JP3627372B2 - Diesel engine exhaust purification system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a diesel engine in which nitrogen dioxide (NO) in exhaust gas is used.₂The present invention relates to an exhaust emission control device for a diesel engine that suppresses the generation of). More specifically, NO in the exhaust gas of a diesel engine without using multiple types of oxidation catalysts and without suppressing the catalytic activity of the oxidation catalyst.₂The ratio is reduced.
[0002]
[Prior art]
Conventionally, an oxidation catalyst is attached to the exhaust system of a diesel engine. The oxidation catalyst purifies exhaust gas by oxidizing mainly hydrocarbons (HC), carbon monoxide (CO), and particulates (unburned components including soot, sulfate, soluble organic matter (SOF), etc.) in the exhaust gas. Is. In particular, platinum (Pt) -based catalysts having good low-temperature activity and high durability against SOF are frequently used as oxidation catalysts for diesel engines.
[0003]
By the way, in a Pt-based oxidation catalyst, after traveling for a long time in a high load state, if a shift is made to a low load state such as idling, a problem occurs due to the active power of the catalyst having a high temperature. That is, not only HC and CO are oxidized by the Pt-based oxidation catalyst, but also nitrogen monoxide (NO) in nitrogen oxide (NOx) is converted to nitrogen dioxide (NO₂) Will be oxidized. This NO₂Is further oxidized to nitric acid (HNO₃) And causes acid odor. Therefore, for example, in Japanese Patent Laid-Open No. 6-22936, a palladium (Pd) -based oxidation catalyst is disposed downstream of a Pt-based oxidation catalyst, and NO is produced by this Pd-based oxidation catalyst.₂NOx in exhaust gas by decomposing or reducing₂
A technique for reducing the ratio of the above is disclosed.
[0004]
[Problems to be solved by the invention]
However, mounting a Pd-based oxidation catalyst in addition to the Pt-based in series increases exhaust pressure loss and leads to deterioration of fuel consumption. In addition, since the Pd-based oxidation catalyst is an expensive member, mounting it will be reflected in the cost increase of the completed vehicle itself. Here, NO in exhaust gas without using Pd-based oxidation catalyst₂As a means for reducing the ratio, it is conceivable to suppress the catalytic activity of the Pt-based oxidation catalyst. However, when the activity is suppressed, there is a possibility that the ability of the Pt-based oxidation catalyst to oxidize HC, CO, particulates and the like, which are the original purposes, may be reduced.
[0005]
The present invention has been made to solve the above-mentioned problems, and its purpose is to supply a reducing agent from the upstream side of the oxidation catalyst in accordance with the operating state, thereby reducing NO in the exhaust gas.₂To reduce the percentage of
[0006]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, as shown in FIG. 1, an air flow rate detection means M1 for detecting the air flow rate of the outside air taken into the diesel engine or an air flow rate equivalent value, and The temperature detection means M3 for detecting the temperature of the oxidation catalyst M2 or the exhaust gas or a temperature equivalent value, and the air flow rate or the air flow equivalent value detected by the air flow rate detection means M1 are not more than a predetermined value. In addition, the temperature or temperature equivalent value detected by the temperature detecting means M3 isNO is oxidized by the oxidation catalyst to generate NO2.PredeterminedtemperatureJudgment means M4 for judging the above and the judgment result of the judgment means M4Is determined that the air flow rate or the air flow equivalent value is not more than the predetermined value, and that the temperature or temperature equivalent value is not less than the predetermined temperature,Reducing agent supply means M5 for supplying the reducing agent from the upstream side of the oxidation catalyst is used.
[0007]
In the first aspect of the invention thus configured, the air flow rate or the like or the equivalent value corresponding to the air flow rate is detected by the air flow rate detection means M1. On the other hand, the temperature detection means M3 detects the temperature of the oxidation catalyst M2 or the exhaust gas or an equivalent value corresponding to these temperatures. The determination means M4 determines a predetermined air flow rate, that is, what kind of operating state it is from the detected air flow rate or its equivalent value, and determines the temperature state in the oxidation catalyst M2 from the detected temperature or its equivalent value. To do. If the result of determination is that purification is required, the reducing agent supply means M5 supplies the reducing agent from the upstream side of the oxidation catalyst in response to a request from the determination means M4.
[0008]
Further, in the invention of claim 2, the configuration as shown in FIG. 1 is adopted, and the air flow rate detected by the air flow rate detection means M1 in the determination means M4 in the invention of claim 1 is not more than a predetermined value, and The temperature detected by the temperature detection means M3 isA predetermined temperature at which NO is oxidized by the oxidation catalyst and NO2 is generated.When it is within the range, the purification process is required. That is, the invention of claim 2 differs from the invention of claim 1 in that the determining means M4, A predetermined temperature at which NO is oxidized to NO2 by the oxidation catalystDetermine if it is in range. That is, it is determined from the detected temperature whether the temperature in the oxidation catalyst M2 is high enough to require purification treatment, and whether it is very high enough not to supply the reducing agent. If the result of determination is that purification is required, the reducing agent supply means M5 supplies the reducing agent from the upstream side of the oxidation catalyst in response to a request from the determination means M4.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
(Embodiment 1)
Embodiments of an exhaust emission control device for a diesel engine according to the present invention will be described below in detail with reference to the drawings.
[0010]
As shown in FIG. 2, a diesel engine (hereinafter simply referred to as an engine) 1 has a plurality of cylinders including a combustion chamber 2. In the intake process of the engine 1, the intake port 3 provided for each cylinder is opened by the intake valve 4, so that the outside air drawn into the intake passage 6 through the air cleaner flows into each combustion chamber 2. The first fuel injection nozzle 7 provided for each cylinder injects the fuel pressure-fed from the first fuel injection pump 8 through the fuel line 7 a into each combustion chamber 2. In the compression process of the engine 1, the fuel and the outside air introduced into each combustion chamber 2 are pressurized by the upward movement of the piston 9 to explode and burn, whereby the crankshaft 10 rotates by the downward movement of the piston 9, A driving force is obtained in the engine 1. In the exhaust process of the engine 1, the exhaust port 11 provided for each cylinder is opened by the exhaust valve 12, whereby exhaust gas generated in each combustion chamber 2 is introduced into the exhaust passage 13 and further discharged to the outside. .
[0011]
A Pt-based oxidation catalyst 14 is attached to the exhaust passage 13. For example, the oxidation catalyst 14 is made of alumina (Al₂O₃Coated) and mono
It is obtained by immersing and sintering a squirrel carrier in an ammonium nitrate solution of Pt. A second fuel injection nozzle 15 as a reducing agent supply means is provided between the exhaust port 11 and the oxidation catalyst 14. The second fuel injection nozzle 15 injects the fuel pressure-fed through the fuel line 15 a from the second fuel injection pump 16 as a reducing agent supply means into the exhaust passage 13.
[0012]
A throttle valve 17 provided in the intake passage 6 operates in conjunction with the operation of the accelerator pedal 18 to selectively open and close the intake passage 6. In accordance with the opening of the throttle valve 17, the amount of outside air sucked into the intake passage 6, that is, the intake flow rate Qc is adjusted. The first fuel injection pump 8 has a drive shaft 8 a that is connected to the crankshaft 10. Accordingly, the drive shaft 8 a is rotated in synchronization with the rotation of the crankshaft 10, and the first fuel injection pump 8 is driven in conjunction with the rotation of the engine 1.
[0013]
An air flow meter 61 as an intake flow rate detecting means provided adjacent to the air cleaner 5 measures the intake flow rate Qc sucked into the intake passage 6 and outputs a signal corresponding to the amount. An intake air temperature sensor 62 provided adjacent to the air flow meter 61 detects an outside air temperature (intake air temperature) THA sucked into the intake passage 6 and outputs a signal corresponding to the detected temperature. A throttle sensor 63 as an accelerator opening detecting means provided in the vicinity of the throttle valve 17 detects the opening (throttle opening) TA of the valve 17 and outputs a signal corresponding to the detected value. An intake pressure sensor 64 provided in the intake passage 6 detects the intake pressure PM in the intake passage 6 and outputs a detection signal corresponding to the pressure. The rotational speed sensor 65 provided in the first fuel injection pump 8 indirectly detects the rotational speed of the crankshaft 10, that is, the rotational speed NE of the engine 1 based on the rotation of the drive shaft 8a, and according to the speed. Output a series of pulse signals. A catalyst temperature sensor 66 as temperature detecting means provided in the oxidation catalyst 14 detects the temperature (catalyst temperature) Tc of the oxidation catalyst 14 and outputs a signal corresponding to the detected temperature.
[0014]
Here, the ECU (electronic control unit) 71 inputs signals output from the various sensors 61 to 66 described above. The ECU 71 controls the second fuel injection pump 16 based on the intake flow rate Qc and the catalyst temperature Tc from the air flow meter 61 and the catalyst temperature sensor 66 among those input signals. Here, the control of the second fuel injection pump 16 means that the second fuel injection pump 16 is driven to drive the second fuel when the oxidation catalyst 14 is within the predetermined temperature range and the load of the engine 1 is lower than the predetermined value. Control in which light oil is injected into the intake passage 6 from the injection valve 15 is meant.
[0015]
The ECU 71 includes a central processing unit (CPU) 72, a read only memory (ROM) 73, a random access memory (RAM) 74, a backup RAM 75, and the like. The ECU 71 constitutes a logical operation circuit in which these units 72 to 75 are connected to an external input circuit 76 including an A / D converter, an external output circuit 77, and the like through a bus 78. The CPU 71 as a determination unit has a function for arithmetic control and a counter function, and executes a control program stored in the ROM 72. The ROM 72 stores a predetermined control program, function data, and the like in advance. The RAM 73 temporarily stores the calculation result of the CPU 72 and the like. Each sensor 61-66 described above is connected to an external input circuit 77. The second fuel injection pump 16 described above is connected to an external output circuit 76. The backup RAM 74 stores various data in the RAM 73 so that the data is not erased even when the power supply to the ECU 71 is stopped. The CPU 72 reads signals from the sensors 61 to 66 input via the external input circuit 76 as input values. And control of the 2nd fuel injection pump 16 is performed based on those values.
[0016]
Next, among various processes executed by the CPU 72, an injection control of light oil from the second fuel injection nozzle 15, that is, an “injection control routine” for controlling the second fuel injection pump 16 is shown in FIG. 3 and FIG. 4 will be described. The CPU 72 executes this routine periodically at a predetermined time interval.
[0017]
First, in step 100, the CPU 72 reads the catalyst temperature Tc and the intake air flow rate Qc based on detection signals from the catalyst temperature sensor 66 and the air flow meter 61, respectively. In step 110, the CPU 72 determines whether or not the catalyst temperature Tc is within a predetermined set value T1 and set value T2. Here, the set value T1 and the set value T2 of the catalyst temperature Tc are determined by NO being oxidized by the oxidation catalyst 14 in a state where the air flow rate is small.₂Is a value that demarcates the temperature range in which is generated. In the first embodiment, FIG. 4 shows the set value T1 and the set value T2 when the air flow rate is low and the engine is in the idle state.
[0018]
The graph of FIG. 4 shows NO in the catalyst temperature Tc and NOx in the idle state (small air flow rate).₂It shows the relationship with the generation amount. According to this graph, the total amount of NOx generated does not vary greatly despite the change in the catalyst temperature Tc. However, when the catalyst temperature Tc gradually decreases from an extremely high temperature state, the NOx in NOx becomes a boundary at the set value T2.₂Tend to increase. That is, NO is oxidized by the oxidation catalyst 14 and NO.₂Is generated. This NO₂HNO as oxidation proceeds further₃It causes a strange odor. On the other hand, if the catalyst temperature Tc further decreases, the NO again after the set value T1₂Tends to decrease and become NO-based NOx.
[0019]
In step 110, the CPU 72 determines that the catalyst temperature Tc is NO.₂If it is determined that the temperature range is between the set value T1 and the set value T2 set as the temperature range in which the intake occurs, it is determined in step 120 whether the intake air amount Qc is smaller than a predetermined set value Q1. Here, the determination of the intake air amount Qc in step 110 is to detect whether or not the engine 1 is in an idle state (the air flow rate is small). In the first embodiment, the CPU 72 that executes the processing of step 110 and step 120 corresponds to a determination unit.
[0020]
Next, in step 130, the CPU 72 determines whether or not the engine 1 is currently being driven from the fuel injection state of the first fuel injection pump 8. When the CPU 72 determines in step 130 that fuel is being injected, that is, the engine 1 is currently being driven, in step 140, the second fuel injection pump 16 is driven and controlled from the second fuel injection valve 15 during idling. A predetermined amount of diesel oil is injected into the intake passage 6. The main component of the injected light oil is HC, which acts as a reducing agent in the oxidation catalyst 14. That is, the generated NO₂Is deprived of oxygen by light oil and reduced to NO. On the other hand, the light oil is further oxidized by the oxidation catalyst 14 to form H.₂, CO₂Etc. Thus, when the catalyst temperature Tc is larger than the set value T1 and smaller than the set value T2 by supplying light oil, NO₂Is reduced, its generation is most suppressed, and in turn HNO₃Is not generated, and the off-flavor in the idle state is prevented. Further, since oxygen in the oxidation catalyst 14 is more likely to react with light oil than NO, NO is NO.₂It becomes difficult to be oxidized. In the first embodiment, the CPU 72 that executes the process of step 140 corresponds to a reducing agent injection control means.
[0021]
On the other hand, if the catalyst temperature Tc is not between the set value T1 and the set value T2 in step 110, the process is temporarily ended. That is, when the catalyst temperature Tc is smaller than the set value T1, NO is oxidized because the temperature of the oxidation catalyst 14 is low, without needing to inject the light oil, and NO.₂This is because is not generated. Furthermore, the injection of light oil leads to a deterioration in fuel consumption. Conversely, if the catalyst temperature Tc is higher than the set value T2, NO is not required even if light oil is not injected.₂Production is reduced. That is, NO and NO₂The oxidation reaction system with
2NO + O₂ＮＯ2NO₂
This is because the reaction moves in the left direction in spite of the oxidizing power of the oxidation catalyst 14 particularly at high temperatures. Rather, the addition of light oil at a high temperature promotes the generation of sulfate and leads to deterioration of fuel consumption.
[0022]
Further, when the intake air amount Qc is greater than or equal to the predetermined set value Q1 in step 120, the processing is once ended. In this case, for example, in a high load state such as during traveling, there is a sufficient intake amount and the intake amount Qc is equal to or greater than a predetermined set value Q1. Therefore, HNO generated due to a large amount of exhaust gas.₃Will be diluted in the exhaust gas. Therefore, as long as the standard emission amount of NOx as a whole is cleared, NO₂It does not matter if it occurs. Further, the processing is ended also when the fuel is not being injected in step 130, that is, when the engine 1 is currently stopped.
[0023]
As described above, according to the exhaust gas purification apparatus for a diesel engine of the first embodiment, the following effects are exhibited.
(1) When the temperature of the oxidation catalyst 14 rises in a low load state where the intake / exhaust amount is small, such as in an idle state, NO is oxidized by the catalyst 14 and NO₂Is generated. However, in the above embodiment, when the catalyst temperature Tc is high, the second fuel injection pump 16 is controlled to inject a predetermined amount of light oil into the intake passage 6 from the second fuel injection valve 15. . Therefore, NO is oxidized and NO₂Is no longer generated, and the generated NO₂Is reduced to NO. Therefore, NO₂The derived nitric acid is not produced, and there is no off-flavor. Furthermore, there is no need to install a Pd-based oxidation catalyst as in the prior art, and NO₂It is not necessary to reduce the oxidizing power of the oxidation catalyst 14 in order to suppress the generation of the oxidation.
[0024]
(2) Light oil is injected only when the catalyst temperature Tc is larger than the set value T1 and smaller than the set value T2. That is, NO₂NO to NO, or NO NO₂Since the light oil injection is performed only when there is an effect in preventing the oxidation of the fuel, reduction in fuel consumption can be prevented as much as possible.
[0025]
(3) Since the catalyst temperature Tc is directly detected by the catalyst temperature sensor 66 provided in the oxidation catalyst 14, the temperature error of the catalyst temperature Tc is small and the second fuel injection valve 15 can be controlled more delicately. It becomes.
[0026]
(Embodiment 2)
Next, a second embodiment of the exhaust emission control device for a diesel engine according to the present invention will be described in detail with reference to the drawings. In the second embodiment, the same members as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted. In the second embodiment, the differences from the first embodiment will be mainly described.
[0027]
In the second embodiment, as can be seen from FIG. 5, there is no catalyst temperature sensor 65 provided in the first embodiment. In the second embodiment, the catalyst temperature Tc is estimated by calculation based on the fuel injection amount smoothed value FMC and the idle state duration. Further, the air flow rate is estimated by being in an idle state. FIG. 6 shows “NO” for detecting the air flow equivalent value and the temperature equivalent value.₂It is a flowchart which shows a generation | occurrence | production detection routine. The CPU 72 executes this routine periodically at a predetermined time interval.
[0028]
In step 200, the CPU 72 calculates a fuel injection amount smoothing value FMC according to the following equation.
FMC = (n−1 / n) * FMC0 + (1 / n) * Fi
That is, the CPU 72 adds the current fuel injection amount Fi weighted by (1 / n) to the fuel injection amount smoothed value FMC0 accumulated up to the previous time weighted by (n−1 / n), and adds the current fuel injection amount Fi. An injection amount smoothing value FMC is calculated. In general, regarding the relationship between the output and the supplied fuel, for example, when shifting from a low output state to a high output state, the fuel injection amount needs to gradually reach the target injection amount without promptly responding to the output change. In other words, this is to reduce the shock at the time of sudden acceleration or sudden deceleration caused by a sudden change in operating conditions. The fuel injection amount smoothing value FMC is a parameter employed for that purpose, and always weights the previous fuel injection amount FMC0 and the current fuel injection amount Fi, and the cumulative fuel injection amount up to the present time. Is calculated. In other words, since the past driving history is reflected in reality, the greater the fuel injection amount smoothing value FMC, the higher the load. In the second embodiment, 64 coefficients are given to the weight n.
[0029]
Next, in step 210, the CPU 72 determines whether or not the engine 1 is in an idle state from the throttle opening degree TA detected by the throttle sensor 63. If the CPU 72 determines in step 210 that the engine 1 is in an idle state, in step 220, the CPU 72 determines whether or not the current fuel injection amount smoothing value FMC is greater than the set value FMC1. If it is determined that the value is larger than the set value FMC1, the process proceeds to step 230. That is, if the fuel injection amount smoothing value FMC is large, it means that high load operation has continued and it can be estimated that the oxidation catalyst 14 is also hot. Accordingly, the CPU 72 determines in step 230 that the oxidation catalyst 14 is in a high temperature state, and sets the high temperature state determination flag FG. In step 240, the CPU 72 increments the counter value CFC, which is a temperature-equivalent value reflecting the predetermined time, by “1”, and once ends the process. In the second embodiment, step 210 corresponds to accelerator opening detection means.
[0030]
On the other hand, if the CPU 72 determines in step 210 that the engine 1 is not in the idle state, the CPU 72 resets the counter value CFC to “0” in step 250 and then ends the process. If the CPU 72 determines in step 220 that the current fuel injection amount smoothing value FMC is not greater than the set value, the process proceeds to step 240. In the second embodiment, steps 200 to 250 correspond to air flow equivalent value and temperature equivalent value detection means.
[0031]
Next, an “injection control routine” for controlling the second fuel injection pump 16 will be described based on the flowchart of FIG. The CPU 72 executes this routine periodically at a predetermined time interval.
[0032]
In step 300, the CPU 72 executes the above “NO”.₂It is determined whether or not the counter value CFC obtained in the “occurrence detection routine” is within the range of the set value CFC1 and the set value CFC2. That is, if it is determined that the counter value CFC is equal to or greater than the set value CFC2, the temperature of the oxidation catalyst 14 has already been lowered and it is not necessary to inject light oil, assuming that the idle state (low air flow rate) has continued for a long time. If it is determined that the counter value CFC is equal to or less than the set value CFC1, it can be determined that the idle state is short or not in the idle state. If the CPU 72 determines that the counter value CFC is not within the range of the set value CFC1 and the set value CFC2, the CPU 72 resets the flag in step 310 and ends the process once.
[0033]
On the other hand, when the CPU 72 determines in step 300 that the counter value CFC is within the range between the set value CFC1 and the set value CFC2, in step 320, the “NO”₂It is determined whether or not the high temperature state determination flag FG of the “occurrence detection routine” is set. Here, the fact that the flag FG is not set means that the current fuel injection amount smoothing value FMC is not larger than the set value FMC1, that is, the oxidation catalyst 14 is NO.₂This means that the temperature is not high enough to generate, and the process is temporarily terminated. However, if it is determined that the flag FG is set, the oxidation catalyst 14 is NO.₂In step 330, the second fuel injection pump 16 is driven and controlled, and a predetermined amount of light oil is injected into the intake passage 6 from the second fuel injection valve 15. The process is temporarily terminated. In the second embodiment, steps 300 and 320 correspond to determination means. The CPU 72 that executes the process of step 330 corresponds to a reducing agent injection control means.
[0034]
As described above, according to the exhaust gas purification apparatus for a diesel engine of the second embodiment, the following effects are exhibited in addition to the effects (1) and (2) of the first embodiment.
(1) Since the fuel injection amount smoothing value FMC and the idle duration time are detected as the temperature equivalent value of the catalyst temperature Tc, it is not necessary to provide the catalyst temperature sensor 66, and the cost for the sensor 66 is reduced. .
[0035]
(2) Since the throttle sensor 63 is used as the air flow rate detection means and the throttle opening degree TA as the air flow rate equivalent value is obtained, it is not necessary to directly detect the air flow rate value, and the air flow meter 61 is necessarily provided. There is no.
[0036]
(3) Besides using the fuel injection amount smoothing value FMC, the temperature equivalent value and the air flow rate equivalent value can be detected only by using the detection value of the throttle sensor 63, and a plurality of sensors are not required.
[0037]
The present invention can be embodied in another embodiment as follows. Also in the following other embodiments, the same operations and effects as the above-described embodiments can be obtained.
(1) In Embodiments 1 and 2 described above, light oil as a reducing agent is injected during idling. However, light oil may be injected when the air flow rate is low even when the vehicle is not idling. In that case, the CPU 72 changes the light oil injection amount according to the detection value of the throttle sensor 63.
[0038]
(2) In the first and second embodiments, the temperature or the temperature equivalent value is within the predetermined range. In the first embodiment, in step 110 of the injection control routine, it is determined whether or not the catalyst temperature Tc is between the set value T1 and the set value T2. In the second embodiment, it is determined whether or not the counter value CFC, which is a temperature equivalent value, is within the range between the set value CFC1 and the set value CFC2. However, the upper limit is not necessarily set as long as the temperature or the temperature equivalent value is equal to or greater than a predetermined value.
[0039]
(3) In the first embodiment, the air intake volume is detected by the air flow meter 61 as the air flow rate. However, an exhaust gas flow sensor may be provided on the downstream side of the engine 1 to directly detect the air flow as the exhaust gas.
[0040]
(4) In the second embodiment, the throttle sensor 63 is used as the air flow rate equivalent value, and the throttle opening degree TA as the air flow rate equivalent value is obtained. You may make it detect. An exhaust gas flow sensor may be provided.
[0041]
(5) Although the detected value detected by the fuel injection amount smoothing value FMC and the idle duration time is used as the temperature equivalent value in the second embodiment, the catalyst temperature sensor 66 may be used.
[0042]
(6) In Embodiments 1 and 2, light oil is used as the reducing agent. However, hydrocarbon HC (propane gas or the like) other than light oil, hydrogen, urea, ammonia, or the like may be used.
(7) In the first and second embodiments, the second fuel injection nozzle 15 as the reducing agent supply means is provided between the exhaust port 11 and the oxidation catalyst 14. However, since the ratio of light oil in the exhaust gas may be increased, the position is not limited to this. For example, it may be the combustion chamber 2. In this case, it is possible to use the first fuel injection nozzle 7 as a reducing agent supply means instead of the second fuel injection nozzle 15. In other words, the first fuel injection nozzle 7 may be controlled to inject fuel in the normal compression process of the engine 1, and light oil may be injected in the expansion or exhaust process.
[0043]
(8) The first fuel injection pump 8 may be shared instead of the second fuel injection pump 16.
(9) The oxidation catalyst may be an oxidation catalyst other than the Pt-based oxidation catalyst of the first and second embodiments.
[0044]
Further, other technical ideas grasped by the above embodiments are described below together with the effects thereof.
(A) The exhaust gas purification apparatus for a diesel engine according to claim 1 or 2, wherein the air flow rate detection means is an intake flow rate detection means for detecting an intake flow rate. If comprised in this way, in addition to the effect | action and effect of Claim 1 or 2, the air flow rate can be detected even if it does not bother to provide an exhaust flow rate detection means.
[0045]
(B) The exhaust gas purification apparatus for a diesel engine according to claim 1 or 2, wherein the air flow rate detection means is an accelerator opening degree detection means for detecting an accelerator opening degree as an air flow rate equivalent value. If comprised in this way, in addition to the effect | action and effect of Claim 1 or 2, it can detect as an air flow rate equivalent value equivalent to an air flow rate, without providing the means to detect an air flow rate directly.
[0046]
(C) The temperature equivalent value of the temperature detection means is the integrated value of the fuel injection amount calculated by the fuel injection amount calculation means and the duration of the low output state calculated by the accelerator opening duration calculation means. Item 1. An exhaust emission control device for a diesel engine according to any one of item 1, item 2, item (a), or item (b). If comprised in this way, in addition to the effect | action and effect of any one of Claim 1, Claim 2, an appendix (a), or an appendix (b), it is the temperature equivalent to a catalyst temperature, without providing the means to detect a catalyst temperature directly It can be detected as a value.
[0047]
(D) An exhaust emission control device for a diesel engine, wherein the fuel injection amount calculation means in (c) calculates a fuel injection amount smoothing value.
(E) The exhaust gas purification device for a diesel engine according to claim 1, wherein the reducing agent supply means is provided between the engine and the oxidation catalyst, or any one of appendices (a) to (d).
[0048]
(F) The reducing agent supply means is a fuel injection nozzle, and the fuel injection nozzle responds to an air flow rate or an air flow rate equivalent value from a fuel injection pump separate from the fuel injection pump for supplying fuel to the engine. The exhaust gas purification apparatus for a diesel engine according to claim 1 or 2 or appendices (a) to (e), wherein the predetermined fuel is pumped. Therefore, the fuel can be supplied to the catalyst without applying a load to the fuel injection pump for the engine in the diesel engine.
[0049]
(G) The reducing agent supply means is a fuel injection nozzle that injects light oil. An exhaust emission control device for a diesel engine according to any one of claims 1 and 2, or additional notes (a) to (f). If it does in this way, fuel can be supplied to a catalyst using the light oil of the most common fuel in a diesel engine.
[0050]
【The invention's effect】
According to the first aspect of the present invention, in a state where the air flow rate is small, such as an idle state, the reducing agent is injected by the reducing agent supply means even if the temperature of the oxidation catalyst rises.₂Generation is suppressed.
[0051]
According to the second aspect of the present invention, when the temperature of the oxidation catalyst rises in a state where the air flow rate is low, such as in an idle state, NO is detected.₂NO in order to inject the reducing agent by the reducing agent supply means in the temperature range where it is most likely to be generated.₂Generation is suppressed.
[Brief description of the drawings]
FIG. 1 is a conceptual configuration diagram showing the configuration of the present invention.
FIG. 2 is a schematic configuration diagram of an engine system according to Embodiment 1 of the present invention.
FIG. 3 is a flowchart showing an “injection control routine” according to the first embodiment;
FIG. 4 shows the catalyst temperature at the time of idling and NO in the NOx.₂The graph which shows the relationship with the amount of generation.
FIG. 5 is a schematic configuration diagram of an engine system according to a second embodiment of the present invention.
FIG. 6 shows “NO” in the second embodiment.₂8 is a flowchart showing an “occurrence detection routine”.
FIG. 7 is a flowchart showing an “injection control routine” according to the second embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Engine as diesel engine, 14 ... Oxidation catalyst, 15 ... Second fuel injection valve as reducing agent supply means, 16 ... Second fuel injection pump as reducing agent supply means, 63 ... Detection means for air flow rate, intake air A flow rate detection means, a throttle sensor as an accelerator opening detection means, 66... A catalyst temperature sensor as a temperature detection means, 72... A temperature detection means, a determination means, a CPU as a reducing agent injection control means.

Claims (2)

In the exhaust purification device of a diesel engine provided with an oxidation catalyst in the exhaust passage,
Detecting means such as an air flow rate for detecting an air flow rate of the outside air taken into the diesel engine or an air flow rate equivalent value;
A temperature detection means for detecting the temperature of the oxidation catalyst or exhaust gas or a temperature equivalent value; and
The air flow rate or the air flow equivalent value detected by the air flow rate detection means is equal to or less than a predetermined value, and the temperature or temperature equivalent value detected by the temperature detection means is NO2 oxidized by the oxidation catalyst, so that NO2 Determining means for determining that the temperature is equal to or higher than a predetermined temperature to be generated ;
If the determination result of the determining means is that the air flow rate or the air flow equivalent value is less than or equal to the predetermined value and the temperature or temperature equivalent value is greater than or equal to the predetermined temperature, the reducing agent is added to the oxidation catalyst. An exhaust emission control device for a diesel engine, comprising reducing agent supply means for supplying from an upstream side. In the exhaust purification device of a diesel engine provided with an oxidation catalyst in the exhaust passage,
Detecting means such as an air flow rate for detecting an air flow rate of the outside air taken into the diesel engine or an air flow rate equivalent value;
A temperature detection means for detecting the temperature of the oxidation catalyst or exhaust gas or a temperature equivalent value; and
The air flow rate or the air flow equivalent value detected by the air flow rate detection means is equal to or less than a predetermined value, and the temperature or temperature equivalent value detected by the temperature detection means is NO2 oxidized by the oxidation catalyst, so that NO2 Determining means for determining that is within a predetermined temperature range in which
If the determination result of the determination means is that the air flow rate or the air flow equivalent value is less than or equal to the predetermined value and the temperature or temperature equivalent value is within the predetermined temperature range, the reducing agent is oxidized. An exhaust emission control device for a diesel engine, comprising reducing agent supply means for supplying the catalyst from upstream of the catalyst.

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