JP2002206448A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To significantly reduce generation amount of smoke and NOx over a wide operation region and moreover restrain deterioration of fuel consumption. SOLUTION: When engine output is in an intermediate load region, a fuel injection time is delayed in a range where the fuel consumption amount is not greatly increased, (for example, in a range where the fuel consumption deterioration is 5% or less), and an EGR amount is increased compared to the conventional level, and an EGR amount is increased to the region wherein the smoke amount is reduced after peaking. When the engine output is in a low load region, the EGR amount is increased further than in the case of the intermediate load region, and the fuel injection time is made to advance to a degree where the generation amount of the NOx is not increased greatly. Thus, the generation both of the smoke and the NOx can be restrained over a wide operation region, while improving the fuel consumption.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust purification system for an internal combustion engine (particularly, a diesel engine).

[0002]

2. Description of the Related Art In recent years, in diesel engines,
Smoke (so-called black smoke), which is a harmful component in exhaust gas, and N
In order to simultaneously reduce Ox (nitrogen oxide), various diesel combustion technologies are being studied. For example, Patent No. 2
Japanese Patent Publication No. 864896 discloses a technique for simultaneously suppressing the generation of smoke and NOx by performing a large amount of exhaust gas recirculation (EGR) and delaying the fuel injection timing until after the top dead center. This is because the generation of NOx is suppressed by lowering the combustion temperature, and most of the combustion is converted to premixed combustion by greatly extending the ignition delay period.
That is, the generation of smoke is suppressed by promoting the mixing of air and fuel.

[0003]

However, in the above-described combustion method, since only the EGR is increased in a region before the amount of smoke generation reaches a peak, both smoke and NOx are significantly reduced in this region. It is difficult to reduce. Further, since a large amount of EGR and the retardation of the injection timing both cause deterioration of combustion, there is also a problem that when these are performed in the entire operation region, fuel efficiency is deteriorated.

Further, the conventional method cannot significantly reduce the amount of smoke emitted. Therefore, when a trap filter is used as an exhaust gas purifying means, frequent regeneration operations are required to incinerate and remove the collected smoke. . This could lead to a significant decrease in the durability of the filter. In order to avoid this, it is necessary to reduce the reproduction frequency by using a larger filter, but it is practically difficult in consideration of the mountability to a vehicle. The present invention has been made based on the above circumstances, and an object of the present invention is to provide an exhaust gas purification device for an internal combustion engine that can significantly reduce the amount of smoke and NOx generated over a wide operation range and suppress deterioration of fuel efficiency. To provide.

[0005]

When the output of the internal combustion engine enters a medium load range, the exhaust gas recirculation amount is increased with the calculated fuel injection timing delayed. The amount of smoke discharged from the internal combustion engine gradually increases with the increase in the amount of exhaust gas recirculation, and shows a characteristic that decreases after reaching a peak.When this characteristic is referred to as a medium load region smoke characteristic, the combustion temperature reducing means The output calculated by the output calculation means is a predetermined value T1 indicating a middle load range and a predetermined value T2 (T1> T
2) If the fuel consumption of the internal combustion engine does not increase significantly, the fuel injection timing is retarded until the smoke characteristic in the medium load range is obtained, and until the smoke amount decreases after the peak. The exhaust gas recirculation amount is increased. The “range in which the fuel consumption does not greatly increase” is, for example, a “range in which fuel consumption deterioration is within 5%”.

The operation of the present invention will be described with reference to FIGS. FIG. 5 shows the exhaust gas recirculation amount (hereinafter referred to as EGR) when the engine output is in a middle load range (for example, output torque of 30 to 70 Nm).
(Referred to as an amount), the relationship between the emission and the fuel consumption (fuel consumption) when the fuel consumption is increased. The broken line in the figure is the case where fuel is injected at the basic injection timing, and the solid line in the figure is
This is a case where fuel is injected with a delay from the basic injection timing.

The relationship between the EGR amount and smoke, NOx, and fuel consumption will be described below. a) Smoke: When the EGR amount is increased, the amount of smoke generated gradually increases due to deterioration of combustion in the cylinder. Conventionally, the EGR amount has been determined within this range (a range in which the amount of smoke generation increases with an increase in the EGR amount) in consideration of NOx and other items. In this case, it is possible to reduce smoke by retarding the injection timing (reduced from the broken line to the solid line in FIG. 5A).
Within this range, it is not possible to sufficiently increase the EGR amount while suppressing the generation of smoke, so that the NOx
Is difficult to reduce. In other words, in this case, although the smoke is reduced by promoting the mixing of the fuel and the air, it has been difficult to reduce the amount by itself.

However, when the EGR amount is further increased as compared with the prior art, as shown by a solid line in FIG. 5, the smoke amount once reaches a peak, then drops sharply, and thereafter hardly occurs. This mechanism is based on the fact that a large amount of EGR (ultra-high amount of EGR exceeding 70%) increases the inert gas in the cylinder and lowers the oxygen concentration, so that the combustion becomes slower and the heat capacity in the cylinder increases. This is because the temperature in the cylinder during fuel combustion decreases. In this region, the unburned HC in the cylinder does not become steamed due to lack of oxygen, so that it does not become smoked, or it remains as it is or SOF (a component soluble in an organic solvent among particulate matter contained in exhaust gas).
Is discharged as This is not simply an extension of conventional diesel combustion, but a new low smoke combustion.

The HC and SOF emitted as a result of this combustion
Is easily purified by the action of the oxidation catalyst carried by the exhaust purification means provided in the exhaust pipe. If these are once smoked in a steamed state, a large and complicated after-treatment device is required for purification, but according to the combustion of the present invention, the amount of smoke discharged is extremely small. Therefore, the post-processing device is unnecessary. Further, in the present invention, since the priority is given to suppressing fuel consumption deterioration, the EGR is not excessively increased until the fuel consumption is significantly deteriorated. Therefore, depending on the conditions, smoke may be discharged, although the amount is extremely small as compared with the conventional case. However, since the amount is small, it is easily purified by a simple exhaust gas purifying means.

B) NOx: As the amount of EGR increases, the oxygen concentration in the cylinder decreases and the heat capacity in the cylinder increases, so that combustion becomes slow and the temperature in the cylinder during combustion decreases. As a result, rapid heat generation accompanying premix combustion is suppressed, and the amount of generated thermal NOx is reduced. The generation amount of NOx decreases as the EGR amount increases. In a region where the amount of smoke generation exceeds the peak, a much larger amount of EGR than ever before is possible, so that very small amounts of smoke and NOx can be burned.

C) Fuel efficiency: An increase in the amount of EGR causes a decrease in thermal efficiency due to deterioration of combustion.
As shown in FIG. 5C, the fuel consumption increases. However, as a result of the experiment, even if the smoke generation amount exceeds the peak EGR amount, there is a region (the region in FIG. 5B) where the fuel consumption does not increase so much for a while. Was. Based on this, the EGR amount is
By increasing to the region of FIG. 5B, smoke and NOx
It is possible to significantly reduce the fuel consumption while significantly reducing the generation amount of both.

Next, when the engine output is in the middle load range, a large amount of EGR is performed (region (B) of FIG. 5), and then the emission and fuel consumption are increased when the amount of retard of the injection timing is increased. FIG. 6 shows the relationship. Hereinafter, the relationship between the injection timing retard amount, smoke, NOx, and fuel consumption will be described. d) Smoke: When the retard amount is increased, the smoke decreases, but as shown in FIG. 6D, when the retard amount is too small, the decrease amount of the smoke is small. When the retard amount is further increased, the smoke rapidly decreases and hardly occurs. This is because the fuel burns in a state where the temperature in the cylinder is lowered due to a large amount of EGR and the retardation of the injection timing, so that the combustion is slowed down. This is because the steamed state does not occur, so that the smoke is not generated and is discharged as it is or as SOF. This is easily purified by exhaust gas purification means provided in the exhaust pipe.

E) NOx: The temperature in the cylinder during combustion decreases as the retard amount increases. As a result, thermal NO
The generation amount of x decreases. The generation amount of NOx decreases as the retard amount increases. In a region where the amount of smoke generation exceeds the peak, a much larger amount of EGR than ever before is possible, so that very small amounts of smoke and NOx can be burned.

F) Fuel efficiency: An increase in the amount of retardation causes a decrease in thermal efficiency due to deterioration of combustion, and if this is done excessively, an increase in fuel consumption will occur, as shown in FIG. 6 (F). However, as a result of the experiment, it became clear that there is a region where the fuel consumption does not increase so much (the region in FIG. 6 (E)) for a while even after almost no smoke is generated. Therefore, the amount of retard of the injection timing is calculated as shown in FIG.
By increasing to the region (E), it is possible to significantly reduce both the amount of smoke and the generation of NOx and to suppress the deterioration of fuel efficiency.

As described above, smoke and NOx
In order to simultaneously reduce the temperature, it is important to lower the temperature in the cylinder during fuel combustion, and the effect is very large. So, to bring out this effect more effectively,
An intake gas cooling unit is provided for cooling the intake gas taken into the internal combustion engine. Thus, the temperature of the intake gas sucked into the cylinder can be reduced, so that the temperature in the cylinder during fuel combustion can be reduced. Also,
The combustion temperature reducing means, the detected oxygen concentration in the exhaust,
The exhaust gas recirculation amount is corrected so as to have a predetermined value obtained from the output of the operating state detecting means. As shown in FIG. 5, the range of the EGR amount that achieves both low smoke and low NOx is relatively narrow.
If this deviates from the appropriate amount, there is a possibility that emission or fuel consumption will be greatly deteriorated.

On the other hand, in practice, the EGR amount may deviate from an appropriate value due to a variation in performance or a change with time of characteristics of each part or a delay in an increase in fresh air or recirculated exhaust gas during vehicle acceleration. In particular, the emission characteristics of smoke
Since it is sensitive to the EGR amount, highly accurate EGR control is required for suppressing smoke. In contrast,
In the present invention, EGR feedback control is performed in order to prevent the EGR amount from deviating from an appropriate value. At this time, the oxygen concentration in the exhaust gas including the information on the combustion state and closely related to the emission (especially, smoke) is detected.
As a result, all errors included in the intake system, the EGR system, and the injection system can be absorbed, and highly accurate feedback control can be performed.

According to a second aspect of the present invention, in the exhaust gas purifying apparatus for an internal combustion engine according to the first aspect, the intake gas cooling means includes:
This is a recirculation exhaust gas cooling means provided in the middle of the exhaust gas recirculation passage to cool the exhaust gas recirculating to the intake side through the exhaust gas recirculation passage. As the recirculated exhaust gas cooling means, for example, a water-cooled type having high cooling performance is used. As a result, the temperature of the exhaust gas flowing into the intake pipe through the exhaust gas recirculation passage decreases, so that the temperature of the intake gas sucked into the cylinder can be reduced.

According to a third aspect of the present invention, in the exhaust gas purifying apparatus for an internal combustion engine according to the second aspect, the capacity of the recirculation exhaust gas cooling means is made larger than the displacement of the internal combustion engine. This allows
Since the recirculated exhaust gas can be sufficiently cooled, the emission can be easily reduced.

According to a fourth aspect of the present invention, in any one of the first to third aspects, the compression ratio of the internal combustion engine is made smaller than usual. Thus, the compression end temperature before the fuel combustion can be reduced, so that the cylinder internal temperature during the fuel combustion can be reduced.

According to a fifth aspect of the present invention, in the exhaust gas purifying apparatus for an internal combustion engine according to any one of the first to third aspects, when the output of the internal combustion engine is in a medium load range, the compressor of the internal combustion engine is set to a smaller one. Change to Thus, the compression end temperature before the fuel combustion can be reduced, so that the cylinder internal temperature during the fuel combustion can be reduced.

(Means of Claim 6) In the exhaust gas purifying apparatus for an internal combustion engine according to claim 3 or 4, the compression ratio of the internal combustion engine is set to 18 or less. This aims at lowering the peak temperature after combustion by reducing the temperature of the gas in the cylinder just before the fuel burns (the gas compression temperature in the cylinder at the compression top dead center). It is.
By setting the compression ratio, which is conventionally set at 18 to 20, to 18 or less, it is possible to more easily realize combustion that can achieve both low smoke and low NOx.

(Embodiment 7) In the exhaust gas purifying apparatus for an internal combustion engine according to any one of claims 1 to 6, the exhaust gas purifying means is a trap filter carrying an oxidation catalyst.
Unburned HC or SOF generated by the combustion of the present invention
The fraction can be easily purified with an oxidation catalyst. In addition, smoke generated in small amounts depending on the conditions is collected by the trap filter and gradually deposited, but since the amount of generated smoke is small,
The frequency of filter regeneration is low. In addition, since the oxidation catalyst is supported, the smoke deposited on the filter can be easily incinerated even at a relatively low temperature such as the exhaust temperature of the internal combustion engine. Therefore, the exhaust gas purifying means can have a simple configuration as compared with the conventional one.

(Eighth Means) In the exhaust gas purifying apparatus for an internal combustion engine according to any one of the first to seventh aspects, the combustion temperature reducing means may be configured so that the output calculated by the output calculating means indicates a low load range. When the value is equal to or less than the value T2, the fuel injection timing calculated by the injection timing calculation means is advanced. When the engine output is in a low load range (for example, an output torque of 30 Nm or less),
FIG. 7 shows the relationship between emission and fuel efficiency when the injection timing is set in the region of FIG. 8E and the EGR amount is increased.

At low load, air (oxygen) in the cylinder
Since the amount is large, almost no smoke occurs even if the EGR amount is increased. However, when the EGR amount becomes too small (the region in FIG. 7A), the generation of NOx increases, and when the EGR amount becomes too large (the region in FIG. 7C), the fuel efficiency deteriorates. Therefore, the EGR amount is set in a range (the region of FIG. 7B) in which both the prevention of NOx emission and the prevention of deterioration of fuel efficiency can be achieved. As a result, the discharge of smoke can also be prevented.

On the other hand, FIG. 8 shows the relationship between the emission and the fuel efficiency when the injection timing is changed by setting the EGR amount in the region shown in FIG. 7B. Under this condition, since the amount of air (oxygen) in the cylinder is large, no smoke is generated even if the amount of retard is increased. NOx does not increase significantly unless the injection timing is advanced extremely as shown in FIG. 8D. On the other hand, the fuel consumption increases as the injection timing is retarded. Accordingly, as shown in FIG. 8 (f), when the injection timing is retarded in the same manner as in the case of the medium load, only the fuel efficiency is deteriorated. The injection timing is advanced to the extent shown in FIG.
(E) area). Thereby, it is possible to suppress the generation of smoke and NOx while improving the fuel efficiency.

According to a ninth aspect of the present invention, in the exhaust gas purifying apparatus for an internal combustion engine according to any one of the first to eighth aspects, the injection amount correcting means included in the combustion temperature reducing means includes an output calculated by the output calculating means. Is changed from a value less than the predetermined value T1 to a value greater than T1, or from a value greater than T1 to a value less than T1 or the output calculated by the output calculation means is a value greater than T2 from a value less than the predetermined value T2 Or T
When the value changes from a value greater than 2 to a value equal to or less than T2, the fuel injection amount is corrected so that the output of the internal combustion engine changes continuously.

When the combustion according to the present invention is performed, in a region where the EGR amount or the injection timing retard amount is large, the combustion is slightly deteriorated, so that the thermal efficiency is reduced as compared with the conventional combustion. Further, when the injection timing is advanced at an extremely low load, the thermal efficiency is improved as compared with the middle load region. Therefore, depending on the operation state of the internal combustion engine, the output torque obtained even when the same amount of fuel is injected may differ. That is, the operation range of the internal combustion engine is a medium load range and a high load range (a range larger than the predetermined value T1).
Or between the middle load range and the low load range, it is necessary to correct the fuel injection amount after the change in the operating range so that the output torque changes smoothly.

[0028]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a flowchart showing a processing procedure of the exhaust gas purification device, and FIG. 2 is a schematic configuration diagram of the exhaust gas purification device. As shown in FIG. 2, the diesel engine 1 to which the present exhaust emission control device is applied is provided with a common rail type fuel injection device, in which high-pressure fuel pumped from a high-pressure pump (not shown) is constantly stored in the common rail 2. Is injected from the injector 3 at the pressure, injection amount, and injection timing.

The exhaust gas purifier includes an exhaust gas recirculation pipe 6 connecting the exhaust pipe 4 and the intake pipe 5 of the engine 1,
EGR amount control valve 7 provided in the inside, EGR cooling device 8 provided in the middle of exhaust gas recirculation pipe 6, intake throttle valve 9 provided in intake pipe 5, trap filter 10 provided in exhaust pipe 4, and the present system And an electronic control unit (hereinafter, referred to as an ECU 11) for controlling the operation of the ECU.

The EGR amount control valve 7 and the intake throttle valve 9 are provided with high-response valves which are directly driven by, for example, an electric motor.
The valve opening can be set quickly according to the operating condition of the engine 1. The EGR cooling device 8 receives cooling water (not shown) and cools the EGR gas by heat exchange with the cooling water. For example, a laminated fin type having high cooling efficiency is used. However, the capacity of the EGR cooling device 8 (the capacity of the cooling water passage portion + the capacity of the EGR gas passage portion) is set to be larger than the displacement of the engine 1.

Conventionally, the EGR is performed in accordance with the difference between the pressure in the intake pipe 5 and the pressure in the exhaust pipe 4 mainly by setting the opening of the EGR amount control valve 7 to a predetermined amount. In contrast, in the present embodiment, an intake throttle valve 9 and an EGR cooling device 8 are provided in addition to the EGR amount control valve 7 in order to perform a large amount of EGR for realizing low emission. That is,
When the intake throttle valve 9 is greatly throttled (opening degree is reduced) and the EGR amount control valve 7 is opened while the pressure in the intake pipe 5 is low, E
The differential pressure across the GR amount control valve 7 is increased, and the EGR amount can be greatly increased as compared with the related art.

At this time, the EGR gas flowing back to the intake pipe 5 is cooled by the EGR cooling device 8 so that the high-density EGR gas that has been cooled and contracted, instead of being expanded at a high temperature, is transferred from the intake pipe 5 into the cylinder. Can be introduced.
As a result, the heat capacity of the gas in the cylinder can be maximized while securing the amount of oxygen necessary for fuel combustion.
As a result, the temperature in the cylinder during fuel combustion drops significantly. Further, by sufficiently cooling the EGR gas, the temperature of the cylinder intake gas can be reduced. This also greatly contributes to the temperature reduction in the cylinder during fuel combustion. Therefore, combustion that can achieve both low smoke and low NOx can be performed.

The trap filter 10 is formed by alternately plugging honeycomb-shaped channels made of porous ceramics such as cordierite and silicon carbide, and has a filter surface containing a precious metal such as Pt or Pd as a main component. Oxidation catalyst is carried. The trap filter 10 is connected to the exhaust pipe 4
The engine 1 is installed downstream of the turbo 12
When the exhaust containing smoke discharged from the filter passes through the wall surface of the porous ceramic, smoke particles larger than the filter pore diameter are mainly collected on the filter surface. HC, CO, S discharged during combustion by the action of the oxidation catalyst.
The OF can be oxidized and easily purified.

The ECU 11 controls the injector 3 based on the operating state of the engine 1 detected by various sensors described later.
In addition to controlling the opening and closing operations of the electromagnetic valve 13, the intake throttle valve 9, and the EGR amount control valve 7, which drive the ECU, the opening degrees of the intake throttle valve 9 and the EGR amount control valve 7 are corrected and controlled according to the exhaust oxygen concentration.

Various sensors include an engine rotation sensor 14 for detecting an engine rotation speed, an accelerator opening sensor 15 for detecting an accelerator opening from an amount of depression of an accelerator pedal (not shown), and an injection pressure sensor for detecting an injection pressure in the common rail 2. 16. An exhaust oxygen concentration sensor 17 (for example, a limiting current method) for detecting the oxygen concentration in the exhaust pipe 4 upstream of the trap filter 10 is provided.

The compression ratio of the diesel engine 1 is
Usually, it is set to about 18 to 20, but in this embodiment, 1 is set.
8 or less. As a result, the temperature in the cylinder at the compression top dead center is reduced, and as a result, the temperature in the cylinder during fuel combustion can be significantly reduced.

Next, the operation of the exhaust gas purifying apparatus will be described with reference to the flowchart shown in FIG. However, here
Only the part that sets the EGR amount and the injection timing according to the operating conditions of the engine 1 and the like will be described. Step 100: The engine speed NE and the accelerator opening are read from the outputs of the engine rotation sensor 14 and the accelerator opening sensor 15. Step 101 (output calculation means of the present invention): The output torque T of the engine 1 is calculated from the sensor output read in Step 100. The relationship between the two is stored in the memory of the ECU 11 in advance.

Step 102: It is determined whether or not the operating range of the engine 1 has changed. Specifically, the output torque calculated last time is compared with the output torque calculated this time, and both are compared with those in FIG.
It is determined whether the torque straddles the torque T1 or T2 (T1> T2). If the operating region of the engine 1 is changing, that is, if the vehicle is straddling T1 or T2, the process proceeds to Step 103. If the operating region of the engine 1 is not changing, that is, if the vehicle is not straddling T1 or T2, Proceed to Step104.

Step 103 (Injection amount correction means of the present invention): An injection amount correction amount for preventing a sudden change in output torque is calculated. When the operating region of the engine 1 changes between the high load region and the medium load region shown in FIG. 3, or between the medium load region and the low load region, the combustion efficiency slightly increases even with the same fuel consumption. Since they are different (and better than and better), the output torque slightly changes. Therefore,
The injection amount is corrected in order to prevent drivability from being deteriorated due to a sudden change in torque due to this difference.

As an example, a case where the output torque changes over T1 will be described with reference to FIGS. For example, when the accelerator is depressed and the vehicle is rapidly accelerated, the operating conditions change from a medium load region (a combustion region in which low smoke and low NOx are compatible) shown in FIG. 3 to a high load region (the same combustion region as in the past). At this time, assuming that the fuel injection amount is the same (Q0 in FIG. 4) without considering the change in the combustion state, the output torque sharply increases from TT0 to TT1. This causes a torque shock and deteriorates drivability.

Therefore, immediately after the operating conditions change, the output torque TT0 is maintained by setting the injection amount to Q1 reduced and corrected by ΔQ (see FIG. 4). Thereby, it is possible to prevent the drivability from being deteriorated due to the instantaneous change in the output torque. On the other hand, when the operating range changes from to, the fuel injection amount is increased and corrected. It should be noted that this correction amount gradually decreases after a lapse of a predetermined time after the output torque changes over T1, and eventually becomes zero.
By so setting, the output torque can be continuously changed. The same applies to the case where the output torque changes across T2.

Step 104... The magnitude relationship between the output torque T calculated in Step 101 and the first predetermined value T1 is determined. In addition,
T1 is an output in a medium load range, for example, an output torque of 70N
m. Here, in the case of T> T1 (high load range shown in FIG. 3), since the engine output is large and the combustion temperature during combustion is high, if EGR or the injection timing retard is forcibly performed in this state, the fuel consumption etc. High deterioration, low smoke and low NO
Since it is difficult to establish a combustion that satisfies x, the process proceeds to Step 108 to perform the conventional combustion. On the other hand, in the case of T <T1 (the middle load range and the low load range shown in FIG. 3), the combustion proceeds to low smoke and low NOx.

Step 105: The magnitude relationship between the output torque T calculated in Step 101 and the second predetermined value T2 is determined. In addition,
T2 is an output in a low load range, for example, an output torque of 30 N
m. Here, if T> T2 (medium load region shown in FIG. 3), the process proceeds to Step 106, and if T <T2 (low load region shown in FIG. 3), the process proceeds to Step 107.

Step 106: A larger amount of EGR is performed than before, and an EGR amount and a retard amount are calculated for delaying the injection timing to lower the cylinder temperature during fuel combustion. The EGR amount and the retard amount are determined based on operating conditions of the engine 1 read by various sensors, and are determined in advance by the ECU 11.
Is stored in the memory. The basic fuel injection timing is calculated by the ECU 11 by a known method.

Step 107... In a low load range, since the amount of air (oxygen) in the cylinder is large, no smoke is generated even if the EGR amount is increased. Accordingly, a larger amount of EGR is performed than in the past, and the injection timing is advanced and set in order to suppress deterioration in fuel efficiency. The EGR amount and the advance angle amount for this are calculated. Note that the EGR amount and the advance amount are determined based on the operating conditions of the engine 1 read by various sensors,
It is stored in the memory of U11.

Step 108: The result of the above Step 103 and St
EGR and fuel injection are performed based on the results calculated in ep106 and Step107. The EGR is determined by the intake throttle valve 9 and E
This is performed by setting the degree of opening of the GR amount control valve 7 to a predetermined value.
The injection timing is changed (retarded or advanced) by changing the valve opening command time output from the ECU 11 to the solenoid valve 13.

Step 109: The output of the exhaust oxygen concentration sensor 17 is read. Step 110: The value read in Step 109 is compared with the target value, and it is determined whether or not the deviation from the target value is larger than a predetermined value. The target value is determined from the engine speed, the accelerator opening, and the like, and is stored in the memory of the ECU 11 in advance. Here, when the deviation from the target value is larger than the predetermined value, the process proceeds to Step 111, and when it is smaller than the predetermined value, the process returns to Step 100.

Step 111: The opening of the intake throttle valve 9 is corrected and controlled so as to reduce the difference between the actual exhaust oxygen concentration and the target value. Here, as shown in FIG. 5, the range of the EGR amount that achieves both low smoke and low NOx in the middle load region of the engine 1 is relatively narrow, and if it deviates from the appropriate amount, the emission and fuel consumption are greatly deteriorated. There is. However, in practice, the EGR amount may deviate from an appropriate amount due to performance variation of each component (for example, the EGR amount control valve 7 or the like) or a change in characteristics over time.
Feedback control is performed.

At this time, highly accurate control can be performed by detecting the oxygen concentration in the exhaust including information on the combustion state of the fuel. When the oxygen concentration deviating from the target value is corrected, either the opening degree of the intake throttle valve 9 or the opening degree of the EGR amount control valve 7 may be changed, but if both are changed simultaneously, the control system becomes unstable. Therefore, in this system, the intake throttle valve 9
Modify only. However, instead of the intake throttle valve 9, EGR
Only the quantity control valve 7 may be modified.

(Effect of this Embodiment) According to the above-mentioned exhaust gas purifying apparatus, when the engine output is in the middle load range, as long as the fuel consumption of the engine 1 does not increase significantly, FIG.
And the conventional EGR
By increasing the EGR amount up to the region of FIG. 5B (the region where the smoke amount decreases after the peak), which is larger than the amount, the smoke generation amount and the NOx generation amount in the medium load region are both significantly reduced, and the fuel consumption is reduced. Deterioration can be suppressed.

When the engine output is in a low load range,
The EGR amount is further increased up to the region of FIG. 7B than in the middle load region (see FIG. 9), and the fuel injection timing is advanced to the region of FIG. It is possible to suppress generation of smoke and NOx while improving fuel efficiency.

FIGS. 5 and 7 show characteristics when the injection timing is fixed and only the EGR amount is changed. FIGS. 6 and 8 show the characteristics when the EGR amount is fixed and only the injection timing is changed. In this case, the EGR amount and the injection timing are changed simultaneously as shown in FIG.
However, FIG. 9 is merely an example, and for example, T2 <T <
In the region of T1, the EGR amount is not necessarily required to be constant as shown in the figure, but may be set to decrease as the torque increases.

The same applies to the injection timing. In the region below T2, the amount of advance is reduced with an increase in torque, and
In the range of 2 <T <T1, it is also possible to set so that the retard amount is reduced as the torque increases. Note that the vertical axis in FIG. 9 is not an absolute amount but a relative amount as an increase / decrease amount with respect to the conventional EGR amount or an advance amount and a retard amount with respect to the conventional injection timing.

Further, according to the combustion of the present system, a small amount of smoke may be generated even though the amount is small compared to the conventional combustion, depending on conditions. However, a small amount of generated smoke is trapped in the trap filter 1 installed in the exhaust pipe 4.
After being collected on the zero surface, the filter temperature is increased and incinerated. At this time, due to the action of the oxidation catalyst carried on the filter surface, the smoke particles have a lower temperature than before (a temperature of 600 ° C. or higher is required to burn the smoke particles without a catalyst. Is 450 ° C
Therefore, the amount of temperature rise of the filter is small, and it is possible to regenerate the filter only at the exhaust gas temperature during high-speed operation.

As a result, it is possible to minimize problems such as deterioration of fuel efficiency due to temperature rise for filter regeneration. Further, it is possible to prevent a decrease in durability due to exposing the trap filter 10 to a high temperature. The regeneration time of the trap filter 10 is determined based on the output of a sensor that measures the differential pressure across the filter (not shown), and is determined by a known method such as an intake throttle or post-injection of the common rail 2 (injected after the main injection). The method raises the filter temperature and regenerates.

In the above embodiment, the engine 1 is designed to reduce the temperature of the gas in the cylinder immediately before the combustion of the fuel and to reduce the peak temperature after the combustion by that much.
The compression ratio is set to 18 or lower, which is lower than usual. However, besides the method of lowering the compression ratio itself, for example, in a middle load region, the closing timing of the intake valve is delayed by using a known variable valve timing mechanism. Thus, a method of delaying the compression start timing to lower the effective compression ratio may be used. Also,
The gas amount in the cylinder may be reduced by reducing the opening of both the intake throttle valve 9 and the EGR amount control valve 7. In either method, the compression temperature before combustion ignition decreases,
As a result, the combustion temperature can be reduced.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a processing procedure of an exhaust gas purification device.

FIG. 2 is a schematic configuration diagram of an exhaust gas purification device.

FIG. 3 is a characteristic diagram showing an operation range in a relationship between an engine speed and a torque.

FIG. 4 is a characteristic diagram showing a relationship between a torque and a fuel injection amount with respect to an operation range.

FIG. 5 is a characteristic diagram showing a relationship between an EGR amount and an emission in a medium load region.

FIG. 6 is a characteristic diagram showing a relationship between an injection timing and an emission in a medium load region.

FIG. 7 is a characteristic diagram showing a relationship between an EGR amount and an emission in a low load region.

FIG. 8 is a characteristic diagram showing a relationship between injection timing and emission in a low load region.

FIG. 9 is a characteristic diagram showing a correlation between an EGR amount and an injection timing with respect to an output torque.

[Explanation of symbols]

 Reference Signs List 1 engine (internal combustion engine) 4 exhaust pipe 5 intake pipe 6 exhaust recirculation pipe (exhaust recirculation passage) 7 EGR amount control valve (exhaust recirculation means) 8 EGR cooling device (recirculation exhaust cooling means) 9 intake throttle valve (exhaust recirculation means) Reference Signs List 10 trap filter (exhaust gas purifying means) 11 ECU (combustion temperature reducing means, injection timing calculating means) 17 exhaust oxygen concentration sensor (oxygen concentration detecting means)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 43/00 301 F02D 43/00 301Z 3G301 310 310A F01N 3/02 321 F01N 3/02 321A 321D 321H 321Z 3 / 24 3/24 ERS F02D 15/04 F02D 15/04 BC 21/08 301 21/08 301D 301E 41/04 385 41/04 385C 41/14 310 41/14 310N 310P 45/00 314 45 / 00 314Z 320 320A F02M 25/07 F02M 25/07 AB 550 550A 550G 550R 580 580E (72) Inventor Toshio Kondo 1-chome, Showa-cho, Kariya-shi, Aichi, Japan Denso Co., Ltd. (72) Inventor Tatsuya Fujita Aichi 1-1, Showa-cho, Kariya-shi (72) Inventor Kiyonori Sekiguchi 1-1-1, Showa-cho, Kariya-shi, Aichi Prefecture In-house Denso (72) Inventor, Masumi Kinukawa 1-1-1, Showa-cho, Kariya-shi, Aichi Prefecture In-house Denso, Inc. F-term (reference) 3G062 AA01 AA03 AA05 AA06 BA04 BA05 BA06 CA06 DA01 DA02 EA10 ED08 FA12 GA00 GA04 GA06 GA17 3G084 AA01 AA03 AA04 BA05 BA08 BA09 BA13 BA15 BA20 BA22 BA24 CA03 CA04 CA05 DA10 DA27 EA11 FA03 A01 FA01 FA01 FA01 FA01 BA01 DA01 DA10 DA18 DA20 EA05 EA06 EA07 3G091 AA02 AA10 AA11 AA18 AA28 AB02 AB13 BA00 BA14 BA15 BA19 BA36 CA13 CB02 CB03 CB07 CB08 DA01 DA02 DB10 DC01 EA00 EA01 EA07 EA34 FA11 FA17 GB10 GB01 GA06 GBX GA06 HB06 3G092 AA02 AA06 AA12 AA13 AA17 AA18 AB03 BA01 BA04 BA06 BA07 BB01 BB06 DB03 DC03 DC08 DC09 DC10 DC14 DC15 DD07 DD10 DE03S DE06S DF01 DF06 DG07 EA03 EA04 EA11 EC01 FA17 FA18 HA03 HEB03X08 HD03 HB03X01 HA13 HA15 JA24 JA25 JA26 KA06 LA03 LB11 MA01 MA11 MA18 NA07 NA08 ND01 ND03 NE01 NE06 NE11 NE12 NE15 PB08A PB08Z PD02A PD02Z PE01A PE01Z PF03A PF03Z

Claims (9)

[Claims] An output calculating unit that calculates an output of the internal combustion engine; an operating state detecting unit that detects an operating state of the internal combustion engine; an injection timing calculating unit that calculates a fuel injection timing to the internal combustion engine; An exhaust recirculation passage connecting an exhaust pipe and an intake pipe of the internal combustion engine, and an exhaust recirculation unit that returns a part of exhaust discharged from the internal combustion engine through the exhaust recirculation passage to intake air; An intake gas cooling unit that cools the intake gas to be sucked in, a fuel injection timing calculated by the injection timing calculation unit based on an output of the internal combustion engine, and an exhaust gas recirculation amount changed by the exhaust gas recirculation unit. Combustion temperature reducing means for reducing the temperature in the cylinder during fuel combustion of the internal combustion engine; exhaust purification means carrying an oxidation catalyst installed in an exhaust pipe of the internal combustion engine; and oxygen concentration installed in the exhaust pipe. An exhaust gas purification device for an internal combustion engine comprising a degree detection means, wherein when the output of the internal combustion engine enters the medium load range, the exhaust gas recirculation amount is increased with the calculated fuel injection timing delayed. The amount of smoke discharged from the internal combustion engine gradually increases with an increase in the amount of exhaust gas recirculation, and shows a characteristic of decreasing after reaching a peak.When this characteristic is called a medium load region smoke characteristic, The temperature reducing means is configured to determine whether the output calculated by the output calculating means is a predetermined value T1 and a predetermined value T2 indicating the middle load range.
(T1> T2), the fuel injection timing is retarded until the smoke characteristic in the middle load range is obtained, and the smoke amount is reduced within a range where the fuel consumption of the internal combustion engine does not greatly increase. The exhaust gas recirculation amount is increased to a region that decreases after the peak, and the exhaust gas recirculation amount is corrected so that the oxygen concentration in the exhaust gas detected at that time becomes a predetermined value obtained from the output of the operating state detecting means. An exhaust gas purification device for an internal combustion engine. 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein said intake gas cooling means is provided in a middle of said exhaust gas recirculation passage, and recirculates exhaust gas recirculated to an intake side through said exhaust gas recirculation passage. An exhaust gas purification device for an internal combustion engine, which is a recirculation exhaust gas cooling means for cooling. 3. An exhaust gas purifying apparatus for an internal combustion engine according to claim 2, wherein a capacity of said recirculating exhaust gas cooling means is larger than a displacement of said internal combustion engine. 4. An exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein a compression ratio of said internal combustion engine is made smaller than usual. 5. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein a compression ratio of the internal combustion engine is changed to a smaller one when an output of the internal combustion engine is in a middle load range. An exhaust gas purification device for an internal combustion engine, comprising: 6. The exhaust gas purification apparatus for an internal combustion engine according to claim 3, wherein the compression ratio of the internal combustion engine is 18 or less. 7. An exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein said exhaust gas purifying means is a trap filter carrying an oxidation catalyst. . 8. An exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein said combustion temperature reducing means is configured to output said predetermined value T2 indicating that the output calculated by said output calculating means indicates a low load range. In the following cases,
An exhaust purification device for an internal combustion engine, wherein the fuel injection timing calculated by the injection timing calculation means is advanced. 9. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein said combustion temperature reducing means corrects a fuel injection amount of the internal combustion engine based on an output of the internal combustion engine. The injection amount correcting means changes the output calculated by the output calculating means from a value equal to or less than the predetermined value T1 to a value greater than T1 or from a value greater than T1 to a value equal to or less than T1. Or when the output calculated by the output calculating means changes from a value less than the predetermined value T2 to a value greater than T2, or from a value greater than T2 to a value less than T2, the output of the internal combustion engine is continuously An exhaust gas purifying apparatus for an internal combustion engine, wherein a fuel injection amount is corrected so as to change in a timely manner.