JP3351349B2 - Exhaust gas heating device for in-cylinder injection internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for raising the temperature of exhaust gas of a direct injection internal combustion engine.

[0002]

2. Related Art An in-cylinder injection type internal combustion engine is configured such that fuel can be directly injected into a cylinder not only in an intake stroke but also in a compression stroke, and thereby an air-fuel ratio is set to a stoichiometric air-fuel ratio (value of 14.7). ), The air-fuel ratio is controlled to a super lean air-fuel ratio not less than a target value (for example, value 24) on the super lean side, that is, the lean side.
It is possible to improve the fuel efficiency characteristics of the engine.

In the above-described engine, the air-fuel ratio becomes a lean air-fuel ratio.
There is a problem that Ox (nitrogen oxide) cannot be sufficiently purified, and recently, a NOx catalyst capable of purifying NOx even in an oxygen-excess atmosphere has been developed and put into practical use. By the way, in a cylinder injection type internal combustion engine equipped with a NOx catalyst, as in the case of the conventional internal combustion engine, it is desired that the temperature of the exhaust gas be raised at the early stage at the time of cold start, the catalyst be activated early, and the exhaust gas characteristics be improved. There is a request.

[0004] The NOx catalyst is roughly classified into a selective reduction type NOx catalyst for selectively reducing NOx in exhaust gas in an oxygen-excess atmosphere, and a NOx catalyst for storing NOx in exhaust gas in an oxygen-excess atmosphere and in an oxygen-low concentration atmosphere. NOx
There is an occlusion type NOx catalyst which reduces and releases the above from the catalyst. When the occlusion type NOx catalyst is used, the S component (sulfur component) contained in the fuel reacts with oxygen to form SOx (sulfur oxide), The SOx is stored in the storage NOx catalyst instead of the NOx, and there is a problem that the catalyst carrier is poisoned by the SOx and the purification efficiency of the catalyst is reduced. However, it is known that the SOx thus occluded is removed (SOx purge) by setting the exhaust air-fuel ratio to a rich state and setting the temperature of the catalyst to a high temperature. There is a request to make.

[0005] Therefore, in a direct injection internal combustion engine, for example, by performing a sub-injection into the cylinder separately from the main injection of the main combustion (compression stroke injection) during the expansion stroke, that is, by performing a two-stage injection. The technology for raising the temperature of exhaust gas is disclosed in
It is disclosed in JP-A-2012015.

[0006]

When two-stage injection is performed in such a direct injection type internal combustion engine, the temperature rise of the catalyst is determined by the fuel amount of the sub-injection. In other words, the catalyst temperature rises rapidly and reaches a high temperature when the fuel amount of the sub-injection is large, but does not rise so much when the fuel amount of the sub-injection is small. Therefore, when raising the temperature of the catalyst from a state where the load and rotation speed of the engine are low, that is, a state where the catalyst temperature is low, it is necessary to increase the fuel amount of the sub injection as much as possible.
On the other hand, when the catalyst temperature is raised from a state where the load and rotation speed of the engine are high, that is, a state where the catalyst temperature is high to some extent, it is not necessary to increase the fuel amount of the sub-injection so much. As a result, the temperature may exceed the heat resistant temperature of the catalyst.

Therefore, for example, it has been considered to variably set the fuel amount of the sub-injection to an appropriate amount in accordance with the load and the rotational speed of the engine. In the case of increasing the fuel amount of the injection, the fuel amount of the main injection is reduced to increase the air-fuel ratio of the main injection (lean), while the sub-injection is performed while keeping the overall air-fuel ratio at a predetermined air-fuel ratio. When the fuel amount of the main injection is reduced, the fuel amount of the main injection is increased so that the air-fuel ratio by the main injection is reduced (enriched).

However, when the fuel amount of the main injection is increased or decreased in this way, when the main injection is performed in the compression stroke, there is a limit to the enrichment. For example, if the air-fuel ratio becomes smaller than 24, combustion becomes unstable. On the other hand, when the main injection is the intake stroke injection, there is a limit to leaning,
For example, when the air-fuel ratio is larger than the value 22, combustion becomes unstable.

The present invention has been made in order to solve such a problem, and an object of the present invention is to provide an in-cylinder in which the temperature of a catalyst can be efficiently raised without causing combustion instability. An object of the present invention is to provide an exhaust gas heating device for an injection type internal combustion engine.

[0010]

In order to achieve the above object, according to the first aspect of the present invention, a system for controlling exhaust gas temperature rise is provided.
With injecting a portion of the amount of fuel corresponding to the constant by the target air-fuel ratio as a main injection in the intake stroke, the first second stage injection means for injecting the auxiliary injection and the remainder in the expansion stroke, the set target In addition to injecting part of the amount of fuel corresponding to the air-fuel ratio as the main injection in the compression stroke,
The second 2 which injects the remainder as an auxiliary injection in the expansion stroke
When the temperature of the exhaust gas needs to be raised, the injection means selection means selects the first two-stage injection means and the second two-stage injection means according to the load or rotational speed state information from the operating state detection means. Either of the injection means is selected.

According to a preferred embodiment, when the load and rotation speed of the engine are relatively high and the exhaust temperature is somewhat high, the first two-stage injection means is selected and used for controlling the exhaust gas temperature rise.
Under the set target air-fuel ratio, the main injection is performed in the intake stroke and the sub-injection is performed in the expansion stroke, and the combustion by the main injection is in the range of the air-fuel ratio equal to or less than the upper limit (for example, value 22) of achieving combustion. In the exhaust passage, the fuel is satisfactorily burned and heat is generated in the exhaust passage in the presence of excess oxygen, and the exhaust gas is efficiently and suitably brought to a desired temperature. The temperature is raised.

In this case, when the load and rotation speed of the engine are low and the exhaust gas temperature is low, the second two-stage injection means is selected and the main injection is performed in the compression stroke under the target air-fuel ratio. The sub-injection is performed in the expansion stroke. That is,
In the compression stroke injection, combustion at a super-lean air-fuel ratio (up to a value of about 50) is possible, and while the fuel amount of the main injection is made extremely small, the fuel amount of the sub-injection can be increased accordingly.
In the case where the fuel amount of the main injection is extremely small as described above, the combustion by the main injection is the lower limit value of the establishment of the combustion (for example,
In the range of the super lean air-fuel ratio not less than the value 24), the combustion is also performed favorably without instability of the combustion. On the other hand, a large amount of fuel due to the sub-injection is satisfactorily burned in the exhaust passage in the presence of excess oxygen to generate high heat. As a result, the temperature of the exhaust gas is efficiently and quickly raised to a desired temperature.

Further, according to the invention of claim 2, further,
An exhaust gas temperature detecting means for detecting an exhaust gas temperature;
The two-stage injection means and the second two-stage injection means
Keep exhaust temperature constant based on detection information from temperature detection means
To maintain the ratio between the main injection fuel amount and the sub injection fuel amount
Temperature feedback to change and increase or decrease the fuel amount of sub-injection
Characterized by comprising a lock control means. this
As a result, the in-cylinder injection type internal combustion engine
When performing SOx removal, the SOx removal
During the operation, the temperature of the storage NOx catalyst is
It can be maintained at a constant high temperature, and SOx is sufficiently removed
Prevents overheating of the storage NOx catalyst, three-way catalyst, etc.
Is done. Further, according to the invention of claim 3, the first 2
The stage-injection means is configured to determine whether the air-fuel ratio of the main combustion
The main injection during the intake stroke within the range of not more than the air-fuel ratio and
Performing the sub-injection in the expansion stroke;
The stage-injection unit is configured to perform the second combustion when the air-fuel ratio of the main combustion is satisfied.
Main injection in the compression stroke within the range of air-fuel ratio or more
And a sub-injection in the expansion stroke.
When the temperature of the exhaust gas needs to be raised, the air-fuel ratio of the main combustion is reduced to the first air-fuel ratio.
When the value is between the fuel ratio and the second air-fuel ratio,
Injects all fuel in the amount corresponding to the target air-fuel ratio as main injection
Ignition timing retarding means to retard ignition timing
It is characterized by comprising. That is, the lower limit of the air-fuel ratio at which combustion is established when fuel is injected in the compression stroke ( the
2 and an upper limit of the air-fuel ratio ( first air-fuel ratio) at which combustion is achieved when fuel is injected in the intake stroke.
Ratio, for example, a value 22), there is a discontinuous region of the air-fuel ratio, and in fact, a request for operation in such a discontinuous region is made in accordance with the engine load and the rotation speed information. 1 of 2
In some cases, neither the two-stage injection unit nor the second two-stage injection unit can be selected.
Instead of performing step injection, the ignition timing is retarded (retarded) . Note that this case, the air-fuel ratio to the lower limit value of the main injection (e.g., the value 24) above the upper limit air-fuel ratio of the or main injection performing main injection fixed to the compression stroke (for example,
The two-stage injection may be performed by fixing the value 22) and performing the main injection in the intake stroke. Further, when the load or rotation speed of the engine becomes considerably high, there are cases where it is difficult to perform two-stage injection due to restrictions of an injector driver or the like. It is better to respond with retard. Thus, regardless of the operating state of the engine, the exhaust gas temperature can be always efficiently, appropriately, and reliably increased without making combustion unstable.

[0014]

Further, when the ratio between the fuel amount of the main injection and the fuel amount of the sub-injection is changed for the temperature feedback control as in the second aspect , the air-fuel ratio of the main injection changes and the non-fuel ratio is changed. In some cases, a continuous region may be reached. In such a case, the ignition timing may be retarded without performing the two-stage injection as described above. Further, when the air-fuel ratio of the main injection changes across the discontinuous region, it is preferable to switch the injection means between the first two-stage injection means and the second two-stage injection means. Thus, the exhaust gas temperature is more stably maintained, and when the in-cylinder injection type internal combustion engine has a storage type NOx catalyst, the temperature of the storage type NOx catalyst is more appropriately maintained at a predetermined high temperature. Is done.

[0016]

Embodiments of the present invention will be described below with reference to the accompanying drawings. First, a first embodiment will be described. Referring to FIG. 1, there is shown a schematic configuration diagram of an exhaust gas heating device for a direct injection internal combustion engine according to the present invention mounted on a vehicle, and based on the drawing, an exhaust gas heating device according to the present invention will be described below. Will be described.

Engine body (hereinafter simply referred to as engine) 1
For example, in-cylinder injection spark ignition capable of performing fuel injection in an intake stroke (intake stroke injection mode) or fuel injection in a compression stroke (compression stroke injection mode) by switching a fuel injection mode (operation mode), for example. It is an inline 4-cylinder gasoline engine. The in-cylinder injection type engine 1 can be easily operated at a stoichiometric air-fuel ratio (stoichiometric ratio), at a rich air-fuel ratio (rich air-fuel ratio operation), or at a lean air-fuel ratio (lean air-fuel ratio). In particular, in the compression stroke injection mode, it is possible to operate at a super lean air-fuel ratio.

As shown in FIG. 1, the cylinder head 2 of the engine 1 is provided with an electromagnetic fuel injection valve 6 together with a spark plug 4 for each cylinder, whereby fuel is injected into the combustion chamber 8. Direct injection is possible. A fuel supply device (both not shown) having a fuel tank is connected to the fuel injection valve 6 via a fuel pipe. More specifically, the fuel supply device is provided with a low-pressure fuel pump and a high-pressure fuel pump, whereby the fuel in the fuel tank is supplied to the fuel injection valve 6 at a low fuel pressure or a high fuel pressure. From the fuel injection valve 6 into the combustion chamber at a desired fuel pressure. At this time, the fuel injection amount depends on the fuel discharge pressure of the high-pressure fuel pump and the valve opening time of the fuel injection valve 6,
That is, it is determined from the fuel injection time.

An intake port is formed in the cylinder head 2 in a substantially upright direction for each cylinder, and one end of an intake manifold 10 is connected to communicate with each intake port. A throttle valve 11 is connected to the other end of the intake manifold 10. The throttle valve 11 is provided with a throttle sensor 11a for detecting a throttle opening θth.

An exhaust port is formed in the cylinder head 2 in a substantially horizontal direction for each cylinder, and one end of an exhaust manifold 12 is connected to communicate with each exhaust port. Reference numeral 13 in the figure denotes a crank angle sensor for detecting a crank angle, and the crank angle sensor 13 is capable of detecting an engine rotation speed Ne.

The in-cylinder injection type engine 1 is already known, and a detailed description of its configuration is omitted here. As shown in FIG. 1, an exhaust pipe (exhaust passage) 14 is connected to the exhaust manifold 12, and a small close three-way catalyst 20 and an exhaust purification catalyst device 30 close to the engine 1 are connected to the exhaust pipe 14. A muffler (not shown) is connected via the terminal. The exhaust pipe 14 is provided with a high temperature sensor 16 for detecting the exhaust gas temperature.

The exhaust purification catalyst device 30 is provided with two catalysts, that is, a storage NOx catalyst 30a and a three-way catalyst 30b, and the three-way catalyst 30b uses the storage NOx catalyst 3b.
0a is disposed downstream. The storage NOx catalyst 30a temporarily stores NOx in an oxidizing atmosphere,
It has a function of reducing NOx to N ₂ (nitrogen) or the like mainly in a reducing atmosphere where CO is present. More specifically, the storage NOx catalyst 30a is configured as a catalyst having platinum (Pt), rhodium (Rh), or the like as a noble metal, and an alkali metal such as barium (Ba) or an alkaline earth metal as a storage material. Has been adopted.

A NOx sensor 32 for detecting the NOx concentration is provided between the storage type NOx catalyst 30a and the three-way catalyst 30b.
Is provided. Further, an input / output device, a storage device (R
OM, RAM, nonvolatile RAM, etc.), central processing unit (C
PU), an ECU (electronic control unit) 40 including a timer counter and the like.
With 0, comprehensive control of the exhaust gas heating apparatus according to the present invention including the engine 1 is performed. Various sensors such as the high-temperature sensor 16 and the NOx sensor 32 described above are connected to the input side of the ECU 40, and detection information from these sensors is input.

On the other hand, the output side of the ECU 40 is connected to the above-described ignition plug 4 and the fuel injection valve 6 via an ignition coil. The ignition coil, the fuel injection valve 6 and the like are connected to various sensors. The optimum values such as the fuel injection amount and the ignition timing calculated based on the detection information are output.
As a result, an appropriate amount of fuel is injected from the fuel injection valve 6 at an appropriate timing, and ignition is performed by the spark plug 4 at an appropriate timing.

Actually, the ECU 40 determines the target in-cylinder pressure corresponding to the engine load, that is, the target average effective pressure, based on the throttle opening information θth from the throttle sensor 11a and the engine rotation speed information Ne from the crank angle sensor 13. Pe is obtained (operating state detecting means), and the fuel injection mode is set from a map (not shown) according to the target average effective pressure Pe and the engine speed information Ne. I have. For example, when the target average effective pressure Pe and the engine rotation speed Ne are both low, the fuel injection mode is the compression stroke injection mode, and fuel is injected in the compression stroke, while the target average effective pressure Pe increases or the engine rotation speed increases. When the speed Ne increases, the fuel injection mode is set to the intake stroke injection mode, and fuel is injected during the intake stroke.

From the target average effective pressure Pe and the engine speed Ne, a target air-fuel ratio (target A / A
F) is set, and the appropriate amount of fuel injection is set to the target A /
It is determined based on F (target air-fuel ratio setting means). The catalyst temperature Tcat is estimated from the exhaust gas temperature information detected by the high temperature sensor 16. Specifically, the high temperature sensor 16
In order to correct an error that occurs due to the inability to directly install the NOx catalyst 30a in the storage NOx catalyst 30a, a temperature difference map (not shown) is obtained in advance by an experiment or the like in accordance with the target average effective pressure Pe and the engine rotation speed information Ne. ) Is set, so that the catalyst temperature Tcat is uniquely estimated when the target average effective pressure Pe and the engine rotation speed information Ne are determined.

Hereinafter, the operation of the thus configured exhaust gas heating apparatus according to the present invention will be described. Here, a control procedure of the exhaust gas temperature raising control used when the SOx stored in the storage NOx catalyst 30a is desorbed from the catalyst will be described. Referring to FIG. 2, there is shown a flowchart of a control routine for performing the exhaust gas temperature raising control, which will be described below with reference to the flowchart.

First, at step S10, it is determined whether or not the NOx catalyst has deteriorated by S (sulfur), that is, whether or not the amount of SOx stored in the storage type NOx catalyst 30a (poisoned S amount Qs) has reached a predetermined amount. Is determined. Here, the poisoning S amount Qs is a value obtained by estimation. Hereinafter, a method of estimating the poisoning S amount Qs will be described. The poisoning S amount Qs is basically set based on the fuel injection integrated amount Qf, and is calculated by the following equation for each execution cycle of the fuel injection control routine.

Qs = Qs (n−1) + ΔQf · K−Rs (1) where Qs (n−1) is the previous value of the poisoning S amount, and ΔQf is the integrated fuel injection amount per execution cycle. , K is a correction coefficient, Rs
Indicates the reproduction S amount per execution cycle. That is, the current poisoning S amount Qs is obtained by correcting the fuel injection integrated amount ΔQf per execution cycle with the correction coefficient K and integrating the same, and subtracting the regeneration S amount Rs per execution cycle from the integrated value. Can be

As shown in the following equation (2), the correction coefficient K is an S poisoning coefficient K1 corresponding to the air-fuel ratio A / F, an S poisoning coefficient K2 corresponding to the S content in the fuel, and a catalyst. It consists of the product of three correction coefficients of the S poisoning coefficient K3 according to the temperature Tcat. K = K1, K2, K3 (2) As shown in FIG. 3, the S poisoning coefficient K1 corresponding to the air-fuel ratio A / F is set to a small value for the rich air-fuel ratio based on the experimental data, (For example, 1/4 at the rich air-fuel ratio and 2/3 at the stoichiometric ratio with respect to the lean air-fuel ratio). That is, engine 1
Is operating at a rich air-fuel ratio, it is considered that SOx is hardly stored in the storage NOx catalyst 30a. On the other hand, when the engine 1 is operating at a lean air-fuel ratio, it is substantially constant according to the fuel amount. It is considered that the amount of SOx is stored in the storage type NOx catalyst 30a.

Further, the S poisoning coefficient K2 according to the S content
As shown by a solid line in FIG. 4, based on experimental data, the larger the S content in the fuel, the larger the value (for example, a proportional relationship). That is, since the amount of SOx generated depends on the S component contained in the fuel, the correction is performed according to the content of the S component. By the way, since it is actually impossible to measure the S content every fuel replenishment, the knocking generated at the time of combustion is detected by a knock sensor (not shown) instead, and is currently used. Estimate the S content in the fuel. This is based on the fact that a low-octane-number low-quality fuel generally has a high S content, and a high-octane-number high-quality fuel has a low S content. That is, for example, in a combustion state in which knocking is likely to occur due to information from the knock sensor, that is, when the ignition timing cannot be advanced so much due to knocking (when the ignition timing advance correction value is small), the octane number is low. When it can be determined that the content is large, and when knocking is unlikely to occur, that is, when the ignition timing can be advanced a lot (when the ignition timing advance correction value is large), it can be determined that the S content is small with a high octane number. It is.

In Japan, two types of fuels, such as regular gasoline and premium gasoline, whose quality is kept constant, are sold. In such a case, these are indicated by broken lines in FIG. As described above, the S content is divided into two steps in a stepwise manner. That is, it is determined that the quality is high and the S content is very small in the case of premium gasoline, and the S poisoning coefficient K2 is set to a value close to 0, and is set to a large value in the case of regular gasoline.

Further, the S poisoning coefficient K3 according to the catalyst temperature
As shown in FIG. 5, is set to a large value when the catalyst temperature Tcat is a medium temperature (for example, about 300 to 500 ° C.) based on experimental data. That is,
When the catalyst temperature Tcat is low, the degree of activity is low, and when the catalyst temperature Tcat is high, the SOx is in a purging direction. Therefore, it is determined that the amount of SOx stored in the storage NOx catalyst 30a is relatively small.

Thus, the amount of poisoning S per execution cycle Δ
Qs will be more accurately estimated. The reproduction S amount Rs per execution cycle is calculated from the following equation (3). Rs = α · R1 · R2 · dT (3) where α is a regeneration rate (set value) per unit time, dT indicates an execution cycle of the fuel injection control routine, and R1 and R2 are respectively A regeneration capacity coefficient according to the catalyst temperature Tcat and a regeneration capacity coefficient according to the air-fuel ratio A / F are shown.

The regeneration capacity coefficient R1 according to the catalyst temperature Tcat
As shown in FIG. 6, based on the experimental data, is set to increase exponentially as the catalyst temperature Tcat increases. That is, SOx tends to be exponentially and rapidly removed from the storage NOx catalyst 30a as the catalyst temperature Tcat increases, and therefore the regeneration capacity coefficient R1
Is to be increased accordingly.

Regeneration capacity coefficient R2 according to air-fuel ratio A / F
Is based on the experimental data, as shown in FIG.
/ F is substantially constant at a rich air-fuel ratio, and decreases as the air-fuel ratio becomes super lean. That is, as described above, SOx is favorably removed in a reducing atmosphere having a rich air-fuel ratio, whereas when the air-fuel ratio becomes a lean air-fuel ratio, it is occluded by the occlusion type NOx catalyst 30a. The performance coefficient R2 is set accordingly.

That is, SOx is reduced and removed when the catalyst temperature Tcat is heated to a high temperature and the air-fuel ratio A / F becomes a rich air-fuel ratio. Based on these FIGS. 6 and 7, the catalyst temperature Tcat, By obtaining the regeneration capacity coefficients R1 and R2 corresponding to the air-fuel ratio A / F, it is possible to properly calculate the regeneration S amount Rs per execution cycle.
The quantity Qs can be determined more accurately.

If the result of the determination in step S10 is false (No), and if it is determined that the poisoning S amount Qs obtained as described above has not yet reached the predetermined amount, no action is taken in this routine. Through. On the other hand, when the determination result of step S10 is true (Yes) and it is determined that the poisoning S amount Qs has reached the predetermined amount, the process proceeds to step S12, and the control mode is switched to the S purge mode. This removes the SOx stored in the storage NOx catalyst 30a, that is, removes SOx.
Purge is started.

When the S purge is started, step S14
In, it is determined whether or not the target average effective pressure Pe is smaller than a predetermined value Pe1 (a map for the engine rotation speed Ne). Specifically, based on the main injection mode selection map shown in FIG. 8, whether or not the target average effective pressure Pe is within the range of the region A smaller than the region C ′ (hatched portion) in relation to the engine rotation speed Ne. Is determined.

The result of the determination in step S14 is true (Yes).
If the target average effective pressure Pe is smaller than a predetermined value Pe1 (a map for the engine rotation speed Ne), that is, if the engine load and the engine rotation speed are small such as when idling or running at low speed, the next step Proceed to S16 (injection means selection means). In step S16, the fuel injection mode of the main injection is set to the compression stroke injection mode irrespective of the normal setting described above, and the sub-injection is performed in the expansion stroke (particularly, in the middle stage of the expansion stroke or later). That is, as described above, when performing the S purge, 2
Step injection is performed so that the fuel supplied into the combustion chamber 8 by the sub-injection burns in the combustion chamber 8 or the exhaust pipe 14,
As a result, the temperature of the exhaust gas rises, and the NOx storage catalyst 30a is heated to a high temperature. Target average effective pressure P
e, when the engine rotation speed Ne is in the region A in FIG. 8, two-stage injection is performed by compression stroke injection and expansion stroke injection (second two-stage injection means).

The target A / F, that is, the total target A / F including the main injection and the sub-injection, that is, the total A / F
F is forcibly set to a predetermined rich air-fuel ratio (for example, value 12), and the target air-fuel ratio of the main injection is determined according to the target average effective pressure Pe and the engine speed Ne based on the main injection mode selection map of FIG. (Main A / F) is determined. Here, the entire A / F is set to the predetermined rich air-fuel ratio (for example,
The main A / F is set while keeping the value 12). As a result, the fuel injection ratio of the main injection amount (part) and the sub injection amount (remainder) is properly determined while the overall fuel injection amount is kept constant and the reducing atmosphere is well formed. Is done.

Normally, the smaller the target average effective pressure Pe or the engine rotation speed Ne, the more the storage NOx catalyst 30a
, Ie, the catalyst temperature Tcat can be regarded as low. Therefore, as shown in FIG. 8, the value of the main A / F is set to be larger as the engine load and the engine rotation speed are smaller, and to be the air-fuel ratio on the super lean air-fuel ratio side (for example, the upper limit value 50 side). That is, the lower the catalyst temperature Tcat, the smaller the main injection amount and the larger the sub injection amount.

As a result, when the engine load and the engine speed are low, a large amount of fuel is discharged into the exhaust pipe 14, and the excess N is stored in the exhaust pipe 14 or the storage type N in the presence of excess oxygen.
As a result, the NOx storage catalyst 30a is rapidly heated to a predetermined high temperature Tcat1 (for example, 650 ° C.) at which the S-purging can be performed even if the catalyst temperature Tcat is low. Become. Therefore, even when the engine load and the engine rotational speed are small and the storage type NOx catalyst 30a is in a low temperature state, for example, during low-speed running, the air-fuel ratio of the main injection is set to the super lean air-fuel ratio (for example, the upper limit value). 50, the sub-injection amount contributing to the temperature rise of the exhaust gas can be extremely increased without affecting the operation of the engine 1.
a can be rapidly heated to the predetermined high temperature Tcat1 that can be S purged.

In the next step S18, feedback control (catalyst temperature F / B control) is performed in accordance with the catalyst temperature Tcat while maintaining the overall A / F at a predetermined rich air-fuel ratio (for example, a value of 12). . Here, first, it is determined whether or not a predetermined time t1 (for example, 2 minutes) has elapsed since the start of the S purge by the execution of step S12 and the catalyst temperature Tcat has reached a predetermined high temperature Tcat1 (for example, 650 ° C.). Is determined. Then, if the determination result is true (Yes), the predetermined time t1 has elapsed, and the catalyst temperature Tcat is equal to the predetermined high temperature T.
When it is determined that the temperature has reached cat1, the main A / F set based on the main injection mode selection map of FIG. 8 is corrected in accordance with the temperature deviation integration ΣΔTcat of the catalyst temperature Tcat.

More specifically, the temperature deviation integration ΣΔTcat is given by the following equation.
It is calculated from (4). ΣΔTcat = ΣΔTcat (n−1) + ΔTcat (4) where ΔTcat is a temperature deviation, and the ΔTcat is the predetermined high temperature Tcat1 (for example, 650 ° C.) and the high temperature sensor 16.
Is calculated from the following equation (5) based on the current catalyst temperature Tcat estimated based on

ΔTcat = Tcat1−Tcat (5) Actually, the temperature deviation integration ΣΔTcat and the correction value of the main A / F are mapped in advance as shown in Table 1 by experiments or the like. Is corrected based on the correction value map of the main A / F (integral correction).

[0047]

[Table 1]

Here, of the correction values of the main A / F, a plus sign (+) indicates a correction to the lean side, and a minus sign (-) indicates a correction to the rich side. That is, if the storage NOx catalyst 30a is heated by overshoot exceeding a predetermined high temperature Tcat1 (for example, 650 ° C.), the temperature deviation integrated ΣΔTcat becomes a negative value, and in this case, the main A / F Is corrected to the negative side, that is, the rich side, that is, the fuel amount of the sub-injection is reduced and returned to the predetermined high temperature Tcat1. Thereafter, when the undershoot occurs and the temperature deviation integration ΣΔTcat becomes a positive value, the main A / F is corrected to the positive side, that is, the lean side, that is, the fuel amount of the sub injection is increased and the catalyst temperature Tcat is increased. Is again raised to a predetermined high temperature Tcat1.

When the main A / F is corrected in this way, the catalyst temperature Tcat stabilizes at a predetermined high temperature Tcat1 (for example, 650 ° C.).
a is maintained at the predetermined high temperature Tcat1. When the catalyst temperature Tcat is stabilized in this way, thereafter, it is only necessary to perform a temperature increase control for maintaining the predetermined high temperature Tcat1. In other words, the main injection amount is increased by setting the main A / F to a small value, while the auxiliary injection amount is reduced.

However, when performing fuel injection in the compression stroke injection mode, there is a restriction on the air-fuel ratio at which combustion is established, and the lower limit is set to, for example, the value 24. That is, even if the main A / F is reduced as described above, the main A / F cannot be less than the lower limit 24 in the compression stroke injection mode. So, like this, the main A /
When F reaches the lower limit 24 and the target average effective pressure Pe and the engine rotation speed Ne reach the region C ′ (hatched portion) in FIG. 8, the entire A / F is reduced to a predetermined rich air-fuel ratio (for example, the value 12). ), Only the main injection is performed in the intake stroke without performing the two-stage injection, and the temperature rise control is performed by correcting the ignition timing. That is, generally, even if the ignition timing is retarded to delay the combustion, the exhaust gas temperature can be raised. Therefore, the main A / F becomes the lower limit value 24, and when the temperature increase needs to be adjusted, the ignition timing is corrected. It is intended to complement the temperature rise control.

The ignition timing correction amount is set in accordance with the above-described temperature deviation integration ΣΔTcat. Actually, the temperature deviation integration ΣΔTcat and the ignition timing correction amount are mapped in advance as shown in Table 2 by experiments or the like, and the ignition timing is corrected based on the ignition timing correction amount map (integration correction). . Note that during normal combustion control, the reference ignition timing is basically set to the advanced side as much as possible so as to generate the most torque. It is necessary to correct the timing to the advance side. Therefore, in this control, the reference ignition timing is set to a neutral position between the advance and the retard in order to leave a correction margin on the advance side.

[0052]

[Table 2]

Here, in the ignition timing correction amount, a positive sign (+) indicates correction to the advance side, and a negative sign (-) indicates correction to the retard side. That is, as described above, when the storage NOx catalyst 30a is heated by overshoot exceeding a predetermined high temperature Tcat1 (for example, 650 ° C.), the temperature deviation integration ΣΔTcat becomes a negative value,
In this case, the ignition timing correction amount is corrected to the positive side, that is, the advance side, and the temperature raising effect is reduced. Thereafter, when the undershoot occurs and the temperature deviation integration ΣΔTcat becomes a positive value, the ignition timing correction amount is corrected to the negative side, that is, the retard side, the temperature increasing effect is enhanced, and the catalyst temperature Tcat is again set to the predetermined value. Is raised to the high temperature Tcat1.

The correction based on the ignition timing is determined by the main A /
It can also be used when F reaches the upper limit (for example, value 50) at which combustion is established. On the other hand, the determination result of step S14 in FIG. 2 is false (No), and the target average effective pressure Pe
Is the predetermined value Pe1 (map for the engine speed Ne)
If the engine load and the engine rotation speed are medium as in the case of the middle speed running, the process proceeds to step S20.
(Injection means selection means).

In step S20, the fuel injection mode of the main injection is set to the intake stroke injection mode irrespective of the normal setting described above, and the sub-injection is performed in the expansion stroke (particularly, in the middle stage or later of the expansion stroke). . That is, when the target average effective pressure Pe and the engine rotation speed Ne are in the region B in FIG. 8, two-stage injection is performed by the intake stroke injection and the expansion stroke injection (first two-stage injection means).

That is, when the vehicle is running at a medium speed and the engine load and the engine speed are medium, the storage type N
It can be considered that the Ox catalyst 30a is heated to some extent. In such a case, a predetermined high temperature Tcat1 (for example, a predetermined high temperature Tcat1 capable of sufficiently purging the storage NOx catalyst 30a with S without increasing the sub injection amount so much) 650 ° C.), and in such a case,
The main injection is performed in the intake stroke in which the main A / F can be reduced.

Then, similarly to the above, the entire A / F is forcibly set to a predetermined rich air-fuel ratio (for example, a value of 12), and the target average effective pressure Pe and the engine speed are determined based on the main injection mode selection map of FIG. Main A / F according to speed Ne
To determine. As a result, the fuel injection ratios of the main injection amount (part) and the sub injection amount (remaining) are properly adjusted while the overall fuel injection amount is maintained constant and the reducing atmosphere is well formed. A predetermined high temperature Tcat at which the storage-type NOx catalyst 30a can be purged with S when the vehicle is running at medium speed.
Heat quickly to 1 (eg, 650 ° C.).

Then, in the next step S22, similarly to step S18, the catalyst temperature Tca is maintained while the overall A / F is maintained at a predetermined rich air-fuel ratio (for example, a value of 12).
Feedback control according to t (catalyst temperature F / B control)
I do. Since the details of the control are as described above, the description is omitted here. However, even when the fuel injection is performed in the intake stroke injection mode, the air-fuel ratio at which combustion is established is restricted, and the upper limit is, for example, The value is set to 22. That is, when the main A / F is increased, the main A / F cannot be made larger than the upper limit value 22 in the intake stroke injection mode.

Therefore, when the main A / F reaches the upper limit value 22 and the target average effective pressure Pe and the engine rotation speed Ne reach the region C '(shaded area) in FIG.
While maintaining the overall A / F at a predetermined rich air-fuel ratio (for example, value 12), only the main injection is performed in the intake stroke without performing the two-stage injection, and the temperature increase control is performed by correcting the ignition timing. I do. The ignition timing correction is as described above, but this ignition timing correction is performed by the main A / F.
Can also be used when reaches the lower limit (for example, value 12).

The vehicle is running at high speed, the engine speed Ne and the target average effective pressure Pe are large, the engine load is high, the main A / F is smaller than the lower limit value 16, and the stoichiometric air-fuel ratio (stoichiometric) ), The target average effective pressure Pe, the engine speed Ne
Is in the region C in FIG. 8, it is difficult to perform the two-stage injection due to the restriction of the injector driver and the like, but the combustion heat is large, the exhaust temperature is sufficiently high, and the ignition timing correction is less than the two-stage injection. However, the storage NOx catalyst 30a
It can be determined that heating to a predetermined high temperature Tcat1 (for example, 650 ° C.) that can be purged is possible. Therefore, in this case, only the main injection is performed in the intake stroke without performing the two-stage injection, and the temperature rise control is performed by correcting the ignition timing.
Note that, also in this case, the overall A / F is set to a predetermined rich air-fuel ratio (for example, a value of 12).

In the case where the engine speed Ne and the target average effective pressure Pe are extremely large and the main A / F has a rich air-fuel ratio, that is, the target average effective pressure Pe and the engine rotation speed Ne in FIG. When it is in the D region, it can be determined that the combustion heat is extremely large and the exhaust gas temperature is high enough to perform the S purge without performing the temperature increase control. In this case,
The exhaust gas temperature rise control itself is not performed.

At the start of the control, the target average effective pressure Pe,
In some cases, the engine speed Ne is in the region C ′ (hatched portion) in FIG. 8 and the main A / F is set between the values 22 and 24. Is set to a predetermined rich air-fuel ratio (for example, value 12), only the main injection is performed in the intake stroke without performing the two-stage injection, and the temperature increase control is performed by the ignition timing correction as described above.

As a result, the storage NOx catalyst 30a is sufficiently heated to a predetermined high temperature Tcat1 (for example, 650 ° C.) and is stably maintained at the predetermined high temperature Tcat1, so that the S purge is always performed satisfactorily. Will be. FIG.
In step S24, it is determined whether a predetermined time t2 has elapsed since the start of the S purge mode. The predetermined time t2 is a time preset by experiments or the like as a time during which SOx can be sufficiently removed when the storage NOx catalyst 30a is maintained at a predetermined high temperature Tcat1 in a reducing atmosphere.

The determination result of step S24 is false (No)
If it is determined that the predetermined time t2 has not yet elapsed, the process returns to step S12 to continue the temperature increase control in the S purge mode. On the other hand, if the determination result of step S24 is true (Yes) and it is determined that the predetermined time t2 has elapsed, it is assumed that SOx has been sufficiently removed, and the routine exits to terminate the exhaust gas temperature raising control.

As described above, in the exhaust gas temperature raising apparatus for a direct injection internal combustion engine according to the present invention, the storage NOx catalyst 3
When the amount of SOx occluded at 0a, that is, the poisoning S amount Qs reaches a predetermined amount, the entire A / F is set to a predetermined rich air-fuel ratio (for example, a value of 12) and the main injection and the sub injection are performed. Two-stage injection is performed, and it is determined whether the injection timing of the main injection is to be the compression stroke or the intake stroke in accordance with the target average effective pressure Pe and the engine rotation speed Ne at that time. . That is, when the target average effective pressure Pe is small and the engine rotational speed Ne is small, the main injection is performed in the compression stroke to increase the target A / F of the main injection, that is, the main A / F as much as possible to increase the sub injection amount. When the engine load and the engine rotation speed are moderate, the main injection is performed in the intake stroke so that the main A / F is relatively small and the sub injection amount is reduced to perform the exhaust gas temperature increase control.

In the case where the main injection is performed in the compression stroke, for example, the value 24 is set as the lower limit of the main A / F when the main injection is performed in the compression stroke. The upper limit of F is set according to the target average effective pressure Pe, the engine speed Ne, or the catalyst temperature F.
This discontinuous area (range of value 22 to value 24) during / B control
Is selected as the main A / F,
The overall A / F is maintained at a predetermined rich air-fuel ratio (for example, a value of 12), and the ignition timing is corrected to complement the exhaust gas temperature rise control.

Therefore, even when the storage type NOx catalyst 30a is in a low temperature state, such as immediately after the engine is started or when the engine load and the engine speed are low and the engine speed is low, the storage type NOx catalyst is high in the engine load and engine speed. 3
0a is relatively heated even if it is relatively heated.
By performing the stage injection, the exhaust gas temperature can always be increased sufficiently and sufficiently with less deterioration of fuel efficiency, and a predetermined high temperature Tcat1 (for example,
650 ° C.).

Next, a second embodiment will be described. In the second embodiment, the configuration of the device is the same as that of the first embodiment, and the discontinuous region in the exhaust gas temperature raising control, that is, the complement of the C ′ region (hatched portion) of the main injection mode selection map in FIG. 8 is complemented. Only the method is different. Therefore, only the portions different from the first embodiment will be described here.

Referring to FIG. 9, there is shown a main injection mode selection map according to the second embodiment, which will be described below with reference to FIG. It should be noted that the region C "in the figure corresponds to the region C '. In the second embodiment, the target average effective pressure Pe and the engine rotational speed Ne are in the region C" at the start of control or due to a change in the operating state. In this case, the fuel injection mode selected at that time is selected as it is, and the temperature increase control is performed. In other words, when the compression stroke injection mode is selected in the normal setting, or when the engine shifts from the area A to the area C "due to changes in the target average effective pressure Pe and the engine rotation speed Ne, the main injection is performed in the compression stroke. At the same time, the main A / F is set to the value 24 and the ignition timing is corrected. On the other hand, when the intake stroke injection mode is selected in the normal setting, or when the target average effective pressure P
e, when the engine speed Ne shifts due to a change in the engine rotation speed Ne, the main injection is performed in the intake stroke, and the main A / F is set to the value 22 to correct the ignition timing.

As a result, the storage NOx catalyst 30
a is quickly and sufficiently heated to a predetermined high temperature Tcat1 (for example, 650 ° C.) and the predetermined high temperature Tca1
It is stably held at t1, and the S purge is always satisfactorily performed. By the way, in the above embodiment (Examples 1 and 2), in the catalyst temperature F / B control, the main A / F
When the temperature reaches the lower limit value 24 or the upper limit value 22, the temperature increase control is continued by correcting the ignition timing. However, the fuel injection mode for performing the main injection is switched according to the change of the main A / F to perform the two-stage injection. May be continued.

That is, when the main injection is performed in the compression stroke and the temperature rise control is performed, the main injection is performed in the intake stroke when the main A / F falls below the lower limit 24 and further falls below the value 22. When the main injection is performed during the intake stroke and the temperature rise control is performed, the main injection is performed when the main A / F exceeds the upper limit value 22 and further exceeds the value 24. It may be switched to be performed in the compression stroke.

As a result, the two-stage injection with a high temperature raising effect with less deterioration of fuel efficiency is efficiently performed, and the temperature of the storage NOx catalyst 30a is further stabilized to a predetermined high temperature Tcat1 (for example, 650). C). Further, in the present embodiment, the injection means is operated based on the operating state including the engine load and the engine rotation speed by performing the intake stroke injection (main injection) and the expansion stroke injection (sub-injection) or the compression stroke injection (main injection) and the expansion stroke. Although the mode is switched to the injection (sub-injection), the injection means may be switched based on the engine load or the engine speed, that is, one of the target average effective pressure Pe and the engine speed Ne.

Further, in the present embodiment, the case where the exhaust gas temperature raising device according to the present invention is applied to the removal of SOx stored in the storage type NOx catalyst 30a has been described. Can be applied to the activation of the catalyst when the engine is started.

[0074]

As described above in detail, according to the exhaust gas heating apparatus for a direct injection internal combustion engine of the first aspect of the present invention,
A first two-stage injection means for injecting a part of fuel in an amount corresponding to the target air-fuel ratio set for the exhaust gas temperature rise control as a main injection in an intake stroke and injecting the remainder as a sub-injection in an expansion stroke; A second two-stage injection means for injecting a part of fuel in an amount corresponding to the set target air-fuel ratio as a main injection in a compression stroke and injecting a remainder as a sub-injection in an expansion stroke. When the temperature needs to be raised, the first two-stage injection means and the second
One of the stage injection means is selected.

Therefore, when the load and rotation speed of the engine are relatively high and the exhaust gas temperature is somewhat high, the first two-stage injection means is selected and the target air pressure set for the exhaust gas temperature rise control is selected.
Based on the fuel ratio, the main injection can be performed in the intake stroke and the sub-injection can be performed in the expansion stroke. Combustion by the main injection is performed within an air-fuel ratio range equal to or less than the upper limit of combustion establishment (eg, value 22). The fuel can be satisfactorily burned without destabilization, and the fuel by the sub-injection can be satisfactorily burned in the exhaust passage in the presence of excess oxygen to generate heat. Therefore, it is possible to efficiently and suitably raise the temperature of the exhaust gas to a desired temperature.

When the load and rotation speed of the engine are low and the exhaust gas temperature is low, the second two-stage injection means is selected to execute the main injection in the compression stroke under the target air-fuel ratio and the sub-injection. Can be performed in the expansion stroke. That is, in the compression stroke injection, combustion can be performed at a super lean air-fuel ratio (up to a value of about 50), and while the fuel amount of the main injection can be made extremely small, the fuel amount of the sub-injection can be increased accordingly. When the fuel amount of the main injection is extremely small,
Combustion by the main injection is defined as the lower limit of combustion establishment (for example, value 2
4) Within the above range of the super-lean air-fuel ratio, the combustion can be satisfactorily performed without destabilizing the combustion. On the other hand, a large amount of fuel due to the sub-injection is favorably burned in the exhaust passage in the presence of excess oxygen, thereby achieving high heat. Can be emitted. Therefore, it is possible to efficiently and quickly raise the temperature of the exhaust gas to a desired temperature.

Thus, when the in-cylinder injection type internal combustion engine is equipped with the above-mentioned storage NOx catalyst, when the load and rotation speed of the engine are high and the exhaust temperature, that is, the temperature of the storage NOx catalyst is high, Not limited to this, even when the load of the engine and the rotational speed are low and the temperature of the storage NOx catalyst is low, the exhaust gas temperature can always be appropriately raised, and the storage NOx catalyst quickly reaches a predetermined high temperature at which SOx can be removed. Can be heated. In addition, the exhaust gas heating device of the direct injection internal combustion engine according to claim 2 is provided.
According to the arrangement, the in-cylinder injection type internal combustion engine is
In the case where a medium is provided and SOx removal is performed, the SOx removal
The temperature of the storage NOx catalyst during the removal
Can be maintained at a predetermined high temperature and SOx can be sufficiently removed.
Both can prevent overheating of the storage NOx catalyst, three-way catalyst, etc.
Wear. Further, the exhaust gas temperature rise of the in-cylinder injection type internal combustion engine of claim 3
According to the device, the exhaust gas temperature can be raised regardless of the operating state of the engine.
Always perform it efficiently and properly without instability of combustion.
Can be.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an exhaust gas heating device for a direct injection internal combustion engine according to the present invention.

FIG. 2 is a flowchart showing a control routine of exhaust gas temperature rise control according to the present invention.

FIG. 3 is a diagram showing a relationship between an S-poisoning coefficient K1 and an air-fuel ratio A / F according to an air-fuel ratio A / F among correction coefficients of a poisoning S amount Qs.

FIG. 4 is a diagram showing the relationship between the S poisoning coefficient K2 and the S content according to the S content in the correction coefficient of the poisoning S amount Qs.

FIG. 5 is a diagram showing a relationship between an S poisoning coefficient K3 and a catalyst temperature Tcat according to a catalyst temperature Tcat among correction coefficients of the poisoning S amount Qs.

FIG. 6 is a diagram showing the relationship between the regeneration temperature coefficient R1 and the catalyst temperature Tcat in accordance with the catalyst temperature Tcat used for calculating the regeneration S amount Rs.

FIG. 7 is a diagram showing the relationship between the regeneration capacity coefficient R2 and the air-fuel ratio A / F according to the air-fuel ratio A / F used for calculating the regeneration S amount Rs.

FIG. 8 is a main injection mode selection map when performing two-stage injection according to the first embodiment.

FIG. 9 is a main injection mode selection map when performing two-stage injection according to the second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine (in-cylinder injection type internal combustion engine) 4 Spark plug 6 Fuel injection valve 11 Throttle valve 11a Throttle sensor 13 Crank angle sensor 16 High temperature sensor 30a Storage type NOx catalyst 32 NOx sensor 40 Electronic control unit (ECU)

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification code FI F02D 41/02 325 F02D 41/02 325A 41/34 41/34 H F02P 5/15 F02P 5/15 B (56) References JP 8-296485 (JP, A) JP 10-47040 (JP, A) JP 10-122015 (JP, A) JP 11-50894 (JP, A) JP 10-184417 (JP JP, A) JP-A-10-141115 (JP, A) JP-A-10-54287 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F02D 41/00-41/40 F01N 3/00-3/38

Claims (3)

(57) [Claims] 1. A and the target air-fuel ratio setting means for setting a target air-fuel ratio for the exhaust gas Atsushi Nobori control, the operating condition detecting means for detecting a load or speed conditions of the engine, the amount of fuel corresponding to the target air-fuel ratio as well as injection as a main injection in some of the intake stroke of the first second stage injection means for injecting the auxiliary injection and the remainder in the expansion stroke, the compression stroke a part of the fuel of an amount corresponding to the target air-fuel ratio A second two-stage injection means for injecting the remainder as a sub-injection during an expansion stroke while injecting the remainder as an auxiliary injection; and An injection temperature selecting device for selecting one of the first two-stage injection device and the second two-stage injection device. An exhaust gas heating device for a direct injection internal combustion engine, comprising: 2. An exhaust gas temperature detector for detecting an exhaust gas temperature.
Output means, the first two-stage injection means and the second two-stage injection means,
The exhaust gas temperature based on the detection information from the exhaust gas temperature detection
In order to maintain a constant value, the fuel amount of the main injection and the fuel amount of the
Temperature to change the ratio of
Characterized by comprising feedback control means,
The exhaust gas heating device for a direct injection internal combustion engine according to claim 1. 3. The first two-stage injection means comprises a main combustion idler.
In the range where the fuel ratio is equal to or less than the first air-fuel ratio at which combustion is established,
The main injection in the intake stroke and the sub-injection in the expansion stroke
And the second two-stage injection means performs the main combustion
In the range where the fuel ratio is equal to or higher than the second air-fuel ratio where combustion is established,
Main injection in the compression stroke and sub-injection in the expansion stroke
When the temperature of the exhaust gas needs to be raised, the air-fuel ratio of the main combustion is reduced to the first air-fuel ratio.
When the value is between the fuel ratio and the second air-fuel ratio,
Injects all fuel in the amount corresponding to the target air-fuel ratio as main injection
Ignition timing retarding means to retard ignition timing
The in-cylinder injection according to claim 1, characterized in that:
Exhaust temperature raising device for internal combustion engines.