JP2003106220A - Control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device for an internal combustion engine capable of preventing the clogging of an exhaust circulating passage in the internal combustion engine and stabilizing an operating condition. SOLUTION: The internal combustion engine (engine) 1 comprises a NOx catalyst in an exhaust system 40, and further comprises an EGR passage 60 branched from the exhaust system 40 for circulating a part of the exhaust to an intake system 30. The EGR passage 60 is provided with an EGR valve 61, an EGR cooler 62, and an oxidation catalyst. An electronic control unit (ECU) 80 successively estimates an active condition of the oxidation catalyst, and reflects the amount of inactive component in the EGR gas variable corresponding to the active condition, on the control for optimizing an excess air factor. That is, the amount of the inactive component generated by the action of the oxidation catalyst mounted on the way of the EGR passage 60, is correctly reflected on the EGR control, whereby the operating condition of the engine 1 can be constantly stabilized.

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 internal combustion engine having a function of recirculating a part of exhaust gas discharged to an exhaust system to an intake system.

[0002]

2. Description of the Related Art Conventionally, an exhaust gas recirculation device (EG) for recirculating a part of exhaust gas discharged from an internal combustion engine to an intake system of the engine.
R device; Exhaust Gas Recirculation System) is known. This type of device generally includes an exhaust gas recirculation passage (EGR passage) that bypasses between an exhaust system (exhaust passage) and an intake system (intake passage) of an internal combustion engine, and an on-off valve (EGR passage) provided in the middle of the EGR passage. Valve) and
By driving this EGR valve through a command signal from an electronic control unit or the like, the flow rate of exhaust gas (EGR gas) recirculated to the intake system is controlled. During exhaust, H ₂ O, CO ₂ , N ₂
Since a large amount of inactive components such as, etc. are contained, when exhaust gas recirculation is performed, these inactive components are mixed in the air-fuel mixture used for engine combustion, and the combustion temperature decreases, resulting in nitrogen oxides ( The amount of NOx produced is reduced. That is, the amount of NOx in the exhaust gas can be reduced.

By the way, when high temperature exhaust gas is recirculated to the intake passage, the temperature of the air-fuel mixture used for combustion rises. A mechanism (EGR cooler) for cooling the engine is provided. When the inside of the EGR passage is cooled by the EGR cooler, deposits originating from unburned components in the exhaust gas are likely to adhere to the inner wall of the passage. Unlike the exhaust passage, the EGR passage may have a relatively small cross section,
A deposit is likely to adhere to the inner wall of the passage to cause clogging.

To address these problems, a device configuration in which an oxidation catalyst is arranged upstream of the EGR cooler can be considered. According to such a device configuration, the unburned component in the EGR gas is
Oxidative decomposition upstream of the cooler suppresses the formation of deposits.

[0005]

By the way, when an oxidation catalyst is arranged upstream of the EGR cooler, unburned components in the EGR gas are oxidatively decomposed by the oxidation catalyst to generate new inert components. Therefore, as a result, the total amount of inert components in the air-fuel mixture used for engine combustion also changes. Therefore, it is indispensable to perform the operation control in consideration of the influence of the inactive component newly generated by the catalytic action in order to maintain the output characteristics and the exhaust characteristics of the internal combustion engine in a suitable state.

However, as is well known, although the oxidation catalyst has a characteristic of retaining the activated state as a catalyst only when the bed temperature is within a predetermined range, the EGR gas flowing into the oxidation catalyst is The temperature is not always constant but varies. Therefore, the catalyst also irregularly repeats the transition to the activated state and the transition to the non-activated state according to the temperature change of the EGR gas. That is, it is difficult to perform operation control that accurately reflects the amount of the inactive component generated by the catalytic action, and to constantly stabilize the operation state of the internal combustion engine.

The present invention has been made in view of such circumstances, and an object thereof is to prevent the exhaust gas recirculation passage in the internal combustion engine from being blocked and to stabilize the operating state. An object of the present invention is to provide a control device for an internal combustion engine capable of performing the above.

[0008]

To achieve the above object, the present invention provides an exhaust gas recirculation passage for recirculating a part of exhaust gas discharged to an exhaust system of an internal combustion engine to an intake system of the engine, and the exhaust gas. Recirculation amount adjusting means for adjusting the amount of exhaust gas recirculated through the recirculation passage, a catalyst provided in the exhaust gas recirculation passage for reducing deposit forming components in the recirculated exhaust gas, and an active state of the catalyst are recognized. The gist is that the recognition means and the excess air ratio control means for controlling the excess air ratio of the air-fuel mixture to be burned in the engine based on the recognized active state of the catalyst.

The deposit-forming component means a component capable of forming a deposit from the component, for example, unburned hydrocarbons (HC) and the like.

As the recirculation amount adjusting means, for example, a control valve or the like capable of changing the substantial passage area of the exhaust gas recirculation passage can be applied.

Further, the air excess ratio control means controlling the air excess ratio of the air-fuel mixture used for combustion of the engine not only directly controls the air excess ratio but also changes the operating state of the engine. It also includes a case where the excess air ratio is indirectly controlled through the control of other parameters that reflect the excess air ratio and are related to the excess air ratio (for example, the amount of intake air and the amount of exhaust gas recirculated).

When the deposit forming component is reduced by the action of the catalyst (for example, the decomposition action), the amount of the inactive component and the like in the exhaust gas is secondarily increased. On the other hand, the efficiency of such catalysis is solely determined by the active state of the catalyst. However, during the operation of the internal combustion engine, for example, the characteristics of the exhaust gas introduced into the exhaust gas recirculation passage (for example, the temperature of the exhaust gas) change, so that the activation state of the catalyst fluctuates irregularly. According to the configuration, since the excess air ratio of the air-fuel mixture used for combustion in the engine is controlled according to the activation state of the catalyst, while preventing clogging of the exhaust gas recirculation passage due to deposits, It is possible to precisely control the optimization of the operating state of the engine through exhaust gas recirculation.

Further, it is preferable that a cooling means is provided for cooling the recirculated exhaust gas at a predetermined portion of the recirculation passage, and the catalyst is provided upstream of the predetermined portion.

By cooling the recirculated exhaust gas, even if a part of the exhaust gas is recirculated to the intake system, the temperature rise in the intake system can be suppressed appropriately. On the other hand, since the generation of deposits in the exhaust gas that is recirculated is promoted, the need for the catalyst to reduce the deposit-forming components becomes even greater. According to this configuration, the temperature rise of the gas in the intake system due to the exhaust gas recirculation is suppressed by the cooling means, while the intake characteristic of the intake characteristic that is inevitably generated due to the temperature rise suppression of the gas in the intake system is suppressed. Fluctuations (defects due to this fluctuation) are preferably corrected.

Further, it comprises an estimating means for estimating the intake air temperature of the internal combustion engine based on at least one of the engine speed and the fuel injection of the internal combustion engine, and a measuring means for actually measuring the intake air temperature of the internal combustion engine. And, the recognition means is
It is preferable to compare the estimated intake air temperature with the actually measured intake air temperature and recognize the active state of the catalyst based on the comparison result.

When the catalyst is activated and the efficiency of action as a catalyst is increased, the reaction heat generated by the catalytic reaction causes
The temperature of the gas flowing into the intake system via the recirculation passage also rises, which in turn raises the intake air temperature. The fluctuation of the operation efficiency of the catalyst and the change of the intake air temperature are directly and quantitatively related to each other. According to this configuration, as the parameter relating to the intake characteristic, the intake temperature estimated without considering the variation of the activation state of the catalyst, and the measured intake temperature that quantitatively reflects the variation of the activation state of the catalyst. By comparison, the active state of the catalyst is accurately recognized based on the comparison result. Therefore, even when the amount of the inert component of the recirculated gas fluctuates due to the fluctuation of the active state of the catalyst, it is possible to precisely perform the optimization control of the operating state of the engine through the exhaust gas recirculation. it can.

Further, it is preferable that the control means varies the target value of the excess air ratio of the air-fuel mixture according to the recognized activation state of the catalyst.

Although the amount of inactive components in the recirculated exhaust gas fluctuates due to the change in the active state of the catalyst, the mixing is performed without taking into account such changes in the amount of inactive components. When the target value of the air excess ratio is set, the excess air ratio does not converge toward an appropriate value. With this configuration, the excess air ratio of the air-fuel mixture converges to an appropriate target value.

Further, it is preferable that the control means varies the control gain for controlling the excess air ratio of the air-fuel mixture used for combustion of the engine in accordance with the recognized activation state of the catalyst.

Although the amount of inactive components in the recirculated exhaust gas fluctuates due to the change in the active state of the catalyst, the mixing is performed without taking into consideration such changes in the amount of inactive components. When the air excess ratio is controlled (when the control gain is determined), it becomes difficult for the excess air ratio to converge to the target value. According to this configuration, when the excess air ratio of the air-fuel mixture is made to converge to the target value, it is possible to obtain a control gain that is sufficient.

Further, a NOx catalyst provided in the exhaust system of the internal combustion engine and having a function of purifying NOx in the exhaust according to the amount of the reducing component in the exhaust, and a reducing component in the exhaust upstream of the NOx catalyst in the exhaust system. And a reducing component amount adjusting means for adjusting the amount.

Since the reducing component in the exhaust gas is also a deposit forming component, in an internal combustion engine equipped with a NOx catalyst that functions by adjusting the reducing component amount in the exhaust gas, the reducing component amount adjusting means is provided in the exhaust gas recirculation passage. It also has a large effect on the amount of deposit-forming components in the flowing exhaust gas. With this configuration, the operational effect obtained by performing the optimization control of the operating state of the engine based on the recognized active state of the catalyst becomes more remarkable.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment in which a control device for an internal combustion engine according to the present invention is applied to a diesel engine system will be described below.

[Structure and Function of Engine System] FIG. 1
In an internal combustion engine (hereinafter referred to as an engine) 1, a fuel supply system 10, a combustion chamber 20, an intake system 30, and an exhaust system 40.
It is an in-line 4-cylinder diesel engine system mainly composed of the above.

First, the fuel supply system 10 comprises a supply pump 11, a common rail 12, a fuel injection valve 13, an engine fuel passage P1 and the like.

The supply pump 11 raises the pressure of the fuel pumped up from a fuel tank (not shown) to the engine fuel passage P1.
Supply to the common rail 12 via. Common rail 1
2 has a function as a pressure accumulator that holds (accumulates) the high-pressure fuel supplied from the supply pump 11 at a predetermined pressure,
This accumulated fuel is distributed to each fuel injection valve 13. The fuel injection valve 13 is an electromagnetic valve having an electromagnetic solenoid (not shown) therein, and is opened appropriately to inject fuel into the combustion chamber 20.

The intake system 30 forms a passage (intake passage) for intake air supplied into each combustion chamber 20. On the other hand, the exhaust system 40 forms a passage (exhaust passage) for exhaust gas discharged from each combustion chamber 20.

The engine 1 is also provided with a known supercharger (turbocharger) 50. The turbocharger 50 includes two turbine wheels 52, 53 connected via a shaft 51. One turbine wheel (intake turbine wheel) 52 is exposed to intake air in the intake system 30, and the other turbine wheel (exhaust turbine wheel) 53 is exposed to exhaust gas in the exhaust system 40. Turbocharger 50 having such a configuration
Uses the exhaust flow (exhaust pressure) received by the exhaust side turbine wheel 52 to rotate the intake side turbine wheel 53 to increase the intake pressure, so-called supercharging.

In the intake system 30, the turbocharger 5
The intercooler 31 provided at 0 forcibly cools the intake air whose temperature has risen due to supercharging. The throttle valve 32 provided further downstream than the intercooler 31 is an electronically controlled opening / closing valve whose opening can be adjusted steplessly, and throttles the flow passage area of intake air under predetermined conditions. , Has a function of adjusting (reducing) the supply amount of the intake air.

Further, the engine 1 is provided with an exhaust gas recirculation passage (EGR passage) 60 that bypasses the upstream side (intake system 30) and the downstream side (exhaust system 40) of the combustion chamber 20. The EGR passage 60 has a function of appropriately returning (recirculating) a part of the exhaust gas to the intake system 30. Here, the EGR passage 60
Exhaust gas that recirculates to the intake system 30 via the above is hereinafter referred to as EGR gas. The EGR passage 60 is opened and closed steplessly by electronic control, and an EGR valve 61 capable of freely adjusting the flow rate of the EGR gas and an EGR valve 61 for cooling the EGR gas are provided.
A GR cooler 62 is provided. In addition, the EGR passage 6
0, a catalyst casing 63 containing an oxidation catalyst is provided upstream of the EGR gas in the recirculation direction. The oxidation catalyst has a property of being activated in a predetermined temperature range (for example, 300 ° C. or higher) and promoting the oxidative decomposition of unburned components (for example, HC) contained in the EGR gas. Due to the action of this oxidation catalyst, the adhesion of deposits to the inner wall of the EGR passage 60 is suppressed.

Further, in the exhaust system 40, the exhaust system 40
A filter casing 42 is provided downstream of the connecting portion of the EGR passage 60. Filter casing 4
A particulate filter (not shown) for purifying soot and other fine particles contained in the exhaust gas together with harmful components such as NOx is contained in the inside of the exhaust gas 2.

The particulate filter has, as a carrier, a honeycomb-shaped structure that defines a plurality of passages, and a NOx catalyst (a combination of a NOx absorbent and a noble metal catalyst) is carried on the surface of the carrier. It is a thing.

As the NOx absorbent, potassium (K),
Sodium (Na), lithium (Li), cesium (C
Alkali metals such as s), barium (Ba), alkaline earths such as calcium (Ca), lanthanum (L)
a) or a rare earth such as yttrium (Y) or the like is applied, and platinum (Pt) or the like is applied as the noble metal catalyst. The honeycomb structure of the particulate filter is made of a porous material that allows gas (exhaust gas) to pass therethrough (eg, a ceramic material such as cordierite, alumina, ceria,
It is formed by wash-coating a coating material such as titania, zirconia, or zeolite), and one end of each passage is closed and the other end is open, so that it flows in from the open end of each passage. The exhaust gas flows into the other adjacent passage by passing through the porous material forming the inner wall of the passage, and is discharged from the open end of the other passage.

The particulate filter having such a structure purifies particulates such as soot and harmful components such as NOx contained in exhaust gas based on the following mechanism.

The NOx catalyst is a constituent element of NOx.
Through the cooperation of the absorbent and the precious metal catalyst, NOx is repeatedly absorbed, released and purified according to the oxygen concentration in the exhaust gas and the amount of reducing components. On the other hand, the NOx catalyst is
In the process of purifying x, it has a characteristic of secondary generation of active oxygen. When exhaust gas passes through the particulate filter, fine particles such as soot contained in the exhaust gas are captured by the structure (porous material). Here, the active oxygen generated by the NOx catalyst has extremely high reactivity (activity) as an oxidant.
Therefore, among the captured fine particles, the fine particles deposited on the surface of the NOx catalyst or in the vicinity thereof react with this active oxygen rapidly (without emitting a bright flame) and are purified.

On the other hand, NO carried on the honeycomb structure
The x-catalyst absorbs NOx when a large amount of oxygen is present in the exhaust gas, and is NO when a large amount of reducing components (for example, unburned components (HC) of fuel) are present.
x is reduced to NO ₂ or NO and released. NO ₂ and N
The NOx released as O is further reduced to N ₂ by rapidly reacting with HC and CO in the exhaust gas. By the way, HC and CO reduce NO ₂ and NO, and are themselves oxidized to H ₂ O and CO ₂ . Here, the engine 1 according to the present embodiment maintains the characteristics of the exhaust gas introduced into the filter casing 42 in a state in which oxygen is excessively present as a normal operating state, and at the same time, the HC component ( The particulate filter and the NOx are controlled by performing control such as increasing the reducing component).
Utilizing the function of the catalyst, HC, CO, NOx and fine particles (soot, etc.) in the exhaust gas are efficiently purified.

Various sensors are attached to each part of the engine 1 to output signals relating to the environmental conditions of the installed part and the operating state of the engine 1.

That is, the rail pressure sensor 70 outputs a detection signal corresponding to the pressure of the fuel stored in the common rail 12. The air flow meter 72 outputs a detection signal according to the flow rate (intake amount) GA of intake air downstream of the throttle valve 32 in the intake system 30. Intake air temperature sensor 7
Reference numeral 8 denotes a detection signal that is provided in the intake system 30 downstream of the connection with the EGR passage 60 and that corresponds to the temperature (intake temperature) of the intake air (correctly, the mixture of intake air and EGR gas) passing through the connection. Is output. The air-fuel ratio (A / F) sensor 73a outputs a detection signal that continuously changes according to the oxygen concentration in the exhaust gas upstream of the filter casing 42 of the exhaust system 40. The A / F sensor 73b is used in the exhaust system 4
A detection signal that continuously changes according to the oxygen concentration in the exhaust gas is output downstream of the filter casing 42 of 0.

The accelerator position sensor 76 is attached to an accelerator pedal (not shown) of the engine 1,
A detection signal corresponding to the depression amount ACC of the pedal is output. The crank angle sensor 77 outputs a detection signal (pulse) every time the output shaft (crankshaft) of the engine 1 rotates by a certain angle. Each of these sensors is electrically connected to an electronic control unit (ECU) 80.

The ECU 80 is a central processing unit (CPU) 8
1, read only memory (ROM) 82, random access memory (RAM) 83 and backup RAM 8
4, a timer counter 85, etc.
85, an external input circuit 86 including an A / D converter, and an external output circuit 87 are connected by a bidirectional bus 88 to provide a logical operation circuit.

The ECU 80 thus configured inputs the detection signals of the above various sensors through an external input circuit,
Based on these signals, various controls relating to the operating state of the engine 1, such as basic control for fuel injection of the engine 1 and EGR control for determining the opening degree of the EGR valve 61, are collectively performed.

A part of the exhaust gas (EGR gas) is recirculated from the exhaust system 40 to the intake system 30, and
The EGR passage 60, the EGR valve 61, the EGR cooler 62, the oxidation catalyst 63, and the like are provided in the ECU 80 as a system for adjusting the gas characteristics and further considering the influence of the recirculation of the EGR gas to optimize the operating state of the engine 1. Together with this, a control device for the engine 1 according to the present embodiment is configured.

[Outline of Fuel Injection Control] The ECU 80 carries out fuel injection control based on the operating state of the engine 1 which is detected from the detection signals of various sensors. In the present embodiment, the fuel injection control relates to execution of fuel injection into each combustion chamber 20 through each fuel injection valve 13, and sets parameters such as a fuel injection amount (injection time), an injection timing, an injection pattern, It refers to a series of processes for executing the opening / closing valve operation of each fuel injection valve 13 based on these set parameters.

The ECU 80 carries out such a series of processes.
This is repeated every predetermined time during the operation of the engine 1. The fuel injection amount and injection timing are basically determined based on the amount of depression on the accelerator pedal and the engine speed by referring to a preset map (not shown).

Regarding the setting of the fuel injection pattern,
The ECU 80 obtains the engine output by performing the fuel injection in the vicinity of the compression top dead center for each cylinder as the main injection, and also selects the fuel injection subsequent to the main injection (hereinafter referred to as the post-stroke injection) as the sub-injection as appropriate. The selected cylinder (combustion chamber) is performed at the selected time.

The fuel supplied into the combustion chamber 20 by the post-stroke injection is reformed into light HC in the combustion gas and discharged to the exhaust system 40. That is, the light HC that functions as a reducing agent is added to the exhaust system 40 through the post-stroke injection to increase the concentration of reducing components in the exhaust.

[Principle of EGR Control in the Present Embodiment] During operation of the engine 1, the ECU 80 controls the amount of fuel injected into each combustion chamber of the engine 1 (fuel amount based on the accelerator depression amount ACC by the operator). (Injection amount) is determined, and intake air and EGR gas are mixed in a distribution commensurate with the fuel injection amount and introduced into each combustion chamber. In this way, the air-fuel mixture used for engine combustion, that is, intake air, E
An excess air ratio (actual excess air ratio) λR of a mixture of GR gas and fuel is maintained at a target value (target excess air ratio) λ0 (the excess air ratio is optimized). Specifically, the amount of EGR gas introduced (the amount of inflow to the intake system 30) required to match the excess air ratio λR with the target value λ0 is calculated based on the fuel injection amount and the intake air amount. Adjustment of the opening of the EGR valve 61 corresponding to the amount of EGR gas introduced (EGR control is performed).

By the way, as described above, in the engine 1, the H in the EGR gas introduced into the EGR passage 60 is caused by the action of the oxidation catalyst contained in the catalyst casing 63.
C and the like are oxidatively decomposed upstream of the EGR cooler 62, and the formation of deposits is suppressed. However, the temperature of the EGR gas flowing into the catalyst casing 63 is not always constant, although the oxidation catalyst has a characteristic of retaining the activated state as a catalyst only when the bed temperature is within a predetermined range. The catalyst also irregularly repeats the transition to the activated state and the transition to the non-activated state according to the temperature change of the EGR gas.

Therefore, the engine 1 according to the present embodiment
The ECU 80 sequentially estimates the active state of the oxidation catalyst in the catalyst casing 63, and changes E depending on the active state.
The amount of the inert component in the GR gas is reflected in the optimization control of the excess air ratio. In other words, the operating state of the engine 1 is constantly stabilized by performing EGR control that accurately reflects the amount of the inactive component generated by the action of the oxidation catalyst provided in the middle of the EGR passage 60.

[Specific Execution Procedure of EGR Control]
Regarding the "EGR control" executed by the control device of the engine 1 according to the present embodiment, a specific processing procedure thereof will be described with reference to a flowchart.

In FIG. 2, the EGR introduced (recirculated) into the intake system 30 through the EGR passage 60 during operation of the engine 1.
The processing content of the "EGR control routine" implemented in order to control a gas amount is shown. This routine process is executed by the ECU 8
Through 0, execution of the engine 1 is started at the same time as the engine 1 is started, and is repeated every predetermined time.

When the processing shifts to this routine, the ECU
First, in step S101, the engine speed N of the engine 1 is N based on the detection signal of the crank angle sensor 77.
E, and the accelerator pedal depression amount ACC is grasped based on the detection signal of the accelerator position sensor 76. Further, the ECU 80 controls the amount of fuel injected into each cylinder of the engine 1 through the fuel injection valve 13 (fuel injection amount).
Q is calculated based on the parameters NE and ACC.

In the following step S102, the ECU 80
Is EGR based on the engine speed NE and the fuel injection amount Q.
The temperature of the exhaust gas flowing into the passage 60 is calculated as an estimated value (hereinafter, referred to as the estimated exhaust gas temperature), and further, based on the exhaust gas temperature and the opening degree of the EGR valve 61, the intake air flowing into each cylinder of the engine 1 is calculated. The air temperature is calculated as an estimated value (hereinafter referred to as an estimated intake air temperature) T0. The temperature of intake air (a mixture of intake air and EGR gas) is generally determined by how much heat is introduced into the intake system 30 through the EGR gas. Therefore, the estimated intake air temperature T0 increases as the estimated exhaust gas temperature increases and as the opening degree of the EGR valve increases.
Tends to be higher. If the oxidation catalyst 63 is functioning normally, the EGR gas will rise in temperature due to the oxidative decomposition of unburned components. However, when the estimated exhaust gas temperature is calculated, the temperature rise of the EGR gas due to this catalytic action should be performed. I will not consider it.

In step S103, the ECU 80
The difference "TR-T0" between the actually measured value of intake air temperature (hereinafter referred to as the actual intake air temperature) TR based on the detection signal of the intake air temperature sensor 78 and the estimated intake air temperature T0 is calculated. Here, since the difference between the measured value TR of the intake air temperature and the estimated intake air temperature T0 mainly occurs due to the catalytic action of the oxidation catalyst 63 (exothermic reaction of unburned components), the difference "TR-T0" is large. It can be estimated that the temperature increasing effect (catalytic action) of the EGR gas by the oxidation catalyst 63 is larger, and the smaller the difference "TR-T0" is, the smaller the temperature increasing effect of the EGR gas is. Therefore, in step S103, the ECU 80 determines that the difference "TR-T
It is determined whether or not "0" exceeds a preset predetermined value Td, and if the determination is affirmative, it is set on the assumption that the oxidation catalyst 63 is significantly acting on the EGR gas. The target value of the excess air ratio (target excess air ratio) λ0 is calculated with reference to the generated map MP1 (step S
104). On the other hand, when the determination in step S103 is negative, the target excess air ratio λ0 is set by referring to the map MP2 set on the assumption that the oxidation catalyst 63 is significantly acting on the EGR gas. Calculate (step S105).

In step S106, the ECU 80
A current excess air ratio (actual excess air ratio) λR determined from the relationship among the intake air amount GA, the fuel injection amount Q, and the opening degree of the EGR valve 61 is calculated.

In step S107, the opening degree of the EGR valve 61 is adjusted so that the actual excess air ratio λR converges to the target value λ0.

After the processing of step S107, E
The CU 80 exits this routine once.

In this manner, the ECU 80 continuously performs control for optimizing the excess air ratio of the air-fuel mixture used for engine combustion during operation of the engine 1.

Here, in the conventional control device, the air excess is assumed without considering the characteristic change of the EGR gas due to the action of the oxidation catalyst or on the assumption that the oxidation catalyst exerts a substantially constant catalytic action on the EGR gas. Parameters such as the rate related to the operating state of the internal combustion engine were controlled. For this reason, from the viewpoint of accurately converging the parameter to be controlled (for example, the excess air ratio) to an optimum value, unreliable control has been performed.

An engine having the function of increasing the reducing component (for example, HC) in the exhaust gas so as to promote the NOx reducing action of the NOx catalyst provided in the exhaust system 40, like the engine 1 according to the present embodiment. System, also EG
In the engine system having the function of cooling the EGR gas like the R cooler 62, the individual functions have excellent working effects in improving the exhaust characteristic of the engine system, while the EGR gas is provided in the EGR passage as described above. The problem caused by the change in the activation state of the catalyst has become more remarkable.

In this respect, the control device according to the present embodiment pays attention to the heat generated when the oxidation catalyst decomposes the deposit forming component in the EGR gas, and whether the EGR gas contains this heat or not. Based on the difference, in other words, based on the temperature change of the intake air downstream of the EGR passage 60 in the intake system 30, the active state of the oxidation catalyst is accurately grasped, and the excess air ratio of the air-fuel mixture used for combustion in the engine 1 is obtained. It is reflected in the control of. As a result, adhesion of deposits to the inner wall of the exhaust gas recirculation passage is suitably prevented by the function of the oxidation catalyst, and the precision of control for maintaining the excess air ratio at an optimum value is also ensured.

In this embodiment, the actual excess air ratio λR is grasped as the calculation result based on the intake air amount GA and the fuel injection amount Q. However, the output of the A / F sensor 73a and the A / F sensor 73b is determined. The actual excess air ratio λR may be grasped based on the signal.

Further, in the present embodiment, two types of maps MP1 and MP2 are applied according to the presence or absence of the active state of the oxidation catalyst. However, the target oxygen excess is determined according to the degree of the active state of the oxidation catalyst. A control structure may be applied in which the rate λ0 is changed in three or more steps or in steps.

Further, in the present embodiment, the actual oxygen excess ratio λ
In controlling the R to converge to the target value λ0, the target value λ0 is made different based on the difference in whether the oxidation catalyst is in the active state or not. Instead of such a control structure, a control gain (EGR in the present embodiment is applied to a control for converging the actual oxygen excess ratio λR to a target value λ0 based on the difference in whether the oxidation catalyst is in the active state or not. The drive current for driving the valve) may be changed or corrected. In particular, for example, to understand the actual oxygen excess ratio λR,
Instead of applying the calculation result based on the intake air amount GA and the fuel injection amount Q, the A / F sensor 73a and the oxygen sensor 73b are not used.
When the actual measurement value such as the detection signal is directly applied, the control gain is further improved by changing (correcting) the control gain rather than changing the target value according to the activation state of the oxidation catalyst. It will be.

Further, the control for converging the actual oxygen excess ratio λR to the target value λ0 is not limited to the operation of the opening degree of the EGR valve 61, but may be the operation of the opening degree of the throttle valve 32, for example.

E due to the difference in the active state of the oxidation catalyst
The change in the characteristics of the GR gas may be reflected not in the control of the oxygen excess ratio but in other control relating to the operating state of the engine 1.

Further, in the present embodiment, the engine speed NE
The estimated intake air temperature T0 is calculated based on the fuel injection amount Q and the like. Instead of this, it is possible to adopt a hardware configuration having a temperature sensor upstream of the catalyst casing 63 of the EGR passage 60, and calculate a parameter corresponding to the estimated intake air temperature T0 based on the detection signal of this temperature sensor.

Further, in the present embodiment, the EGR passage 60
It was decided to adopt a hardware configuration that has an oxidation catalyst in. However, the present invention is not limited to this, and a case where a hardware configuration having a different active state depending on the temperature condition in the EGR passage 60 and having a property of changing the characteristic of the EGR gas due to the different active state is adopted. Also, by applying a control structure that is substantially the same as that of the present embodiment, it is possible to obtain the same or similar effect as the present embodiment.

In this embodiment, the EGR cooler 6 is also used.
2 cools the EGR passage 60, so that the EGR gas is cooled and the temperature rise of the air-fuel mixture used for engine combustion is suitably suppressed. In such a configuration, while the excellent effect of cooling the EGR gas is exhibited, unburned components and the like contained in the EGR gas form a deposit, and the EGR passage 60 is likely to be clogged. The presence of the oxidation catalyst becomes more significant, and the above control structure exerts a remarkable effect in terms of stabilizing the excess air ratio without being affected by the fluctuation of the active state of the oxidation catalyst. However, the control valve (E
Even if the above control structure is applied to a hardware configuration that includes only a GR valve) and a catalyst and does not include an EGR cooler, the effect according to the present embodiment can be obtained.

Further, in each of the above-mentioned embodiments, the fuel injection (hereinafter referred to as the post-stroke injection) subsequent to the main injection is used as the sub-injection, at an appropriately selected time and in the selected cylinder (combustion chamber).
The NOx catalyst was made to function by increasing the concentration of reducing components in the exhaust gas. On the other hand, a configuration may be applied in which a device (for example, an injection valve) that adds a reducing agent is provided upstream of the catalyst casing 42 of the exhaust system 40, and the reducing agent is added to the exhaust system 40 through the device. . In this case, as the reducing agent, other than gasoline and light oil,
Various liquids, gases, and powders having a function of reducing NOx as a reducing component in gas can be applied.

Further, in each of the above embodiments, the exhaust gas purification device of the present invention is applied to the diesel engine 1 as an internal combustion engine, but the present invention is applied to various internal combustion engines equipped with an EGR device. You can

[0072]

As described above, according to the present invention,
It is possible to precisely control the optimization of the operating state of the engine through exhaust gas recirculation, while preventing clogging of the exhaust gas recirculation passage due to deposit deposits.

Further, while the temperature rise of the gas in the intake system due to the exhaust gas recirculation is suppressed by the cooling means, the fluctuation of the intake characteristic inevitably occurs due to the temperature rise suppression of the gas in the intake system. Is preferably modified.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a diesel engine system according to an embodiment of the present invention.

FIG. 2 is a flowchart showing an EGR control procedure according to the same embodiment.

[Explanation of symbols]

1 Diesel engine (internal combustion engine) 10 Fuel supply system 11 Supply pump 12 common rail 13 Fuel injection valve 20 Combustion chamber 30 Intake system 31 Intercooler 32 Throttle valve 40 exhaust system 42 Filter casing 50 turbocharger 51 shaft 52 Exhaust turbine wheel 53 Intake side turbine wheel 60 EGR passage 61 EGR valve 62 EGR cooler 63 catalyst casing 70 Rail pressure sensor 72 Air flow meter 73a, 73b Air-fuel ratio (A / F) sensor 76 Accelerator position sensor 77 Crank angle sensor 78 Intake air temperature sensor 80 Electronic Control Unit (ECU) 81 Central Processing Unit (CPU) 82 Read-only memory (ROM) 86 External input circuit 87 External output circuit 88 interactive bus P1 engine fuel passage

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F02M 25/07 580 F02M 25/07 580E 4D048 B01D 53/94 F01N 3/08 G F01N 3/08 3/24 R 3/24 S F02D 21/08 301A F02D 21/08 301 301C 301E 41/04 355 41/04 355 360A 360 41/14 310L 41/14 310 310M 310N 310P 43/00 301E 43/00 301 301K 301N 301T 301W 301Y 301Z 45/00 314Z 45/00 314 B01D 53/36 103C 103B 101B (72) Inventor Naofumi Kumata 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Hisashi Oki Toyota City, Aichi Prefecture Toyota Town No. 1 Yota Motor Co., Ltd. (72) Inventor Shinobu Ishiyama 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Co., Ltd. (72) Inventor Akihiko Negami 1 Toyota Town, Aichi Prefecture Toyota Motor Corporation F Term (Reference) 3G062 AA01 AA05 BA02 CA00 ED08 ED09 ED10 GA01 GA04 GA05 GA06 GA10 GA12 GA15 3G084 AA01 BA05 BA08 BA09 BA13 BA15 BA18 BA19 BA20 BA23 BA24 CA01 CA02 CA03 CA04 CA05 CA06 DA10 DA19 DA27 EA11 EB01 FA22 FA02 FA02 FA02 FA02 FA02 FA02 FA02 FA02 FA02 FA02 FA02 FA02 FA02 FA02 FA22 FA02 FA10 FA22 FA22 FA38 3G091 AA02 AA10 AA11 AA18 AA28 AB06 AB13 BA00 BA14 CA13 CA18 CB02 CB03 CB07 DA01 DA02 DB06 DB07 DB10 EA00 EA01 EA05 EA07 EA15 EA31 EA34 HA31 HA34 HA06 HA06B37B06A02 GB06B36B06A06B06B36B16B16B16B16B16B16B16B16B16B16B16B16B16B16B16B16B16B16B16B16B16B16B16B16B16B16B16B16B16B16B16B16B16B16B16B16B16B16B16B16B16B16B16B16B16B16B16A06 AA17 AA18 AB03 AB20 BA01 BA04 BA07 BB01 BB06 BB08 DC03 DC09 DC10 DC12 DC14 DC15 DE03S EA01 EA05 EA07 EA11 EC02 FA13 FA17 FA18 FA20 FA41 FB06 GA03 GA08 GA11 GA12 GA13 HA01X03 HE02Z01 HE02 HE02Z01 HE02 HE01 HE02 HE01 HE02Z01 HE02 HE02 HE01 HE02 A02 HA04 HA06 HA13 JA15 JA24 JA25 JB09 LA03 LB11 MA01 MA11 MA18 MA26 NA06 NA07 NA08 ND01 ND04 ND05 NE01 NE06 NE13 NE15 PA01B PA01Z PA10B PA10Z PB08A PB08B PB08Z PD01B02 A02B02A02 A04B04A02 A02B03A02 BA14Y BA15Y BA18Y BA30Y

Claims (6)

[Claims] 1. An exhaust gas recirculation passage for recirculating a part of exhaust gas discharged to an exhaust system of an internal combustion engine to an intake system of the engine, and a recirculation amount for adjusting an amount of exhaust gas recirculated through the exhaust gas recirculation passage. Adjusting means, a catalyst provided in the exhaust gas recirculation passage for reducing a deposit-forming component in the recirculated exhaust gas, recognizing means for recognizing the active state of the catalyst, and the recognizing means based on the active state of the recognized catalyst. A control device for an internal combustion engine, comprising: an excess air ratio control means for controlling an excess air ratio of an air-fuel mixture used for combustion of the engine. 2. The cooling device according to claim 1, further comprising cooling means for cooling the recirculated exhaust gas at a predetermined portion of the recirculation passage, and wherein the catalyst is provided upstream of the predetermined portion. Control device for internal combustion engine. 3. An estimation means for estimating the intake air temperature of the internal combustion engine based on at least one of the engine speed and fuel injection of the internal combustion engine, and an actual measurement means for actually measuring the intake air temperature of the internal combustion engine. 3. The recognizing means compares the estimated intake air temperature with the actually measured intake air temperature, and recognizes the active state of the catalyst based on the comparison result. A control device for an internal combustion engine as described. 4. The control means causes the target value of the excess air ratio of the air-fuel mixture to differ depending on the recognized activation state of the catalyst. Internal combustion engine control device. 5. The control means varies a control gain for controlling an excess air ratio of an air-fuel mixture used for combustion in the engine in accordance with the recognized activation state of the catalyst. The control device for an internal combustion engine according to claim 1. 6. An NOx catalyst provided in the exhaust system of the internal combustion engine and having a function of purifying NOx in the exhaust according to the amount of the reducing component in the exhaust, and a reducing component in the exhaust upstream of the NOx catalyst in the exhaust system. The control device for an internal combustion engine according to any one of claims 1 to 5, further comprising: a reducing component amount adjusting means for adjusting the amount.