JPH10274085A - Exhaust gas purification device for in-cylinder injection internal combustion engine - Google Patents

Abstract

(57) [Summary] [PROBLEMS] An exhaust purification device for a direct injection internal combustion engine.
Without affecting the output torque of the engine so as to reliably supply CO to the lean NO _X catalyst, so that it is possible to reliably desorbed NO _X adhering to the lean NO _X catalyst. In the exhaust purification device provided in A cylinder injection type internal combustion engine, the oxygen concentration is deposited as nitrates NO _X in rich atmosphere, CO and reacted with the carbonate in the exhaust gas of the nitrate in an oxygen concentration lowering atmosphere and the lean NO _X catalyst 9A capable of leaving the generated NO _X and generates CO by reburning in the cylinder to inject additional fuel in addition to the main injection during the expansion stroke for stratified combustion the lean NO _X catalyst 9A NO attached to
Configure a NO _X desorption means 107 to accelerate the elimination of _X.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to relates to an exhaust purification device for purifying exhaust in-cylinder injection type internal combustion engine which directly injects fuel into a combustion chamber, in particular, nitrogen oxides by controlling the fuel injection (NO _X) The present invention relates to an in-cylinder injection type exhaust gas purification apparatus suitable for use in desorption of fuel.

[0002]

2. Description of the Related Art At present, a direct injection internal combustion engine for directly injecting fuel into a combustion chamber has been put into practical use. In such a direct injection internal combustion engine, the timing of fuel injection can be freely set, so that a low load engine can be used. In the operating range, fuel is injected in the compression stroke, and a mixture having a sufficient fuel concentration for ignition is partially collected in the vicinity of the spark plug to perform so-called stratified combustion for ultra-lean combustion to further improve fuel efficiency. I have.

[0003] In such a direct injection type internal combustion engine, an ultra-lean operation is performed in a predetermined operation range, so that it is adopted in an MPI (multipoint injection) engine in terms of exhaust gas purification. It is difficult to improve exhaust gas characteristics by providing only a three-way catalyst, that is, a catalyst having high purification characteristics in the vicinity of stoichiometry. Therefore, a lean NO _X catalyst has been developed so that NO _X can be purified even in an oxygen-excess atmosphere where the oxygen in the exhaust gas becomes excessive, and it is essential to provide this NO _X catalyst.

As this lean NO _X catalyst, those which purify NO _X in exhaust gas by depositing NO _X on the catalyst (storage type lean NO _X catalyst, trap type lean NO _X catalyst) have been developed. ing. This lean NO
_X catalyst has a function of the oxygen-rich atmosphere to adhere the NO _X in the exhaust gas, the oxygen concentration desorbs NO _X adhering to decrease. In other words, the lean NO _X catalyst oxidizes NO in the exhaust gas to generate nitrate in an atmosphere having an excessive oxygen concentration, thereby adhering NO _X, while adhering to the lean NO _X catalyst in an atmosphere having a reduced oxygen concentration. It was reacted with the CO in the nitrate and in the exhaust gas to generate a carbonate, thereby having a function capable of leaving the NO _X.

[0005]

However, in such a lean NO _X catalyst, the amount of NO _{X that} can be adhered has a certain limit, so that the oxygen concentration is low and the HC and CO concentrations are high at regular intervals. there in a state that is present, to elimination reaction is liable to occur in the NO _X, the NO _X adhering to the lean NO _X catalyst is desorbed, it is necessary to reduce.

For this reason, for example, in the technology disclosed in WO 93/07363, in an internal combustion engine that injects fuel into an intake port, the air-fuel ratio of exhaust gas is periodically made stoichiometric or rich by making it lean. decompose the NO _X catalyst NO _X attached to (NO _X adhesion agent), so that desorbed. However, if the fuel amount is increased to make the air-fuel ratio (A / F) a stoichiometric air-fuel ratio or rich, large torque fluctuations will occur.

In order to suppress the torque fluctuation, it is conceivable to retard the ignition timing. However, in such control, the fuel amount can be increased only within a range that can be suppressed by the retardation of the ignition timing. the amount is limited, a sufficient amount of HC to desorb the NO _X adhering to the lean NO _X catalyst, it is difficult to supply the CO.

On the other hand, as shown in FIG. 7, it is conceivable to control the air-fuel ratio (A / F) to be a stoichiometric air-fuel ratio or rich by reducing the intake air amount without changing the fuel amount. In this case, since fuel is consumed by pumping loss generated by closing the throttle and reducing the amount of intake air, it is difficult to adjust the fuel amount to an appropriate amount as described above, and the fuel is supplied to the lean NO _X catalyst. It is difficult to adjust the amounts of HC and CO.

As a technique used for a direct injection internal combustion engine, there is a technique disclosed in, for example, Japanese Patent Application Laid-Open No. 6-117225. This technique, in the lean NO _X catalyst provided in a diesel engine, to reduce NO _X, is intended to purify, expansion stroke, performs fuel injection into a cylinder in the exhaust stroke, not by burning fuel, the hot exhaust is supplied to the lean NO _X catalyst as HC small molecules are thermally decomposed by the gas, reducing the NO _X, it is intended to purify.

However, in this technique, in order to improve the purification efficiency of the lean NO _X catalyst, the fuel is burned to generate CO, and this CO is supplied to the lean NO _X catalyst, so that the CO adheres to the lean NO _X catalyst. rather than the the nO _X that desorbed, no consideration on this point.
The present invention has been in view conceived of the above problems, while not affecting the output torque of the engine, so as to reliably supply CO to the lean NO _X catalyst, attached to the lean NO _X catalyst was the NO _X to be able to reliably desorbed, and an object thereof is to provide an exhaust purification device of a direct injection type internal combustion engine.

[0011]

Therefore, the exhaust gas purifying apparatus for a direct injection type internal combustion engine according to the present invention is provided with a fuel injection valve for directly injecting fuel into a combustion chamber, and at least during a compression stroke. in the exhaust purification device provided in the cylinder injection type internal combustion engine by injecting fuel from the fuel injection valve to perform stratified combustion, provided in an exhaust passage of the internal combustion engine, as nitrates NO _X in an oxygen concentration excess atmosphere and the lean NO _X catalyst for desorbing the NO _X to generate a carbonate is reacted with CO in the exhaust gas in the deposited so oxygen concentration decreases atmosphere the nitrates, during the expansion stroke in addition to main injection for layered combustion NO that injects additional fuel and re-burns in the cylinder to generate CO and promotes desorption of NO _X attached to the lean NO _X catalyst
_X desorption means.

[0012] exhaust gas purifying apparatus for a direct injection type internal combustion engine of the present invention according to claim 2, in the configuration of claim 1, wherein reducing the adhesion ability of the lean NO _X catalyst adhered to the lean NO _X catalyst has a NO _X deposition amount estimating means for estimating a deposition amount of NO _X, is characterized by actuating said sulfur component desorption means in response to an output from the NO _X deposition amount estimating means.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 6 show an exhaust gas purifying apparatus for a direct injection internal combustion engine according to an embodiment of the present invention. First, a description will be given of a direct injection internal combustion engine equipped with the present exhaust gas purification apparatus. This internal combustion engine is configured as shown in FIG. 3 and performs each of intake, compression, expansion, and exhaust strokes in one operation cycle. The engine is an internal combustion engine, that is, a four-stroke engine, which is a spark ignition type and is an in-cylinder injection internal combustion engine (in-cylinder injection engine) that directly injects fuel into a combustion chamber.

An intake passage 2 and an exhaust passage 3 are connected to the combustion chamber 1 so that they can communicate with each other. The communication between the intake passage 2 and the combustion chamber 1 is controlled by an intake valve 4.
The communication between the exhaust passage 3 and the combustion chamber 1 is controlled by an exhaust valve 5. The intake passage 2 is provided with an air cleaner 6 and a throttle valve 7 in order from the upstream side, and the exhaust passage 3 is provided with an exhaust gas purifying catalytic converter 9 and a muffler (not shown) in order from the upstream side. Is provided. Note that a surge tank 2a is provided in the intake passage 2.

An exhaust gas recirculation device (hereinafter, EGR)
10) is provided. That is, the exhaust gas recirculation passage 10b is provided so as to connect the surge tank 2a portion of the intake passage 2 with the upstream side of the exhaust gas passage 3, and the exhaust gas recirculation passage 10b is provided with the EGR valve 10a. The flow rate of exhaust gas (also referred to as exhaust gas or exhaust gas or exhaust gas) from the exhaust passage 3 to the intake passage 2 can be controlled by the EGR valve 10a. The control of the EGR valve 10a is performed according to the operating state of the engine.

The opening of the throttle valve 7 changes in accordance with the amount of depression of an accelerator pedal (not shown), whereby the amount of air introduced into the combustion chamber 1 is adjusted. Reference numeral 16 denotes an idle speed control valve (ISC valve) which is provided in a bypass passage 16A which bypasses a portion of the intake passage 2 where the throttle valve 7 is installed, and is opened and closed by a stepper motor (not shown). The idle speed at the time of closing or almost fully closing is finely adjusted.

Reference numeral 50 denotes an air bypass valve (ABV) which bypasses the portion of the intake passage 2 where the throttle valve 7 is installed, and which bypasses the intake passage 2 upstream of the throttle valve 7 and the surge tank 2a. The air-fuel ratio can be adjusted by adjusting the intake air amount separately from the throttle valve 7. Injector (fuel injection valve)
Reference numeral 8 is arranged so that its opening faces the combustion chamber 1 so as to directly inject fuel toward the combustion chamber 1 in the cylinder. In addition, naturally, the injector 8 is provided for each cylinder. For example, if the engine of the present embodiment is an in-line four-cylinder engine,
That is, it is provided.

With this configuration, the air sucked through the air cleaner 6 according to the opening of the throttle valve 7 is sucked into the combustion chamber 1 by opening the intake valve 4, and the air sucked inside the combustion chamber 1 And the fuel directly injected from the injector 8 are mixed, and the ignition plug 35
Is ignited at an appropriate timing to cause combustion and generate engine torque.
The exhaust gas is exhausted from the inside to the exhaust passage 3, and a catalytic converter (hereinafter, also simply referred to as a catalyst) 9 emits C in the exhaust gas.
O, HC, since the purifying three harmful components NO _x,
The sound is muted by the muffler and desorbed to the atmosphere.

[0019] Particularly, the present engine is able engine savings operation while the air-fuel ratio to lean, because at the time of lean operation, which is only a normal three-way catalyst can not sufficiently purify the NO _x in the exhaust gas, the catalyst 9 Is a combination of a lean NO _x catalyst (NO _x catalyst) 9A and a three-way catalyst 9B. In other words, downstream of the lean NO _x catalyst 9A, CO in the exhaust gas under stoichiometric, HC and NO _x
Is provided with a three-way catalyst 9B having a three-way function capable of purifying the catalyst.

The engine will be further described. In this engine, the intake air flowing into the combustion chamber 1 from the intake passage 2 forms a vertical vortex (reverse tumble flow). Since the flow forms such a vertical vortex, a small amount of fuel is collected, for example, only near the ignition plug 35 disposed at the center of the top of the combustion chamber 1 while utilizing the vertical vortex, and is separated from the ignition plug 35. It is possible to achieve an extremely lean air-fuel ratio state in the portion where the air-fuel ratio has been obtained, and to achieve a stable stratified combustion (stratified super-lean combustion) by setting the stoichiometric air-fuel ratio or the rich air-fuel ratio only in the vicinity of the ignition plug 35. Fuel consumption can be suppressed. The optimal fuel injection timing in this case is the latter half of the compression stroke in which the air flow is weak.

In order to obtain a high output from the engine, the fuel from the injector 8 is homogenized throughout the combustion chamber 1 and the interior of all the combustion chambers 1 is brought to a mixture of stoichiometric air-fuel ratio and lean air-fuel ratio. The stoichiometric air-fuel ratio can provide a higher output than the lean air-fuel ratio. Of course, the timing at which the fuel is sufficiently atomized and vaporized is also used. By performing the fuel injection, a high output can be obtained efficiently. In such a case, the optimal fuel injection timing is set so as to end the fuel injection during the intake stroke so that atomization and vaporization of the fuel can be promoted using the intake air flow.

Incidentally, various sensors are provided to control the engine. First, on the intake passage 2 side, an air flow sensor 11, which detects an intake air amount from Karman vortex information, an intake air temperature sensor 12, which detects an intake air temperature, and an atmospheric pressure sensor 13, which detects an atmospheric pressure, are provided at the portion where the air cleaner is provided. The throttle valve is provided with a potentiometer type throttle sensor 14 for detecting the opening of the throttle valve 7, an idle switch 15 for detecting an idling state, and the like.

On the exhaust passage 3 side, an oxygen concentration sensor 17 (hereinafter simply referred to as an O ₂ sensor 17) for detecting an oxygen concentration (O ₂ concentration) in the exhaust gas is provided upstream of the catalyst 9.
Is provided, and a temperature θ _CC (hereinafter, referred to as a catalyst temperature θ) at or near the catalyst 9 is provided at a downstream portion of the catalyst 9.
Catalyst temperature sensor for detecting a) of _CC (high temperature sensor)
26 are provided.

Further, as other sensors, a water temperature sensor 19 for detecting an engine cooling water temperature, and a crank angle sensor (crank angle detecting means) 21 for detecting a crank angle as shown in FIG. A TDC sensor (cylinder discrimination sensor) 22 for detecting the top dead center of the first cylinder (reference cylinder) is provided near the cam, respectively.

The detection signals from these sensors are input to an electronic control unit (ECU) 23. The ECU 23 is provided with a voltage signal from an accelerator position sensor 24 that detects the amount of depression of an accelerator pedal and a voltage signal from a battery sensor 25 that detects the voltage of a battery, and a cranking switch [or an ignition switch (key switch)] that detects a start time. The signal from the terminal 20 is also input.

By the way, the hardware configuration of the ECU 23 is as shown in FIG. 2. The ECU 23 has a CPU 27 as its main part.
Intake air temperature sensor 12, atmospheric pressure sensor 13, a throttle sensor 14, O ₂ sensor 17, water temperature sensor 19, an accelerator position sensor 24, catalyst temperature sensor 26 and input the detection signal from the battery sensor 25 Interface 28
And an input through an analog / digital converter 30, an air flow sensor 11, a crank angle sensor 21, a TDC sensor 22, an idle switch 15,
Detection signals from the cranking switch 20, the ignition switch, and the like are input via the input interface 29.

Further, the CPU 27 has 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. The fuel injection control signal based on the calculation result by the CPU 27 is output to the solenoid (injector solenoid) 8a of the injector 8 via the injection driver (fuel injection valve driving means) 34 for each cylinder (here, four). It is supposed to be.

In view of the above-described characteristics of the direct injection engine, in this engine, the mode of fuel injection is as follows.
Late injection mode (late lean operation mode) in which fuel is injected during the compression stroke (particularly in the second half of the compression stroke) to achieve lean operation by stratified super-lean combustion and improve fuel efficiency.
The first injection mode (early lean operation mode), in which fuel injection is performed during the intake stroke (particularly in the first half of the intake stroke) to achieve lean operation by premixed combustion and obtain output by slow acceleration, and stoichiometric combustion by premixed combustion A stoichiometric mode (stoichiometric operation mode) in which fuel injection is performed during the intake stroke to achieve operation (stoichiometric air-fuel ratio operation) and improve output compared to the previous injection mode, and a rich operation (predicted by stoichiometric air-fuel ratio) There is provided an enriched mode (open loop mode) for realizing an air-fuel ratio (low air-fuel ratio) and improving the output over the stoichiometric operation mode, and can be switched according to the operating state of the engine. The switching of the operation mode described above means the switching of the combustion state of the engine.

The present exhaust gas purifying apparatus is provided in such an engine (in-cylinder injection type internal combustion engine). Here, the present exhaust gas purifying apparatus will be described. First, the principle of the present device will be described. Here, to describe the lean NO _x catalyst 9A, the lean NO _x catalyst 9A is of a type which purifies NO _X in the exhaust gas by attaching the NO _X on the catalyst (occlusion-type lean NO _X catalyst, trap Type Lean N
O is _X catalyst), as shown in FIG. 4 (a), alumina Al ₂ O ₃ as a carrier, barium Ba and platinum Pt on the support, further comprises rhodium Rh be carried.

[0031] The lean NO _x catalyst 9A is oxygen attached to NO _X in the exhaust gas in the rich atmosphere, deposition of the NO _X as that NO _X in which the oxygen concentration is attached to decline is desorbed, having a desorption function . Here, the function of attaching and detaching NO _X in the lean NO _X catalyst 9A will be described.

In the oxygen-excess atmosphere (lean atmosphere), the lean NO _X catalyst 9A has the following characteristics as shown in FIG.
First, O ₂ adheres to the surface of platinum Pt, and NO 2 in exhaust gas
Reacts with O ₂ on the surface of platinum Pt to form NO ₂ (2
NO + O ₂ → 2NO ₂ ). On the other hand, lean NO _X catalyst 9A
Some of the Ba supported on O ₂ reacts with O ₂ to form barium oxide BaO, and this barium oxide BaO
Further reacts with CO etc. in the exhaust gas to form carbonate BaC
It becomes O ₃ .

Under such circumstances, a part of the generated NO ₂ is further combined with a carbonate (BaCO ₃ ) generated from barium oxide BaO, CO on platinum Pt to form a nitrate [Ba (NO ₃ )]. ₂ ] is produced and the lean NO _X catalyst 9
A adheres to A. When such a reaction is represented by a chemical reaction formula,
The following reaction formula (1) is obtained. BaCO ₃ + 2NO + (3/2) O ₂ → Ba (NO ₃ ) ₂ + CO ₂ (1) On the other hand, in an atmosphere with a reduced oxygen concentration (rich atmosphere), as shown in FIG. the amount of ₂ decreases, the reverse reaction proceeds, N from the lean NO _X catalyst 9A
O ₂ is eliminated.

That is, nitrate [Ba (NO ₃ ) ₂ ] adhering to the lean NO _X catalyst 9A reacts with CO in the exhaust gas on the surface of platinum Pt to form NO ₂ and carbonate (BaC).
O ₃ ) is generated, and NO ₂ is desorbed from the lean NO _X catalyst 9A. This can be represented by the following reaction formula (2) when expressed by a chemical reaction formula. BaCO ₃ + 2NO + O ₂ ← Ba (NO ₃ ) ₂ + CO (2) However, 2NO + O ₂ → 2NO ₂ (part of NO is discharged as it is.) Then, desorbed NO ₂ and NO Means unburned H in exhaust gas
It is reduced by C and CO and discharged as N ₂ .

As described above, the lean NO _X catalyst 9A includes:
Nitrate [Ba (NO ₃ ) ₂ ] and carbonate (BaCO ₃ )
Exists in a state of chemical equilibrium, and a reaction in each direction occurs depending on the atmosphere near the lean NO _X catalyst 9A. Therefore, as shown in the above formula (2), if a large amount of CO, which is a raw material of carbonate (BaCO ₃ ), is supplied in a state where the residual oxygen concentration is extremely low, a chemical reaction that tends to consume this CO, that is, , Nitrate [Ba (NO ₃ ) ₂ ]
Is decomposed to generate a carbonate (BaCO ₃ ) (a reaction direction from right to left in the equation (2)), whereby the lean NO _X catalyst 9 is produced.
It will be able to desorb the NO _X attached to A.

For this reason, in the present embodiment, when the residual oxygen concentration is extremely low, a large amount of CO, which is a raw material of carbonate (BaCO ₃ ) (ie, a large amount of unburned or incompletely burned gas) is supplied. conducted, thereby reliably desorbed NO _X adhering to the lean NO _X catalyst 9A, the lean NO _X catalyst 9
In order to maintain the function of A, additional fuel injection is performed as described later.

This additional fuel injection is performed by the lean NO _X catalyst 9
Carried out based on the amount of NO _X attached to A _(the amount of NO _X to be estimated), but, HC in the exhaust gas, in consideration of the influence of the output torque of the securing or engines CO in the expansion stroke of each cylinder (preferably expanded The timing near the end of the process is preferable.)
, An additional fuel injection is performed. Thus, as shown in FIG. 1, the present apparatus includes a lean NO _X catalyst (NO _X catalyst) 9A, NO _X adhesion amount estimating means 103 for estimating the amount of NO _X adhered to the lean NO _X catalyst 9A, constructed and a NO _X desorption means 107 for positively desorbing NO _X adhering to the lean NO _X catalyst 9A.

That is, in the present apparatus, separately from the fuel injection (main injection) for combustion in the normal combustion chamber as described above, additional fuel is injected at a timing that hardly affects the output of the engine. by reburning of the exhaust gas by adding fuel (auxiliary combustion), HC proper concentration to the catalyst 9, by supplying CO (reducing agent), in NO _X desorption unit 107,
Lean NO _X catalyst 9A to the proper concentrations of HC, by supplying CO to promote chemical reactions, and the NO _X adhering to the lean NO _X catalyst 9A to desorb.

This is because CO, which is a raw material of carbonate (BaCO ₃ ), is supplied in a state where the concentration of residual oxygen is low, and NO _X adhering to the lean NO _X catalyst 9A is surely desorbed so that lean NO _X is removed. _This is for maintaining the function of the _X catalyst 9A. Thus, NO _X desorption unit 107 is subjected to elimination of the NO _X by using the fuel injection control (injector drive control), the NO _X desorption unit 107, shown in the block diagram of FIG. 1 As described above, the additional fuel injection determination means 102 and the additional fuel injection control means 104 provided as a part of the fuel injection control means 101 for performing the fuel injection control.
And a fuel injection valve 8. The fuel injection control means 101 is, of course, provided with a normal fuel injection control means 105 for main fuel injection.

Here, each component shown in FIG. 1 will be described. First, NO _X deposition amount estimating means 103, based on the total fuel injection quantity obtained from the integrated value of injector drive time in the lean operation mode, and estimates the amount of NO _X that has adhered to the lean NO _X catalyst 9A . Incidentally, NO _X deposition amount estimating means 103 is not limited to this,
It may be constructed as to estimate the amount of NO _X that has adhered to the lean NO _X catalyst 9A based on _the amount of NO _X detected by the NO _X sensor, also estimated based on the operating time of the operating area of the vehicle You may comprise as a thing. That is, since the NO _X amount of adhered lean NO _X catalyst 9A is considered to substantially correspond to the driving performance of the vehicle, previous NO _X
Lean operation time and stoichiometric since performs processing of elimination (or rich) may be estimated NO _X adhesion amount based on the operating time and the like during operation.

Further, additional fuel injection determining means 102 is for determining whether or not it is necessary to add a fuel injection control NO _X adhering to the lean NO _X catalyst 9A to desorb, begin these control It is determined whether or not a condition for performing the control (control start condition) and a condition for releasing these controls (control release condition) are satisfied.

[0042] Here, as the control start condition, it NO _X deposition amount is equal to or greater than a predetermined amount, that the primary combustion is late lean operation mode, it is possible two-stage combustion [e.g., air in the main combustion The fuel ratio (A / F) is 20 or more;
Water temperature WT is 10 ° C. or higher], and (all are AND conditions). Here, either NO _X deposition amount is equal to or greater than a predetermined amount, is determined on the basis of the NO _X deposition amount estimated by the NO _X deposition amount estimating means 103, the determination result is sent to the additional fuel injection determining means 102 It has become.

Whether the air-fuel ratio (A / F) of the main combustion is equal to or greater than 20 (ie, whether the air-fuel ratio is lean) depends on the air-fuel ratio of the main combustion normally set by the fuel injection control means 105. It is determined based on. For this reason, information on the air-fuel ratio is sent from the normal fuel injection control means 105 to the additional fuel injection control means 104. The reason for this is that a large amount of oxygen is present in the exhaust gas during the lean operation, so that the additional fuel can be reliably burned.

Further, for example, whether the water temperature WT is equal to or higher than 10 ° C. is determined based on detection information from the cooling water temperature sensor 19. For this reason, the detection information from the cooling water temperature sensor 19 is sent to the additional fuel injection control means 104. The reason for this is that if the water temperature is too low, self-ignition is difficult even when additional fuel injection is performed.

As described above, the additional fuel injection determining means 1
02 determines whether or not the control start condition is satisfied. When all of these control start conditions are satisfied, the additional fuel injection determination means 102 performs additional fuel injection control so as to perform additional fuel injection. A signal is sent to the means 104. On the other hand, the control release condition is a predetermined time (for example, 5 seconds) after the start of the additional fuel injection control.
Seconds) has passed.

Whether or not a predetermined time has elapsed since the start of the additional fuel injection control is determined based on the count result of the timer 106. Therefore, when the additional fuel injection control is started, the timer 106 starts counting, and the count value of the timer 106 is sent to the additional fuel injection determination means 102.

As described above, the additional fuel injection determining means 1
02 determines whether a control release condition is satisfied,
When the control release condition is satisfied, the additional fuel injection control is released. Further, when the additional fuel injection determining means 102 determines that additional fuel injection is necessary, the additional fuel injection control means 104 sets the injection start timing T _INJ of the additional fuel injection, and sets an additional fuel injection timing in each cycle. This is for setting the injection time of the additional fuel.

The injection start timing T of these additional fuel injections
By adjusting _INJ and injection time, lean NO _X
The amounts of HC and CO supplied to the catalyst 9A are adjusted. That is, if the start time T _INJ of the additional fuel injection is set as late as possible, the atomization of the fuel is deteriorated, the oxidation of the fuel can be suppressed, and the amount of HC and CO supplied to the lean NO _X catalyst 9A can be reduced. The amount can be increased. Further, if the injection time of the additional fuel injection is lengthened, the injection amount of the additional fuel can be increased, and the amounts of HC and CO supplied to the lean NO _X catalyst 9A can be increased.

First, the injection start timing T _INJ of the additional fuel injection
Is set such that additional fuel injection is performed during the middle stage of the expansion stroke of each cylinder or during the expansion stroke thereafter. That is, the injection start timing T _INJ of the additional fuel is added near the crank angle of 90 ° after the piston compression TDC from the compression stroke to the expansion stroke based on the detection information from the crank angle sensor 21 as the crank angle detection means. The injection start timing T _INJ is set so as to perform the fuel injection.

The reason why the injection start timing T _INJ is set in this manner is that the fuel injected by the additional fuel injection is reliably burned (hereinafter, also referred to as reburning), and thereby adheres to the lean NO _X catalyst 9A. it is to generate CO necessary to the NO _X desorbed. When the additional fuel injection is performed at the injection start timing T _INJ set in this way, the _preflame reaction product exists in the lean mixture portion formed in the combustion chamber by the main combustion at a concentration near the ignition limit. Therefore, the total amount of the pre-flame reaction products generated from the additional fuel injected into the high-temperature atmosphere in the cylinder exceeds the ignition limit and self-ignites, and the additional fuel burns.

Here, the point at which the preflame reaction product concentration increases and the preflame reaction rate exponentially progresses exponentially beyond the equilibrium concentration is called ignition. At this point, the flame (heat flame) Will happen. The preflame reaction product is an active chemical reactive species effective for promoting the chain branching reaction, and is, for example, CHO, H ₂ O ₂ , OH, or the like. Specifically, the additional fuel injection control means 104 determines the basic fuel injection start timing Tb _INJ which is the basis for the additional fuel injection in the expansion stroke, the cooling water temperature θ _W , the EGR amount, and the ignition timing T _IG in the main combustion. To set the injection start timing T _INJ . For this reason, the ECU 23 is provided with a map for the start timing of the additional fuel injection which is set in advance based on the target A / F of the main combustion.

Next, the injection time of the additional fuel injection, that is, the injector drive time t _PLUS, is set so that the air-fuel ratio of the exhaust gas supplied to the lean NO _X catalyst 9A (the target exhaust air-fuel ratio) is about 14. You. This is because the air-fuel ratio of the total injection amount obtained by adding the additional fuel injection amount to the main combustion fuel injection amount is about 14%.
Set to about. Thus are you set the air-fuel ratio, in order to the NO _X from the lean NO _X catalyst 9A eliminated, many of the HC to the lean NO _X catalyst 9A, CO
It is necessary to supply

More specifically, additional fuel injection control means 104
Sets the injector drive time t _PLUS by correcting the basic drive time t _B, which is the basis for additional fuel injection in the expansion stroke, with the injection start timing T _INJ . Therefore, the target A / F preset NO _X desorption map based on the main combustion is provided in the ECU 23. The NO _X desorption map exhaust target air-fuel ratio of about 1
It is set to be about 0. And this NO
_{The X} desorption map is selected by the additional fuel injection control means 104 when setting the injector drive time t _PLUS for performing additional fuel injection for desorbing NO _X.

The fuel injection control by the normal fuel injection control means 105 will be described. The normal fuel injection control means 105 has a function of setting the fuel injection amount in the normal fuel injection based on information from various sensors 108. Having. That is, the fuel injection amount is set as the fuel injection time (injector drive time, which is referred to as injector drive pulse width in actual control) t _AU , but also in the stoichiometric mode and the former injection mode in the latter period. in the case of injection mode, the engine load (intake air quantity per one stroke) air-fuel ratio to Q / Ne and the target (a / F, hereinafter referred to as AF) on the basis of such a basic drive time t _p is calculated, The engine cooling water temperature detected by the water temperature sensor 19, the intake air temperature detected by the intake air temperature sensor 12, the atmospheric pressure sensor 13
The fuel injection time t _AU is set in consideration of the fuel correction coefficient f set in accordance with the atmospheric pressure and the like detected in the above, the injector dead time (dead time) t _{D, and the} like.

Since the exhaust gas purifying apparatus according to the present embodiment is configured as described above, control relating to exhaust gas purifying is performed, for example, as shown in the flowchart of FIG. First, in step S10, NO _X deposition amount adhered to the lean NO _X catalyst 9A by NO _X deposition amount estimating means (NO _X deposition amount estimating means) 103 is estimated, at step S20, additional fuel injection determining means 102 Thus, it is determined whether or not the estimated NO _X adhesion amount is equal to or more than a predetermined amount.

If the result of this determination is that the estimated NO _X adhesion amount is equal to or greater than the predetermined amount, the flow proceeds to step S30, where the additional fuel injection determination means 102 determines that the air-fuel ratio is
It is determined whether or not the above is true. If the air-fuel ratio is 20 or more, the process proceeds to step S40. In step S40,
The cooling water temperature sensor 1
It is determined whether the water temperature WT detected by step 9 is equal to or higher than 10 ° C., and if the water temperature WT is equal to or higher than 10 ° C., the process proceeds to step S50.

In step S50, the additional fuel injection control means 104 controls the injection start timing T _INJ and the injector drive time t of the additional fuel injection in the expansion stroke.
_PLUS is read from the map, and proceeds to step S60,
The injection start time T _INJ and the injector drive time t
Additional fuel injection in the expansion stroke is performed based on _PLUS .

When the additional fuel injection is started, the timer 106 is started in step S70, and in step 80, it is determined whether or not a predetermined time has elapsed since the start of the additional fuel injection. It is determined by whether or not the value has been exceeded. If it is determined that the additional fuel injection is determined since the start and the predetermined time has elapsed, the process proceeds to step S90, the timer 106 is reset, NO _X adhering to the lean NO _X catalyst 9A is sufficiently It is determined that the fuel has been detached, the additional fuel injection in the expansion stroke ends, and the process returns.

The determination of whether a predetermined time has elapsed since the start of the additional fuel injection in step S80 is repeated until the predetermined time has elapsed. By the way, step S2
If NO _X amount of adhered 0 is determined to less than the predetermined amount, when the air-fuel ratio is determined to not more than 20 at step S30, the water temperature WT detected by the coolant temperature sensor 19 in step S40 is not 10 ° C. or higher If it is determined, NO _X which both adhered to the lean NO _X catalyst 9A
The routine returns without performing additional fuel injection in the expansion stroke for desorbing the fuel.

Since the present exhaust gas purifying apparatus operates as described above, lean NO _X is produced without causing torque fluctuation.
Since CO can be reliably supplied to the catalyst 9A, the desorption reaction of NO _X attached to the lean NO _X catalyst 9A can be promoted, and the lean NO _X catalyst 9A can be surely regenerated. There is an advantage that the performance of the lean NO _X catalyst 9A can be improved.

Further, by changing the injection timing of the additional fuel injection, the concentrations of HC and CO in the exhaust gas can be changed in accordance with the amount of NO _X estimated to be attached to the lean NO _X catalyst 9A. Attached to the lean NO _X catalyst 9A
O _X proper concentration with respect to the amount of HC, can be advantageously supplied CO. That is, when the amount of NO _X estimated to be attached to the lean NO _X catalyst 9A is large, the injection timing of the additional fuel injection in the expansion stroke is delayed as much as possible to worsen the fuel atomization, thereby Is suppressed so that high concentrations of HC and CO are generated.

As described above, since the concentrations of HC and CO in the exhaust gas can be changed, the lean NO _X catalyst 9A can be efficiently made in accordance with the NO _X amount estimated to be attached to the lean NO _X catalyst 9A. there is an advantage that the NO _X adhered can be detached to. In addition, since the additional fuel injection is performed during the expansion stroke, the output torque of the engine is less fluctuated. In particular, when the additional fuel injection is performed during the latter half of the expansion stroke, torque fluctuation hardly occurs due to the additional fuel injection. There are advantages too.

For this reason, as shown in FIG. 6, it is possible to set an additional fuel injection amount as a reducing agent generation amount for desorbing NO _X from the lean NO _X catalyst 9A without considering torque fluctuation. can be injected a number of additional fuel, a number of HC in one cycle, CO and can be supplied to the lean NO _X catalyst 9A, it is possible to reliably desorbed NO _X from the lean NO _X catalyst 9A .

Further, if the air-fuel ratio of the main combustion is lean, additional fuel injection can be performed, so that NO _X can be desorbed from the lean NO _X catalyst 9A in a wide range of operating conditions (for example, during normal operation). There is an advantage that it can be performed. It should be noted that SO _X
Let includes a deposition amount estimating means, in accordance with the amount of adhering SO _X is estimated by the SO _X deposition amount estimating means, when to perform additional fuel injection, de the SO _X adhering to the lean NO _X catalyst 9A The lean NO _X catalyst 9 </ b> A can be prevented from lowering in NO _X adhesion ability, and the performance of the lean NO _X catalyst 9 A can be further improved. However, since the sulfate is more stable than the sulfate, the exhaust air-fuel ratio is made richer, for example, A /
It needs to be about F11.

Here, the SO _X adhering amount estimating means estimates the SO _X amount adhering to the lean NO _X catalyst 9A based on the total fuel injection amount obtained from the integrated value of the injector driving time and the traveling distance of the vehicle. To be configured. Further, in the exhaust gas purifying apparatus of the present embodiment, the additional fuel injection is performed in the middle stage or later of the expansion stroke (for example, near the crank angle of 90 ° after the piston compression top dead center), but is not limited thereto. Instead, if the additional fuel can be reburned while suppressing the torque fluctuation, the additional fuel injection may be performed at another time within the expansion stroke or at the exhaust stroke.

In particular, when the cooling water temperature is low, even if the additional fuel injection is performed in the middle stage or later of the expansion stroke, self-ignition is difficult, so in this case, the first half of the expansion stroke (for example, the piston compression top dead center) The additional fuel injection may be performed during the remaining flame period of the main combustion at a rear crank angle of about 35 ° to 50 °). In this way, even if the cooling water temperature is low, the additional fuel can be reliably reburned.

In the exhaust gas purifying apparatus of this embodiment, the lean NO _X catalyst 9A has platinum Pt and barium Ba supported on a carrier. However, the present invention is not limited to this. A metal or the like supported on a carrier may be used. Furthermore, in the exhaust gas purification apparatus of the present embodiment, the expansion stroke injection is performed sequentially in each cylinder, but the expansion stroke injection may be performed only in a specific cylinder among the four cylinders. Further, in the exhaust gas purification apparatus of the present embodiment, every predetermined cycle (for example, 1 every 2 cycles)
) May be set to perform the expansion stroke injection.

Further, the exhaust gas purifying apparatus of the present embodiment is provided for a spark ignition type direct injection type engine. However, the present invention is not limited to this. For example, it may be provided for a diesel engine. .

[0069]

As described above in detail, according to the exhaust gas purifying apparatus for a direct injection type internal combustion engine of the present invention, it is not necessary to use another device separately, and torque fluctuation does not occur. , can be supplied reliably CO in lean NO _X catalyst, to promote the elimination reaction of the NO _X attached to the lean NO _X catalyst, it is possible to reliably the regeneration of the lean NO _X catalyst, thereby There is an advantage that the performance of the lean NO _X catalyst can be improved.

[0070] According to the exhaust purification system of a cylinder injection type internal combustion engine of the present invention of claim 2, wherein, to estimate the deposition amount of the NO _X in the NO _X catalyst by NO _X deposition amount estimating means, suitable can activate NO _X desorption means the time, N
There is also an advantage that HC and CO at appropriate concentrations can be supplied according to the NO _X amount estimated by the O _X adhesion amount estimation means.

[Brief description of the drawings]

FIG. 1 is a block diagram schematically illustrating a main configuration of a control system of an exhaust gas purification apparatus for a direct injection internal combustion engine according to an embodiment of the present invention.

FIG. 2 is a control block diagram of a direct injection internal combustion engine according to one embodiment of the present invention.

FIG. 3 is an overall configuration diagram of a direct injection internal combustion engine according to an embodiment of the present invention.

FIG. 4 is a schematic diagram for explaining a lean NO _X catalyst in an exhaust purification device for a direct injection internal combustion engine according to an embodiment of the present invention, and FIG. 4A is a diagram showing a configuration of a lean NO _X catalyst; (B) is a diagram showing a function of attaching a lean NO _X catalyst, and (c) is a diagram showing a desorption function of a lean NO _X catalyst.

FIG. 5 is a flowchart showing additional fuel injection control of the exhaust gas purification device for a direct injection internal combustion engine according to one embodiment of the present invention.

FIG. 6 is a diagram illustrating the effect of the exhaust gas purifying apparatus for a direct injection internal combustion engine according to one embodiment of the present invention.

FIG. 7 is a diagram illustrating a problem of a conventional exhaust gas purification apparatus for a direct injection internal combustion engine.

[Explanation of symbols]

8 fuel injection valve 9 lean catalytic converter 9A for exhaust gas purification as the exhaust gas purifying catalyst the NO _x catalyst 9B three-way catalyst 19 the cooling water temperature sensor 23 an electronic control unit (ECU) 101 fuel injection control means 102 additional fuel injection determining means 103 NO _X adhesion amount estimation means 104 Additional fuel injection control means 105 Normal fuel injection control means 106 Timer 107 NO _X desorption means 108 Various sensors

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F01N 3/24 F01N 3/24 B 3/28 301 3/28 301C F02B 17/00 F02B 17/00 F F02D 41/02 301 F02D 41/02 301A

Claims (2)

[Claims] An exhaust purification system provided in an in-cylinder injection type internal combustion engine having a fuel injection valve for directly injecting fuel into a combustion chamber and injecting fuel from the fuel injection valve at least during a compression stroke to perform stratified combustion. in the device, provided in an exhaust passage of the internal combustion engine, an oxygen concentration excess atmosphere is deposited as nitrates NO _X in the nitrate is reacted with CO in the exhaust gas at an oxygen concentration reduction atmosphere to produce a carbonate the NO _X and the lean NO _X catalyst for elimination, the generate CO by reburning in the cylinder to inject additional fuel in addition to the main injection during the expansion stroke for the layered combustion lean N
O _X desorption of the NO _X attached to the catalyst and a NO _X desorption means to promote characterized in that it is configured exhaust gas purification apparatus for a cylinder injection type internal combustion engine. 2. A attached to the lean NO _X catalyst the lean N
It has a NO _X deposition amount estimating means for estimating a deposition amount of the NO _X reducing the adhesion ability of O _X catalyst, actuating the sulfur component desorption means in response to an output from the NO _X deposition amount estimating means The exhaust gas purifying apparatus for a direct injection internal combustion engine according to claim 1, characterized in that: