JP2002047979A - Engine controller ! exhaust air particulate treatment device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an engine controller capable of accurately judging an abnormality of an exhaust air component detection means and performing control of NOx scavenger, monitoring of performance, and control of HC scavenger without making errors even if the exhaust air component detection means detecting the concentration of exhaust air components such as NOx, HC, CO, etc., is deteriorated and its performance is changed. SOLUTION: This controller is provided with the NOx scavenger 15, an NOx sensor 25, and a specific condition judging means which estimates that NOx concentration detected by the NOx sensor 25 is a predetermined value and judges that an engine or NOx scavenger 15 is in a specific condition and is further provided with a means for judging an abnormality of the NOx sensor 25, etc., based on the NOx concentration detected by the NOx sensor 25 when it is judged that it is in the specific condition or a means for compensating the results of detection.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an engine for purifying exhaust components such as NOx, and more particularly to a control device for an engine for purifying properly by a catalyst or a trapping agent by an output of a NOx sensor or the like, and controlling an exhaust component discharged. The present invention relates to an engine control device that can be reduced.

[0002]

2. Description of the Related Art In order to reduce the fuel consumption of an engine, there has been proposed a technique in which the amount of air is excessively increased (hereinafter referred to as "lean") to exceed the stoichiometric air-fuel ratio (hereinafter referred to as "stoichiometric") to burn fuel in a lean manner. For example, a method of injecting fuel near the intake port of the intake pipe (port injection) has an air-fuel ratio of 20 to 25.
Some are realizing a degree of lean combustion, and some are realizing a very lean combustion such as an air-fuel ratio of 40 to 50 by forming a stratified mixture by a method of directly injecting fuel into a cylinder (in-cylinder injection). . In these technologies, lean combustion, that is, an increase in the amount of intake air, can reduce pumping loss and heat loss and improve fuel economy.

However, in the case of stoichiometric combustion, HC, CO and NOx in exhaust gas can be simultaneously oxidized and reduced by a three-way catalyst, but in lean combustion, since exhaust gas is in an excessive oxygen state, NOx reduction is performed. Is difficult. Therefore, when the air-fuel ratio of the exhaust gas is lean, the N
Captured like adsorbed or absorbed ox, air-fuel ratio is fuel-excess (hereinafter referred to as rich) when NOx is released and reduced, or catalytic reaction, such as by reducing the N ₂ by, de-trapped once was NOx A NOx trapping agent capable of recovering the separated trapping performance is disposed in the exhaust passage, and the air-fuel ratio of the exhaust gas is temporarily changed from lean to the stoichiometric air-fuel ratio or rich at a predetermined cycle to be absorbed by the NOx trapping agent. NOx
The causes reduced to N _2, the exhaust gas purification apparatus for an engine which is adapted to recover the NOx trapping performance is proposed.

When such a NOx trapping agent is used, the air-fuel ratio is temporarily changed from lean to the stoichiometric air-fuel ratio or rich in order to recover the trapping performance. It is necessary to appropriately control such factors from the viewpoint of reducing fuel consumption and reducing the amount of exhaust components released into the atmosphere.

[0005] Therefore, a NOx sensor for detecting the concentration of NOx in exhaust gas is arranged downstream of the NOx trapping agent.
There is disclosed a technique for controlling the time when the air-fuel ratio is temporarily changed from lean to the stoichiometric air-fuel ratio or rich, and the time when the air-fuel ratio is returned to lean in order to recover the capturing performance based on the value detected by the Ox sensor. Further, when the performance of the NOx trapping agent is deteriorated, the time when the air-fuel ratio is temporarily changed from lean to the stoichiometric air-fuel ratio or rich to recover the trapping performance, the period during which the air-fuel ratio is changed, the air-fuel ratio, etc. Is appropriately corrected, and a warning or the like is preferably issued when the degree of deterioration of the NOx trapping agent exceeds a predetermined level.

For this reason, a NOx sensor for detecting the concentration of NOx in exhaust gas is arranged downstream of the NOx trap,
A technique for monitoring the performance of a NOx trap based on a value detected by an Ox sensor has also been disclosed. As such a technique, for example, in Japanese Patent Application Laid-Open No. 9-88560, a NOx sensor is provided downstream of a lean NOx catalyst and a NOx adsorption catalyst (a type of NOx trapping agent), and after switching from stoichiometric to lean operation, the NOx sensor When the time required for the output of the device to exceed the predetermined slice level is shorter than the predetermined value, NO
An apparatus for determining that the x adsorption catalyst has deteriorated is disclosed.

[0007] JP-A-10-71325 discloses that NO
A NOx sensor is provided downstream of the x-reduction catalyst and the adsorption means (both are a type of NOx trapping agent).
When the sensor output reaches a predetermined value, the air-fuel ratio is made rich,
A device for desorbing or separating NOx,
An apparatus is disclosed that detects deterioration of the NOx reduction catalyst or the adsorbing means based on the output value of the x sensor, the duration of the lean operation, and the repetition cycle of the lean operation and the rich operation. At this time, N
Ox sensors are not widely used for standard mounting on automobiles, but they are expected to become popular in the future because they meet the above-mentioned requirements for fuel efficiency reduction and stricter exhaust gas regulations. Is done.

On the other hand, exhaust gas regulations for automobiles are becoming stricter year by year. Particularly, in order to reduce HC at low temperature start, HC is trapped at a relatively low temperature, and when the temperature becomes higher than a predetermined temperature, the HC is trapped. Various devices for purifying by releasing, oxidizing, and the like, and devices for monitoring the performance of the HC scavenger have also been disclosed. In this case as well, it is preferable to control the engine and the HC trapping agent and to diagnose the HC trapping agent using an HC sensor that detects HC in the exhaust gas. However, at present, the HC sensor has durability and cost. Because of these issues, it is not widely used as standard equipment for automobiles, but it is expected that it will be widely used in the future in order to meet stricter exhaust gas regulations. Further C
The O sensor is also controlled to reduce the generation of CO and to increase the rate of temperature rise of the catalyst and the like at the time of low temperature start.
It is conceivable that it will be widely used in the future because it is used for control and the like using.

[0009]

SUMMARY OF THE INVENTION However, NO
x, if the exhaust component detecting means itself for detecting the concentration of exhaust components such as HC and CO deteriorates and the performance changes, the control of the NOx trapping agent and the monitoring of the performance as described above;
The control of the HC trapping agent and the like cannot be performed properly, but the prior art does not consider this point.

The present invention has been made in view of such a problem, and an object of the present invention is to determine whether an exhaust gas component detecting means and an exhaust gas purifying device including the same are operating normally. An object of the present invention is to provide an engine control device capable of stably operating an exhaust gas purification device.

[0011]

According to a first aspect of the present invention, there is provided a control apparatus for an engine which is disposed in an exhaust passage of the engine and includes at least one of NOx, HC and CO in exhaust gas. An exhaust component detection unit that detects the concentration of the exhaust component, and an exhaust purification device are provided, and the engine or the exhaust purification device estimates that the concentration of the exhaust component detected by the exhaust component detection unit is a predetermined value. ,
A specific state determining means for determining that the state is a specific state;
At least one of an engine, the exhaust component detection unit, or the exhaust gas purification device is configured based on an estimated value of the exhaust component detection unit in the specific state and an exhaust component concentration detected by the exhaust component detection unit in the specific state. Abnormality determining means for determining an abnormality.

According to this configuration, it is determined that the engine or the exhaust gas purifying device is in a specific state, and based on the estimated value of the exhaust gas component detecting means at this time and the exhaust gas component concentration detected by the exhaust gas component detecting device. Therefore, it is possible to determine at least one abnormality of the engine, the exhaust gas component detection means, or the exhaust gas purification device, and the exhaust gas purification device or the like can quickly detect the abnormal state and give a warning.

According to a second aspect of the present invention, there is provided a control device for an engine.
NOx in exhaust gas, which is arranged in the exhaust passage of the engine,
An exhaust gas detection device for detecting the concentration of at least one exhaust gas component of HC or CO; and an exhaust gas purification device, wherein an engine or the exhaust gas purification device determines that the concentration of the exhaust gas component detected by the exhaust gas component detection device is a predetermined value. The specific state determination unit that determines a specific state, an estimated value of the exhaust component detection unit in the specific state, and the specific state determination unit that is detected by the exhaust component detection unit in the specific state. And correcting means for correcting at least one of the output of the exhaust gas component detecting means or the estimated value based on the exhaust gas component concentration.

According to this configuration, it is determined that the engine or the exhaust gas purifying device is in a specific state, and the estimated value of the exhaust gas component detecting means at this time and the exhaust gas component concentration detected by the exhaust gas component detecting device are used. Thus, the output of the exhaust gas component detecting means or at least one of the estimated values can be corrected, and the exhaust gas purification of the engine can be executed correctly.

According to a third aspect of the present invention, there is provided an engine control device comprising:
In the above-described engine control device, the specific state determination unit determines that the engine is in a fuel cut state. According to this configuration, since the output of the exhaust gas component detection means is in the fuel cut state and the predetermined time has elapsed, the output of the exhaust gas component detection means is assumed to be zero.

According to a fourth aspect of the present invention, there is provided an engine control device comprising:
In the engine control device described above, the exhaust gas purification device is a catalyst that is disposed in the exhaust passage upstream of the exhaust gas component detection unit and purifies at least one exhaust gas component of NOx, HC, or CO in exhaust gas. The specific state determination unit determines that the catalyst is not activated, is in a predetermined temperature range, or determines that the engine is in at least one state of being in a fuel cut state. According to this configuration, it is possible to determine that the engine and the exhaust gas purifying device are in the specific state, and to determine the state of the engine and the exhaust gas purifying device from the value estimated by the exhaust gas component detecting means. It can be carried out.

An engine control device according to a fifth aspect of the present invention
In the engine control device described above, the exhaust purification device is a trapping agent that is disposed in the exhaust passage upstream of the exhaust component detection unit and traps at least one exhaust component of NOx, HC, or CO in exhaust gas. The specific state determination means may be configured to determine whether the trapping agent is not activated, that the trapping agent is in a predetermined temperature range, that the trapped amount of exhaust components is in a saturated state, or that the engine is in a fuel cut state. It is characterized in that it is determined that the state is one state. According to this configuration, it is possible to determine that the engine and the exhaust gas purifying device are in the specific state, and to determine the state of the engine and the exhaust gas purifying device from the value estimated by the exhaust gas component detecting means. Can do it correctly.

An engine control device according to claim 6 is
It is disposed in the exhaust passage of the engine and captures NOx of the exhaust gas by adsorption or absorption when the air-fuel ratio of the inflowing exhaust gas is lean, and releases the captured NOx when the oxygen concentration in the exhaust gas is reduced. An engine that includes a NOx trapping agent that is desorbed by reduction or the like, and that controls the desorption of NOx trapped by the NOx trapping agent at a predetermined timing from a lean air-fuel ratio to a stoichiometric air-fuel ratio or rich. In the control device, the control device is disposed downstream of the NOx trapping agent in the exhaust passage and detects NOx concentration in exhaust gas, and the engine or the NOx trapping agent is detected by the NOx detection unit. It is estimated that the NOx concentration to be performed is a predetermined value, a specific state determining means for determining a specific state, and the specific state determining means Thus, based on the NOx concentration detected by the NOx detecting means when it is determined that the engine or the NOx trapping agent is in a specific state, at least one abnormality of the engine, the NOx detecting means, or the NOx trapping agent is determined. Abnormality determination means for determining According to this configuration, the NOx concentration in the specific state is estimated by the NOx detecting means, and the NOx concentration is estimated.
An abnormality in the engine, the NOx detection means or the NOx trapping agent can be determined based on the concentration, and an abnormality in the exhaust gas purification device or the like can be promptly detected and a warning can be issued.

An engine control device according to claim 7 is
It is disposed in the exhaust passage of the engine and captures NOx of the exhaust gas by adsorption or absorption when the air-fuel ratio of the inflowing exhaust gas is lean, and releases the captured NOx when the oxygen concentration in the exhaust gas is reduced. An engine that includes a NOx trapping agent that is desorbed by reduction or the like, and that controls the desorption of NOx trapped by the NOx trapping agent at a predetermined timing from a lean air-fuel ratio to a stoichiometric air-fuel ratio or rich. In the control device, the control device is disposed downstream of the NOx trapping agent in the exhaust passage and detects NOx concentration in exhaust gas, and the engine or the NOx trapping agent is detected by the NOx detection unit. It is estimated that the NOx concentration to be performed is a predetermined value, a specific state determining means for determining a specific state, and the specific state determining means I, the NOx when the engine or the NOx trap is determined to be a specific state
And correcting means for correcting at least one of the output of the NOx detecting means or the estimated value based on the NOx concentration detected by the detecting means.

According to this configuration, the engine or NOx
It is determined that the scavenger is in a specific state,
Based on the NOx concentration detected by the Ox detection means, at least one of the output of the NOx detection means or the estimated value can be corrected, and the exhaust gas purification of the engine can be executed correctly.

An engine control device according to claim 8 is
In the above-described engine control device, the specific state determination unit determines that the NOx trapping agent is not activated, that the temperature is within a predetermined temperature range, that the NOx trapping amount is in a saturated state, or that the engine is in a fuel cut state. It is characterized in that it is determined that at least one of the operating states is the operating state. According to this configuration, the NOx concentration in the specific state can be easily estimated, and the exhaust gas purification of the engine can be performed correctly.

According to a ninth aspect of the present invention, there is provided the engine control device,
NOx in exhaust gas, which is arranged in the exhaust passage of the engine,
An exhaust component detecting unit that is provided downstream of the capturing unit in the exhaust passage and detects a concentration of the exhaust component; and an exhaust component detecting unit that includes a capturing unit that captures at least one exhaust component of HC or CO. Exhaust component concentration changing means for performing control to change the exhaust component concentration to be detected; and a change in the exhaust component concentration detected by the exhaust component detecting device when the exhaust component concentration is changed by the exhaust component concentration changing device. And abnormality determining means for determining at least one abnormality of the engine, the exhaust component detecting means, the exhaust component concentration changing means or the trapping means based on the above.

According to this structure, the exhaust component concentration changing means controls to change the exhaust component concentration to be detected by the exhaust component detecting means, and when the exhaust component concentration is changed, the control is performed by the exhaust component detecting means. Based on the detected change in the concentration of the exhaust gas component, it is possible to determine at least one abnormality of the engine, the exhaust gas component detecting device, the exhaust gas component concentration changing device, or the capturing device.

According to a tenth aspect of the present invention, in the engine control device described above, the exhaust component detecting means detects the NOx concentration, and the exhaust component concentration changing means detects the NOx concentration discharged from the engine. Preferably, the control device for an engine according to the eleventh aspect is the control device for an engine described above, wherein the exhaust component concentration changing means changes an exhaust component concentration, an exhaust temperature, or an exhaust flow rate discharged from the engine. It is preferable to perform the control for changing. According to this configuration, it is possible to determine the abnormality of the trapping means and the like by changing the NOx concentration and the like and detecting the change at that time.

According to a twelfth aspect of the present invention, in the engine control device described above, when an abnormality is determined by the abnormality determining means, information indicating the abnormality is stored or an abnormality is warned. Preferably, in the engine control device according to the thirteenth aspect, in the engine control device, when the abnormality determination unit determines that an abnormality has occurred, a predetermined diagnosis and / or
Alternatively, it is preferable to prohibit a predetermined operating state. According to this configuration, when the engine control device is abnormal, a warning is issued, a predetermined diagnosis is made, and a preferable operating state can be achieved.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of an engine control device for purifying exhaust gas according to a first embodiment of the present invention. Note that the present embodiment shows an example of the in-cylinder injection method. The intake system 23 of the engine 1 includes an air cleaner 2, an air flow sensor 3 for detecting the amount of intake air, a throttle valve 4 for adjusting the amount of intake air, a throttle valve driving means 5, a throttle opening sensor 5a, a swirl control valve 6, a swirl. A control valve driving means 7 and an intake valve 8 are provided. The swirl control valves 6 are provided immediately before the intake valves 8 for the respective cylinders, and are configured to operate integrally. The combustion chamber 9 of the engine 1 includes a fuel injection valve 10 for directly injecting fuel into the combustion chamber 9 and a spark plug 11.

The exhaust system 24 of the engine 1 is provided with an exhaust temperature sensor 12, an exhaust valve 13, an air-fuel ratio sensor 14, a NOx trap 15 as an exhaust purification device, and a NOx sensor 25. The NOx trap 15 is arranged upstream of the NOx sensor 25. The engine 1 further includes a sensing plate 16 attached to a crankshaft of the engine 1, a crank angle sensor 17 for detecting a rotation speed and a crank angle by detecting a protrusion thereof, and an accelerator sensor 19 for detecting an amount of depression of an accelerator pedal 18. ing. Note that a catalyst may be used as the exhaust gas purification device.

The values detected by the sensors are input to an electronic control unit (hereinafter, referred to as an ECU) 20. The ECU 20 detects an accelerator depression amount, an intake air amount, a rotation speed, a crank angle, an exhaust temperature, a throttle opening, and the like. calculate. Then, based on the result, the amount and timing of the fuel supplied to the engine 1 are calculated to output a drive pulse to the fuel injection valve 10, the opening of the throttle valve 4 is calculated, and a control signal is sent to the throttle valve driving means 5. It outputs an ignition signal, calculates an ignition timing, and outputs an ignition signal to the ignition plug 11.

The ECU 20 is provided with an engine or NO
a specific state determining unit that determines that the x trapping agent 15 is in a specific state described later, and further, for example, an abnormality determining unit that determines that the NOx trapping agent 15 has deteriorated or that determines that the NOx sensor 25 is abnormal. And, if determined, outputs a signal to a warning light 26 for warning the driver. The ECU 20 includes a correction unit that corrects at least one of the estimated value of the NOx sensor 25 or the output of the NOx sensor 25 in the specific state.

The fuel is pressure-fed from a fuel tank (not shown) by a fuel pump and is supplied to a predetermined pressure (5 to 5) by a fuel pressure regulator.
(About 15 MPa) and supplied to the fuel injection valve 10. A predetermined amount of fuel is directly injected into the combustion chamber 9 at a predetermined timing by a drive pulse output by the ECU 20. The operation modes of the engine 1 include a stoichiometric operation, a homogeneous lean operation, a stratified lean operation, and the like. During the homogeneous lean operation, fuel is injected in the intake stroke to mix with air and burn a homogeneous mixture. During the stratified lean operation, fuel is injected in the compression stroke to distribute the fuel in a stratified manner in the air-fuel mixture, and the fuel is collected near the ignition plug 11 so as to form a rich air-fuel mixture.

The intake air adjusted by the throttle valve 4 flows through the intake valve 8 into the combustion chamber 9. On this occasion,
The swirl control valve 6 controls the swirl intensity.
Usually, the swirl intensity is set to be high during the stratified lean operation or the homogeneous lean operation, and to be low in other cases. In particular, during the stratified lean operation, the spark plug 1 is not spread over the entire combustion chamber 9 due to the fuel injection timing and the air flow caused by the swirl and the shape of the cavity 22 provided on the upper surface of the piston 21.
It is gathered near 1.

The mixture of fuel and intake air is supplied to the spark plug 1
It is ignited at 1 and burns. Exhaust gas after combustion is exhaust valve 1
3 to the exhaust system 24. The exhaust gas flows into the NOx trap 15 disposed in the exhaust system 24. The air-fuel ratio sensor 14 outputs a signal corresponding to the oxygen concentration in the exhaust gas upstream of the NOx trap 15 and can detect the actual air-fuel ratio from the output. Based on the actual air-fuel ratio detected by the air-fuel ratio sensor 14, the air-fuel ratio of the air-fuel mixture supplied to achieve the target air-fuel ratio is feedback-controlled.

The NOx sensor 25 is arranged downstream of the NOx trap 15 and outputs a signal corresponding to the NOx concentration in the exhaust gas, and can detect the actual NOx concentration from the output. Control such as determining the amount of NOx trapped by the NOx trap 15 based on the NOx concentration detected by the NOx sensor 25 is executed. For details of the NOx sensor,
For example, it is disclosed in Japanese Patent Application Laid-Open No. 8-271476, and outputs a current corresponding to the NOx concentration in exhaust gas as shown in FIG. A passage and an EGR valve (not shown) are provided from the exhaust system 24 to the intake system 23.
Especially during lean operation, to suppress the generation of NOx,
A large amount of EGR is introduced to suppress the burning rate.

FIG. 3 shows the configuration of the ECU 20. The above-described air flow sensor 3, throttle valve opening sensor 5a, exhaust temperature sensor 12, air-fuel ratio sensor 14, NOx sensor 2
5, signals of the crank angle sensor 17, the accelerator sensor 19, 3s, 5s, 12s, 14s, 25s, 17s, 19s
A signal from a cylinder discrimination sensor 27 (not shown) is input to the input circuit 31. The CPU 30 reads these input signals through the input / output port 32 based on programs and constants stored in the ROM 37 and performs arithmetic processing.

As a result of the arithmetic processing, the ignition timing, injector drive pulse width and timing,
A throttle valve opening command and a swirl control valve opening command are output to an ignition output circuit 33, a fuel injection valve drive circuit 34, a throttle valve drive circuit 35, and a swirl control valve drive circuit 36 via an input / output port 32, and Fuel injection, throttle valve opening control, and swirl control valve opening control are executed.
Further, for example, when it is determined that the NOx trap 15 has deteriorated, the warning light driving circuit 39 turns on the warning light 26. The RAM 38 is used for storing values of input signals, calculation results, and the like. The ECU 20 calculates the fuel injection time Ti based on, for example, the following equation based on the program or constant stored in the ROM 37, injects fuel from the fuel injection valve 10, and supplies the fuel to the engine 1.

Ti = K ・ (Qa / Ne) ・ TGFBA ・ A
LPHA ・ Kr

Here, K is a coefficient based on the characteristics of the fuel injection valve 10 and the like, Qa is the intake air amount, Ne is the engine speed, TGFBA is the target equivalent ratio of the air-fuel mixture to be supplied to the engine 1, and ALPHA is feedback correction. It is a coefficient.
Kr is an air-fuel ratio correction coefficient during air-fuel ratio change control (hereinafter referred to as NOx purge control) for temporarily changing the air-fuel ratio of exhaust gas from lean to stoichiometric air-fuel ratio or rich at a predetermined cycle.

If the target equivalence ratio TGFBA = 1, the air-fuel mixture supplied to the engine 1 becomes stoichiometric. On the other hand, if TGFBA <1, the mixture supplied to the engine 1 is lean, and if TGFBA> 1, the engine 1
Is rich. Target equivalent ratio TGF
BA is, for example, as shown in FIG.
e and a load (for example, a target torque calculated based on a signal from the accelerator sensor 19 for detecting the depression amount of the accelerator pedal 18) are stored in the ROM 37 in advance.

That is, TGFBA <1, ie, lean, in the operating region where the load is lower than the solid line L, and TGFBA = 1, ie, stoichiometric, in the operating region between the solid line L and the solid line R.
In the operation region where the load is higher than the solid line R, TGFBA> 1, that is, rich. Further, in the operation region where the load is lower than the solid line L, a stratified mixture is formed in the operation region where the load is lower than the dotted line S, and combustion with an extremely lean mixture having an air-fuel ratio of 40 to 50 is realized (stratified lean operation). ). In the operation region between the solid line L and the dotted line S, the operation is homogeneous and the air-fuel ratio is 20 to 25.
A degree of lean mixture combustion is realized (homogeneous lean operation).

Stoichiometric operation (TGFBA = 1, Kr =
In 1), based on the actual air-fuel ratio detected by the air-fuel ratio sensor 14, feedback control is performed so that the air-fuel ratio is accurately stoichiometric, a feedback correction coefficient ALPHA is calculated, and is reflected in the fuel injection time Ti. . ALPHA decreases when the actual air-fuel ratio becomes rich, increases when the actual air-fuel ratio becomes lean, and usually moves up and down around 1.0. ALPHA is fixed to a predetermined value or a learning value except during stoichiometric operation.

During lean operation (TGFBA <1, Kr =
In 1), NOx in the exhaust gas is captured by the NOx capturing agent 15. The NOx trapping amount gradually increases. When the NOx trapping amount exceeds a predetermined amount, the NOx concentration downstream of the NOx trapping agent 15 starts to increase. The NOx concentration is detected by the NOx sensor 25,
When the output of the x sensor 25 exceeds a predetermined value, TGAFBA
= 1, Kr ≧ 1, that is, the air-fuel ratio is switched to a stoichiometric or rich low oxygen concentration state (NOx purge control), and NOx trapped by the NOx trapping agent 15 such as adsorbed or absorbed is released and reduced, or The trapped NOx is desorbed by being reduced by a catalytic reaction, etc.
x capture performance is restored.

In the case of the in-cylinder injection type engine according to the present embodiment, when the air-fuel ratio is switched to stoichiometric or rich, the throttle valve 6 is mainly operated by the throttle valve driving means 5 in the closing direction so that the intake air Although the air-fuel ratio is changed by reducing the amount and controlling the supplied fuel amount, the present invention is not limited to such a method.

The NOx trap 15 is configured to have a so-called three-way catalytic performance in order to ensure NOx trapping during lean operation and exhaust gas purifying performance during stoichiometric operation. For example, alumina is used as a carrier, and an alkali metal or alkaline earth such as sodium Na or barium Ba and a noble metal such as platinum Pt or rhodium Rh are supported. In addition, there is a case in which cerium Ce having oxygen storage capacity is supported to improve so-called ternary performance in stoichiometry. When the air-fuel ratio of the inflowing exhaust gas is lean, the NOx trapping agent 15 traps NOx by adsorption or absorption. NOx trapped when the oxygen concentration in the exhaust gas decreases (for example, when it becomes stoichiometric or rich)
Release.

The released NOx is, for example, platinum Pt.
Is reacted with HC and CO in the exhaust gas to be reduced. Some scavengers reduce NOx by causing a contact reaction between the trapped NOx and HC or CO when the oxygen concentration in the exhaust gas decreases. NOx
The reduction process of is not limited to these,
In any case, the trapped NOx is controlled by the NOx purge control.
x is desorbed to recover NOx trapping performance, and the trapped NOx is reduced and purified. In this way, the amount of NOx released into the atmosphere can be reduced.

Further, during the stoichiometric operation, for example, HC and CO in the exhaust gas are oxidized and NOx is reduced by the catalytic action of platinum Pt, so that these exhaust gas components can be reduced. Note that, depending on the type of the NOx trapping agent, there is also one that has an effect of partially reducing NOx by HC and CO in the exhaust gas even when the inflowing exhaust gas has a lean air-fuel ratio.

As described above, when the air-fuel ratio of the exhaust gas is lean, NOx is trapped by the NOx trap 15. However, the NOx trapping capacity of the NOx trapping agent 15 is limited. If NOx is trapped until the trapping capacity is saturated, NOx can no longer be absorbed, and NOx becomes NOx.
It will be released to the atmosphere without passing through the trapping agent 15. Therefore, before the NOx trapping capacity of the NOx trapping agent 15 is saturated, the NOx purge control is executed, and the trapped NOx is desorbed by the NOx purge control to recover the NOx trapping performance, and the trapped NOx is reduced and purified. There is a need.

Further, the exhaust gas regulations are becoming stricter year by year, and it is necessary to keep the concentration of NOx passing downstream of the NOx trapping agent 15 at a considerably low level. On the other hand, FIG.
As shown in (2), when NOx is trapped to a certain extent by the NOx trapping agent 15 during the lean operation, the concentration of NOx passing downstream of the NOx trapping material 15 starts to gradually increase. Therefore, when the NOx concentration downstream of the NOx trapping agent 15 detected by the NOx sensor 25 becomes equal to or higher than the predetermined value NOSL, the NOx purge control is executed.

If the NOx purge control is performed early,
Although the amount of NOx flowing downstream of the NOx trapping agent 15 can be reduced, NOx purge control is frequently performed, which leads to an increase in fuel efficiency, which is not preferable. For this reason, N at optimal timing in terms of exhaust and fuel economy.
It is preferable to perform Ox purge control. NOx sensor 2
By detecting the NOx concentration downstream of the NOx trapping agent 15 with the use of the NOx trap 5, the NOx purge control can be performed at an optimal timing.

As shown by the dotted line in FIG.
5 deteriorates, the time TL from when the lean operation is performed after the execution of the NOx purge control to when the output of the NOx sensor 25 becomes equal to or more than a predetermined value gradually decreases. Therefore, the deterioration of the NOx trap 15 becomes more than a predetermined value, and the TL
Is smaller than the predetermined value (TLNG), it is determined that the NOx trapping performance of the NOx trapping agent 15 has deteriorated. In addition, the predetermined value TLNG for the above-mentioned determination is the operating state of the engine (exhaust flow rate, NOx concentration) and the temperature of the NOx trapping agent even if the engine is normal and the NOx trapping agent 15 is not deteriorated. to be influenced. Therefore, it is preferable to set in advance according to the operating state of the engine.

Since NOx is suppressed by EGR particularly during lean operation, if the EGR valve fails to open due to an abnormality, the NOx generated in the engine 1 increases. Further, when an abnormality occurs in the air flow enhancing means such as the swirl control valve 6, the amount of NOx or the like generated in the engine 1 similarly changes. Further, when an abnormality occurs in the air flow sensor 3, the throttle valve opening sensor 5a, the exhaust gas temperature sensor 12, the air-fuel ratio sensor 14, the crank angle sensor 17, the accelerator sensor 19, etc. Since the operating state such as the fuel ratio cannot be correctly grasped, the predetermined value TLNG also does not become a correct value.

In such a case, there is a possibility that the NOx trapping agent 15 may be erroneously determined to be deteriorated even though it has not deteriorated, or conversely, it may not be possible to determine that the NOx trapping agent 15 has deteriorated although it has deteriorated.
Therefore, it is preferable to monitor whether the EGR valve, the actuator, the sensor, and the like are normal, and stop monitoring the performance of the NOx trapping agent 15 when it is determined that the EGR valve is abnormal. Various methods of monitoring whether these actuators and sensors are normal are disclosed, and a known technique may be used.

Incidentally, even when the NOx sensor 25 is deteriorated or malfunctions, the NOx trapping agent 15
There is a possibility that it may be erroneously determined that the image has deteriorated even though it has not deteriorated, or conversely, it may not be determined that the image has deteriorated although it has deteriorated. Hereinafter, a method of monitoring the NOx sensor will be described.

First, a heater is used inside the NOx sensor 25, and is controlled so as to reach a predetermined temperature. If the heater or the wiring to the heater is disconnected or short-circuited, the temperature cannot be controlled to a predetermined temperature, so that the output characteristics deviate from the normal state. Therefore, while the heater is controlled by the ECU 20, the disconnection and the short circuit are detected by detecting the terminal voltage when the heater is turned ON / OFF. Also when the output of the NOx sensor 25 is out of the design range, it is determined that there is an abnormality. These abnormalities can be detected relatively easily. By the way, NOx
Even if the output of the sensor is within the design range, the output characteristics may deviate from the normal value due to deterioration or the like. Hereinafter, a method for detecting such an abnormality will be described.

(1) When the engine 1 is in the fuel cut state, the estimated value of NOx generated in the engine 1 becomes zero. Therefore, when a specific state is determined by the specific state determination means after a predetermined period in consideration of a delay in transport of exhaust gas, a release time of NOx from the NOx trapping agent 15, and the like, the output of the NOx sensor 25 also has a NOx concentration. It should be the value corresponding to zero. N detected at this time
If the output of the Ox sensor 25 is within a predetermined range, it is determined to be normal. If it is out of the predetermined range, it is determined as abnormal by the abnormality determining means. Then, the warning light 26 is turned on by the warning light driving circuit 37. Thus, the engine, N
It is possible to determine that at least one of the Ox trapping agent 15 and the NOx sensor 25 is abnormal, and the exhaust gas purifying device or the like can promptly detect and warn the abnormal state.

When the value is within the predetermined range, it is preferable that the output value is further stored and used for offset correction of the output of the NOx sensor 25. Also,
If the air-fuel ratio is rich such as during acceleration or the load is relatively low during stoichiometric operation, the NOx concentration downstream of the NOx trap 15 becomes almost zero immediately after the NOx purge control, so that the specific state can be determined. As in the case of the fuel cut, it is possible to determine the abnormality of the NOx sensor 25 and measure and store the value for output correction.

(2) As shown in FIG. 6A, during the lean operation, the NOx trapping agent 15 is trapped until the NOx is saturated. In this case, the NOx concentration generated from the engine 1
Since it can be estimated that the (NOx concentration upstream of the NOx trapping agent 15) and the NOx concentration downstream of the NOx trapping agent 15 become substantially equal, it can be determined that the specific state is established. Engine 1
Can be estimated from the operating state of the engine (rotational speed, load, air-fuel ratio, ignition timing, EGR rate, opening of the swirl control valve 6, etc.). If the output of the NOx sensor 25 detected at this time is within a predetermined range with respect to the estimated value of the NOx concentration estimated from the operation state of the engine, it is determined that the output is normal. If out of range,
An abnormality is determined by the abnormality determining means.

In addition, depending on the type of the NOx trapping agent 15, as shown in FIG. 6B, even if the NOx trapping amount is saturated, NOx is reduced and purified by a reaction. When such a NOx trapping agent 15 is employed, it is preferable to consider it when setting the range of the normal / abnormal judgment from the above-mentioned estimated NOx concentration.

(3) The NOx trapping performance of the NOx trapping agent 15 is strongly affected by the temperature of the inflowing exhaust gas. As shown in FIG. 7, when it is not activated at a low temperature, it does not capture NOx. Conversely, when the temperature becomes high, the NOx release rate exceeds the trapping rate, and therefore, NOx is not substantially trapped. Such temperature characteristics differ depending on the type of the NOx trapping agent 15, but generally do not trap NOx at 200 to 300 ° C or lower and at 400 to 500 ° C or higher.

Also in this case, NO generated from engine 1
Since it is clear that the x concentration and the NOx concentration downstream of the NOx trap 15 become equal, it can be determined that the specific state is established. Therefore, the output of the NOx sensor 25 detected when the exhaust gas temperature or the temperature of the NOx trapping agent 15 is low (inactive state) or high is lower than the estimated value of the NOx concentration estimated from the operating state of the engine. If it is within the predetermined range, it is determined to be normal. If it is out of the range, it is determined as abnormal by the abnormality determining means. Exhaust gas temperature, NOx trapping agent 1
The temperature of 5 is a temperature sensor (for example, exhaust temperature sensor 12)
Or may be estimated from the operating state of the engine 1.

When the NOx trap 15 is not activated, it is preferable not to permit the lean operation. In this case, since the stoichiometric operation is performed, the NOx concentration generated from the engine 1 is higher than during the lean operation. Therefore, it is possible to monitor the output of the NOx sensor 25 in a region where the NOx concentration is high. In addition, during the stoichiometric operation, the variation in the concentration of NOx generated from the engine 1 is often smaller during the stoichiometric operation than during the lean operation. For these reasons, it is preferable from the viewpoint of monitoring the performance of the NOx sensor 25 and from the viewpoint of characteristic correction described later.

As described in (1) to (3), the NOx concentration at the arrangement position of the NOx sensor 25 can be estimated from the state of the engine 1 or the NOx trapping agent 15, that is, the NOx to be detected by the NOx sensor 25. The abnormality of the NOx sensor 25 is determined by comparing the estimated NOx concentration with the NOx concentration detected by the NOx sensor 25 in the specific state of the engine 1 or the NOx trapping agent 15 where the concentration can be estimated to be a predetermined value. Values for detecting or correcting characteristics can be measured and stored.

In (1) to (3), only the specific state in which the NOx concentration can be accurately estimated has been described. However, even in other states, the normal NOx concentration and the NOx concentration detected by the NOx sensor 25 are determined. Is extremely different, it is preferable to determine that the NOx sensor 25 is abnormal. For example, the NOx concentration generated from the engine 1 during the stoichiometric operation is about 2000 ppm at the maximum, and the NOx trap 15 has a catalytic activity of NOx.
Should be purified, but the NOx concentration detected by the NOx sensor 25 is 3000 ppm or more, or even if a predetermined time or more elapses during the lean operation, NO
This is the case where the NOx concentration detected by the x sensor 25 is near zero.

As described above, even when there is an abnormality in the engine 1, the concentration of NOx generated from the engine 1 changes. If the abnormalities of the actuators and sensors that cause these problems are not separately determined, there is a possibility that the NOx sensor 25 and the abnormalities of the exhaust gas purification device including the engine 1 cannot be separated. In that case, the abnormality determination means may determine that an abnormality is present in any of the exhaust gas purification devices such as the NOx sensor 25 and the NOx trapping agent 15.

Further, when it is determined that the NOx sensor 25 or the like is abnormal, for example, the lean operation is prohibited or restricted. Alternatively, monitoring of the performance of the NOx trap 15 is prohibited. As a result, even if an abnormality occurs in the NOx sensor 25, it is possible to prevent the NOx purge control timing from being erroneously released to NOx and released to the atmosphere or to deteriorate fuel efficiency. In addition, it is possible to prevent erroneous monitoring of the performance of the NOx trap 15.

Hereinafter, a second embodiment of the present invention will be described. This embodiment corrects the characteristics of the NOx sensor 25, and an example will be described with reference to FIG. By performing the correction described below, the NOx sensor 25
This makes it possible to compensate for variations and deterioration to some extent, and to perform exhaust gas purification with high accuracy.

First, the NOx concentration detected by the NOx sensor 25 in the specific state where the estimated NOx concentration is estimated to be almost zero (= x) is stored as X, and the estimated NOx concentration is relatively high (= y). The NOx concentration detected by the NOx sensor 25 in the specific state is stored as Y. The NOx concentration detected by the NOx sensor 25 is
As the correction value, NOc expressed by the following equation (1) is adopted.

NOc = y / (Y− (X−x)) × NOs
− (X−x) (1)

That is, the offset is corrected by the detected value X at the point where the estimated NOx concentration is x, and the slope of the characteristic is corrected by the detected values X and Y at the point where the estimated NOx concentration is x and y. With the above correction, the correction value NOc becomes substantially equal to the reference value, and the variation and deterioration of the characteristics of the NOx sensor 25 are compensated.

Note that the correction method is not limited to the above, and only the offset or only the inclination may be corrected according to the durability performance of the NOx sensor, the estimation accuracy of the NOx concentration, and the like. Further, the present invention is not limited to the calculation method or the method of measuring the detection value for correction at only two points, and may measure the number of points at more points to obtain a regression line, for example.

Further, using the corrected NOx sensor 25 detected value NOc, the NOx trap 15
Purge control, monitoring of the performance of the NOx trapping agent 15, and the like are executed. Thus, even when the characteristics of the NOx sensor 25 vary or deteriorate, it is possible to prevent the NOx purge control timing from being erroneously released to release NOx to the atmosphere or to deteriorate fuel efficiency.

As described above, even when the engine 1 is abnormal, the NOx concentration generated from the engine 1 changes. In the case where the abnormality of the actuators and sensors that cause these is not separately determined, that is, the estimated NO
If it is difficult to guarantee the accuracy of the x concentration, the NOx sensor 25
Output may be erroneously executed. In such a case, even if the actuators and sensors fail, the specific state in which the NOx concentration is hardly affected, for example,
The correction is performed based on the output of the NOx sensor 25 measured in a specific state such as during fuel cut, during stoichiometric operation, or during rich operation. Further, in a specific state in which the influence on the NOx concentration is likely to occur when the actuators and sensors break down, for example, in the specific state during the lean operation, the abnormality of the actuators and sensors and the like is determined or the estimated NO.
It is preferable to correct the x density.

In the above, the abnormality determination of the NOx sensor 25 and the like and the correction of the output and the like of the NOx sensor 25 are separately described as the first embodiment of the present invention and the estimated NOx concentration and When the deviation from the output of the NOx sensor 25 is within a predetermined range, the correction may be made, and when the deviation is out of the predetermined range, the combination may be determined to be abnormal.

Next, a flowchart relating to the first and second embodiments of the present invention will be described. FIG. 9 is a flowchart showing the air-fuel ratio control process. This control is started every predetermined time (for example, 20 ms) from a main routine (not shown). First, in step 100, it is checked whether or not the specific state is suitable for determining an abnormality of the NOx sensor 25 and correcting the output. The specific state, as described above, for example, after a predetermined time has elapsed since the fuel cut,
The air-fuel ratio is rich, such as during acceleration, or the NOx trap is not activated, or the temperature is high.
Although not shown, in order to facilitate abnormality determination and output correction of the NOx sensor 25, for example, NO
It is also possible to saturate the x capture agent 15.

If it is in the specific state, step 101
The routine proceeds to subroutine, which will be described later, to execute abnormality determination of the NOx sensor 25 and to correct the output, and then proceeds to step 102. If it is not in the specific state, the process proceeds directly to step 102. Next, at step 102, it is checked whether or not the engine is in the lean operation range. Here, it is checked whether the load, rotation speed, cooling water temperature, vehicle speed, and the like of the engine 1 are within predetermined ranges. If it has been determined that the NOx sensor 25 is abnormal, the lean operation region is limited to a narrow range to reduce the fuel consumption while suppressing the rebound such as deterioration of the exhaust gas. If it has been determined that the NOx sensor 25 is abnormal, the lean operation may be prohibited.

If it is determined in step 102 that the vehicle is not in the lean operation range, the routine proceeds to step 112, where T
GFBA is set to 1, and Kr is set to 1. That is, the stoichiometric operation is performed. Next, the routine proceeds to step 113, where the feedback control of the air-fuel ratio is executed based on the output of the air-fuel ratio sensor 14 by another control flow (not shown), and then the routine proceeds to step 117.

If it is determined in step 102 that the engine is in the lean operation range, the routine proceeds to step 103, where EG
It is checked whether the R valve and the swirl control valve 6 are normal. Specifically, reference is made to a determination result determined by another control flow (not shown). If not, the lean operation is prohibited, and the routine proceeds to step 112.

If the EGR valve and the swirl control valve 6 are normal, the routine proceeds to step 104, where the target equivalent ratio TGFB
In A, a corresponding value (<1) is searched and set from the map of the rotation speed and the load of the engine 1 shown in FIG. Next, the routine proceeds to step 105, and if a NOx purge request determination flag described later is set (= 1), the routine proceeds to step 114.
After the NOx purge control subroutine (described later) is executed, and then the degradation determination subroutine (described later) of the NOx trapping agent 15 is executed in step 115, the counter TL of the lean operation continuation time is initialized (= 0) in step 116. Then, the process proceeds to step 117.

If the NOx purge request determination flag has not been set, the routine proceeds to step 106, where the feedback coefficient ALPHA = 1 and the air-fuel ratio correction coefficient Kr = 1 during NOx purge control are set. Next, the routine proceeds to step 107, where the fuel injection time Ti is calculated by the following equation.

Ti = K · (Qa / Ne) · TGFBA · ALPHA · Kr = K · (Qa / Ne) · TGFBA That is, the lean operation according to the target equivalent ratio TGFBA is executed.

In the next step 108, while the lean operation continues, the counter TL of the lean operation continuation time is counted up. Then, the next steps 109 and 110
When the NOx sensor is normal (NOx sensor NG flag = 0), the corrected NOx detection value NOc is equal to or greater than the threshold value NOSL, and when the NOx sensor is determined to be abnormal (NOx According to the sensor NG flag = 1), it is determined that the lean operation continuation time TL has become equal to or longer than the threshold value TLSL.

If any of the conditions hold, step 111
Then, the NOx purge request flag is set (= 1). If both are not established, the process proceeds to step 117. In step 117, the concentration of NOx generated from the engine 1 is estimated by another control flow (not shown). The estimated NOx concentration is, for example, the operating state of the engine.
(Rotational speed, load, air-fuel ratio, ignition timing, EGR rate, opening of swirl control valve 6, etc.).

FIG. 10 is a diagram showing the N shown by 114 in FIG.
It is a flowchart which shows an Ox purge control process.
From the control flow shown in FIG. 9, when the NOx purge control request flag is set, it is started as a subroutine. First, in step 200, the feedback coefficient A
LPHA = 1, target equivalent ratio TGFBA = 1, NO
An air-fuel ratio correction coefficient Kr at the time of x purge control is set. Further, control such as correction of the ignition timing is executed in order to reduce a shock caused by a change in the generated torque of the engine 1 caused by changing the air-fuel ratio.

When the operation mode before the start of the NOx purge control is a stratified lean operation mode (an extremely lean combustion operation mode in which the air-fuel ratio is about 40 to 50 by forming a stratified mixture), the operation mode is further homogenized. Control for switching to the operation mode (operation mode for uniformly supplying fuel) is also executed. For this purpose, the control of the opening of the swirl control valve 6 and the EGR
Control such as controlling the amount, changing the fuel injection timing, or reducing the amount of intake air is performed. Next, at step 201, the fuel injection time Ti is calculated by the following equation.

Ti = K · (Qa / Ne) · TGFBA · ALPHA · Kr = K · (Qa / Ne) · Kr

In the next step 202, the counter TR for the execution time of the NOx purge control is counted up.
In step 203, it is checked whether the NOx sensor is normal (NOx sensor NG flag = 0). If normal,
Proceeds to step 204 and is determined to be abnormal (NOx
If the sensor NG flag = 1), the process proceeds to step 207.

In step 204, as shown in FIG. 11, the corrected NOx sensor output NOc is set to a threshold value knos.
Check if it is below P, and if it is,
It is determined that the desorption of NOx has ended, and the routine proceeds to step 205 for end processing. If NOc is still equal to or greater than KNOSP, it is determined that the desorption of NOx has not ended, and this control flow ends. In step 207, NOx
Instead of the output of the sensor 25, the completion of NOx desorption is determined based on the NOx purge time TR. TR is the threshold value KTRS
If not less than P, it is determined that the desorption of NOx has been completed, and the routine proceeds to step 205. If KTRSP has not been reached, this control flow ends.

At step 205, the NOx purge request flag is cleared (= 0), and at step 206, NO
The x purge time TR is initialized (= 0), and this control flow ends. If the operation mode before the start of the NOx purge control is the stratified lean operation mode, control for switching the operation mode from the homogeneous operation mode to the stratified lean operation is also executed, and then this control flow is ended. Figure 1
1 shows the air-fuel ratio and NOc when the above control flow is executed.
Here is an example of the behavior of

FIG. 12 is a flowchart showing the control for judging the deterioration of the NOx trapping agent 15 indicated by 115 in FIG. From the control flow shown in FIG. 9, the subroutine is started after the execution of the NOx purge control subroutine. First,
In step 300, it is checked whether the condition for permitting the determination of the deterioration of the NOx trap 15 is satisfied. As the deterioration determination permission condition, the NOx sensor 25 downstream of the NOx trap 15
Is normal, that the temperature detected by the exhaust gas temperature sensor 12 is within a predetermined range, that the stoichiometric or rich operation is not immediately after shifting to the lean operation after continuing for a predetermined time or more, and that the operating state during the lean operation is The change in the operating state is within a predetermined range within a predetermined range, the change in the operating state during the NOx purge control is within a predetermined range, and the operating state is within a predetermined range. If the deterioration determination permission condition is satisfied, the process proceeds to step 301. If the condition is not satisfied, the control flow ends (the deterioration determination is not performed). In the present embodiment, when the EGR valve or the like is abnormal, the lean operation is prohibited according to the flowchart shown in FIG. 9, and the deterioration determination of the NOx trap 15 is not executed.

In step 301, the lean operation continuation time TL at the time when the NOx purge control is started is set to the threshold value TL.
Check whether it is NG or less. NO if TLNG or less
It is determined that the NOx trapping performance of the x trap 15 has deteriorated,
A NOx trap deterioration determination flag is set (= 1). T
When L is longer than TLNG, it is determined that the NOx trapping performance is sufficient, and the NOx trapping agent deterioration determination flag is cleared (= 0).

Note that the NOx trap 15
The TLNG is preferably made variable according to the operating state during the lean operation.
When the NOx trapping agent deterioration determination flag is set, a code indicating deterioration of the NOx trapping agent 15 is stored by a control (not shown), and a warning to the driver such as turning on a warning lamp is executed.

FIG. 13 is a flowchart showing a process of determining an abnormality of the NOx sensor 25 and correcting the output indicated by reference numeral 101 in FIG. Step 10 of the control flow shown in FIG.
From 0, it is started as a subroutine only when it is determined to be in the specific state. First, in step 400, NO
It is checked whether or not the conditions for permitting the abnormality determination and the correction of the x sensor 25 are satisfied. For example, the following are checked as the permission conditions.

(1) The NOx sensor 25 is not determined to be abnormal by another diagnosis (not shown). For example, a heater is used inside the NOx sensor 25, and the temperature is controlled to a predetermined temperature. If the heater or the wiring to the heater is disconnected or short-circuited, the temperature cannot be controlled to a predetermined temperature, so that the output characteristics deviate from the normal state. Therefore, while the heater is controlled by the ECU 20, the disconnection and the short circuit are detected by detecting the terminal voltage and the current value when the heater is turned ON / OFF. Also, when the output of the NOx sensor 25 is out of the design range, it is determined that there is an abnormality. If it is determined that these diagnoses are abnormal,
Since it is not an abnormality such as a slight deviation of characteristics but an obvious abnormality, no abnormality determination or correction based on this control flow is performed.

(2) The NOx concentration is normal and does not fluctuate. For example, it is determined that the EGR valve, the swirl control valve 6 and the like are not abnormal by a diagnosis (not shown). The temperature detected by the exhaust gas temperature sensor 12 is within a predetermined range. It is not immediately after shifting to the lean operation after the stoichiometric or rich operation has continued for a predetermined time or more, the operating state during the lean operation is within a predetermined range and the operating state is within a predetermined range, the operation during the NOx purge control Conditions such as a state fluctuation within a predetermined range and an operating state within a predetermined range are checked.

When the conditions for permitting abnormality determination and correction of the NOx sensor 25 are satisfied, the routine proceeds to step 401.
If the condition is not satisfied, the control flow is terminated (abnormality determination and correction are not performed). In step 401, N
It is checked whether the Ox sensor 25 is in the specific state 1 or 2 suitable for abnormality determination and output correction. The specific state 1 is a state in which the estimated NOx concentration NOc is substantially zero (= x). As described above, for example, after a predetermined time has elapsed since the fuel cut, or when the air-fuel ratio is rich during acceleration or the like. State. The specific state 2 is the estimated NOx concentration N
This is a state where Oc is relatively high (= y), and as described above, for example, a state where the NOx trapping agent is not activated or a state where the temperature is high. Although not shown, NO
For example, it is also possible to forcibly saturate the NOx trapping agent 15 in order to facilitate abnormality determination and output correction of the x sensor 25.

The corrected NOx concentration estimated value NOc is
Constant or engine 1 for each specific state
Is stored in advance as a map constant corresponding to the operating state such as the rotation speed, load, air-fuel ratio, and the like, and is calculated by another control flow (not shown). In the case of the specific state 1, the process proceeds to step 402. In the case of the specific state 2, the process proceeds to step 407. If neither is the case, the control flow is terminated (no abnormality determination or correction is performed).

In step 402, the difference or ratio between the actually measured value (= X) of the NOx sensor 25 and the estimated NOx concentration value (= x) is checked.
Proceed to. If it is out of the predetermined range, it is determined that there is an abnormality, and the routine proceeds to step 406, where a flag indicating the abnormality of the NOx sensor 25 (NOx sensor NG flag 1) is set (= “1”).
In step 403, the estimated NOx concentration x
, And the actual measurement value X, Kofs (offset) is calculated by the following equation and stored. When the storage is completed, a flag NOCFN1 indicating the completion is set (= "1").

Kofs = X−x

It is preferable that Kofs is not determined by a single operation but an average value of a plurality of results is used. In step 407, the difference or ratio between the actual measurement value (= Y) of the NOx sensor 25 and the estimated NOx concentration value (= y) is checked.
Proceed to. If it is out of the predetermined range, it is determined that there is an abnormality, and the routine proceeds to step 409, where a flag indicating the abnormality of the NOx sensor 25 (NOx sensor NG flag 2) is set (= ”
1 "). In step 408, the value of Y is stored,
When the storage is completed, a flag NOCF indicating completion is stored.
N2 is set (= “1”). It is preferable that the value of Y is not obtained only once, but the result of plural times is stored and used in association with the value of y.

After both steps 403 and 408, the process proceeds to step 404. In step 404, the NOCFN
Check whether 1 and NOCFN2 are both set. If both are set, the process proceeds to step 405. If both or any of them have not been set, this flow is once ended, and the process waits until both flags are set. In step 405, the following gradient correction coefficient Kgrd is calculated, and the control flow ends.

Kgrd = y / (Y-Kofs)

Using the coefficients calculated in this control flow, in a control flow (not shown), the detection result of the NOx sensor 25 is calculated based on the following equation.

NOc = Kgrd * NOs−Kofs (2)

Here, NOc is the corrected NOx concentration, N
Os is the NOx concentration detected by the NOx sensor 25. The above equation (2) is substantially the same as the above equation (1). The NOx concentration and the measured N
The Ox concentration is shown as NOc and NOs in FIG.

When the NOx sensor abnormality judgment flag (NOx sensor NG flags 1 and 2) is set, a code indicating an abnormality of the NOx sensor 25 is stored by control (not shown), and the operation such as turning on the warning lamp 26 is performed. To warn the person. In the first and second embodiments of the present invention described above, the abnormality determination and the correction method of the NOx sensor 25 disposed downstream of the NOx trap 15 in the in-cylinder injection type gasoline engine have been described. It is not limited to this. For example, a NOx trap 15 or NOx
A sensor 25 may be used and is applicable. Furthermore, even in the case of an HC or CO sensor, the basic principle of the NOx trapping agent 15 does not change even if the HC trapping agent or the three-way catalyst is not downstream but upstream of the three-way catalyst. Absent.

That is, in a specific state in which the concentration of the exhaust component to be measured by the exhaust component detecting means can be estimated from the state of the engine 1, the exhaust gas purification device, and the like, the exhaust component concentration detected by the exhaust component detecting means and Based on the estimated exhaust component concentration, the abnormality of the exhaust component detecting means or the like is determined, and the output of the exhaust component detecting means or the estimated exhaust component concentration is corrected.

The specific contents of the specific state and the like differ depending on the type of the exhaust component detecting means constituting the exhaust gas purifying apparatus. For example, when the exhaust component detection means is disposed downstream of a catalyst that only captures and does not capture exhaust components, such as a three-way catalyst, the saturated state cannot be adopted as the specific state. In this case, the state where the catalyst is not activated or a state where the temperature is within a predetermined temperature range (for example, above a predetermined temperature, the concentration of CO or HC downstream of the three-way catalyst becomes almost zero), A state such as a fuel cut state is defined as a specific state.

As another embodiment, a method for detecting an abnormality of the HC sensor when the HC sensor is arranged downstream of the HC trapping agent will be described below. The HC trapping agent traps HC at a low temperature, and traps HC at a predetermined temperature or higher.
Release. The released HC is oxidized and purified by a catalyst provided in the HC trap or a catalyst disposed downstream. HC scavengers are being adopted mainly to reduce HC emissions after cold start, in order to meet increasingly stringent exhaust gas regulations. When the HC sensor is arranged downstream of the HC trapping agent having the HC catalytic ability, the specific state for detecting the abnormality of the HC sensor and the estimated HC concentration at that time are as follows, for example.

(1) Immediately after starting at a low temperature, the HC concentration downstream of the HC scavenger becomes almost zero. Note that the HC during the previous operation was
If the release of HC from the trapping agent is not sufficient, HC may flow downstream even immediately after starting, so in such a case, it is not adopted as a specific state. (2) At low load and high temperature, the HC concentration downstream of the HC scavenger becomes almost zero.

(3) After a predetermined time from the fuel cut, the HC concentration downstream of the HC scavenger becomes almost zero. (4) After the low temperature start, if the amount of trapped HC is saturated before reaching the HC release temperature, the concentration of HC generated from the engine 1 and H
It is almost equal to the HC concentration downstream of the C scavenger. It should be noted that the basics for separation from abnormalities of actuators and sensors that affect the concentration of HC generated from the engine 1 and for correction of the output of the HC sensor and the estimated concentration of HC are the same as those described above.
The content is the same as that described for the x trap 15 and the NOx sensor 25.

Next, a third embodiment of the present invention will be described. In this embodiment, the NO generated from the engine 1
The NOx sensor 25 and the NOx trap 1 based on the change in the detection value of the NOx sensor 25 when the x concentration is changed.
5 to determine the abnormality of the means for changing the NOx concentration. In this method, it is not possible to accurately monitor the deviation of the characteristics of the NOx sensor, but it is not necessary to be in a specific state unlike the above-described first and second embodiments. This makes it possible to determine immediately even if an abnormality occurs suddenly.

A specific embodiment will be described. During the lean operation, particularly during the stratified lean operation, the fuel injection timing, the ignition timing, the EGR rate, and the opening of the swirl control valve 6 are changed. Alternatively, the fuel injection amount is divided and the fuel is injected in a plurality of times or the fuel pressure is changed. By these operations, the concentrations of HC and NOx generated from the engine 1 can be changed in a wide range.

Immediately after the execution of the NOx purge control, even if the NOx concentration generated from the engine 1 is changed, the NOx
NOx on the downstream side is trapped by the trapping agent 15
At the position of the sensor 25, the NOx concentration does not change (almost zero). Therefore, NOx trapping agent 15
It is preferable to carry out the process in a state where NOx has been captured and NOx has started to flow downstream. As described above, the NOx trapping agent 1
5 is not activated, when the temperature is low or high, or when it is saturated, NO generated from the engine 1
Since the x concentration and the NOx concentration downstream of the NOx trapping agent 15 are substantially equal, if the operation is performed in such a specific state, the N
The output of the Ox sensor 25 easily changes, and the determination of an abnormality becomes easy. Further, even in the stoichiometric operation, the HC concentration is changed by changing the fuel injection timing,
It is also possible to change the NOx concentration by changing the ignition timing.

In addition to changing the concentration of NOx generated from the engine 1, the temperature of the exhaust gas, the flow rate of the exhaust gas, the air-fuel ratio may be changed, or air or fuel may be introduced into the exhaust passage. Even if the exhaust passage is switched, NOx
Since the NOx concentration downstream of the trapping agent 15 can be changed, the abnormality may be determined based on the change in the detection value of the NOx sensor 25 at this time.

Further, NO is forcibly set for abnormality determination.
Instead of changing the x concentration, for example, when the operation mode is switched or when the fuel cut is executed, N
An abnormality may be determined based on a change in the detection value of the Ox sensor 25. When the NOx concentration or the like is forcibly changed, there is a possibility that the emission of NOx or the like to the atmosphere may increase or the driving performance may rebound. In this case, the rebound does not occur. I'm done.

In any case, even if the NOx concentration at the position of the NOx sensor 25 is changed, if the change in the detection value of the NOx sensor 25 is equal to or smaller than a predetermined value, the NOx sensor 25 is abnormal. Is determined. In addition,
Even if the change in the detection value of the NOx sensor 25 is equal to or less than a predetermined value, the means used to change the NOx concentration, for example,
If there is an abnormality in the EGR valve or the swirl control valve 6, or if there is an abnormality in the engine 1 or the exhaust gas purifying device other than that, and the abnormality is not separately determined, And the abnormality of the NOx sensor 25 cannot be separated.

In such a case, for example, when the EGR rate is N
After changing the Ox concentration, the NOx concentration is changed at the ignition timing, and in both cases, when the change in the detection value of the NOx sensor 25 is equal to or less than a predetermined value, the NOx sensor 25 is determined to be abnormal. To Also, for example, EGR
NOx sensor 2 only when the NOx concentration is changed
In the case where the change in the detection value of No. 5 is equal to or less than the predetermined value and the NOx concentration is changed at the ignition timing and exceeds the predetermined value (the NOx sensor 25 determines that there is no abnormality), the EGR valve is abnormal. May be determined.

In the third embodiment of the present invention described above, the NOx trapping agent 1 is used in a cylinder injection type gasoline engine.
Determination of an abnormality of the NOx sensor 25 and the like disposed downstream of
Although the correction method has been described, the present invention is not limited to this. For example, the NOx sensor 25 is sometimes used in a port injection type gasoline engine or a diesel engine, and the present invention is applicable. Furthermore, even in the case of an HC or CO sensor, the basic principle of the NOx trapping agent 15 does not change even if the HC trapping agent or the three-way catalyst is not downstream but upstream of the three-way catalyst. Absent. That is, the exhaust component generated from the engine 1, the exhaust temperature, the exhaust flow rate, and the like are changed so that the exhaust component detected by the exhaust component detector changes, and the detected value of the exhaust component detector at that time changes. The abnormality of the exhaust gas component concentration means is determined based on this.

[0118]

According to the present invention, for example, the specific state of the engine or the NOx trapping agent, in which the NOx trapping agent and the NOx concentration detected by the NOx sensor are estimated to be a predetermined value, is determined. A specific state determining means for determining, based on the NOx concentration detected by the NOx sensor when the specific state is determined, determining an abnormality of the NOx sensor or the like or correcting a detection result or the like. Accordingly, at least one abnormality of the engine, the NOx trapping agent, and the NOx sensor can be promptly determined, and the NOx trapping agent and the like can be corrected. Or, for example, based on the detection value of the NOx sensor when changing the NOx concentration detected by the NOx sensor,
An abnormality of the NOx sensor or the like can be determined, or a detection result or the like can be corrected.

Therefore, even if the performance of the NOx sensor changes due to deterioration of the NOx sensor, it is possible to accurately determine the abnormality of NOx, to control the NOx trapping agent, to monitor the performance, and to control the HC trapping agent. It is possible to provide an engine control device that does not make a mistake, and it is possible to prevent exhaust gas such as NOx from being released to the atmosphere and to reduce fuel consumption.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an engine control device for purifying exhaust gas according to the present invention.

FIG. 2 is a characteristic diagram of a NOx sensor.

FIG. 3 is a configuration diagram of an ECU.

FIG. 4 is a map diagram of a target equivalent ratio for each operation region.

FIG. 5 is a diagram illustrating an example of a NOx sensor output waveform downstream of a NOx trap and an example of NOx purge timing.

FIG. 6 is a diagram illustrating an example of a relationship between an output waveform of a NOx sensor downstream of a NOx trap and an NOx concentration on an upstream side.

FIG. 7 is a view showing an example of the relationship between the NOx trapping performance of a NOx trapping agent and the exhaust gas temperature.

FIG. 8 is a diagram illustrating an example of a method of correcting the output of the NOx sensor.

FIG. 9 is a flowchart illustrating an air-fuel ratio control process.

FIG. 10 is a flowchart illustrating a NOx purge control process.

FIG. 11 is a diagram illustrating an example of a NOx sensor output waveform downstream of a NOx trap and an end timing of NOx purge.

FIG. 12 is a flowchart illustrating a deterioration determination process of a NOx trap.

FIG. 13 is a flowchart illustrating a process of determining an abnormality of the NOx sensor and correcting the output.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Engine, 4 ... Throttle valve, 6 ... Swirl control valve, 10 ... Fuel injection valve, 11 ... Spark plug, 12 ... Temperature sensor, 14 ... Air-fuel ratio sensor, 15 ... NOx trapping agent, 2
0: ECU, 25: NOx sensor, 26: warning light.

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Claims (13)

[Claims] 1. An engine control device provided in an exhaust passage of an engine, comprising: an exhaust component detection unit configured to detect a concentration of at least one exhaust component of NOx, HC, or CO in exhaust gas; The control device may determine whether the engine or the exhaust gas purification device is in a specific state in which the concentration of the exhaust gas component detected by the exhaust gas component detection means is estimated to be a predetermined value. State determination means, an engine, the exhaust component detection means, or the exhaust purification, based on an estimated value of the exhaust component detection means in the specific state and an exhaust component concentration detected by the exhaust component detection means in the specific state. An engine control device comprising: an abnormality determination unit configured to determine that at least one of the devices is abnormal. 2. An engine control device provided in an exhaust passage of an engine, comprising: an exhaust component detection means for detecting a concentration of at least one exhaust component of NOx, HC or CO in exhaust gas; The control device may determine whether the engine or the exhaust gas purification device is in a specific state in which the concentration of the exhaust gas component detected by the exhaust gas component detection means is estimated to be a predetermined value. State determination means, an output of the exhaust component detection means or the estimated value based on an estimated value of the exhaust component detection means in the specific state, and an exhaust component concentration detected by the exhaust component detection means in the specific state. And a correcting means for correcting at least one of the following. 3. The engine control device according to claim 1, wherein the specific state determination unit determines that the engine is in a fuel cut state. 4. The exhaust gas purifying device is disposed in the exhaust passage upstream of the exhaust gas component detecting means.
A catalyst that purifies at least one exhaust component of Ox, HC, or CO, wherein the specific state determination unit determines that the catalyst is not activated, that the temperature is within a predetermined temperature range, or that the engine is in a fuel cut state. 3. The engine control device according to claim 1, wherein it is determined that the state is at least one of the following. 5. The exhaust gas control apparatus according to claim 1, wherein the exhaust gas purification device is disposed in the exhaust passage upstream of the exhaust gas component detection means.
A trapping agent for trapping at least one exhaust component of Ox, HC or CO, wherein the specific state determination means is that the trapping agent is not activated, or that the trapping agent is in a predetermined temperature range, or the trapped amount of the exhaust component 3. The engine control device according to claim 1, wherein it is determined that the engine is in a saturated state or at least one of a state in which the engine is in a fuel cut state. 6. When the air-fuel ratio of the inflowing exhaust gas is arranged in the exhaust passage of the engine, the NO
a NOx trapping agent that desorbs by trapping x by adsorption or absorption and releasing and reducing the trapped NOx when the oxygen concentration in the exhaust gas is reduced, and at a predetermined timing the air-fuel ratio of the exhaust gas From lean to stoichiometric air-fuel ratio or rich as NOx trapped by the NOx trap
An engine control device for controlling desorption of NOx, wherein the control device is disposed downstream of the NOx trapping agent in the exhaust passage, and detects NOx concentration in exhaust gas.
Detecting means; a specific state determining means for determining that the engine or the NOx trapping agent is in a specific state in which the NOx concentration detected by the NOx detecting means is estimated to be a predetermined value; The engine or the N
When it is determined that the Ox trapping agent is in a specific state, the engine, the NOx detecting unit, or the NOx based on the NOx concentration detected by the NOx detecting unit.
An engine control device comprising: an abnormality determining unit that determines at least one abnormality of the trapping agent. 7. When the air-fuel ratio of the inflowing exhaust gas is arranged in the exhaust passage of the engine, the exhaust gas NO
a NOx trapping agent that desorbs by trapping x by adsorption or absorption and releasing and reducing the trapped NOx when the oxygen concentration in the exhaust gas is reduced, and at a predetermined timing the air-fuel ratio of the exhaust gas From lean to stoichiometric air-fuel ratio or rich as NOx trapped by the NOx trap
An engine control device for controlling desorption of NOx, wherein the control device is disposed downstream of the NOx trapping agent in the exhaust passage, and detects NOx concentration in exhaust gas.
Detecting means; a specific state determining means for determining that the engine or the NOx trapping agent is in a specific state in which the NOx concentration detected by the NOx detecting means is estimated to be a predetermined value; The engine or the N
Correcting means for correcting at least one of the output of the NOx detecting means or the estimated value based on the NOx concentration detected by the NOx detecting means when the Ox trapping agent is determined to be in a specific state; A control device for an engine, comprising: 8. The specific state judging means judges that the NOx trapping agent is not activated, that the temperature is within a predetermined temperature range, that the NOx trapping amount is in a saturated state, or that the engine is in a fuel cut state. The control device for the engine according to claim 6, wherein it is determined that at least one of the above operating states is present. 9. A control device for an engine, comprising: a capture unit disposed in an exhaust passage of the engine and configured to capture at least one exhaust component of NOx, HC, or CO in exhaust gas. Exhaust component detecting means installed in the passage downstream of the capturing means for detecting the concentration of the exhaust component, and exhaust component concentration changing means for performing control for changing the exhaust component concentration to be detected by the exhaust component detecting means An engine, the exhaust component detecting means, the exhaust component concentration change based on a change in the exhaust component concentration detected by the exhaust component detecting means when the exhaust component concentration changing means changes the exhaust component concentration. Control means for determining whether or not at least one of the catching means is abnormal. . 10. The engine control device according to claim 9, wherein said exhaust component detecting means detects a NOx concentration, and said exhaust component concentration changing means changes a NOx concentration discharged from the engine. 11. The engine control device according to claim 9, wherein the exhaust component concentration changing means performs control for changing an exhaust component concentration, an exhaust temperature, or an exhaust flow rate discharged from the engine. 12. The method according to claim 1, wherein information indicating the abnormality is stored or a warning is issued when the abnormality is determined by the abnormality determining means. An engine control device according to any one of the preceding claims. 13. The system according to claim 1, wherein a predetermined diagnosis and / or a predetermined operation state is prohibited when the abnormality is determined by the abnormality determining means. Engine control device.