shaft (not shown) of a vehicle (not shown) on which the engine 10 is mounted, and a signal corresponding to a predetermined rotation of the drive shaft, that is, a signal corresponding to the vehicle speed V is provided. Is output.

The outputs of these sensor groups are sent to an electronic control unit (hereinafter referred to as “ECU”) 60.

The ECU 60 includes an input circuit 60a, a CPU 6
0b, storage means 60c, and output circuit 60d. The input circuit 60a performs processes such as shaping input signal waveforms from various sensors, converting a signal level to a predetermined level, and converting an analog signal value to a digital signal value. The storage unit 60c stores various calculation programs executed by the CPU 60b, calculation results, and the like.

The CPU 60b counts the CRK signal to detect the engine speed NE, calculates a basic fuel injection amount (injector valve opening time) from the engine speed NE and the intake pipe absolute pressure PBA, and calculates a target air-fuel ratio. The engine speed NE and the intake pipe absolute pressure PB
The basic ignition timing is calculated from A and corrected by the water temperature or the like.

Further, as will be described subsequently, the CPU 60b retards the ignition timing to increase the exhaust gas temperature and corrects the intake air amount to increase.

Next, the above-described operation of the apparatus according to the present application will be described with reference to the flowchart of FIG. The illustrated program is executed for each TDC, for example.

In the following, first, in S10, it is determined whether or not the vehicle is in the lean operation. If the result is NO, the subsequent processing is skipped. Here, lean operation means that the vehicle is in an operation state in which the target air-fuel ratio is controlled to a lean air-fuel ratio of around 22: 1.

When the result in S10 is affirmative, the program proceeds to S12,
It is determined whether or not SOx (sulfur oxide) has adhered to the NOx absorbent 24 in a predetermined amount or more, that is, whether or not it is poisoned by S (sulfur), more specifically, SOx (sulfur oxide).

This determination may be made by estimating from the traveling distance in the same manner as in the above-mentioned prior art.
As proposed in Japanese Patent Application Laid-Open No. 6129, estimation may be performed from the NOx absorption amount or the like.
The detection may be performed by detecting the concentration of SOx in the exhaust gas using an SOx sensor proposed in Japanese Patent Application Laid-Open No. 692 or Japanese Patent Application Laid-Open No. 9-189678.

When the result in S12 is negative, the subsequent processing is skipped. When the result is affirmative, the process proceeds to S14, where it is determined whether or not the vehicle is in a cruise driving state. this is,
The determination is made based on the output of the vehicle speed sensor 50 as to whether or not the vehicle is in a driving state in which the change in the vehicle speed V is small.

When the result in S14 is negative, the subsequent processing is skipped. When the result is affirmative, the process proceeds to S16, in which it is determined whether or not the amount of change in crank angular speed (change in crank angular speed) ΔME is equal to or greater than a predetermined value SM. The amount of change in the crank angular velocity is obtained by calculating the first-order difference value (or differential value) of the cycle of the TDC signal or the CRK signal output from the crank angle sensor 34 described above.

The processing in S16 is specifically performed by the engine 1
0 rotation fluctuation, more specifically engine output (torque)
Is an operation for determining whether or not the variation of the predetermined value is relatively large. The predetermined value SM is selected and set as appropriate from the intention.

If the result of the determination in S16 is negative, that is, if the variation in crank angular speed ΔME is smaller than the predetermined value SM, in other words, it is determined that the fluctuation of the output (torque) of the engine 10 is relatively small, the routine proceeds to S18, in which the ignition timing is reduced by a predetermined amount. Correct the retard angle.

The ignition timing control is performed by a separate routine (not shown). As described above, a preset characteristic (map) is searched from the intake pipe absolute pressure PBA obtained from the engine speed NE and the intake pipe absolute pressure PBA. The basic ignition timing is calculated and corrected based on the water temperature or the like to determine the output ignition timing.

In step S16, a preset second characteristic (map; characteristic not shown) is retrieved from the engine speed NE and the intake pipe absolute pressure PBA to calculate the ignition timing retard amount, and the output ignition is calculated by that amount. The timing is corrected for delay.

As a result, the combustion timing is delayed, the exhaust gas temperature is raised with time, and the SOx adhered to the NOx absorbent 24 is burned and removed. Thereby, the NOx absorbent 24 can be regenerated from sulfur poisoning.

When the exhaust gas temperature rises above the regeneration temperature, the rich air-fuel ratio below the stoichiometric air-fuel ratio, for example, 1
When 2: 1 is supplied, the attached SOx is reduced by a reducing agent such as unburned HC and unburned CO in the exhaust gas, and
Since the NOx absorbent 2 is desorbed from the Ox absorbent 24, the NOx absorbent 2
4 can be more effectively regenerated from sulfur poisoning.

On the other hand, when the result in S16 is affirmative, and when it is determined that the crank angular speed change amount ΔME is equal to or greater than the predetermined value SM, in other words, the fluctuation of the engine output (torque) due to the retard correction is relatively large, the routine proceeds to S20, The air amount is increased and corrected by a predetermined amount.

More specifically, a predetermined third characteristic (map) is searched from the engine speed NE and the intake pipe absolute pressure PBA to calculate an increase correction amount of the intake air amount. Then, the EACV valve is opened by an amount corresponding to an amount calculated in an EACV control routine (not shown). As a result, an air amount corresponding to the calculated increase correction amount passes through the bypass air passage 26 and is taken in by the intake air. Flowed into tube 12.

The fuel injection is also performed in a separate routine (not shown). As described above, the preset fourth characteristic (map) is retrieved from the engine speed NE and the intake pipe absolute pressure PBA to calculate the basic fuel injection amount. Then, the output fuel injection amount is appropriately corrected based on the output of the O ₂ sensor 46 and the like, and the output fuel injection amount is calculated based on the valve opening time of the injector 18.

The above-described processing is carried out at the temperature of the NOx absorbent TCA.
Repeat until T reaches the regeneration temperature described above.

In this embodiment, as described above,
It is provided in an exhaust system (exhaust pipe 22) of an internal combustion engine (engine 10). When the air-fuel ratio of the exhaust gas is lean, it absorbs nitrogen oxides NOx in the exhaust gas, and the air-fuel ratio of the exhaust gas becomes the stoichiometric air-fuel ratio or A cruise operation state for detecting whether or not the internal combustion engine is in a cruise operation state in an exhaust gas purification apparatus for an internal combustion engine having a nitrogen oxide purification means (NOx absorbent 24) for reducing nitrogen oxides absorbed when rich. Detecting means (ECU 60, S14), when it is detected that the internal combustion engine is in a cruise operation state, a change in crank angular velocity of the internal combustion engine (crank angular velocity change amount) Δ
Comparison means (ECU for detecting ME and comparing with a predetermined value SM
60, S16), when the detected change in the crank angular velocity is less than a predetermined value, and when the nitrogen oxide purifying means is poisoned by sulfur, the ignition timing supplied to the internal combustion engine is retarded and the exhaust gas is exhausted. Exhaust temperature increasing means for increasing the temperature (ECU 60, S12, S18), and intake air amount increasing means for increasing the amount of intake air supplied to the internal combustion engine when the detected change in the crank angular speed is equal to or greater than a predetermined value ( ECU60, S20).

In the above description, the temperature of the NOx absorbent is detected from the sensor, but it may be estimated using appropriate logic.

Although a NOx absorbent having a three-way catalyst function is used, a three-way catalyst may be provided independently.

[0049]

According to the first aspect, when it is determined that the engine output (torque) by the retard correction is relatively large, the intake air amount is increased, and more specifically, the intake air amount is increased and corrected by a predetermined amount. The engine output (torque) reduced by the ignition timing retard correction can be increased (recovered), and the fluctuation of the engine output can be suppressed, so that the drivability, particularly, the drivability in a cruise driving state can be improved. it can.

Further, the increase correction of the intake air amount is performed when it is determined that the fluctuation of the engine output (torque) due to the retard angle correction is relatively large, so that the intake air amount is not unnecessarily increased. Therefore, the fuel injection amount is not unnecessarily increased.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an entire control device of an internal combustion engine including an exhaust gas purification device for an internal combustion engine according to the present invention.

FIG. 2 is a flowchart showing the operation of the exhaust gas purifying apparatus for an internal combustion engine according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Internal combustion engine (engine) 12 Intake pipe 16 Throttle valve 18 Injector 22 Exhaust pipe 24 NOx absorbent (NOx absorption catalyst. Nitrogen oxide purification means) 30 EACV (bypass air control valve) 34 Crank angle sensor 40 Absolute pressure sensor 48 Temperature Sensor 60 ECU (electronic control unit)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F01N 3/24 F01N 3/24 R 3/28 301 3/28 301C F02D 41/04 310 F02D 41/04 310A F02P 5/15 F02P 5/15 B F term (reference) 3G022 AA03 AA06 CA00 DA02 EA00 GA00 GA01 GA05 GA07 GA08 GA09 GA10 GA19 3G084 AA03 AA04 BA06 BA13 BA17 CA05 DA10 DA11 EA11 EB09 EB12 FA00 FA05 FA10 FA11 FA20 FA30 FA38 FA39 3G091 AA12 AA28 AB06 BA11 BA14 CB02 CB05 DA07 DC03 EA00 EA01 EA07 EA16 EA17 EA19 EA33 EA34 EA38 EA39 FA18 FB03 FC02 HA36

Claims (1)

[Claims] 1. An exhaust system for an internal combustion engine, which absorbs nitrogen oxides in an exhaust gas when the air-fuel ratio of the exhaust gas is lean, and absorbs the nitrogen oxides in the exhaust gas when the air-fuel ratio of the exhaust gas is a stoichiometric air-fuel ratio or rich. An exhaust gas purification apparatus for an internal combustion engine having a nitrogen oxide purifying means for reducing nitrogen oxides, comprising: a. Cruise operation state detection means for detecting whether the internal combustion engine is in a cruise operation state, b. Comparing means for detecting a change in the crank angular speed of the internal combustion engine and comparing it with a predetermined value when it is detected that the internal combustion engine is in a cruise operation state; c. When the detected change in the crank angular speed is less than a predetermined value, and when the nitrogen oxide purifying means is poisoned by sulfur, the ignition timing supplied to the internal combustion engine is retarded to increase the exhaust temperature. Temperature increasing means; and d. An intake air amount increasing means for increasing an amount of intake air supplied to the internal combustion engine when the detected change in the crank angular speed is equal to or greater than a predetermined value.