JP3888115B2 - Control device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a control device for an internal combustion engine having a function of returning a part of exhaust discharged to an exhaust system to an intake system.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an exhaust gas recirculation device (EGR device; Exhaust Gas Recirculation System) that recirculates a part of exhaust gas discharged from an internal combustion engine to an intake system of the engine 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) provided in the middle of the EGR passage. The EGR valve is driven through a command signal from an electronic control device or the like to control the flow rate of exhaust gas (EGR gas) recirculated to the intake system. H during exhaust₂O, CO₂, N₂As the exhaust gas recirculation is performed, these inert components are mixed into the air-fuel mixture supplied to the engine combustion, and the combustion temperature is lowered and the nitrogen oxide ( NOx) is reduced. That is, the amount of NOx in the exhaust gas can be reduced.
[0003]
By the way, since the temperature of the air-fuel mixture used for combustion rises when high-temperature exhaust gas is recirculated to the intake passage, the inside of the EGR passage is cooled in the EGR passage in order to suppress the temperature rise of the air-fuel mixture. A mechanism (EGR cooler) 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, and deposits may easily adhere to the inner wall of the passage.
[0004]
An apparatus configuration in which an oxidation catalyst is disposed upstream of the EGR cooler can be considered for such problems. According to such an apparatus configuration, since unburned components in the EGR gas are oxidatively decomposed upstream of the EGR cooler, generation of deposits is suppressed.
[0005]
[Problems to be solved by the invention]
By the way, when an oxidation catalyst is disposed upstream of the EGR cooler, unburned components in the EGR gas are oxidatively decomposed by the oxidation catalyst to generate new inactive components, resulting in use for engine combustion. The total amount of inactive components in the air-fuel mixture will also change. For this reason, it is indispensable to perform operation control that takes into account the influence of the inert component newly generated by the catalytic action in order to maintain the output characteristics and exhaust characteristics of the internal combustion engine in a suitable state.
[0006]
However, as is well known, the temperature of the EGR gas flowing into the oxidation catalyst is not necessarily limited even though the oxidation catalyst has a characteristic of maintaining the activated state only when the bed temperature is within a predetermined range. It is not constant but fluctuates. Therefore, the catalyst also irregularly repeats the transition to the activated state and the transition to the non-activated state according to the temperature fluctuation of the EGR gas. That is, it is difficult to perform operation control that accurately reflects the amount of the inert component generated by the catalytic action and to constantly stabilize the operation state of the internal combustion engine.
[0007]
The present invention has been made in view of such circumstances, and an object of the present invention is to achieve both prevention of clogging of the exhaust gas recirculation passage and stabilization of the operating state in an internal combustion engine. An object of the present invention is to provide a control device for an internal combustion engine.
[0008]
[Means for Solving the Problems]
  In order 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,
  Recirculation amount adjusting means for adjusting the amount of exhaust gas recirculated through the exhaust recirculation passage;
  Deposit generating components in the exhaust gas recirculated provided in the exhaust gas recirculation passageOxidation to oxidizeA catalyst,
Determination means for determining whether or not the oxidation catalyst is in an active state;
When the oxidation catalyst is in an active state, the target value of the excess air ratio is calculated reflecting the amount of inactive components generated by the action of the oxidation catalyst, and the oxidation catalyst is not in the active state In this case, the target value of the excess air ratio is calculated without reflecting the amount of inert components generated by the action of the oxidation catalyst.Excess air ratio control means;
  It is a summary to provide.
[0009]
The deposit-generating component means a component that can form a deposit from the component, for example, unburned hydrocarbons (HC).
[0010]
As the recirculation amount adjusting means, for example, a control valve capable of changing the substantial passage area of the exhaust recirculation passage can be applied.
[0011]
The excess air ratio control means controls the excess air ratio of the air-fuel mixture provided for combustion of the engine, not only directly controlling the excess air ratio but also reflecting the operating state of the engine, In addition, the case where the excess air ratio is indirectly controlled through the control of other parameters related to the excess air ratio (for example, the intake air amount or the amount of exhaust gas recirculated) is also included.
[0012]
When the deposit generation component is reduced by the action (for example, decomposition action) of the catalyst, the amount of the inert component in the exhaust gas is secondarily increased. On the other hand, the efficiency of such catalytic action is determined solely 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 active state of the catalyst fluctuates irregularly. According to this configuration, since the excess air ratio of the air-fuel mixture supplied to the combustion of the engine is controlled according to the active state of such a catalyst, it is possible to prevent clogging of the exhaust gas recirculation passage due to deposit adhesion, Optimization control of the operating state of the engine through exhaust gas recirculation can be performed precisely.
[0013]
Further, it is preferable that cooling means for cooling the recirculated exhaust gas at a predetermined portion of the recirculation passage is provided, and the catalyst is provided upstream of the predetermined portion.
[0014]
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 is suitably suppressed. On the other hand, since the generation of deposits in the recirculated exhaust gas is promoted, the necessity for reducing the deposit generating components by the catalyst is further increased. According to this configuration, while the temperature rise of the gas in the intake system due to the exhaust gas recirculation is suppressed by the cooling means, the intake characteristic inevitably generated with the suppression of the temperature rise of the gas in the intake system is suppressed. The fluctuation (the defect caused by this fluctuation) is preferably corrected.
[0015]
And 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, and Preferably, 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.
[0016]
When the catalyst is activated and the working efficiency as a catalyst is enhanced, the temperature of the gas flowing into the intake system through the reflux passage increases due to the generation of reaction heat based on the catalytic reaction, and the intake temperature also increases. . This variation in the working efficiency of the catalyst and the change in the intake air temperature are directly and quantitatively related. According to this configuration, the intake air temperature estimated without considering the variation in the active state of the catalyst and the actually measured intake air temperature that quantitatively reflects the variation in the active state of the catalyst are used as parameters relating to the intake characteristics. In 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 varies due to the variation in the active state of the catalyst, the optimization control of the operating state of the engine through the exhaust gas recirculation can be precisely performed. it can.
[0017]
Moreover, it is preferable that the control means makes the target value of the excess air ratio of the air-fuel mixture different according to the recognized active state of the catalyst.
[0018]
Despite the fact that the amount of inert components in the recirculated exhaust gas varies due to fluctuations in the active state of the catalyst, the air in the mixture does not take into account such variations in the amount of inert components. When the target value of the excess ratio is set, the excess air ratio does not converge toward an appropriate value. According to this configuration, the excess air ratio of the air-fuel mixture converges to an appropriate target value.
[0019]
Further, it is preferable that the control means varies a control gain for controlling the excess air ratio of the air-fuel mixture provided for combustion of the engine in accordance with the recognized active state of the catalyst.
[0020]
Despite the fact that the amount of inert components in the recirculated exhaust gas varies due to fluctuations in the active state of the catalyst, the air in the mixture does not take into account such variations in the amount of inert components. When the excess rate is controlled (when the control gain is determined), it becomes difficult for the excess air rate to converge to the target value. According to this configuration, a control gain without excess or deficiency can be obtained in converging the excess air ratio of the mixture to the target value.
[0021]
Further, the NOx catalyst provided in the exhaust system of the internal combustion engine and having a function of purifying NOx in the exhaust gas according to the amount of reducing component in the exhaust gas, and the amount of reducing component in the exhaust gas upstream of the NOx catalyst in the exhaust system are adjusted. And a reducing component amount adjusting means.
[0022]
Since the reducing component in the exhaust gas is also a deposit generation component, in an internal combustion engine equipped with a NOx catalyst that functions through adjustment of the reducing component amount in the exhaust gas, the reducing component amount adjusting means is in the exhaust gas flowing into the exhaust gas recirculation passage. It also has a large effect on the amount of deposit generation components. In 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]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, 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.
[0024]
[Engine system structure and function]
In FIG. 1, an internal combustion engine (hereinafter referred to as an engine) 1 is an in-line four-cylinder diesel engine system that includes a fuel supply system 10, a combustion chamber 20, an intake system 30, an exhaust system 40, and the like as main parts.
[0025]
First, the fuel supply system 10 includes a supply pump 11, a common rail 12, a fuel injection valve 13, an engine fuel passage P1, and the like.
[0026]
The supply pump 11 makes the fuel pumped up from a fuel tank (not shown) into a high pressure and supplies it to the common rail 12 via the engine fuel passage P1. The common rail 12 has a function as a pressure accumulation chamber that holds (accumulates) the high-pressure fuel supplied from the supply pump 11 at a predetermined pressure, and distributes the accumulated fuel to each fuel injection valve 13. The fuel injection valve 13 is an electromagnetic valve provided with an electromagnetic solenoid (not shown) therein, and is appropriately opened to inject and supply fuel into the combustion chamber 20.
[0027]
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.
[0028]
The engine 1 is provided with a known supercharger (turbocharger) 50. The turbocharger 50 includes two turbine wheels 52 and 53 that are connected via a shaft 51. One turbine wheel (intake side turbine wheel) 52 is exposed to intake air in the intake system 30, and the other turbine wheel (exhaust side turbine wheel) 53 is exposed to exhaust in the exhaust system 40. The turbocharger 50 having such a configuration performs so-called supercharging in which the intake side turbine wheel 53 is rotated using the exhaust flow (exhaust pressure) received by the exhaust side turbine wheel 52 to increase the intake pressure.
[0029]
In the intake system 30, an intercooler 31 provided in the turbocharger 50 forcibly cools the intake air whose temperature has been raised by supercharging. The throttle valve 32 provided further downstream than the intercooler 31 is an electronically controlled on-off valve whose opening degree can be adjusted in a stepless manner, and restricts the flow area of the intake air under predetermined conditions. The function of adjusting (reducing) the supply amount of the intake air is provided.
[0030]
Further, an exhaust gas recirculation passage (EGR passage) 60 that bypasses the upstream (intake system 30) and the downstream (exhaust system 40) of the combustion chamber 20 is formed in the engine 1. The EGR passage 60 has a function of returning (refluxing) a part of the exhaust to the intake system 30 as appropriate. Here, the exhaust gas recirculated to the intake system 30 via the EGR passage 60 is hereinafter referred to as EGR gas. The EGR passage 60 is provided with an EGR valve 61 that can be opened and closed steplessly by electronic control and can freely adjust the flow rate of the EGR gas, and an EGR cooler 62 for cooling the EGR gas. A catalyst casing 63 containing an oxidation catalyst is provided in the EGR passage 60 and upstream of the EGR gas in the reflux direction. The oxidation catalyst is activated in a predetermined temperature range (for example, 300 ° C. or more), and has a characteristic that promotes oxidative decomposition of an unburned component (for example, HC) contained in the EGR gas. Due to the action of this oxidation catalyst, deposits on the inner wall of the EGR passage 60 are suppressed.
[0031]
Further, in the exhaust system 40, a filter casing 42 is provided downstream of the communication part of the exhaust system 40 and the EGR passage 60. A particulate filter (not shown) for purifying particulates such as soot contained in the exhaust gas together with harmful components such as NOx is accommodated in the filter casing 42.
[0032]
The particulate filter has a honeycomb-shaped structure that defines a plurality of passages as a carrier, and is configured by supporting a NOx catalyst (a combination of a NOx absorbent and a noble metal catalyst) on the surface of the carrier. is there.
[0033]
NOx absorbents include alkali metals such as potassium (K), sodium (Na), lithium (Li) and cesium (Cs), alkaline earths such as barium (Ba) and calcium (Ca), lanthanum (La ) Or rare earth such as yttrium (Y) is applied, and platinum (Pt) or the like is applied as the noble metal catalyst. The honeycomb structure of the particulate filter is formed of a porous material that allows gas (exhaust) to permeate (for example, a ceramic material such as cordierite, which is coated with a coating material such as alumina, ceria, titania, zirconia, or zeolite). In addition, since one end of each passage is closed and the other end is opened, the exhaust gas flowing from the opening end of each passage passes through the porous material forming the inner wall of the passage. It flows into another adjacent passage and is discharged from the open end of the other passage.
[0034]
The particulate filter having such a structure purifies particulates such as soot contained in the exhaust gas and harmful components such as NOx based on the following mechanism.
[0035]
The NOx catalyst repeatedly absorbs, releases, and purifies NOx according to the oxygen concentration in the exhaust gas and the amount of the reducing component in cooperation with the NOx absorbent and the noble metal catalyst that are constituent elements. On the other hand, the NOx catalyst has a characteristic of generating active oxygen as a secondary in the process of purifying NOx. When the 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, since the active oxygen generated by the NOx catalyst has extremely high reactivity (activity) as an oxidant, fine particles deposited on or near the surface of the NOx catalyst among the captured fine particles are the active oxygen. Reacts quickly (without emitting a luminous flame) and is purified.
[0036]
On the other hand, the NOx catalyst supported on the honeycomb structure absorbs NOx in a state where a large amount of oxygen is present in the exhaust gas, and a large amount of reducing component (for example, unburned component (HC) of fuel) is present. NOx is changed to NO when₂Alternatively, it is reduced to NO and released. NO₂NOx released as NO or NO is further reduced by reacting quickly with HC and CO in the exhaust, and N₂It becomes. By the way, HC and CO are NO₂By reducing NO and NO, it is oxidized and H₂O and CO₂It becomes. Here, the engine 1 according to the present embodiment maintains the characteristics of the exhaust gas introduced into the filter casing 42 in a normal operation state in a state where oxygen is excessively present, and at an appropriate timing, the HC component ( By performing control such as increasing the amount of reducing component), the functions of the particulate filter and NOx catalyst are utilized to efficiently purify HC, CO, NOx and particulates (eg, soot) in the exhaust.
[0037]
Further, various sensors are attached to each part of the engine 1, and signals related to the environmental conditions of the installation part and the operating state of the engine 1 are output.
[0038]
That is, the rail pressure sensor 70 outputs a detection signal corresponding to the fuel pressure stored in the common rail 12. The air flow meter 72 outputs a detection signal corresponding to the flow rate (intake amount) GA of intake air downstream of the throttle valve 32 in the intake system 30. The intake air temperature sensor 78 is provided downstream of the intake system 30 connected to the EGR passage 60, and corresponds to the temperature (intake air temperature) of intake air (more precisely, a mixture of intake air and EGR gas) that passes through that area. The detected signal is output. The air-fuel ratio (A / F) sensor 73a outputs a detection signal that continuously changes in accordance with the oxygen concentration in the exhaust gas upstream of the filter casing 42 of the exhaust system 40. The A / F sensor 73b outputs a detection signal that continuously changes according to the oxygen concentration in the exhaust gas downstream of the filter casing 42 of the exhaust system 40.
[0039]
The accelerator position sensor 76 is attached to an accelerator pedal (not shown) of the engine 1 and outputs a detection signal corresponding to the depression amount ACC of the pedal. 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.
[0040]
The ECU 80 includes a central processing unit (CPU) 81, a read only memory (ROM) 82, a random access memory (RAM) 83, a backup RAM 84, a timer counter 85, and the like. These units 81 to 85 and an A / D converter are provided. The external input circuit 86 including the external output circuit 87 includes a logical operation circuit configured by being connected by a bidirectional bus 88.
[0041]
The ECU 80 configured as described above inputs detection signals of the various sensors via an external input circuit, and determines basic control for fuel injection of the engine 1 and the opening of the EGR valve 61 based on these signals. Various control related to the operating state of the engine 1 such as EGR control is performed.
[0042]
It is to be noted that a part of the exhaust gas (EGR gas) is recirculated from the exhaust system 40 to the intake system 30, the characteristics of the EGR gas are adjusted, and the influence of the recirculation of the EGR gas is further taken into account to optimize the operating state of the engine 1. As a system for achieving this, the EGR passage 60, the EGR valve 61, the EGR cooler 62, the oxidation catalyst 63, and the like constitute a control device for the engine 1 according to the present embodiment together with the ECU 80.
[0043]
[Overview of fuel injection control]
The ECU 80 performs fuel injection control based on the operating state of the engine 1 that is grasped from detection signals of various sensors. In the present embodiment, the fuel injection control is related to the implementation of fuel injection into each combustion chamber 20 through each fuel injection valve 13, and parameters such as fuel injection amount (injection time), injection timing, and injection pattern are set. It refers to a series of processes for executing the opening / closing operation of the individual fuel injection valves 13 based on the set parameters.
[0044]
The ECU 80 repeats such a series of processes every predetermined time during the operation of the engine 1. The fuel injection amount and the injection timing are basically determined on the basis of the depression amount to the accelerator pedal and the engine speed with reference to a preset map (not shown).
[0045]
Further, regarding the setting of the fuel injection pattern, the ECU 80 obtains engine output by performing fuel injection in the vicinity of compression top dead center for each cylinder as well as obtaining engine output, and fuel injection following the main injection (hereinafter referred to as a subsequent stroke). The sub-injection is referred to as “subject injection”, and the selected cylinder (combustion chamber) is performed at an appropriately selected time.
[0046]
The fuel supplied into the combustion chamber 20 by the rear stroke injection is reformed into light HC in the combustion gas and discharged to the exhaust system 40. That is, light HC that functions as a reducing agent is added to the exhaust system 40 through post-stroke injection, and the concentration of reducing components in the exhaust is increased.
[0047]
[Principle of EGR control in this embodiment]
During operation of the engine 1, the ECU 80 determines the amount of fuel (fuel injection amount) to be injected and supplied to each combustion chamber of the engine 1 based on the accelerator depression amount ACC by the operator, and further supplies intake air and EGR gas. Mix in proportion to the fuel injection amount and introduce into each combustion chamber. In this way, the excess air ratio (actual excess air ratio) λR of the air-fuel mixture used for engine combustion, that is, the mixture of intake air, EGR gas, and fuel is maintained at the target value (target excess air ratio) λ0. (Optimize the excess air ratio). Specifically, based on the fuel injection amount and the intake air amount, an introduction amount of EGR gas required to make the excess air ratio λR coincide with the target value λ0 (inflow amount into the intake system 30) is calculated. Adjustment of the opening degree of the EGR valve 61 corresponding to the amount of EGR gas introduced (performs EGR control).
[0048]
Incidentally, as described above, in the engine 1, HC and the like in the EGR gas introduced into the EGR passage 60 are oxidatively decomposed upstream of the EGR cooler 62 by the action of the oxidation catalyst built in the catalyst casing 63 to generate deposits. Is suppressed. However, the temperature of the EGR gas flowing into the catalyst casing 63 is not always constant even though the oxidation catalyst has a characteristic of maintaining the activated state 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 unactivated state according to the temperature fluctuation of the EGR gas.
[0049]
Therefore, the ECU 80 of the engine 1 according to the present embodiment sequentially estimates the active state of the oxidation catalyst in the catalyst casing 63, and calculates the amount of inert components in the EGR gas that fluctuates according to this active state as the excess air ratio. Reflect in optimization control. In other words, the operation state of the engine 1 is constantly stabilized by performing EGR control that accurately reflects the amount of the inert component generated by the action of the oxidation catalyst provided in the middle of the EGR passage 60.
[0050]
[Specific execution procedure of EGR control]
Hereinafter, with respect to “EGR control” performed by the control device for the engine 1 according to the present embodiment, a specific processing procedure thereof will be described with reference to flowcharts.
[0051]
FIG. 2 shows the processing contents of an “EGR control routine” executed to control the amount of EGR gas introduced (refluxed) into the intake system 30 via the EGR passage 60 during operation of the engine 1. This routine process is started simultaneously with the start of the engine 1 through the ECU 80, and is repeated every predetermined time.
[0052]
When the process shifts to this routine, the ECU 80 first determines the engine speed NE of the engine 1 based on the detection signal of the crank angle sensor 77 in step S101.
Further, the accelerator pedal depression amount ACC is grasped based on the detection signal of the accelerator position sensor 76. Further, the ECU 80 calculates a fuel amount (fuel injection amount) Q injected and supplied to each cylinder of the engine 1 through the fuel injection valve 13 based on the parameters NE and ACC.
[0053]
In the subsequent step S102, the ECU 80 calculates the temperature of the exhaust gas flowing into the EGR passage 60 as an estimated value (hereinafter referred to as an estimated exhaust temperature) based on the engine speed NE and the fuel injection amount Q, Based on the opening degree of the EGR valve 61, the temperature of the intake air flowing into each cylinder of the engine 1 is calculated as an estimated value (hereinafter referred to as an estimated intake temperature) T0. The temperature of the intake air (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. For this reason, the estimated intake air temperature T0 tends to increase as the estimated exhaust gas temperature increases and the opening degree of the EGR valve increases. When the oxidation catalyst 63 is functioning normally, the EGR gas is heated by oxidative decomposition of unburned components. However, when calculating the estimated exhaust gas temperature, the EGR gas is heated by this catalytic action. Do not consider.
[0054]
  In step S103, the ECU 80 calculates a difference “TR−T0” between the actual measured value of the 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. Here, the difference between the actual measured value TR of the intake air temperature and the estimated intake air temperature T0 is mainly caused by the catalytic action (the exothermic reaction of the unburned component) by the oxidation catalyst 63, so the difference “TR−T0” is large. It can be estimated that the temperature increase effect (catalytic action) of the EGR gas by the oxidation catalyst 63 is larger, and that the temperature increase effect of the EGR gas is smaller as the difference “TR−T0” is smaller. Therefore, in step S103, the ECU 80 determines whether or not the difference “TR−T0” exceeds a predetermined value Td that is set in advance. If the determination is affirmative, the oxidation catalyst 63 for EGR gas is determined. Referring to the map MP1 set as a precondition that is significantly acting, the target value (target excess air ratio) λ0 of the excess air ratio is calculated (step S104). On the other hand, if the determination in step S103 is negative, the oxidation catalyst 63 is acting significantly on the EGR gas.AbsentWith reference to the map MP2 set as a precondition, the target excess air ratio λ0 is calculated (step S105).
[0055]
In step S106, the ECU 80 calculates 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.
[0056]
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.
[0057]
After the processing in step S107, the ECU 80 once exits this routine.
[0058]
In this way, the ECU 80 continuously performs control for optimizing the excess air ratio of the air-fuel mixture provided for engine combustion during operation of the engine 1.
[0059]
Here, the conventional control device does not consider the change in the characteristics of the EGR gas due to the action of the oxidation catalyst, or assumes that the oxidation catalyst exerts a substantially constant catalytic action on the EGR gas. The parameters related to the operating state of the internal combustion engine were controlled. For this reason, from the viewpoint of accurately converging a parameter to be controlled (for example, an excess air ratio) to an optimum value, control without reliability is performed.
[0060]
In addition, like the engine 1 according to the present embodiment, an engine system having a function of increasing the amount of reducing components (for example, HC) in the exhaust in order to promote the NOx reduction action of the NOx catalyst provided in the exhaust system 40, or In an engine system having a function of cooling EGR gas, such as the EGR cooler 62, each function has an excellent effect in improving the exhaust characteristics of the engine system, and is provided in the EGR passage as described above. Problems caused by fluctuations in the activation state of the obtained catalyst have become more prominent.
[0061]
In this regard, the control device according to the present embodiment focuses on the heat generated when the oxidation catalyst decomposes the deposit generation component in the EGR gas, and is based on the difference in whether or not the EGR gas includes this heat. In other words, the active state of the oxidation catalyst is accurately grasped based on the temperature change of the intake air downstream of the EGR passage 60 in the intake system 30, and the excess air ratio of the air-fuel mixture supplied to the combustion of the engine 1 is controlled. I try to reflect it. As a result, the deposit of deposits on the inner wall of the exhaust gas recirculation passage is suitably prevented by the action of the oxidation catalyst, and the control of maintaining the excess air ratio at the optimum value is also ensured.
[0062]
In this embodiment, the actual excess air ratio λR is grasped as a calculation result based on the intake air amount GA and the fuel injection amount Q. However, based on the output signals of the A / F sensor 73a and the A / F sensor 73b. Thus, the actual excess air ratio λR may be grasped.
[0063]
In this embodiment, two types of maps MP1 and MP2 are applied depending on whether or not the oxidation catalyst is in an active state. However, the target oxygen excess rate λ0 is set in accordance with the degree of the oxidation catalyst active state. A control structure that changes in three or more stages or steplessly may be applied.
[0064]
Further, in the present embodiment, when performing the control for converging the actual oxygen excess rate λR to the target value λ0, the target value λ0 is made different based on the difference in whether or not the oxidation catalyst is in the active state. did. Instead of such a control structure, a control gain (EGR in the present embodiment) applied to control for converging the actual oxygen excess rate λR to the target value λ0 based on the difference in whether or not the oxidation catalyst is in an active state. The driving current for driving the valve may be changed or corrected. In particular, for example, in order to grasp the actual oxygen excess rate λR, the calculation results based on the intake air amount GA and the fuel injection amount Q are not applied, but the actual measurement values such as detection signals of the A / F sensor 73a and the oxygen sensor 73b are used. In the case of applying directly, the reliability of the control is further improved by changing (correcting) the control gain rather than changing the target value according to the activation state of the oxidation catalyst.
[0065]
Further, the control for converging the actual oxygen excess rate λR to the target value λ0 is not limited to the operation of the opening degree of the EGR valve 61, and for example, the opening degree of the throttle valve 32 may be operated.
[0066]
Further, the characteristic change of the EGR gas due to the difference in the activation state of the oxidation catalyst may be reflected in other control related to the operation state of the engine 1 instead of the control of the oxygen excess rate.
[0067]
In the present embodiment, the estimated intake air temperature T0 is calculated based on the engine speed NE, the fuel injection amount Q, and the like. Instead, a hardware configuration including a temperature sensor upstream of the catalyst casing 63 of the EGR passage 60 may be employed, and a parameter corresponding to the estimated intake air temperature T0 may be calculated based on a detection signal of the temperature sensor.
[0068]
In the present embodiment, a hardware configuration having an oxidation catalyst in the EGR passage 60 is adopted. However, the present invention is not limited to this, and the case where a hardware configuration having another catalyst having a property of changing the characteristics of the EGR gas due to a difference in the active state depending on the temperature condition in the EGR passage 60 is adopted. In addition, by applying a control structure substantially similar to that of the present embodiment, an effect equivalent to or equivalent to that of the present embodiment can be achieved.
[0069]
In the present embodiment, the EGR cooler 62 cools the EGR passage 60 so that the EGR gas is cooled and the temperature rise of the air-fuel mixture provided for engine combustion is suitably suppressed. . In such a configuration, while the excellent effect of cooling the EGR gas is exhibited, unburned components contained in the EGR gas form deposits, and the EGR passage 60 is likely to be clogged. The presence of the oxidation catalyst becomes more significant, and the control structure exhibits a remarkable effect in that the excess air ratio is stabilized without being affected by fluctuations in the activation state of the oxidation catalyst. However, even if the control structure is applied to a hardware configuration that includes only the control valve (EGR valve) and the catalyst in the EGR passage and does not include the EGR cooler, the effect equivalent to the present embodiment can be obtained.
[0070]
Further, in each of the above embodiments, fuel injection following the main injection (hereinafter referred to as “rear stroke injection”) is performed as a sub-injection, and is performed for the selected cylinder (combustion chamber) at an appropriately selected time. The NOx catalyst was made to function by increasing the concentration of the reducing component. On the other hand, a configuration in which an apparatus (for example, an injection valve) for adding 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 apparatus may be applied. . In this case, as the reducing agent, various liquids, gases, and powders having a function of reducing NOx as a reducing component in the gas can be applied in addition to gasoline and light oil.
[0071]
In each of the above embodiments, the exhaust purification device of the present invention is applied to the diesel engine 1 as an internal combustion engine. However, the present invention can be applied to various internal combustion engines including an EGR device.
[0072]
【The invention's effect】
As described above, according to the present invention, it is possible to precisely perform optimization control of the operating state of the engine through exhaust gas recirculation while preventing clogging of the exhaust gas recirculation passage due to deposit adhesion.
[0073]
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 characteristics that inevitably occur due to the suppression of the temperature rise of the gas in the intake system is suitably performed. Will be corrected.
[Brief description of the 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 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 side 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 bidirectional bus
P1 Engine fuel passage

Claims (5)

An exhaust gas recirculation passage for recirculating a part of the exhaust gas discharged to the exhaust system of the internal combustion engine to the intake system of the engine;
Recirculation amount adjusting means for adjusting the amount of exhaust gas recirculated through the exhaust recirculation passage;
An oxidation catalyst that is provided in the exhaust gas recirculation passage and oxidizes deposit generating components in the recirculated exhaust gas;
Determination means for determining whether or not the oxidation catalyst is in an active state;
When the oxidation catalyst is in an active state, the target value of the excess air ratio is calculated reflecting the amount of inactive components generated by the action of the oxidation catalyst, and the oxidation catalyst is not in the active state An excess air ratio control means for calculating the target value of the excess air ratio without reflecting the amount of the inert component generated by the action of the oxidation catalyst ,
A control device for an internal combustion engine, comprising: An exhaust gas recirculation passage for recirculating a part of the exhaust gas discharged to the exhaust system of the internal combustion engine to the intake system of the engine;
Recirculation amount adjusting means for adjusting the amount of exhaust gas recirculated through the exhaust recirculation passage;
An oxidation catalyst that is provided in the exhaust gas recirculation passage and oxidizes deposit generating components in the recirculated exhaust gas;
Estimating means for estimating an intake air temperature of the internal combustion engine based on at least one of an engine speed and fuel injection of the internal combustion engine;
Actual measurement means for actually measuring the intake air temperature of the internal combustion engine;
A determination unit that compares the estimated intake air temperature with the actually measured intake air temperature, and determines whether or not the oxidation catalyst is in an active state based on the comparison result;
When the oxidation catalyst is in an active state, the target value of the excess air ratio is calculated reflecting the amount of inactive components generated by the action of the oxidation catalyst, and the oxidation catalyst is not in the active state An excess air ratio control means for calculating the target value of the excess air ratio without reflecting the amount of the inert component generated by the action of the oxidation catalyst ,
A control device for an internal combustion engine, comprising: A cooling means for cooling the exhaust gas the reflux at a predetermined portion of the return passage, and internal combustion engine according to claim 1 or 2 wherein the oxidation catalyst is characterized in that it is provided on the upstream side of said predetermined portion Control device. 2. The excess air ratio control means makes a control gain for controlling an excess air ratio of an air-fuel mixture supplied for combustion of the engine different according to an active state of the oxidation catalyst. The control apparatus for an internal combustion engine according to any one of? A NOx catalyst provided in the exhaust system of the internal combustion engine and having a function of purifying NOx in the exhaust gas in accordance with the amount of reducing component in the exhaust gas;
Reducing component amount adjusting means for adjusting the amount of reducing component in the exhaust upstream of the NOx catalyst in the exhaust system;
The control apparatus for an internal combustion engine according to any one of claims 1 to 4 , further comprising:

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