JPH09287436A - Exhaust emission control device for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To regenerate a catalyst with proper fuel in a short time by judging completion of the catalyst heating in the case where the integrating time in a condition in which a catalyst temperature exceeds a prescribed temperature exceeds a setting time, and feed of fuel is stopped, in a device for raising the catalyst temperature by injecting adding fuel. SOLUTION: A device is provided with a means 101 for estimating the rate of excess oxygen after combustion after burning in a combustion chamber on the basis of the output of an air-fuel ratio sensor 14, and a means 102 for calculating a fuel rate for only carrying out complete combustion the excess oxygen having an estimated rate. The device is provided with a means 104A for judging whether or not it is in a condition in which a lean NOx catalyst 13A have to be heated. When the judgment is 'YES,' fuel having a rate to be calculated is supplied to the upstream of the catalyst 13A by a fuel supplying means 3, and the fuel is burnt. A catalyst temperature is estimated by a means 106. In the case where an integrating time in a condition in which the catalyst temperature exceeds a prescribed temperature exceeds a setting time, completion of heating is judged (104B) so as to stop feed of fuel.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to NO in exhaust gas.
TECHNICAL FIELD The present invention relates to an exhaust gas purifying apparatus for an engine, which is equipped with a lean NOx catalyst for removing x, and in particular, determines whether or not it is necessary to heat the lean NOx catalyst and heats the lean NOx catalyst when the heating becomes necessary. Control to
The present invention relates to an exhaust gas purifying device for an engine.

[0002]

2. Description of the Related Art There are internal combustion engines (hereinafter referred to as "engines") mounted on automobiles, which are designed to burn a lean air-fuel mixture. In such an engine, the amount of NOx in exhaust gas during lean operation is high. Will increase. Therefore, in order to purify exhaust gas in such an engine, a lean NOx catalyst or a lean N catalyst is provided in the exhaust system.
There is one in which an Ox catalyst and a three-way catalyst are installed in combination.

In such a lean NOx catalyst, a NOx absorbent that absorbs NOx when the air-fuel ratio of the inflowing exhaust gas is lean and releases the absorbed NOx when the oxygen concentration in the inflowing exhaust gas decreases in the exhaust passage. The NOx absorbent absorbs NOx generated when the lean air-fuel mixture is burned, and the purification efficiency of the lean NOx catalyst decreases. Therefore, there is a method in which the air-fuel ratio of the exhaust gas flowing into the NOx absorbent is temporarily made rich before the NOx absorbing capacity is saturated, thereby reducing NOx from the NOx absorbent and releasing it. .

By the way, since sulfur is contained in the fuel and lubricating oil of the engine, the exhaust gas also contains a sulfur component such as sulfate (hereinafter, simply referred to as sulfur), and this sulfur also absorbs NOx together with NOx. Absorbed by the agent. However, since this sulfur is not released from the NOx absorbent even if the air-fuel ratio of the exhaust gas flowing into the NOx absorbent is simply made rich, the amount of sulfur in the NOx absorbent gradually increases. NO as the amount of absorption increases
The amount of NOx that can be absorbed by the x absorbent gradually decreases, and finally the NOx absorbent can hardly adsorb NOx.

Sulfur absorbed in the NOx absorbent is NO
When the x-absorbent is heated, it decomposes and is released from the NOx absorbent. Moreover, if the air-fuel ratio is made rich or stoichiometric at this time, the sulfur released from the NOx absorbent causes unburned sulfur in the exhaust gas. It is immediately reduced by HC and CO. Therefore, for example, in the technique disclosed in Japanese Patent Laid-Open No. 6-66129, paying attention to such characteristics, the temperature of the NOx absorbent is raised and further rich operation or stoichio operation is performed when a certain specific condition is satisfied. By that,
It is configured to release sulfur from the NOx absorbent, further oxidize it, and discharge it. The specific condition in this case is that the amount of sulfur absorbed by the NOx absorbent has reached a predetermined amount, and heating of the NOx absorbent is performed by operating an electric heater installed in the exhaust system. It is like this.

As a known example of heating a catalyst by a simple system without operating an electric heater, a catalyst is provided in an exhaust system of a cylinder injection type internal combustion engine, and a fuel injection valve is re-used in an exhaust stroke of the engine. A technique for heating the catalyst by operating it to perform additional fuel injection is disclosed in Japanese Patent Laid-Open No. 183922/1992. As with other exhaust gas purification catalysts, the lean NOx catalyst may sometimes be able to sufficiently exhibit its purification performance when kept at a temperature appropriately higher than room temperature. That is, in the NOx adsorption type lean NOx catalyst, not only the case where sulfur is removed to restore the purification efficiency of the catalyst, but there is also a state where another lean NOx catalyst (for example, a catalytic reduction type lean NOx catalyst) should be heated.

[0007]

By the way, when the catalyst is required to be heated, the condition in which the purification efficiency of the catalyst is lowered is generally dealt with. It is desired to raise the temperature and suppress the deterioration of exhaust gas. However, in the above-mentioned known example, there is a fear that the additional fuel in the exhaust stroke may not be properly injected, and for example, too much additional fuel may cause incomplete combustion in the exhaust system, resulting in deterioration of exhaust gas, or conversely There is a problem in that the catalyst temperature does not reach the predetermined temperature in a short time because the amount of the catalyst is too small and sufficient combustion cannot be obtained.

The present invention was devised in view of the above problems, and in a system for raising the temperature of a catalyst by injecting additional fuel, it is possible to regenerate the catalyst in a short time by supplying an appropriate fuel to an exhaust system. The purpose is to do so. Moreover, the secondary objective is to configure such a system more simply.

[0009]

Therefore, an exhaust gas purifying apparatus for an engine according to a first aspect of the present invention has an exhaust passage for discharging exhaust gas from a combustion chamber and a lean combustion operation installed in the exhaust passage. A lean NOx catalyst that purifies or absorbs nitrogen oxides (NOx) in the exhaust gas in an oxygen excess atmosphere at the time, an excess oxygen amount estimating means that estimates the amount of excess oxygen after combustion in the combustion chamber, and the excess oxygen amount. A fuel amount calculation means for calculating a fuel amount enough for complete combustion with the surplus oxygen of the amount estimated by the oxygen amount estimation means, and a heating determination means for determining whether or not the lean NOx catalyst should be heated. A fuel supply means for supplying the amount of fuel calculated by the fuel amount calculation means to the upstream side of the catalyst for combustion when the heating determination means determines that the fuel should be heated; Supplied by the supply means Catalyst temperature estimating means for estimating the temperature state of the catalyst by calculating the combustion heat of fuel based on the air-fuel ratio in the exhaust gas, and integration of the state in which the catalyst temperature estimated by the catalyst temperature estimating means is equal to or higher than a predetermined temperature. When the time exceeds a preset time, completion determination means for stopping the fuel supply by the fuel supply means on the assumption that the catalyst heating is completed is provided.

According to a second aspect of the present invention, there is provided an exhaust gas purifying apparatus for an engine according to the first aspect, wherein a fuel injection valve for injecting fuel directly into the combustion chamber is provided, and the fuel supply means includes the fuel injection valve. And a fuel injection control means for controlling the fuel injection valve so that the amount of fuel calculated by the fuel quantity calculation means is supplied during the exhaust stroke of the engine. I am trying.

An exhaust gas purifying apparatus for an engine according to a third aspect of the present invention is the apparatus according to the first or second aspect, wherein oxygen in the exhaust gas is arranged upstream of the lean NOx catalyst in the exhaust passage. The catalyst upstream side oxygen concentration detecting means capable of detecting the concentration is provided, and the excess oxygen amount estimating means determines the amount of excess oxygen after combustion in the combustion chamber based on the detection result of the catalyst upstream side oxygen concentration detecting means. It is characterized in that it is configured to estimate.

According to a fourth aspect of the present invention, there is provided an exhaust gas purifying apparatus for an engine according to any one of the first to third aspects, wherein an operating state detecting means for detecting an operating state of the engine is provided. The surplus oxygen amount estimating means is configured to estimate the amount of surplus oxygen after combustion in the combustion chamber based on the detection result of the operating state detecting means.

An exhaust gas purifying apparatus for an engine according to a fifth aspect of the present invention is the apparatus according to any one of the first to third aspects, wherein a three-way catalyst or an oxidation catalyst is provided on the downstream side of the lean NOx catalyst. , The catalyst downstream side air-fuel ratio detecting means is arranged downstream of the lean NOx catalyst and upstream of the oxidation catalyst, and the catalyst downstream side air-fuel ratio detecting means outputs the lean NOx catalyst to the lean NOx catalyst. It is characterized in that it is provided with control means for controlling the fuel supply means so that the air-fuel ratio of the inflowing air-fuel mixture becomes close to the stoichiometric air-fuel ratio.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. First, an exhaust gas purifying apparatus for an engine according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 2 is a schematic configuration diagram showing an internal combustion engine having an engine exhaust gas purifying apparatus according to the present embodiment. In FIG. 2, reference numeral 1 is a gasoline engine body of an automobile engine, including a combustion chamber and an intake system. The ignition system and the like are configured to allow lean combustion.

The engine body 1 is particularly configured as an in-cylinder injection engine that directly injects fuel into each cylinder. Therefore, each cylinder has its combustion chamber 2 directly exposed to the injection port. In this way, the fuel injection valve (injector) 3 as the fuel supply means is attached. Further, in this embodiment, the engine body 1 is configured as a 4-cylinder in-line engine, but the number of cylinders is not limited to this.
Regarding the engine type, it can be applied to various engines such as a V-type engine and a horizontal counter engine.

The intake passage 5 communicating with the combustion chamber 2 via the intake valve 4 has an intake port 5 formed for each cylinder.
A, an intake manifold 5B connected to each of the intake ports 5A, a surge tank 5C provided in the upstream portion of the intake manifold 5B, and an intake pipe 5D connected to the upstream end of the intake manifold 5B. It In such an intake passage 5, from the upstream side, an air cleaner 6, an air flow sensor 7 for detecting an intake air amount Af, a throttle valve 8, an ISC (idle speed control).
A valve (not shown) is provided. An intake air temperature sensor 9 and an atmospheric pressure sensor 10 are provided in the case of the air cleaner 6.

As the air flow sensor 7, for example, a Karman vortex type air flow sensor or the like is used. Also, I
The SC valve is for controlling the idling speed, and adjusts the valve opening according to the variation of the engine load Le due to the operation of an air conditioner (not shown) to change the intake air amount and stabilize the idling operation. . Also,
This ISC valve is operated to the valve opening side during the air-fuel ratio correction control, which will be described later, and acts so as to compensate for the output reduction due to the air-fuel ratio correction execution.

The exhaust passage 12 communicating with the combustion chamber 2 via the intake valve 11 has an exhaust port 12A formed for each cylinder, an exhaust manifold 12B connected to each exhaust port 12A, and an exhaust gas. The exhaust pipe 12C is connected to the upstream side of the manifold 12B. An exhaust gas purification catalyst (hereinafter referred to as a catalyst) 13 is installed in the exhaust passage 12 as described above.

The catalyst 13 is configured as an underfloor catalyst installed under the floor of a vehicle, for example, and the lean NOx catalyst 1 is used.
With two catalysts, 3A and three-way catalyst 13B, lean N
The Ox catalyst 13A is arranged upstream of the three-way catalyst 13B. The lean NOx catalyst 13A is provided with a NOx absorbent, and the lean NOx catalyst 13A contains N in an oxidizing atmosphere such as during lean air-fuel ratio operation (lean combustion operation).
It has a function of adsorbing Ox (nitrogen oxide) and reducing NOx to N ₂ (nitrogen) in a reducing atmosphere in which HC (hydrocarbon) is present.

As this NOx catalyst 13A, for example,
A catalyst composed of Pt and alkaline rare earth such as lanthanum and cerium, which have heat deterioration resistance, is used. On the other hand, the three-way catalyst 13B has a function of oxidizing HC and CO (carbon monoxide) and reducing NOx, and the reduction of NOx by the three-way catalyst 13B reduces the stoichiometric air-fuel ratio (1
It is most promoted in the vicinity of 4.7).

An air-fuel ratio sensor (catalyst upstream oxygen concentration detecting means) 1 is provided at a location near the combustion chamber 2 upstream of the catalyst 13.
4 are equipped. As the air-fuel ratio sensor 14,
For example, a linear A / F sensor (whole range air-fuel ratio sensor) is used, and the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber 2 can be detected in a wide range based on the oxygen concentration of the exhaust gas discharged from the combustion chamber 2. It is like this.

Further, the intake port 5 is provided in the engine body 1.
A spark plug 17 for igniting a mixture of air supplied from A to the combustion chamber 2 and fuel supplied from the injector 3 into the combustion chamber 2 is arranged for each cylinder. Also,
Reference numeral 18 is a throttle opening sensor (throttle sensor) for detecting the opening θTH of the throttle valve 7, and 19 is a water temperature sensor for detecting the cooling water temperature TW.

In order to perform the air-fuel ratio control, the ignition timing control, the intake air amount control, the control of the exhaust gas purifying catalyst 13, which will be described later, etc. in the engine, E
A CU (electronic control unit) 23 is installed. The hardware configuration of the ECU 23 is as shown in FIG. 3. The ECU 23 has a CPU 27 as its main part, and the CPU 27 is provided with the intake air temperature sensor 9, the atmospheric pressure sensor 10, the air-fuel ratio sensor. In addition to the detection signals from 14, the throttle sensor 18, and the water temperature sensor 19,
An input interface 28 also receives detection signals from an accelerator position sensor 24 that detects the amount of depression of the accelerator pedal, a battery sensor 25 that detects the voltage of the battery, and a distance meter 26 that counts the traveling distance of the vehicle by the integrated value of vehicle speed pulses. And analog / digital converter 3
It is designed to be input via 0.

Further, an air flow sensor 7, a cranking switch [or an ignition switch (key switch)] 20 for detecting a start time, a crank angle sensor 21 for detecting a crank angle synchronizing signal θCR from an encoder which interlocks with a camshaft, a first Detection signals from a TDC sensor (cylinder discrimination sensor) 22, an idle switch 33, an ignition switch, etc. for detecting the top dead center of a cylinder (reference cylinder) are input through an input interface 29.

Since the engine rotation speed (engine rotation speed) Ne is calculated from the generation time interval of the crank angle synchronization signal θCR detected by the crank angle sensor 21, the crank angle sensor 21 for detecting the crank angle rotates the engine rotation speed. It also serves as a rotation speed sensor that detects the number. The crank angle sensor 21 and the TDC sensor 22 are provided in the distributor.

Further, the CPU 27 is a ROM for storing program data and fixed value data via a bus line.
31, a RAM 32 that is updated and rewritten sequentially, a free running counter 48, and a battery backup RAM (not shown) that is backed up while the battery is connected by holding the stored contents while the battery is connected. It gives and receives.

The data in the RAM 32 is erased and reset when the ignition switch is turned off. Although FIG. 3 mainly shows the part relating to the fuel injection control, the fuel injection control signal based on the calculation result by the CPU 27 is (in this case, four) injection driver (fuel injection valve drive) for each cylinder. Means) 34, and the injection driver 34 opens and closes the injector 3 while controlling the power supply from the battery to the solenoid (injector solenoid) 3a of the injector 3 (more precisely, the transistor for the injector solenoid 3a). It is like this.

Now, focusing on the fuel injection control (air-fuel ratio control), the fuel injection control signal calculated by the CPU 27 is output via the driver 34, and four injectors 3, for example, are sequentially driven. ing. And
Due to the features of the in-cylinder injection engine as described above, in this engine, as a mode of fuel injection, a late injection mode in which fuel is injected in the late stage of the compression stroke in order to realize an operation by lean combustion (lean operation), and a theoretical space In order to realize the operation by the fuel ratio combustion (theoretical air-fuel ratio operation or stoichiometric operation), the first-term injection mode in which the fuel injection is finished in the early or the first term of the intake stroke is provided. In this stoichiometric air-fuel ratio operation, when the amount of fuel to be supplied is large, fuel injection may start from the latter half or the latter half of the exhaust stroke, and may end in the early or the first half of the intake stroke.

Explaining the part of the function of the CPU 27 relating to the exhaust gas purifying device of the present engine, as shown in FIG.
1, fuel amount calculation means 102, and heating determination means 104
Fuel injection control means 105 and catalyst temperature estimation means 10
6 is provided. Of these, the excess oxygen amount estimation means 101 estimates the amount of excess oxygen in the exhaust system after combustion in the combustion chamber 2, but the excess oxygen amount estimation means 101 of the present embodiment is an air-fuel ratio sensor (linear The excess oxygen β (i) in the exhaust system after combustion in the combustion chamber 2 is calculated from the air-fuel ratio AF (i) detected by the A / F sensor) 14, the intake air amount detected by the air flow sensor 7, and the like. It is supposed to do. As shown in FIG. 6, this excess oxygen β (i) is 0 in the stoichio state, and in the lean state in which the air-fuel ratio AF (i) is larger than that in the stoichio, the air-fuel ratio AF
It increases according to (i).

The fuel amount calculating means 102 calculates the fuel amount γ (i) for complete combustion with the surplus oxygen amount β (i) estimated by the surplus oxygen amount estimating means 101.

The heating determination means 104 determines that the state of the lean NOx catalyst 13A is a condition for starting the revival control period, that is, a state in which substances having a reduced purification capacity such as sulfur content should be removed (ie, the state in which the lean NOx catalyst 13A should be restored). , Hereinafter, referred to as a recovery mode), it is determined that the lean NOx catalyst 13A should be heated, and the heating start determination unit 104A.
And a heating completion determination unit (completion determination means) 104B.

In other words, the NOx absorbent provided in the lean NOx catalyst 13A absorbs the sulfur content such as sulfate in the exhaust gas, so that the amount of NOx that can be absorbed gradually decreases. Therefore, with the heating start determination unit 104A of the heating determination unit 104, the purification capacity lowering substance such as sulfur is accumulated to some extent, and the operating state of the engine is in the recovery mode region set as follows. Or not.

The determination as to whether or not the substance having a reduced purification capacity such as sulfur has accumulated is made here simply based on the traveling distance D of the vehicle detected by the distance meter 26.
In other words, the mileage D since the last recovery mode was completed
Is stored in the RAM 32, and when the stored running distance D portion becomes equal to or greater than the predetermined value D ₁ , it is determined that the purification capacity lowering substance (sulfur content) has accumulated to some extent.

The predetermined value D ₁ can be set, for example, according to the experimental result, and in particular, the predetermined value D ₁ is set to the experimental result in order to set the prediction error of the retention amount of the sulfur content etc. on the safe side. It is conceivable to set a relatively smaller value than the corresponding one. In addition, the traveling distance D stored in the RAM 32 is reset to 0 when the vehicle-mounted battery (not shown) is removed. Therefore, when the battery is removed based on the detection information from the battery sensor 25, the actual traveling distance D is actually changed. Regardless of the value of the traveling distance D, the same processing as when the sulfur content or the like is accumulated to some extent is performed.

As a condition for starting the other recovery mode, it is set that the engine is in a stable operating state region. The stable operating state of the engine is when the engine is in the medium load range to the high load range (however, the high load range below a certain limit), and the volume which is an element of the engine rotation speed Ne and the engine load Le. Efficiency ηv
The cooling water temperature TW can be used as a determination target, and it is determined whether or not each value falls within the range of the inequalities shown in the following (1) to (3).

Ne1 ≦ Ne ≦ Ne2 (1) ηv1 ≦ ηv ≦ ηv2 (2) TW1 ≦ TW (3) The volume efficiency ηv is the air flow rate detected by the air flow sensor 7. It is calculated from Af and the engine rotation speed Ne, etc., and is corrected by the atmospheric pressure Pa detected by the atmospheric pressure sensor 10, the intake air temperature Ta detected by the intake air temperature sensor 9, and the like. Further, the engine load Le is equal to the throttle sensor 1
It can be calculated from the throttle opening degree θTH detected by 8, the volume efficiency ηv, and the like.

Further, Ne1, Ne2, ηv1, ηv2 and TW1 represent threshold values, for example, Ne1 is 1500 rp.
m 2 and Ne 2 are 5000 rpm, ηv 1 is 30%, ηv 2 is 80%, and TW 1 is set to, for example, 50 ° C. at which warm-up operation can be regarded as completed. In this way, the condition that the refresh operation is performed is such that the operating state of the engine 1 changes from the medium load range to the high load range.
This is because, for example, if the refresh operation is performed in a low load range smaller than Ne1 and ηv1, the output of the engine body 1 may not be stable and the driving feeling may deteriorate, and the values of Ne and ηv may be Ne2. , Ηv2, the exhaust gas temperature is high in a high load range, which further heats the NOx catalyst value 13a,
This is because there is a risk of burning out.

On the other hand, the heating completion judging section (completion judging means) 1
In 04B, the completion of the heating control for revival is determined. This determination is made based on the catalyst temperature T (i) estimated by the catalyst temperature estimation means 106, and the catalyst temperature T
(I) is the predetermined temperature T ₁ (first set value, this first set value T
₁ is, for example, about 650 ° C.) or longer duration t _C
Is a predetermined time t ₁ (T ₁ is, for example, about 600 seconds) or more, it is determined that the heating control (recovery control) is completed.

Further, the catalyst temperature T (i) is the predetermined temperature T
_Two(Second set value T_Two, This second set value T _TwoIs the first set value
T₁ Higher than, for example, above 750 ° C)
Temperature rises too much, and in this case, H
Since C etc. increases and the exhaust gas component deteriorates,
In such cases, prevent excessive temperature rise and avoid deterioration of exhaust gas components
In order to do so, the heating completion determination unit (completion determination means) 104B
Then, it is determined that the heating control (recovery control) should be ended.
I do.

Here, the catalyst temperature estimation means 106 will be described. In this device, the catalyst temperature sensor for directly detecting the temperature of the catalyst body is not provided in the catalyst 13, and instead of this, a catalyst for estimating the temperature state of the catalyst 13 is provided in the ECU (electronic control unit) 23. A temperature estimating means 106 is provided so that the central temperature of the catalyst body can be estimated.

The catalyst temperature estimating means 106 determines the volume efficiency ηv.
(I), the catalyst temperature [center temperature of the catalyst 13 or bed temperature of the underfloor catalyst (UCC)] Tu (i) before starting the recovery control is calculated based on the engine speed Ne (i), and after the recovery control is started Is the catalyst temperature Tu before the start of this restoration control
In contrast to (i), the temperature increase amount ΔT (i) generated by the combustion due to the exhaust stroke injection is added for each control cycle.

The catalyst temperature Tu before the restoration control is started
(I) is obtained based on the volume efficiency η (i) and the rotation speed Ne (i) using a map as shown in FIG.
That is, as shown in FIG. A, a map is provided so that the catalyst temperature Tu can be obtained from the intake air amount A / N per unit speed and the engine speed Ne obtained based on the volume efficiency η (i). ing. As shown, the catalyst temperature T
The map for estimating u is set based on the characteristic that the catalyst temperature Tu rises as the intake air amount A / N increases and the engine speed Ne increases.

The temperature rise amount ΔT can be calculated by the following equation. ΔT = [{ηc · ma · Hu} / {14.7 · ρg · Fg · Wg · Cpg} · k ₂ (4) where ηc is the combustion efficiency represented by the following equation (5),
The volumetric efficiency ηv (i) and the engine speed Ne (i) can be obtained corresponding to the volumetric efficiency ηv (i) and the volumetric efficiency ηv (i) obtained for each stroke cycle by a map as shown in FIG. 7, for example. The combustion efficiency ηc (i) in each stroke cycle is obtained in correspondence with the engine speed Ne (i). The map shown in FIG. 7 shows the volume efficiency ηv (i)
It is based on the characteristic that the combustion efficiency ηc increases as the engine speed Ne increases, but the combustion efficiency ηc decreases as the engine speed Ne (i) increases. η c (i) = calorific value due to actual combustion / calorific value upon complete combustion (5) Further, ma is the mass flow rate of air and Hu is the fuel injection amount [γ (i)
+ Γ (AF1 (i-1)] lower calorific value (calorific value excluding water vaporized into water vapor), 14.7 is theoretical air-fuel ratio, ρg is combustion gas density, Fg is combustion gas passage cross-sectional area,
Wg is combustion gas velocity, and Cpg is combustion gas specific heat.

The air mass flow rate ma, the lower heating value Hu, the combustion gas density ρg, the combustion gas velocity Wg, and the combustion gas specific heat Cpg, which can be changed in each stroke cycle, are values for each stroke cycle. ma (i), Hu (i), ρ
It can be expressed as g (i), Wg (i), and Cpg (i). Also, k
₂ is a coefficient (where 0 <k ₂ ≦ 1) for correcting the exhaust gas temperature due to the exhaust stroke injection.

The fuel injection control means 105 has two functions,
That is, there are a catalyst heating fuel injection control unit 105A and a normal fuel injection control unit 105B, and the normal fuel injection control unit 105B controls the fuel injection for combustion in the combustion chamber 2 (injection from the intake stroke to the compression stroke). ) Is performed, but the catalyst heating fuel injection control means 105A controls the fuel injection for heating the catalyst for catalyst recovery.

That is, the catalyst injection fuel injection control means 10
In 5A, when the heating determination means 104 determines that the catalyst heating control for catalyst recovery should be performed, the amount of fuel calculated by the fuel amount calculation means 102 is lean NOx.
Performing control for supplying the catalyst 13A upstream,
When the heating completion determination unit 104B determines that the heating control has been completed, this is ended. As described above, the fuel injection during the heating control is performed by using the injector (fuel supply means) 3, but is the fuel injection for heating the lean NOx catalyst 13A, and the fuel injection for combustion in the combustion chamber 2 is performed. Different from jetting.

Particularly, in order not to affect the combustion in the combustion chamber 2, the fuel injection for heating the catalyst is, as shown in FIG. 4, within the exhaust stroke of each cylinder (specifically, from the end of the expansion stroke). This is done during the opening of the exhaust valve 5 during the exhaust stroke). The injection in the intake stroke shown in FIG. 4 is a normal fuel injection for combustion in the combustion chamber 2.

An ignition unit and the like are connected to the output side of the ECU 23 in addition to the injector 3 described above, and the fuel injection amount and ignition timing calculated based on the detection information from various sensors are calculated. The optimum value is output. The exhaust gas purifying apparatus for an engine as the first embodiment of the present invention is configured as described above, and therefore operates as shown in FIGS. 8 and 9, for example.

The flowchart shown in FIG. 8 is executed by the ECU 23.
Shows the procedure for determining the start of heating control, which is executed each time the engine body 1 is started. Heating control
NOx adhering to the lean NOx catalyst 13a as described above.
When it is determined that the deposits (substances with reduced purifying ability) other than, for example, sulfur and its compounds (that is, sulfur content) have reached a predetermined amount, the NOx catalyst 13a is heated to a high temperature to recover the catalyst. The operation is carried out and the substance having a reduced purification capacity is discharged from the lean NOx catalyst 13a while being rendered harmless.

First, in step A10, the ECU 23
Indicates that the amount of adhered substances having reduced purification ability increases substantially in proportion to the traveling distance (driving distance after completion of heating control) D of the vehicle. Therefore, the traveling distance D of the vehicle is read by the distance meter 25 and the purification performance is lowered. The amount of the substance adhering to and depositing on the NOx catalyst 13a is estimated. Next, in step A20, it is determined whether or not the substance having a reduced purification capacity has reached a predetermined amount.
The traveling distance D read in 10 is a predetermined value D1 (for example, 1
000 km) or more to determine. This predetermined value D
1 is set to an appropriate value through experiments, etc., and is within a range in which the amount of adhering purification capacity-reducing substances does not exceed the permissible amount, for example, the NOx emission amount that increases due to the attachment of purification capacity-reducing substances exceeds the regulation value of the law. It is set to a value within the range.

When the traveling distance D is not less than the predetermined value D1,
It can be determined that the amount of the substance having a reduced purification capacity exceeds the predetermined amount, and the process proceeds to step A40. On the other hand, when the traveling distance D has not reached the predetermined value D1, the process proceeds to step A30. Step A30 is a step of determining whether or not the battery, which is the control power source, has just been disconnected and then reconnected for the purpose of vehicle maintenance or the like. In this determination, when the battery is removed, the stored value of the traveling distance D stored in the ECU 23, which is a storage unit, is once reset to a zero value,
This is carried out in order to prevent inaccurate estimation of the adhered amount in step A10 due to inconsistency between the traveling distance D and the adhered amount of the purification capacity lowering substance.

If it is determined No in step A30, the battery is connected, but step A2
It can be determined that the determination result of the traveling distance D at 0 has not yet reached the predetermined value D1, and in this case, the routine is ended without doing anything. On the other hand, immediately after the reconnection of the battery, the determination result of step A30 is Yes (affirmative), so that the process proceeds to step A40 similarly to the determination result of Yes (affirmative) of step A20. Even if the battery is removed, if the value of the traveling distance D is surely stored by the backup function of the ECU 23 or the like, the determination in step A30 may not be performed.

At step A40, it is determined whether or not the operating state of the engine body 1 is in a state in which the catalyst heating operation for the recovery control may be performed (recovery control region), by various sensors serving as operating condition detecting means. It is determined based on the signal value from the class. Here, the volumetric efficiency ηv and the cooling water temperature TW, which are elements of the engine rotation speed Ne and the engine load Le, are the targets of the determination, and whether the respective values are within the range of the inequalities shown in the above (1) to (3). Is determined.

If the operating state of the engine body 1 is in the revival control region, the revival mode (revival control mode), that is, the catalyst heating is executed (step A50).
The routine is ended without executing the recovery mode, that is, the catalyst heating. When the restoration mode is executed, the processing shown in FIG. 9 is periodically performed according to the operation cycle of the engine. That is, first, initial setting is performed (step B1).
0). In this initial setting, the control cycle number i is set to zero.

Then, in step B20, the volume efficiency ηv
(I) Based on the engine speed Ne (i), the catalyst temperature (center temperature of the catalyst 13) Tu (i) before the start of the recovery control is calculated from the map as shown in FIG. Since i = 0 at the start of the recovery mode, the volume efficiency ηv at this time is
(I), engine speed Ne (i) and catalyst temperature Tu
(I) is ηv (0) and engine speed Ne, respectively.
(0) and the catalyst temperature Tu (0). Further, in the control cycle after this, the values of i are 1, 2, 3
... and increase.

Then, in step B30, step B2
It is determined whether the catalyst temperature Tu (i) obtained from the map at 0 is higher than the determination catalyst temperature T (i) calculated at 140 or B150 to the step described later, and the catalyst temperature Tu (i) obtained from the map is determined. When (i) is higher than the determination catalyst temperature T (i), the process proceeds to step B40, and the catalyst temperature Tu (i) is set as the determination catalyst temperature T (i).

The processing of steps B30 and B40 is as follows.
When the engine is accelerated, the volume efficiency ηv (i) and the engine speed Ne are normally set in the recovery mode.
The determination catalyst temperature T obtained by integrating the temperature increase amount ΔT described later, rather than the value of the catalyst temperature Tu (i) obtained based on (i)
(I) is larger, but during a transition such as acceleration, the judgment catalyst temperature T (i) increases by integrating the temperature increase amount ΔT with respect to the actual catalyst temperature increase due to a rapid increase in engine rotation. Instead of catching up, the value of the catalyst temperature Tu (i) obtained from the map as shown in FIG. 5 increases rather, and it becomes easier to obtain a value close to the actual catalyst temperature. Therefore, in order to avoid excessive temperature rise of the catalyst 13 even during such a transition, the volume efficiency ηv (i) and the engine speed Ne are increased.
Catalyst temperature Tu (i) obtained from the map based on (i)
The larger one of the judgment catalyst temperature T (i) obtained by integrating the temperature rise amount ΔT and the judgment catalyst temperature T (i) is set as the judgment catalyst temperature T (i).

Subsequent to step B30 or step B40, the process proceeds to step B50, where the determination catalyst temperature T
It is determined whether (i) is the second set value (for example, 750 ° C.) or more. If the determination catalyst temperature T (i) is equal to or higher than the second set value, the restoration is completed (revival mode is completed), but normally,
At the start of the recovery mode, the determination catalyst temperature T (i) is set to the second value.
Since the temperature has not risen to the set value, the process proceeds to step B60.

In step B60, the air-fuel ratio AF1 (i) after combustion in the cylinder is detected. Then, step B70
Then, the excess oxygen amount estimating means 101 determines the excess oxygen amount β in the exhaust system based on the detected air-fuel ratio AF1 (i), the intake air amount detected by the air flow sensor 7, and the like.
(I) is calculated. Then, in step B80, the amount of fuel γ that completely burns is calculated with respect to the calculated amount of excess oxygen β (i).
(I) is calculated from a known theoretical formula.

Then, the fuel amount γ thus calculated
Exhaust stroke injection is performed as shown in FIG. 4 at a fuel injection time corresponding to (i) (step B90). In addition,
In this exhaust stroke injection, in order to accelerate the temperature rise of the catalyst, the calculated fuel amount γ (i) has a coefficient k ₁ (1 ≦ k ₁ ≦
Fuel injection may be performed with the injection amount k ₁ γ (i) multiplied by 2).

Following this, steps B100 to B20
At 0, it is determined whether or not the recovery of the lean NOx catalyst 13A is completed. That is, in step B100, the lower heating value Hu for the fuel injection amount γ (i) or k ₁ γ (i)
(I) is calculated. Further, in step B110, based on the volume efficiency ηv (i) and the engine speed Ne (i),
The combustion efficiency η c (i) is read from the map shown in FIG. Then, the process proceeds to step B120, the combustion efficiency ηc
(i), air mass flow rate ma (i), lower heating value Hu (i), combustion gas density ρg (i), combustion gas cross section Fg, combustion gas velocity Wg (i), combustion gas specific heat Cpg (i), Based on the correction coefficient k ₂ , the temperature rise amount ΔT is calculated by the above equation (4).

Then, in step B130, it is determined whether i is 0, that is, whether it is the first control cycle in which the recovery mode is started. If i is 0, that is, the control cycle immediately after the start of the recovery mode, the process proceeds to step B140, and if i is not 0, that is, the second or later control cycle after the recovery mode is started, the process proceeds to step B150.

In step B140, the catalyst temperature Tu (i) obtained in step B20 [where i = 0
Therefore, the catalyst temperature becomes Tu (0)] and the temperature increase amount ΔT is added to obtain the determination catalyst temperature T (i + 1). However, since i = 0 here, the determination catalyst temperature is T (1).
Becomes In step B150, the temperature increase amount ΔT is added to the determination catalyst temperature T (i) obtained in step B140, step B150, or step B40 of the previous control cycle to obtain the determination catalyst temperature T (i + 1). obtain.

Further, in step B160, the catalyst temperature T (i) estimated this time is the first set value (for example, 650 ° C.).
It is determined whether it is greater than or equal to. Since the catalyst temperature T (i) does not normally reach the first set value at the start of control,
The process proceeds to step B170, the control cycle number i is incremented, and the process waits for execution of the recovery mode routine of the next cycle. In this case, in the next cycle, the process starts from step B20.

When the lean NOx catalyst 13A rises in temperature and the estimated value T (i) of the catalyst temperature becomes larger than the first set value, the timer starts counting when it becomes larger for the first time, and thereafter the catalyst temperature When the estimated value T (i) is larger than the first set value, the count value of the timer is integrated and the duration t _{0 of the} state in which the catalyst temperature T (i) is larger than the first set value is counted. (Step B180). Then, in step B190, it is determined whether the duration time t ₀ is longer than a predetermined time (for example, 600 seconds).

Immediately after the catalyst temperature T (i) has become higher than the first set value, the timer count has not advanced, so it is judged "No" in step B190, and step B17
The process proceeds to 0, increments the control cycle numbers i and j, respectively, and waits for execution of the recovery mode routine of the next cycle (starting from step B20). on the other hand,
When the state in which the catalyst temperature T (i) exceeds the first set value becomes longer than a predetermined time (for example, 600 seconds), the restoration is completed (revival mode is ended). In this case, the timer value t _{0 is set} to 0.
At the same time as resetting, the traveling distance D after completion of the restoration control is reset to zero.

In this way, even if the high temperature sensor for detecting the catalyst temperature is not provided, it is possible to judge the restoration completion (end of the restoration mode) while estimating the catalyst temperature T (i), and the catalyst can be surely restored. In addition, exhaust stroke injection for catalyst recovery can be efficiently performed without waste. In other words, in the recovery mode, the lean NOx catalyst 13A is supplied with the air-fuel mixture in the stoichiometric air-fuel ratio state, in which the surplus oxygen after combustion and the amount of fuel that is completely combusted with this surplus oxygen are mixed, Part of the supplied fuel is lean NO
In the process of reaching the x-catalyst 13A, the rest of the supplied fuel reaches the lean NOx catalyst 13A, is subjected to a catalytic action, and burns.

Therefore, the temperature of the lean NOx catalyst 13A is rapidly raised, and the sulfur content absorbed by the NOx absorbent of the lean NOx catalyst 13A is decomposed and released from the NOx absorbent, whereby the lean NOx absorbent is released. Catalyst 13
A is back. Also, at this stage, the sulfur content is in a harmful state such as sulfur oxide SO ₃ , but at this time, the air-fuel ratio of the air-fuel mixture supplied to the lean NOx catalyst 13A is brought to the stoichiometric air-fuel ratio state, so The released sulfur content is immediately reduced by the unburned HC and CO in the exhaust gas.

Therefore, there is an advantage that the lean NOx catalyst restoration control can be performed without giving a feeling of discomfort to the driver even in a low load region or a low rotation region such as during lean driving during traveling. Also, according to the exhaust stroke injection,
The injected fuel is supplied almost directly to the catalyst in the unburned state together with the exhaust gas without being used for combustion in the combustion chamber. There is an advantage that can be completed.

Further, according to the exhaust stroke injection, even when the recovery control is performed, the additional fuel injection is performed for the control of the normal fuel injection (that is, the fuel injection from the end of the exhaust stroke to the intake stroke). The same can be done regardless of whether or not. Further, since there is no adverse effect on the normal engine operation in the recovery mode, the predetermined value D ₁ that is the reference for starting the recovery mode is set to a small value on the safe side so that the sulfur content etc. does not stay excessively. Revival control can be performed diligently.

Further, it is possible to control the exhaust stroke injection so that the air-fuel ratio becomes the stoichiometric state, which has the advantage that the catalyst recovery control can be performed while suppressing the deterioration of fuel efficiency. Furthermore, the completion of the recovery mode is judged by detecting the catalyst temperature and the recovery mode ends, so that the recovery of the catalyst can be ensured and the exhaust stroke injection for efficient recovery of the catalyst can be performed without waste. You can

Further, it is possible to prevent the catalyst temperature from rising excessively to the second set value T ₂ or higher, and it is possible to avoid the deterioration of the exhaust gas due to the excessive temperature rising of the catalyst. Further, since the temperature of the catalyst 9 can be raised without adding a hardware structure such as a heater for heating the catalyst to the apparatus, the catalyst can be restored while suppressing the cost increase. Further, since the recovery control, that is, the heating control is performed by the exhaust stroke injection separately from the fuel injection for normal combustion, the recovery control () is performed without affecting the normal combustion and therefore without causing the torque fluctuation. Heating control)
Can be done.

Next, an engine exhaust gas purifying apparatus according to a second embodiment of the present invention will be described with reference to FIGS. 10 corresponds to FIG. 1 in the first embodiment, and in FIG. 10, the same reference numerals as those in FIG. 1 indicate the same members or functions, and here, the same portions as those in FIG. 1 (first embodiment). The description will be omitted, and only the part different from FIG. 1 will be described.

As shown in FIG. 10, in this embodiment, an air-fuel ratio sensor (catalyst downstream side air-fuel ratio detecting means) 15 is added to that of the first embodiment, and further, as a function in the CPU 27, the fuel amount is set. Correction means 103 for correcting the fuel amount calculated by the calculation means 102 is added. Air-fuel ratio sensor 15
Is mounted on the downstream side of the catalyst 13 and near the catalyst 13, and detects the air-fuel ratio AF2 (i) of the exhaust gas discharged downstream of the catalyst 13 after the exhaust stroke injection. As the air-fuel ratio sensor 15, for example, a linear A / F sensor (whole area air-fuel ratio sensor) can be used, whereby it is supplied to the combustion chamber 2 based on the oxygen concentration of the exhaust gas discharged from the combustion chamber 2. The air-fuel ratio of the air-fuel mixture can be detected in a wide range.

The correcting means 103 is a lean NOx catalyst 13
So that the oxygen amount according to the stoichiometric air-fuel ratio is on the downstream side of A,
The fuel amount γ (i) calculated by the fuel amount calculation means 102 is corrected. That is, in the correction means 103, the detection information from the air-fuel ratio sensor (catalyst downstream side air-fuel ratio detection means) 15 arranged on the downstream side of the lean NOx catalyst 13A, that is, in the exhaust gas discharged from the lean NOx catalyst 13A. The fuel amount γ (i) is adjusted based on the information as to whether the oxygen concentration is on the rich side or the lean side of the stoichiometric air-fuel ratio. For example, if the exhaust gas discharged from the lean NOx catalyst 13A is on the rich side, the fuel amount γ (i) is decreased by a certain amount,
If the exhaust gas discharged from the lean NOx catalyst 13A is on the lean side, the fuel amount γ (i) is increased by a fixed amount.

In addition to this, it has the same members and functions as those of the first embodiment, such as a catalyst temperature estimating means 106 for estimating the temperature state of the catalyst 13. Since the engine exhaust gas purifying apparatus according to the second embodiment of the present invention is configured as described above, the ECU 23 determines the start of the heating control in the procedure as shown in FIG. 8 as in the first embodiment. Then, when executing the recovery mode, for example, the processing shown in FIG. 11 is periodically performed according to the operation cycle of the engine. Note that, in FIG. 11, steps having the same reference numerals as those in FIG. 9 have similar processing contents, but here, these will also be described again based on FIG. 11.

First, initialization is performed (step B1).
2). In this initial setting, the control cycle numbers i and j are both set to 0 and the lean NOx catalyst 13a is set.
The air-fuel ratio AF2 (0) on the downstream side of is set to 0 (theoretical air-fuel ratio). Then, in step B20, the volume efficiency ηv
(I) Based on the engine speed Ne (i), the catalyst temperature (center temperature of the catalyst 13) Tu (i) before the start of the recovery control is calculated from the map as shown in FIG.

Since i = 0 at the start of the recovery mode, the volume efficiency ηv (i) and the engine speed N at this time are set.
e (i) and the catalyst temperature Tu (i) are respectively ηv
(0), engine speed Ne (0) and catalyst temperature Tu
It can be represented as (0). Further, in the subsequent control cycle, the value of i increases to 1, 2, 3, ...
Then, in step B30, the catalyst temperature Tu (i) obtained from the map in step B20 is changed to step 1 described later.
40 or B150 for judgment catalyst temperature T (i)
If the catalyst temperature Tu (i) obtained from the map is higher than the determination catalyst temperature T (i), the process proceeds to step B40 and the catalyst temperature Tu (i) is determined.
Is the determination catalyst temperature T (i).

The processing of steps B30 and B40 is as follows.
When the engine is accelerated, the volume efficiency ηv (i) and the engine speed Ne are normally set in the recovery mode.
The determination catalyst temperature T obtained by integrating the temperature increase amount ΔT described later, rather than the value of the catalyst temperature Tu (i) obtained based on (i)
(I) is larger, but during a transition such as acceleration, the judgment catalyst temperature T (i) increases by integrating the temperature increase amount ΔT with respect to the actual catalyst temperature increase due to a rapid increase in engine rotation. Instead of catching up, the value of the catalyst temperature Tu (i) obtained from the map as shown in FIG. 5 increases rather, and it becomes easier to obtain a value close to the actual catalyst temperature. Therefore, in order to avoid excessive temperature rise of the catalyst 13 even during such a transition, the volume efficiency ηv (i) and the engine speed Ne are increased.
Catalyst temperature Tu (i) obtained from the map based on (i)
The larger one of the judgment catalyst temperature T (i) obtained by integrating the temperature rise amount ΔT and the judgment catalyst temperature T (i) is set as the judgment catalyst temperature T (i).

Following step B30 or step B40, the process proceeds to step B50, where the determination catalyst temperature T
It is determined whether (i) is the second set value (for example, 750 ° C.) or more. If the determination catalyst temperature T (i) is equal to or higher than the second set value, the restoration is completed (revival mode is completed), but normally,
At the start of the recovery mode, the determination catalyst temperature T (i) is set to the second value.
Since the temperature has not risen to the set value, the process proceeds to step B60.

In step B60, the air-fuel ratio AF1 (i) after combustion in the cylinder is detected. Then, step B70
Then, the excess oxygen amount estimating means 101 determines the excess oxygen amount β in the exhaust system based on the detected air-fuel ratio AF1 (i), the intake air amount detected by the air flow sensor 7, and the like.
(I) is calculated. Next, in step B82, the amount of fuel γ that completely burns is calculated with respect to the calculated amount of excess oxygen β (i).
This fuel amount γ is calculated by calculating (i) from a known theoretical formula.
The correction value Δγ (AF2 (i-1)) is added to (i) for correction.

Then, the exhaust stroke injection is performed as shown in FIG. 4 at the fuel injection time corresponding to the fuel injection amount [γ (i) + γ (AF2 (i-1)] calculated in this way ( Step B92), which is followed by Step B101
Then, the lower heating value Hu (i) for the fuel injection amount [γ (i) + γ (AF2 (i-1)] is calculated.

Next, in Step B102, the air-fuel ratio AF2 (i) of the exhaust gas after the exhaust stroke injection detected on the downstream side of the catalyst 13 by the catalyst downstream-side air-fuel ratio detecting means 15 is detected.
Is detected. Further, in step B103, the air-fuel ratio AF
It is determined whether 2 (i) is equal to the stoichiometric air-fuel ratio, or is richer or leaner than the stoichiometric air-fuel ratio. Air-fuel ratio AF2 (i)
Is equal to the stoichiometric air-fuel ratio, the process proceeds to step B104, the correction value Δγ (AF2 (i)) is set to 0 and no correction is performed, and the air-fuel ratio AF2 (i) is richer or leaner than the stoichiometric air-fuel ratio. If there is, the process proceeds to steps B105 and B106 to set the correction value Δγ (AF2 (i)). That is, in the case of rich, the correction value Δγ (AF
2− (i)) is set to −Δγ (j), and in the case of lean, the correction value Δγ (AF2 (i)) in step C130.
Δγ (j) is set as The correction amount Δγ (j)
Is set according to the air-fuel ratio AF2 (i) on the downstream side of the catalyst.

In this way, the correction value Δγ (AF2
After setting (i)), steps B110 to B200
Then, it is determined whether or not the recovery of the lean NOx catalyst 13A is completed. That is, in step B110, the volume efficiency η
Based on v (i) and the engine speed Ne (i), the combustion efficiency ηc (i) is read from the map as shown in FIG. Then, the process proceeds to step B120, the combustion efficiency ηc (i), the air mass flow rate ma (i), the lower heating value Hu (i), the combustion gas density ρg (i), the combustion gas cross-sectional area Fg, the combustion gas velocity Wg (i). )
Based on the combustion gas specific heat Cpg (i) and the correction coefficient k ₂ , the temperature rise amount ΔT is calculated by the above equation (4).

Then, in step B130, it is determined whether or not i is 0, that is, whether or not it is the first control cycle in which the recovery mode is started. If i is 0, that is, the control cycle immediately after the start of the recovery mode, the process proceeds to step B140, and if i is not 0, that is, the second or later control cycle after the recovery mode is started, the process proceeds to step B150.

In step B140, the catalyst temperature Tu (i) obtained in step B20 [here, i = 0
Therefore, the catalyst temperature becomes Tu (0)] and the temperature increase amount ΔT is added to obtain the determination catalyst temperature T (i + 1). However, since i = 0 here, the determination catalyst temperature is T (1).
Becomes In step B150, the temperature increase amount ΔT is added to the determination catalyst temperature T (i) obtained in step B140, step B150, or step B40 of the previous control cycle to obtain the determination catalyst temperature T (i + 1). obtain.

Further, in step B160, the catalyst temperature T (i) estimated this time is the first set value (for example, 650 ° C.).
It is determined whether it is greater than or equal to. Since the catalyst temperature T (i) does not normally reach the first set value at the start of control,
The process proceeds to step B170, the control cycle number i is incremented, and the process waits for execution of the recovery mode routine of the next cycle. In this case, in the next cycle, the process starts from step B20.

When the lean NOx catalyst 13A rises in temperature and the estimated value T (i) of the catalyst temperature becomes larger than the first set value, the timer starts counting when it becomes larger for the first time, and thereafter the catalyst temperature When the estimated value T (i) is larger than the first set value, the count value of the timer is integrated and the duration t _{0 of the} state in which the catalyst temperature T (i) is larger than the first set value is counted. (Step B180). Then, in step B190, it is determined whether the duration time t ₀ is longer than a predetermined time (for example, 600 seconds).

Immediately after the catalyst temperature T (i) has become higher than the first set value, the timer count has not advanced, so it is judged "No" in step B190, and step B17
The process proceeds to 0, increments the control cycle numbers i and j, respectively, and waits for execution of the recovery mode routine of the next cycle (starting from step B20). on the other hand,
When the state in which the catalyst temperature T (i) exceeds the first set value becomes longer than a predetermined time (for example, 600 seconds), the restoration is completed (revival mode is ended). In this case, the timer value t _{0 is set} to 0.
At the same time as resetting, the traveling distance D after completion of the restoration control is reset to zero.

In this way, even if the high temperature sensor for detecting the catalyst temperature is not provided, it is possible to judge the restoration completion (end of the restoration mode) while estimating the catalyst temperature T (i), and the catalyst can be surely restored. In addition, it is possible to efficiently perform exhaust stroke injection for catalyst recovery without waste.
In addition to obtaining the same effects and advantages as the embodiment,
There are also the following effects and advantages.

That is, when the fuel injection amount is set only in accordance with the air-fuel ratio state on the upstream side of the lean NOx catalyst 13A detected by the air-fuel ratio sensor 14, calculation (or estimation) error or supply of the excess oxygen amount or supply The air-fuel mixture actually supplied to the lean NOx catalyst may not have the stoichiometric air-fuel ratio due to an error in the fuel amount, and further, due to combustion (oxidation) of the sulfur content absorbed in the catalyst 13A, etc. Even if a mixture of stoichiometric air-fuel ratio is supplied to the lean NOx catalyst,
The exhaust gas discharged from the lean NOx catalyst may not have the oxygen amount according to the stoichiometric air-fuel ratio.

However, in the present exhaust gas purifying apparatus, the fuel injection amount is corrected according to the air-fuel ratio state on the downstream side of the lean NOx catalyst 13A, so that the air-fuel mixture supplied to the lean NOx catalyst 13A is stoichiometric. Since it can be brought closer to the state, there is an advantage that the detoxified sulfur content can be efficiently and surely discharged. Further, since the recovery control, that is, the heating control is performed by the exhaust stroke injection separately from the fuel injection for normal combustion, without affecting normal combustion,
Therefore, the recovery control (heating control) can be performed without causing torque fluctuation.

As the catalyst upstream side oxygen detecting means 14 in the first and second embodiments, an air-fuel ratio sensor (Linear A
/ F sensor), other oxygen detection means may be used,
Alternatively, the operating state of the engine may be used. In this case, the operating state of the engine is considered to be the operating mode of the engine such as lean combustion operation mode or stoichiometric air-fuel ratio combustion operation mode, and the one in which the engine load, the rotational speed, etc. are added. Since the means for detecting (operating state detecting means) is generally existing in automobile engines and the like, there is an advantage that fuel supply control for catalyst restoration can be performed at low cost without providing a special sensor.

Further, as the catalyst downstream side air-fuel ratio detecting means 15 in the second embodiment, an air-fuel ratio sensor (linear A / F) is used.
It is also conceivable to use, for example, an oxygen sensor (O ₂ sensor) instead of the sensor). In this case, it is possible to determine whether the air-fuel ratio AF2 (i) of the exhaust gas after exhaust stroke injection downstream of the catalyst 13 is richer or leaner than the theoretical air-fuel ratio, but the air-fuel ratio itself is detected. Therefore, it is conceivable to set a preset fixed value (for example, Δγ ₁ ) as the correction amount Δγ (j).

In each of the above-mentioned embodiments, the catalyst is heated to recover the catalyst. However, not only for recovering the catalyst, for example, the temperature of the catalyst is maintained in a temperature range suitable for the catalytic reaction. It is also possible to heat the catalyst for the purpose. Further, the present apparatus may be a system in which a fuel injection valve is provided in the exhaust system and the amount of fuel injection from this fuel injection valve is controlled according to the amount of excess oxygen in the exhaust system to heat the lean NOx catalyst. Further, the present invention is not limited to the type of engine such as the in-cylinder injection engine as in each embodiment, but can be applied to various engines.

[0096]

As described in detail above, according to the exhaust gas purifying apparatus for an engine of the present invention as set forth in claim 1, an exhaust passage for exhausting exhaust gas from the combustion chamber, and a lean passage installed in the exhaust passage. Lean NOx that purifies or absorbs nitrogen oxides (NOx) in exhaust gas in an oxygen excess atmosphere during combustion operation
A catalyst, a surplus oxygen amount estimating means for estimating the amount of surplus oxygen after combustion in the combustion chamber, and a fuel amount sufficient for complete combustion with the surplus oxygen amount estimated by the surplus oxygen amount estimating means. A fuel amount calculation means, a heating determination means for determining whether or not the lean NOx catalyst should be heated, and a heating determination means for determining whether or not the lean NOx catalyst should be heated,
Fuel supply means for supplying the amount of fuel calculated by the fuel amount calculation means to the upstream side of the catalyst for combustion, and combustion heat of the fuel supplied by the fuel supply means based on the air-fuel ratio in the exhaust gas. And a catalyst temperature estimation means for estimating the temperature state of the catalyst, and heating the catalyst when the accumulated time of the state where the catalyst temperature estimated by the catalyst temperature estimation means is equal to or higher than a predetermined temperature exceeds a preset time. By the configuration in which the completion determining means for stopping the fuel supply by the fuel supply means is provided when the completion of the above is completed, the lean NOx catalyst can be reliably heated, and thereby the lean NOx catalyst can be heated to a desired temperature state in a short time. The temperature of the lean NOx catalyst can be fully raised to the full extent. In particular, in the NOx adsorption type catalyst, even if the high temperature sensor for detecting the catalyst temperature is not provided, the purification capacity-reducing substance such as sulfur adsorbed on the lean NOx catalyst is released from the lean NOx catalyst and is reduced. With this, exhaust gas can be discharged from the exhaust passage.

According to the exhaust gas purifying apparatus for an engine of the present invention described in claim 2, in the apparatus described in claim 1, a fuel injection valve for directly injecting fuel is provided in the combustion chamber,
The fuel supply means includes the fuel injection valve and fuel injection control means for controlling the fuel injection valve so that the amount of fuel calculated by the fuel amount calculation means is supplied during the exhaust stroke of the engine. With this configuration, even if fuel is supplied to restore the lean NOx catalyst, combustion in the normal combustion chamber is not affected, so the lean NOx catalyst can be restored without causing engine torque fluctuations. . Therefore, the lean NOx catalyst can be restored even in the low load region and the low rotation region of the engine. Further, as in the case where the catalyst is not restored, normal fuel injection control can be executed.

According to the exhaust gas purifying apparatus for an engine of the present invention as set forth in claim 3, in the apparatus as set forth in claim 1 or 2, the exhaust gas is disposed in the exhaust passage upstream of the lean NOx catalyst. Of the excess oxygen amount after the combustion in the combustion chamber based on the detection result of the catalyst upstream side oxygen concentration detection means. By being configured to estimate the amount, the amount of surplus oxygen after combustion in the combustion chamber can be reliably estimated, and the lean NOx catalyst can be efficiently heated.

According to the exhaust gas purifying apparatus for an engine of the present invention as defined in claim 4, in the apparatus as defined in any one of claims 1 to 3, an operating condition detecting means for detecting the operating condition of the engine is provided. , The excess oxygen amount estimating means is configured to estimate the amount of excess oxygen after combustion in the combustion chamber based on the detection result of the operating state detecting means, thereby utilizing the existing detecting means. On the other hand, the fuel supply control for heating the catalyst and reviving by heating can be performed at low cost.

An exhaust gas purifying apparatus for an engine according to a fifth aspect of the present invention is the apparatus according to any of the first to third aspects, wherein a three-way catalyst or an oxidation catalyst is provided on the downstream side of the lean NOx catalyst. , The catalyst downstream side air-fuel ratio detecting means is arranged downstream of the lean NOx catalyst and upstream of the oxidation catalyst, and the catalyst downstream side air-fuel ratio detecting means outputs the lean NOx catalyst to the lean NOx catalyst. By providing the control means for controlling the fuel supply means so that the air-fuel ratio of the inflowing air-fuel mixture becomes close to the stoichiometric air-fuel ratio, heating of the lean NOx catalyst and restoration by heating can be surely performed while efficiently utilizing the fuel. It

[Brief description of drawings]

FIG. 1 is a block diagram schematically showing a main part configuration of an exhaust gas purifying apparatus for an engine as a first embodiment of the present invention.

FIG. 2 is an overall configuration diagram of an engine system in an engine exhaust gas purification apparatus according to a first embodiment of the present invention.

FIG. 3 is a control block diagram of the engine in the exhaust gas purifying apparatus for an engine as the first embodiment of the present invention.

FIG. 4 is a diagram showing a fuel injection characteristic in the engine exhaust gas purification apparatus as the first embodiment of the present invention.

FIG. 5 is a diagram showing a catalyst temperature estimation map in the engine exhaust gas purification apparatus according to the first embodiment of the present invention.

FIG. 6 is a diagram showing characteristics of an excess oxygen amount in the exhaust system of the exhaust gas purifying apparatus for an engine as the first embodiment of the present invention.

FIG. 7 is a diagram showing a combustion efficiency detection map in the engine exhaust gas purification apparatus as the first embodiment of the present invention.

FIG. 8 is a flowchart illustrating an operation of the exhaust gas purifying apparatus for an engine according to the first embodiment of the present invention.

FIG. 9 is a flowchart illustrating an operation of the exhaust gas purifying apparatus for an engine as the first embodiment of the present invention.

FIG. 10 is a block diagram schematically showing a main part configuration of an exhaust gas purifying apparatus for an engine as a second embodiment of the present invention.

FIG. 11 is a flowchart illustrating an operation of the engine exhaust gas purifying apparatus as the second embodiment of the present invention.

[Explanation of symbols]

1 Engine Main Body 2 Combustion Chamber 3 Fuel Injection Valve (Injector) as Fuel Supply Means 3a Injector Solenoid 4 Intake Valve 5 Intake Passage 5A Intake Port 5B Intake Manifold 5C Surge Tank 5D Intake Pipe 6 Air Cleaner 7 Air Flow Sensor 8 Throttle Valve 9 Intake Temperature Sensor 10 Atmospheric pressure sensor 11 Intake valve 12 Exhaust passage 12A Exhaust port 12B Exhaust manifold 12C Exhaust pipe 13 Exhaust gas purification catalyst 13A Lean NOx catalyst 13B Three-way catalyst 13C Oxygen catalyst 14 Air-fuel ratio sensor (catalyst upstream oxygen detecting means) 15 Oxygen Sensor (catalyst downstream side air-fuel ratio detecting means) 16 Catalyst temperature sensor 17 Spark plug 18 Throttle opening sensor (throttle sensor) 19 Water temperature sensor 20 Cranking switch [ignition switch (key Switch)] 21 crank angle sensor (engine speed sensor) 22 TDC sensor (cylinder discrimination sensor) 23 ECU (electronic control unit) 24 accelerator position sensor 25 battery sensor 26 distance meter 27 CPU 28, 29 input interface 30 analog / digital Converter 31 ROM 32 RAM 33 Idle switch 34 Injection driver 48 Free running counter 34 Injection driver (fuel injection valve driving means) 101 Excess oxygen amount estimation means 102 Fuel amount calculation means 103 Correction means 104 Heating determination means 104A Heating start determination part 104B Heating Completion determination unit 105 Fuel injection control means 105A Catalyst heating fuel injection control means 105B Normal fuel injection control means 106 Catalyst temperature estimation means

Claims (5)

[Claims] 1. An exhaust passage for exhausting exhaust gas from a combustion chamber, and lean NOx installed in the exhaust passage for purifying or absorbing nitrogen oxides (NOx) in the exhaust gas in an oxygen excess atmosphere during lean combustion operation. A catalyst, a surplus oxygen amount estimating means for estimating the amount of surplus oxygen after combustion in the combustion chamber, and a fuel amount for complete combustion with the surplus oxygen amount estimated by the surplus oxygen amount estimating means. Fuel amount calculation means, heating determination means for determining whether or not the lean NOx catalyst should be heated, and the fuel amount calculation when the heating determination means determines that the lean NOx catalyst should be heated. A fuel supply means for supplying the amount of fuel calculated by the means to the upstream side of the catalyst for combustion, and calculating the combustion heat of the fuel supplied by the fuel supply means based on the air-fuel ratio in the exhaust gas. Estimate the temperature condition of the catalyst And a catalyst temperature estimating means for controlling the temperature of the fuel by the fuel supplying means when the catalyst heating is completed when the accumulated time of the catalyst temperature estimated by the catalyst temperature estimating means exceeds a preset time. An exhaust gas purifying apparatus for an engine, characterized in that a completion determining means for stopping the supply is provided. 2. A fuel injection valve for directly injecting fuel into the combustion chamber is provided, and the fuel supply means supplies the fuel injection valve and the fuel of the amount calculated by the fuel amount calculation means to the exhaust gas of the engine. The exhaust gas purifying apparatus for an engine according to claim 1, further comprising: a fuel injection control unit that controls the fuel injection valve to be supplied during a stroke. 3. A catalyst upstream-side oxygen concentration detecting means, which is arranged upstream of the lean NOx catalyst in the exhaust passage, and is capable of detecting oxygen concentration in exhaust gas, wherein the surplus oxygen amount estimating means is provided. The exhaust gas of an engine according to claim 1 or 2, characterized in that the amount of surplus oxygen after combustion in the combustion chamber is estimated based on the detection result of the catalyst upstream side oxygen concentration detection means. Gas purification device. 4. An operating state detecting means for detecting an operating state of the engine is provided, and the surplus oxygen amount estimating means is based on a detection result of the operating state detecting means, and surplus oxygen after combustion in the combustion chamber. The exhaust gas purifying apparatus for an engine according to any one of claims 1 to 3, wherein the exhaust gas purifying apparatus is configured to estimate the amount of the exhaust gas. 5. A three-way catalyst or an oxidation catalyst is provided on the downstream side of the lean NOx catalyst, and the catalyst downstream side air-fuel ratio detecting means is arranged on the downstream side of the lean NOx catalyst and on the upstream side of the oxidation catalyst. And a control means for controlling the fuel supply means so that the air-fuel ratio of the air-fuel mixture flowing into the lean NOx catalyst by the output of the catalyst downstream side air-fuel ratio detection means becomes close to the stoichiometric air-fuel ratio. The exhaust gas purifying device for an engine according to claim 1, wherein the exhaust gas purifying device is for an engine.