JP4154589B2 - Combustion control device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a combustion control device for an internal combustion engine, and more particularly to a combustion control device for an internal combustion engine applied to steady rich combustion control for a NOx storage catalyst.
[0002]
[Prior art]
In general, the NOx storage catalyst stores NOx (nitrogen oxide) in the exhaust when the exhaust air-fuel ratio is lean (lean), and releases and reduces the stored NOx when the exhaust air-fuel ratio is excessive (rich). This is a storage-type NOx catalyst that performs (NOx purge).
Specifically, NOx in the exhaust gas is occluded as nitrate in an oxygen excess state (oxidation atmosphere), and the occluded NOx is reduced to nitrogen in an excess carbon monoxide state (reduction atmosphere). The internal combustion engine then periodically switches to rich combustion in which the excess air ratio is low (low λ) so that the exhaust air-fuel ratio is controlled to the stoichiometric air-fuel ratio or a value close thereto before the NOx storage amount is saturated. To regenerate the NOx storage catalyst. Thereby, purification of exhaust gas is performed satisfactorily.
[0003]
Further, in the NOx storage catalyst, SOx (sulfur oxide) due to oxidation of the S component (sulfur component) in the fuel is also deposited as sulfate, so that the deposited S component is released (S purge). Similar to the above, rich combustion is periodically performed to regenerate the NOx storage catalyst.
Here, the rich combustion condition may be created by performing a large amount of EGR using an exhaust gas recirculation (EGR) valve or an air supply throttle that adjusts an air supply amount. And the technique of the exhaust gas purification apparatus for improving the NOx reduction | restoration efficiency in the above NOx storage catalysts is proposed (for example, refer patent document 1).
[0004]
In this apparatus, while rich combustion is performed by a large amount of EGR based on the control map, especially when the value of the catalyst temperature by the catalyst temperature sensor is less than a predetermined value, regeneration of the NOx storage catalyst is prohibited, and NOx reduction efficiency is improved. Improvements and suppression of black smoke emissions are made.
[0005]
[Patent Document 1]
JP 2000-356127 A (paragraph numbers 0005 to 0018, FIG. 1 etc.)
[0006]
[Problems to be solved by the invention]
By the way, in the exhaust gas purifying apparatus described above, rich combustion is prohibited when the catalyst temperature of the NOx storage catalyst does not reach the reproducible temperature. As described above, it is generally known that when the temperature of the NOx storage catalyst is low, the combustion deteriorates, so that the black smoke also deteriorates.
[0007]
On the other hand, in the rich combustion, it is necessary to perform steady rich combustion in which the rich state (low λ) is constant and maintained for a long period of time depending on the storage amount of NOx and the accumulation amount of S. However, there is a problem that the generation amount of black smoke gradually increases with the passage of time, even though the operating condition is such that λ is constant so that steady rich combustion is performed.
[0008]
FIG. 4 is a timing chart of a conventional engine system that performs rich combustion.
As shown in the figure, when the condition of rich combustion is satisfied and λ is set to the low λ side, the amount of black smoke generated can be temporarily suppressed at this setting time point. However, if this rich combustion is continued over a long period of time, the amount of black smoke generated begins to increase gradually, and may increase, for example, to nearly 100% even after about 10-15 minutes. In steady rich combustion, the exhaust temperature, the EGR gas temperature, and the supply air temperature, which indicate the situation in the cylinder, all rise by being set to the low λ side.
[0009]
In this way, black smoke deteriorates even during the period when steady rich combustion is performed. In this case, even if steady rich combustion is simply performed using the control map as in the above-described prior art, the amount of black smoke generated gradually increases, so that the deterioration of black smoke cannot be prevented. is there.
The present invention has been made in view of such problems, and an object of the present invention is to provide a combustion control device for an internal combustion engine that can prevent deterioration of black smoke in steady rich combustion control for a NOx storage catalyst. .
[0010]
[Means for Solving the Problems]
In order to achieve the above object, a combustion control apparatus for an internal combustion engine according to claim 1 is provided in an exhaust passage communicating with a cylinder of the internal combustion engine, and in the exhaust passage, and occludes NOx in the exhaust and occludes during lean combustion. NOx occlusion catalyst that releases and reduces the NOx by rich combustion, temperature correlation value detection means for detecting the temperature correlation value in the cylinder, NOx occluded in the NOx occlusion catalyst, and S component adhering to the NOx occlusion catalyst During a period in which rich combustion is performed in a steady manner to release , the temperature correlation value detected by the temperature correlation value detecting means is compared with a predetermined value, and if the temperature correlation value exceeds a predetermined value, rich combustion is prohibited for a certain period. And a combustion control means.
[0011]
As described above, the invention according to claim 1 gradually increases so that the amount of black smoke gradually rises to the right despite the steady rich combustion state where the ignition conditions for the fuel are in place. It solves the problem of getting worse. Here, the cause of the deterioration of the black smoke during the rich combustion is, for example, that the in-cylinder temperature is already high after the high load operation, and that it is easily influenced by the operation history immediately before the rich combustion is performed. Conceivable. In other words, depending on the previous operation history, etc., it is considered that black smoke may be deteriorated due to the heat load, so simply perform steady rich combustion using the control map, or temporarily set the upper limit period of rich operation with a timer etc. Even if it is set, the deterioration of black smoke cannot be prevented.
[0012]
Therefore, in the combustion control apparatus for an internal combustion engine according to claim 1, the temperature correlation value in the cylinder is provided as an index indicating the immediately preceding operation history, and the occurrence state of black smoke is determined based on the temperature correlation value in the cylinder. Therefore, the steady rich combustion is prohibited for a certain period, so that the black smoke is prevented from deteriorating regardless of the operation history.
The internal combustion engine is preferably a diesel engine. This is because even if the constant state is maintained at a low λ, the temperature in the cylinder rises as the time elapses, and the self-ignition of fuel occurs earlier than the assumed ignition period, and rich combustion This is because, in combination with the small amount of air, the black smoke is considered to deteriorate.
[0013]
In the invention according to claim 2, the combustion control means prohibits the rich combustion until a predetermined period of time set in advance as a time required for the temperature to decrease to the inside temperature of the cylinder where the amount of generated black smoke is suppressed. It is characterized by that.
Therefore, a predetermined period is set in advance as the time required for the temperature to decrease to the temperature in the cylinder where the generation amount of black smoke is suppressed, and rich combustion is prohibited until the predetermined period elapses.
The invention according to claim 3 is characterized in that the temperature correlation value in the cylinder is an exhaust temperature of the exhaust passage.
In this way, the cause of the early ignition is considered to be due to the rise in the temperature in the cylinder, that is, the engine temperature. Therefore, the temperature correlation value in the cylinder is used as the exhaust passage through which the gas in the cylinder is sent immediately. By setting the exhaust temperature to be, the deterioration of black smoke is prevented early and reliably.
[0014]
Further, in the invention according to claim 4 , the internal combustion engine includes an EGR passage that communicates the intake passage and the exhaust passage that communicate with the cylinder, and the temperature correlation value in the cylinder is the EGR gas temperature of the EGR passage. It is a feature.
As described above, the EGR gas temperature in the EGR passage can be easily measured as a representative value of the engine temperature in the same manner as the exhaust gas temperature. Therefore, the black smoke can be easily and reliably deteriorated by calculating the temperature correlation value in the cylinder. To be prevented.
[0015]
According to a fifth aspect of the present invention, the internal combustion engine includes an EGR passage that communicates an intake passage communicating with the cylinder and an exhaust passage, and the temperature correlation value in the cylinder is an EGR gas in the EGR passage and an intake air in the intake passage. It is the supply air temperature after merging with.
As described above, the supply air temperature can also be easily measured as a representative value of the engine temperature, similarly to the exhaust gas temperature and the EGR gas temperature. Therefore, the black smoke can be easily deteriorated by calculating the temperature correlation value in the cylinder. And reliably prevented.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows an engine system configuration diagram including a four-cylinder diesel engine (hereinafter simply referred to as an engine) 1 to which a combustion control device according to an embodiment of the present invention is applied. A configuration of a combustion control device for an internal combustion engine according to the invention will be described.
[0017]
As shown in the figure, the cylinder block 2 of the engine 1 includes an intake manifold 6 for introducing fresh air (intake air) to each cylinder 4 in addition to a fuel supply system (not shown) having a fuel injection device, An exhaust manifold 18 that collects exhaust gas discharged from each cylinder 4 is connected.
An intake passage 8 extends from the intake manifold 6, a supercharger 14 is interposed upstream of the intake passage 8, and an air cleaner 16 is connected to the tip of the intake passage 8. The intake passage 8 is provided with an air supply throttle 10 and an intercooler 12 is interposed. The intercooler 12 cools fresh air passing through the intake passage 8 to increase its volumetric efficiency.
[0018]
On the other hand, an exhaust passage 20 extends from the exhaust manifold 18, and a NOx storage catalyst 22 is connected to the downstream side of the exhaust passage 20. The NOx storage catalyst 22 stores NOx in the exhaust when the exhaust air-fuel ratio is lean, and releases and reduces the stored NOx when the exhaust air-fuel ratio is rich and HC and CO exist in the exhaust gas (NOx This NOx occlusion catalyst has a known configuration.
[0019]
Further, an exhaust circulation passage (EGR passage) 24 is branched and extended from the exhaust manifold 18, and the tip of the EGR passage 24 is inhaled at a downstream side of the intake passage 8 where the intake throttle 10 is disposed. It is connected to the passage 8. The EGR passage 24 recirculates a part of exhaust gas (EGR gas) into the intake passage 8 to suppress NOx emission. The EGR passage 24 is provided with an EGR cooler 26 that cools the EGR gas and an EGR valve 28 that is electrically connected to an electronic control unit (ECU) 36, and the flow area of the EGR passage 24 by the EGR valve 28 is provided. Is adjusted.
[0020]
The air supply throttle 10 is also electrically connected to the ECU 36. By adjusting the flow passage area of the intake passage 8, the EGR gas amount at the time of rich in the cylinder is adjusted, and the EGR passage 24 and the intake air The air supply amount after merging with the passage 8 is adjusted.
The fresh air from the air cleaner 16 reaches the intercooler 12 through the supercharger 14 and is adjusted by the air supply throttle 10, and then merges with the EGR gas to be supplied to the intake manifold 6 to reach each cylinder. 4 is led. Then, the crankshaft and the flywheel (both not shown) are operated by the combustion of the fuel supplied from the fuel supply system. When the combustion is completed, the exhaust gas is discharged to the exhaust manifold 18 and sent to the NOx storage catalyst 22.
[0021]
Here, in the exhaust passage 20, an exhaust temperature sensor 30 is disposed at an appropriate position downstream of the exhaust manifold 18 and upstream of the NOx storage catalyst 22. In the EGR passage 24, an EGR gas temperature sensor 32 is disposed at an appropriate position downstream of the EGR cooler 26. Further, an air supply temperature sensor 34 is disposed at an appropriate position of the intake manifold 6. All of these various sensors are electrically connected to the ECU 36.
[0022]
In addition to the exhaust gas temperature sensor 30, EGR gas temperature sensor 32, and supply air temperature sensor 34 described above, various sensors that detect the operating state of the engine 1 are electrically connected to the input side of the ECU 36. Are electrically connected to various actuators such as the air supply throttle 10 and the EGR valve 28 described above.
As described above, since NOx is also deposited on the NOx storage catalyst 22 along with the oxidation of the S component in the fuel, the rich combustion is periodically performed to perform the S purge together with the NOx purge, and the NOx storage catalyst. It is necessary to try to reproduce.
[0023]
Thus, the ECU 36 stores the NOx in the exhaust gas in the NOx storage catalyst 22 in an oxidizing atmosphere, and performs air-fuel ratio control so that steady rich combustion is performed. In other words, the engine 1 is regularly maintained in a low λ state and maintained for a long period of time to perform NOx purge and S purge to regenerate the NOx storage catalyst.
[0024]
As the steady rich combustion in the present embodiment, a large amount of EGR is performed, that is, the EGR valve 28 and the supply air throttle 10 are used, and rich combustion conditions are created by in-cylinder rich that uses carbon monoxide emission due to incomplete combustion. If this condition is satisfied, NOx purge or S purge is performed.
Here, in particular, the ECU 36 is provided with a combustion control unit (combustion control means) 38 according to the present invention. In the combustion control unit 38, various actuators are provided to prohibit the rich combustion for a certain period and perform the lean combustion when the temperature correlation value in the cylinder 4 exceeds a predetermined threshold during the period when the steady rich combustion is performed. Is outputting a signal.
[0025]
FIG. 2 is a diagram illustrating determination logic at the time of rich combustion in the combustion control unit 38.
Thus, in the combustion control unit 38, the exhaust gas temperature from the exhaust gas temperature sensor 30, the EGR gas temperature from the EGR gas temperature sensor 32, and the supply air temperature from the supply air temperature sensor 34 are used as temperature correlation values in the cylinder 4. And is compared with various threshold maps provided in the ECU 36 based on each engine speed and injection amount. That is, the combustion control unit 38 compares the exhaust gas temperature from the exhaust gas temperature sensor 30 with the exhaust gas temperature threshold value in the various threshold maps, and the EGR gas temperature from the EGR gas temperature sensor 32 and the EGR gas in the various threshold maps. Comparison with the gas temperature threshold value and comparison with the supply air temperature from the supply air temperature sensor 34 and the supply air temperature threshold value in the various threshold maps are performed.
[0026]
When any one of the exhaust gas temperature, EGR gas temperature, or supply air temperature, that is, the temperature correlation value in the cylinder 4 exceeds a threshold value, a certain period of time elapses from the combustion control unit 38 via the OR circuit. A signal prohibiting rich combustion is output until That is, steady rich combustion is prohibited for a certain period when any temperature exceeds a corresponding threshold value. This fixed period is a period required to achieve the temperature in the cylinder 4 that enables the amount of black smoke to be suppressed, and is set in advance by experiments or the like. Note that lean combustion is performed during a period during which rich combustion is prohibited.
[0027]
As a result, for example, in the case where the in-cylinder temperature is already high after high-load operation, fuel self-ignition occurs earlier than the assumed ignition period, and moreover, early ignition and richer ignition occur. Combined with the small amount of air due to combustion, the heat load on the cylinder 4 increases, and it is considered that the amount of black smoke generated gradually increases and worsens the black smoke. By prohibiting rich combustion for a certain period based on the correlation value, such deterioration of black smoke is prevented.
[0028]
FIG. 3 is an example of a timing chart during rich combustion in the combustion control apparatus.
As shown in the figure, when the rich combustion condition is satisfied, λ is set to the low λ side, and when the rich operation is permitted, the exhaust gas temperature, the EGR gas temperature, and the supply air temperature all increase.
[0029]
Here, the generation amount of black smoke begins to gradually increase according to the immediately preceding operation state as the steady rich combustion time elapses, but in this embodiment, the exhaust temperature first reaches the exhaust temperature threshold. Yes. Therefore, the rich combustion prohibition logic is established in the determination logic of FIG. 2, and the combustion control unit 38 outputs a signal for prohibiting the rich combustion to the engine 1 and causing the lean combustion. When the rich operation is prohibited and λ is set to the high λ side, the amount of air increases, so the temperature in the cylinder 4 decreases, and the temperature correlation in the cylinder 4 that is the exhaust temperature, the EGR gas temperature, and the supply air temperature. The value also decreases. And the generation amount of black smoke is suppressed compared with the case where steady rich combustion is continued as it is.
[0030]
As described above, in the present invention, the exhaust passage 20 communicating with the cylinder 4 of the diesel engine 1, the NOx storage catalyst 22 provided in the exhaust passage 20, the exhaust temperature in the exhaust passage 20, the EGR in the EGR passage 24. Using the gas temperature and the supply air temperature in the intake manifold 6 as temperature correlation values in the cylinder 4, the rich combustion is performed in a steady manner so that NOx stored in the NOx storage catalyst 22 and S component adhering to the NOx storage catalyst 22 are released. For example, when the exhaust gas temperature exceeds the exhaust gas temperature threshold, the combustion control unit 38 is configured to inhibit the rich combustion for a certain period and perform the lean combustion, so that the black smoke is deteriorated even during the steady rich combustion control. Can be prevented quickly.
[0031]
The description of one embodiment of the present invention is finished above, but the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.
For example, according to FIG. 3 of the above embodiment, the rich combustion is prohibited for a certain period when the exhaust temperature of the exhaust passage 20 reaches the exhaust temperature threshold, but this is not necessarily limited to this embodiment. Depending on the size of the intercooler 12 and the EGR cooler 26, the maximum value of the supply air temperature or the EGR gas temperature changes. Therefore, when the EGR gas temperature or the supply air temperature exceeds the temperature threshold, rich combustion is performed. It may be prohibited, or it may be prohibited to make rich combustion from the combination of exhaust gas temperature, EGR gas temperature or supply air temperature. In these cases, the deterioration of black smoke is more reliably prevented. can do.
[0032]
In addition, the enrichment method performs rich combustion with a large amount of EGR as in the present embodiment, and in-cylinder rich utilizing the emission of carbon monoxide due to incomplete combustion, as well as unburned fuel (HC) during the exhaust stroke. The in-cylinder rich supplied by post injection or the out-cylinder rich supplied HC to the NOx storage catalyst may be used.
Further, the engine is preferably a diesel engine, but is not limited to this, and the combustion control device of the internal combustion engine of the present invention is applicable to all engine systems that have a NOx storage catalyst in the exhaust passage and can perform rich operation. Can be made.
[0033]
【The invention's effect】
As can be understood from the above description, according to the combustion control device for an internal combustion engine of the present invention according to claims 1 and 2 , black smoke is used in spite of a steady rich combustion state in which ignition conditions for the fuel are in place. In view of the fact that the amount of generation increases gradually and gets worse, the combustion control means makes the black smoke based on the temperature correlation value in the cylinder as an index indicating the previous operation history. Therefore, the steady rich combustion is prohibited for a certain period, so that the black smoke can be prevented from deteriorating regardless of the operation history.
[0034]
Further, according to the third aspect of the invention, it is considered that the increase in the engine temperature, which is the temperature in the cylinder, can be considered as a cause of the early ignition, and the temperature correlation value in the cylinder is immediately determined by the gas in the cylinder. By setting the exhaust temperature of the exhaust passage to be sent, deterioration of black smoke can be prevented early and reliably.
Further, according to the fourth aspect of the present invention, the EGR gas temperature in the EGR passage can be easily measured as a representative value of the engine temperature in the same manner as the exhaust gas temperature. Smoke deterioration can be easily and reliably prevented.
[0035]
According to the fifth aspect of the present invention, the supply air temperature can also be easily measured as a representative value of the engine temperature in the same manner as the exhaust gas temperature and the EGR gas temperature. Therefore, the deterioration of black smoke can be easily and reliably prevented.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an engine system to which a combustion control device according to an embodiment of the present invention is applied.
FIG. 2 is a diagram showing determination logic at the time of rich combustion in the combustion control device of FIG. 1;
FIG. 3 is a timing chart at the time of rich combustion in the combustion control device of FIG. 1;
FIG. 4 is a timing chart during rich combustion in a conventional combustion control device.
[Explanation of symbols]
1 Diesel engine (internal combustion engine)
4 cylinder 8 intake passage 20 exhaust passage 22 NOx occlusion catalyst 24 EGR passage 30 exhaust temperature sensor 32 EGR gas temperature sensor 34 supply air temperature sensor 36 electronic control unit (ECU)
38 Combustion control unit (combustion control means)

Claims (5)

An exhaust passage communicating with the cylinder of the internal combustion engine;
A NOx storage catalyst that is provided in the exhaust passage and stores NOx in the exhaust during lean combustion and releases and reduces the stored NOx by rich combustion;
Temperature correlation value detecting means for detecting a temperature correlation value in the cylinder;
The temperature correlation value detected by the temperature correlation value detection means and a predetermined value during a period in which the rich combustion is performed in a steady manner to release NOx stored in the NOx storage catalyst and S component adhering to the NOx storage catalyst. a combustion control means for a predetermined period of time prohibits the rich combustion when compared bets, the temperature correlation value exceeds a predetermined value,
A combustion control device for an internal combustion engine, comprising: 2. The rich combustion is prohibited until the predetermined period of time, which is set as a time required for the combustion control means to decrease to the temperature in the cylinder in which the generation amount of black smoke is suppressed, is elapsed. Combustion control device for internal combustion engine. Temperature correlation value within said cylinder, a combustion control apparatus according to claim 1 or 2, wherein the internal combustion engine, wherein said an exhaust temperature of the exhaust passage. The internal combustion engine includes an EGR passage that communicates the intake passage and the exhaust passage that communicate with the cylinder, and the temperature correlation value in the cylinder is an EGR gas temperature in the EGR passage. The combustion control device for an internal combustion engine according to any one of 1 to 3 . The internal combustion engine includes an EGR passage that communicates an intake passage that communicates with the cylinder and an exhaust passage, and a temperature correlation value in the cylinder is obtained after merging of the EGR gas in the EGR passage and the intake air in the intake passage. The combustion control device for an internal combustion engine according to any one of claims 1 to 4 , wherein the supply air temperature of the internal combustion engine.

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