Patent Grant
8249793
1. Field of the Invention
The invention relates to an air-fuel ratio control apparatus for an internal combustion engine, and more particularly, to an air-fuel ratio control apparatus and an air-fuel ratio control method for an internal combustion engine that perform air-fuel ratio feedback control on the basis of a state of exhaust gas.
2. Description of the Related Art
As disclosed in Japanese Patent Application Publication No. 2002-276419 (JP-A-2002-276419), there is known a system in which an ammonia sensor is disposed in an exhaust passage of an internal combustion engine. In this system, the ammonia sensor is disposed at a post-stage of a catalyst disposed in the exhaust passage. Further, together with the ammonia sensor, an oxygen sensor is disposed at the post-stage of the catalyst.
NOx are likely to be contained in exhaust gas of the internal combustion engine when the air-fuel ratio of exhaust gas is lean. Thus, when the air-fuel ratio of exhaust gas continues to be lean, NOx may flow out to the post-stage of the catalyst. On the other hand, under a situation where the air-fuel ratio of exhaust gas is rich, NH3 (ammonia) is likely to be produced through a reaction of nitrogen in exhaust gas with hydrogen. Thus, under the situation where the air-fuel ratio of exhaust gas is rich, NH3 may be discharged to the post-stage of the catalyst.
The ammonia sensor is sensitive to NOx as well as NH3. Thus, the ammonia sensor disposed at the post-stage of the catalyst outputs a value corresponding to the concentration of NH3 under a rich atmosphere, and on the other hand, outputs a value corresponding to the concentration of NOx under a lean atmosphere.
The aforementioned system determines, on the basis of the output of the oxygen sensor disposed downstream of the catalyst, whether the air-fuel ratio of exhaust gas is rich or lean. Then, when the ammonia sensor outputs a value larger than a criterial value under a situation where the air-fuel ratio of exhaust gas is rich, this system determines that a large amount of NH3 has been generated, and attempts to make the air-fuel ratio lean. Further, when the ammonia sensor outputs a value larger than the criterial value under a situation where the air-fuel ratio of exhaust gas is lean, this system determines that a large amount of NOx has been generated, and attempts to make the air-fuel ratio rich.
According to the aforementioned processing, the air-fuel ratio of the internal combustion engine can be controlled such that the amounts of NH3 and NOx flowing out to a region downstream of the catalyst become sufficiently small. Thus, this system can ensure that the internal combustion engine acquires good emission properties.
However, for the first time when the ammonia sensor outputs a value larger than the criterial value under a lean atmosphere, the aforementioned system determines that the air-fuel ratio is deviant to a lean side, and makes the air-fuel ratio rich. According to this control, a certain amount of NOx inevitably flows out to the region downstream of the catalyst. In this respect, the aforementioned system leaves room for further improvement from the standpoint of the suppression of the discharge amount of NOx.
The invention provides an air-fuel ratio control apparatus for an internal combustion engine that can sufficiently suppress the amount of NOx discharged to a region downstream of a catalyst.
A first aspect of the invention relates to an air-fuel ratio control apparatus for an internal combustion engine that is equipped with an air-fuel ratio adjustment mechanism for adjusting an air-fuel ratio of the internal combustion engine, exhaust gas air-fuel ratio detection means for detecting an air-fuel ratio of exhaust gas, first feedback means for subjecting the air-fuel ratio adjustment mechanism to first feedback control such that the air-fuel ratio of exhaust gas becomes close to a target air-fuel ratio in a neighborhood of a stoichiometric air-fuel ratio, an ammonia sensor disposed in an exhaust system of the internal combustion engine, and second feedback means for subjecting the air-fuel ratio adjustment mechanism to second feedback control based on an output value of the ammonia sensor.
According to the foregoing aspect of the invention, the air-fuel ratio of exhaust gas can be controlled to the value in the neighborhood of the stoichiometric air-fuel ratio by the first feedback means. Furthermore, the air-fuel ratio of exhaust gas can be finely adjusted by the second feedback means. The second feedback means performs the second feedback control on the basis of an output of the ammonia sensor. In the neighborhood of the stoichiometric air-fuel ratio, the ammonia sensor outputs a linear value for the concentration of NH3. Further, in an air-fuel ratio range on a rich side with respect to an air-fuel ratio to which an oxygen sensor is sensitive, the ammonia sensor outputs a linear value for the concentration of NH3. Thus, according to the second feedback means, a control target of the air-fuel ratio can be shifted to the rich side in comparison with feedback control based on the output of the oxygen sensor. The amount of NOx in exhaust gas abruptly increases even when the air-fuel ratio of exhaust gas becomes slightly lean with respect to the stoichiometric air-fuel ratio. On the other hand, the amounts of HC and CO in exhaust gas do not very abruptly increase even when the air-fuel ratio of exhaust gas deviates to the rich side in the neighborhood of the stoichiometric air-fuel ratio. Thus, if the control target of the air-fuel ratio can be made slightly richer than the air-fuel ratio where the output of the oxygen sensor abruptly changes, the emission properties of the internal combustion engine can be improved as a whole. The aforementioned requirement can be met by the second feedback means. Therefore, the emission properties of the internal combustion engine can be improved as a whole, in comparison with a case where the air-fuel ratio is finely adjusted using the oxygen sensor.
Further, the air-fuel ratio control apparatus may be equipped with a catalyst so disposed in the exhaust system as to be located upstream of the ammonia sensor. The exhaust gas air-fuel ratio detection means may be equipped with an air-fuel ratio sensor disposed upstream of the catalyst. The first feedback means may perform the first feedback control on a basis of an output of the air-fuel ratio sensor.
According to the foregoing aspect of the invention, the first feedback control can be performed on the basis of the output of the air-fuel ratio sensor disposed upstream of the catalyst. Thus, through the first feedback control, the air-fuel ratio at the stage where exhaust gas flows into the catalyst can be controlled to a value in the neighborhood of the target air-fuel ratio. Further, the second feedback control can be performed on the basis of the output of the ammonia sensor disposed downstream of the catalyst. Thus, through the second feedback control, the air-fuel ratio can be finely adjusted such that desirable emission properties are obtained downstream of the catalyst.
Further, the air-fuel ratio control apparatus may be equipped with operation state detection means for detecting an operation state of the internal combustion engine. The second feedback means may be equipped with control parameter setting means for setting a control parameter of the air-fuel ratio on a basis of a result of a comparison between an output of the ammonia sensor and an ammonia target value, and target value change means for setting the ammonia target value to a rich-side target value under fulfillment of a high-load operation condition and setting the ammonia target value to a lean-side target value, which is leaner than the rich-side target value, under fulfillment of a low-load operation condition.
According to the aforementioned setting, the ammonia target value can be set on the rich side during high-load operation. During high-load operation, components such as NOx, HC, CO, and the like are likely to be discharged. When the ammonia target value is set on the rich side in this situation, HC and CO become more likely to be generated, but the generation amount of NOx can be suppressed. During high-load operation, the catalyst is sufficiently heated. Therefore, the capacity to purify HC and CO is sufficiently ensured. Thus, good emission properties can be realized during high-load operation. Further, the ammonia target value is set on the lean side during low-load operation. During low-load operation, the capacity of the catalyst to purify HC and CO is likely to decrease. When the ammonia target value is set on the lean side under this situation, the generation amounts of HC and CO are suppressed, and hence the discharge of HC and CO can be prevented. Further, during low-load operation, the generation amount of NOx is small, and hence the discharge of an excessive amount of NOx does not occur even when the ammonia target value is set on the lean side. Due to the reason described above, the internal combustion engine can be made to acquire good emission properties.
Further, the second feedback means may be equipped with comparison result reflection means for feeding a result of a comparison between an output of the ammonia sensor and an ammonia target value back to the air-fuel ratio with a predetermined gain, and gain setting means for increasing the gain as an amount of divergence of the output of the ammonia sensor from the ammonia target value increases.
According to the aforementioned setting, the amount of divergence of the output of the ammonia sensor from the ammonia target value can be reflected on the feedback gain. Thus, the accuracy and responsiveness of the second feedback control can be made compatible.
Further, the air-fuel ratio control apparatus may further be equipped with a catalyst so disposed in the exhaust system as to be located upstream of the ammonia sensor, and an oxygen sensor disposed downstream of the catalyst. The exhaust gas air-fuel ratio detection means may be equipped with an air-fuel ratio sensor disposed upstream of the catalyst, and the first feedback means may perform the first feedback control on a basis of an output of the air-fuel ratio sensor. Further, the air-fuel ratio control apparatus may further be equipped with third feedback means for subjecting the air-fuel ratio adjustment mechanism to second feedback control based on output values of the ammonia sensor and the oxygen sensor or an output value of the oxygen sensor, and second feedback selection means for selectively actuating the second feedback means and the third feedback means.
According to the aforementioned setting, the first feedback control can be performed on the basis of the output of the air-fuel ratio sensor located upstream of the catalyst, and the second feedback control can be performed on the basis of at least one of the output of the ammonia sensor located downstream of the catalyst and the output of the oxygen sensor located downstream of the catalyst. The two sensor outputs can be used as the base of the second feedback control. Therefore, high control accuracy can be realized.
Further, the air-fuel ratio control apparatus may further be equipped with operation state detection means for detecting an operation state of the internal combustion engine. The second feedback selection means may select the second feedback means as actuation means under fulfillment of a high-load operation condition, and select the third feedback means as actuation means under fulfillment of a low-load operation condition.
According to the aforementioned setting, during high-load operation, the second feedback control can be performed on the basis of the output of the ammonia sensor. When the second feedback control is performed on the basis of the output of the ammonia sensor, the target air-fuel ratio can be shifted to the rich side in comparison with a case where the second feedback control is performed on the basis of the output of the oxygen sensor. When the target air-fuel ratio is made rich, the production amount of NOx can be suppressed. Thus, good emission properties can be realized even during high-load operation, which tends to cause the generation of a large amount of NOx. During low-load operation, the second feedback control can be performed on the basis of the output of the oxygen sensor. When the second feedback control is performed on the basis of the output of the oxygen sensor, the target air-fuel ratio can be shifted to the lean side. When the target air-fuel ratio is made lean, the generation amounts of HC and CO are suppressed. Accordingly, good emission properties can be realized even during low-load operation, which causes a decrease in the activity of the catalyst.
Further, the air-fuel ratio control apparatus may be equipped with deviation direction determination means for determining whether the air-fuel ratio of exhaust gas is deviant from the target air-fuel ratio to a rich side or to a lean side. The second feedback selection means may select the second feedback means as actuation means under a condition that it be determined that the air-fuel ratio of exhaust gas is deviant to the rich side, and select the third feedback means as actuation means under a condition that it be determined that the air-fuel ratio of exhaust gas is deviant to the lean side.
According to the aforementioned setting, when the air-fuel ratio of exhaust gas is deviant from the target air-fuel ratio to the rich side, the second feedback control is performed on the basis of the output of the ammonia sensor. The ammonia sensor is worse in responsiveness than the oxygen sensor, but on the other hand, outputs a linear value for a slightly rich air-fuel ratio that cannot be stably detected by the oxygen sensor. When the target air-fuel ratio is deviant to the rich side, the generation of a large amount of NOx is unlikely to occur, and hence, responsiveness is not required of the feedback control. In this case, good emission properties can be realized by performing the second feedback control on the basis of the output of the ammonia sensor. Further, when the air-fuel ratio of exhaust gas is deviant from the target air-fuel ratio to the lean side, the second feedback control is performed on the basis of the output of the oxygen sensor. Unlike the ammonia sensor, the oxygen sensor is not sensitive to a range richer than the stoichiometric air-fuel ratio, but on the other hand, has excellent responsiveness. When the target air-fuel ratio is deviant to the lean side, the generation of a large amount of NOx is likely to occur. The discharge amount of NOx can be sufficiently suppressed with excellent responsiveness by performing the second feedback control on the basis of the output of the oxygen sensor under the aforementioned situation.
Further, the deviation direction determination means may determine that the air-fuel ratio of exhaust gas is deviant from the target air-fuel ratio to the rich side when the output of the oxygen sensor is larger than an oxygen target value, and determine that the air-fuel ratio of exhaust gas is deviant from the target air-fuel ratio to the lean side when the output of the oxygen sensor is smaller than the oxygen target value.
According to the aforementioned setting, it can be determined, on the basis of the output of the oxygen sensor, whether the air-fuel ratio of exhaust gas is deviant from the target air-fuel ratio to the rich side or to the lean side. The oxygen sensor has high absolute accuracy and excellent responsiveness. Thus, the aforementioned determination can be accurately made with excellent responsiveness.
Further, the second feedback means may perform the second feedback control such that the output of the ammonia sensor becomes close to an ammonia target value, and the third feedback means may perform the second feedback control such that the output of the oxygen sensor becomes close to an oxygen target value. The air-fuel ratio of exhaust gas for making the output of the ammonia sensor coincident with the ammonia target value may be shifted to the rich side from the air-fuel ratio of exhaust gas for making the output of the oxygen sensor coincident with the oxygen target value.
According to the aforementioned setting, the target air-fuel ratio can be changed depending on whether the second feedback control is performed on the basis of the output of the ammonia sensor or the output of the oxygen sensor.
Further, the third feedback means may be equipped with control parameter setting means for reflecting a result of a comparison between an output of the oxygen sensor and an oxygen target value on a control parameter of the air-fuel ratio with a predetermined gain, and gain setting means for increasing the gain as an amount of divergence of the output of the oxygen sensor from the oxygen target value increases.
According to the aforementioned setting, the amount of divergence of the output of the oxygen sensor from the oxygen target value can be reflected on the feedback gain. Thus, according to the invention, the accuracy and responsiveness of the second feedback control can be made compatible.
The foregoing and further objects, features and advantages of the invention will become apparent from the following description of embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:
[Configuration of First Embodiment]
An output of the air-fuel ratio sensor 12 and an output of the ammonia sensor 18 are supplied to an electronic control unit (ECU) 30. Further, an output of an airflow meter 32 for detecting an intake air amount Ga and an output of a rotational speed sensor 34 for detecting an engine rotational speed Ne are supplied to the ECU 30. Furthermore, an injector 36 for injecting fuel to an intake side of the internal combustion engine 10 is connected to the ECU 30. The ECU 30 performs feedback control of the amount of fuel injected from the injector 36 such that the air-fuel ratio of exhaust gas becomes equal to a target air-fuel ratio, on the basis of the outputs of the aforementioned various sensors.
[Characteristics of Oxygen Sensor and Ammonia Sensor]
The rich output of the oxygen sensor is about 0.9 V at an initial stage (see the characteristic curve 40), but decreases to about 0.6 V in the course of aged deterioration (see the characteristic curve 42). Thus, in order to make a correct determination even after aged deterioration using the oxygen sensor, the criterial value needs to be set to about 0.5 V.
Given that an air-fuel ratio at which the inversion of the output of the oxygen sensor is detected is referred to as “an inversion air-fuel ratio”, the air-fuel ratio shifts to the rich side as the criterial value increases across the inversion air-fuel ratio, and on the other hand, shifts to the lean side as the criterial value decreases across the inversion air-fuel ratio. The upper limit of the criterial value to be compared with the output of the oxygen sensor is about 0.5 V because of the reason described above. Thus, as long as the oxygen sensor is used, the behavior of the air-fuel ratio cannot be detected in a range richer than the inversion air-fuel ratio corresponding to 0.5 V.
A range denoted by a reference numeral 44 in
A solid line denoted by a reference numeral 46 in
In the case where the air-fuel ratio is lean, NOx are likely to be contained in exhaust gas. The leaner the air-fuel ratio becomes, the higher the concentration of NOx in exhaust gas becomes. Thus, in a range where the air-fuel ratio is lean, the leaner the air-fuel ratio becomes, the larger the value output by the ammonia sensor 18 becomes, as indicated by the solid line 48. Due to the reason described above, the ammonia sensor 18 outputs values corresponding to the air-fuel ratio respectively in a rich air-fuel ratio range and in a lean air-fuel ratio range. Especially, the ammonia sensor 18 outputs a value corresponding to the air-fuel ratio in a range outside the inversion air-fuel ratio of the oxygen sensor. Thus, the ammonia sensor 18 can detect the air-fuel ratio over a wider range than the oxygen sensor.
[Features of First Embodiment]
As shown in
In
The system according to this embodiment of the invention performs a combination of main air-fuel ratio feedback control based on the output of the air-fuel ratio sensor 16 disposed upstream of the three-way catalyst 14 and sub-feedback control based on the output of the ammonia sensor 18 disposed downstream of the three-way catalyst 14. The main feedback control serves to adjust the amount of fuel injection such that the air-fuel ratio of exhaust gas discharged from the internal combustion engine 10 becomes equal to the stoichiometric air-fuel ratio.
The internal combustion engine 10 is affected by the accumulation of influences of an individual difference, aged deterioration, and the like. Thus, the air-fuel ratio of exhaust gas obtained as a result of the main air-fuel ratio feedback control may deviate to the rich side or to the lean side. If this tendency continues, there will soon be a situation where rich gas or lean gas blows by in a region downstream of the three-way catalyst 14.
The aforementioned blow-by can be detected by the ammonia sensor 18 disposed downstream of the three-way catalyst 14. The sub-feedback control is intended to eliminate the deviation of the control center of the air-fuel ratio by detecting the influence of the blow-by. This sub-feedback control can be realized by, for example, correcting the amount of fuel injection in a decreasing direction when the output of the ammonia sensor 18 deviates to the rich side, and on the other hand, correcting the amount of fuel injection in an increasing direction when the output of the ammonia sensor 18 deviates to the lean side.
As described with reference to
As described above, the purification rate of the three-way catalyst 14 for NOx decreases in the lean range. On the other hand, the purification rate of the three-way catalyst for each of HC and CO decreases in the rich range. A comparison between both the purification rates shows that the purification rate for NOx tends to decrease more abruptly than the purification rate for each of HC and CO (see
When the ammonia sensor 18 is disposed downstream of the three-way catalyst 14 to shift the control target of the sub-feedback control to the rich side, the air-fuel ratio is likely to deviate to the rich side but unlikely to deviate to the lean side. The purification rate for each of HC and CO does not abruptly decrease when the air-fuel ratio deviates to the rich side. Therefore, the increase in the discharge amount of HC or CO caused by the aforementioned shift is not appreciably large. On the other hand, when the air-fuel ratio is restrained from deviating to the lean side, the discharge amount of NOx is drastically reduced. Thus, according to the system of this embodiment of the invention, an improvement in overall emission properties can be made in comparison with the system in which the oxygen sensor is disposed downstream of the three-way catalyst 14 to perform the sub-feedback control.
[Concrete Processings in First Embodiment]
In the routine shown in
As shown in
The target value used in the aforementioned step 102 corresponds to a value output by the ammonia sensor 18 under an air-fuel ratio of exhaust gas that is slightly richer than the stoichiometric air-fuel ratio (hereinafter referred to as “a rich shift stoichiometric air-fuel ratio). The rich shift stoichiometric air-fuel ratio is slightly richer than the inversion air-fuel ratio (see
When it is determined in the aforementioned step 102 that a condition is fulfilled, namely, that the air-fuel ratio of exhaust gas is located on the lean side with respect to the rich shift stoichiometric air-fuel ratio, a sub-feedback update amount DSFBG is set to −0.01 (step 104). On the other hand, when the condition is denied, the sub-feedback update amount DSFBG is set to 0.01 (step 106).
In the routine shown in
SFBG=SFBG+DSFBG (1)
An AF target value is then calculated according to an expression (2) shown below (step 110). It should be noted herein that “initial value” on the right side of the expression (2) corresponds to the stoichiometric air-fuel ratio (e.g., 14.6).
AF target value=initial value+SFBG (2)
According to the aforementioned processings, when the ammonia sensor 18 detects an air-fuel ratio leaner than the rich shift stoichiometric air-fuel ratio, the AF target value is corrected to a smaller value, namely, a value on the rich side. On the other hand, when the ammonia sensor 18 detects an air-fuel ratio richer than the rich shift stoichiometric air-fuel ratio, the AF target value is corrected to a larger value, namely, a value on the lean side. Thus, through the aforementioned processing, the AF target value can be corrected such that the output of the ammonia sensor 18 becomes equal to a value corresponding to the rich shift stoichiometric air-fuel ratio.
The ECU 30 subjects the amount of fuel injection to the sub-feedback control such that the AF target value set through the aforementioned processings is realized. As a result, in the system according to this embodiment of the invention, the air-fuel ratio of exhaust gas in the internal combustion engine 10 is controlled to the air-fuel ratio range indicated as “RANGE OF USE OF THIS EMBODIMENT OF THE INVENTION” in
In the foregoing first embodiment of the invention, the injector 36 may correspond to “the air-fuel ratio adjustment mechanism”, and the air-fuel ratio sensor 16 may correspond to “the exhaust gas air-fuel ratio detection means”. Further, “the first feedback means” may be realized through the performance of the main feedback control by the ECU 30 on the basis of the output of the air-fuel ratio sensor 16. “The second feedback means” may be realized through the performance of the sub-feedback control by the ECU 30 to realize the AF target value calculated through the processing of step 110.
[Features of Second Embodiment] Next, the second embodiment of the invention will be described with reference to
In the system according to the foregoing first embodiment of the invention, an improvement in emission properties is made by shifting the AF target value of the sub-feedback control to the rich side, focusing attention on the fact that the purification rate of the three-way catalyst 14 tends to decrease differently for HC, CO, and NOx. The purification capacity of the three-way catalyst 14 is not always constant but changes in accordance with the load state of the internal combustion engine 10. Further, the amounts of HC, CO, and NOx discharged from the internal combustion engine 10 also change in accordance with the load state thereof. Thus, when the AF target value of the sub-feedback control is appropriately adjusted in accordance with the load state of the internal combustion engine 10, a further improvement in emission properties can be made in the region downstream of the three-way catalyst 14.
That is, when the internal combustion engine 10 is operated in the high-load range, large amounts of HC, CO, and NOx are all likely to be discharged as the air-fuel ratio fluctuates. On the other hand, during the operation in the high-load range, the three-way catalyst 14 is at a sufficiently high temperature and in a sufficiently activated state. In this case, the three-way catalyst 14 demonstrates a sufficient purification capacity for HC and CO. Under this situation, even though the discharge amounts of HC and CO slightly increase, it is desirable, from the standpoint of obtaining good emission properties, to shift the control center of the air-fuel ratio to the rich side to create a situation where the generation of a large amount of NOx is, easy to suppress.
On the other hand, when the internal combustion engine 10 is operated in the low-load range, the three-way catalyst 14 is low in temperature and has reduced activity. In this case, the purification capacity of the three-way catalyst 14 for HC and CO deteriorates. Therefore, it is undesirable to create a situation where HC and CO are likely to be discharged. On the other hand, when the load of the internal combustion engine 10 is low, the amount of NOx discharged in the lean air-fuel ratio range is not appreciably large either. In this case, with a view to improving emission properties comprehensively, it is desirable to shift the control center of the air-fuel ratio from the center during high-load operation to the lean side.
Due to the reason described above, the load state of the internal combustion engine 10 is reflected on the AF target value of the sub-feedback control. More specifically, in this system, the higher the load of the internal combustion engine 10 becomes, the more the aforementioned AF target value is shifted to the rich side. Further, the lower the load of the internal combustion engine 10 becomes, the more the aforementioned AF target value is shifted to the lean side.
[Concrete Processings in Second Embodiment]
In the routine shown in
A sub-feedback target value, namely, an output target value of the ammonia sensor 18 is calculated (step 124). As shown in
According to the map shown in
As described with reference to
In the routine shown in
Owing to the performance of the processings described above, in this embodiment of the invention, the air-fuel ratio of exhaust gas in the internal combustion engine 10 is accurately controlled to the value in the neighborhood of the stoichiometric air-fuel ratio in the low-load low-rotation range. In the low-load low-rotation range, the generation amount of NOx is small. Therefore, even when the control target is equal to the stoichiometric air-fuel ratio (the target on the lean side with respect to the case of the first embodiment of the invention), the discharge of a large amount of NOx does not occur as a result of a deviation of the air-fuel ratio. On the other hand, in this range, the activity of the three-way catalyst 14 tends to be low, but the generation amounts of HC and CO are also small. Therefore, the discharge of large amounts of HC and CO can also be prevented. Thus, according to this system, good emission properties can be realized in the low-load low-rotation range.
According to the aforementioned processings, the control target of the air-fuel ratio is shifted to the rich side as the engine rotational speed Ne and the engine load rise. The amount of NOx generated as a result of a deviation of the air-fuel ratio to the lean side increases as the load increases and as the rotational speed increases. When the control target is changed as described above as the load and the rotational speed change, the possibility of the deviation of the air-fuel ratio to the lean side decreases as the load and the rotational speed increase. As a result, the generation of NOx can be made unlikely. Thus, according to this system, the discharge amount of NOx can be sufficiently suppressed in the entire operation range of the internal combustion engine 10.
Further, the three-way catalyst 14 enhances the purification capacity for HC and CO as the operation range of the internal combustion engine 10 transits to the high-load high-rotation range. Thus, even when the generation amounts of HC and CO increase due to increases in the load and the rotational speed, the three-way catalyst 14 can appropriately purify HC and CO. Thus, according to this system, the discharge amounts of HC and CO can also be sufficiently suppressed in the entire operation range of the internal combustion engine.
In the system according to the second embodiment of the invention, an improvement in emission properties is made by shifting the control target of the air-fuel ratio to the rich side as the load and the rotational speed increase. In the system equipped with the oxygen sensor downstream of the catalyst, with a view to shifting the control target to the rich side in a similar manner, the output target of the oxygen sensor needs to be set to a value of 0.7 to 0.8 V in or between the intermediate-load intermediate-rotation range and the high-load high-rotation range, as shown in
In the foregoing second embodiment of the invention, “the operation state detection means” may be realized through the performance of the processings of steps 120 and 122 by the ECU 30. Further, “the control parameter setting means” may be realized through the performance of the processings of steps 102 to 110 by the ECU 30. Furthermore, “the target value change means” may be realized through the performance of the processing of step 124 by the ECU 30.
[Features of Third Embodiment] Next, the third embodiment of the invention will be described with reference to
In the foregoing first embodiment of the invention and the foregoing second embodiment of the invention, the output of the ammonia sensor 18 and the target value are compared in magnitude with each other, and the sub-feedback update amount DSFBG is set to −0.01 or 0.01 on the basis of a result of the comparison. That is, in the first embodiment of the invention and the second embodiment of the invention, the sub-feedback learning value SFBG is always increased/reduced with a certain width regardless of the amount of divergence of the output of the ammonia sensor 18 from the target value.
However, in order to swiftly make the air-fuel ratio of exhaust gas in the internal combustion engine 10 coincident with the target air-fuel ratio, the correction width of the sub-feedback learning value SFBG may be increased as the amount of divergence of the output of the ammonia sensor, 18 from the target value increases. Thus, in this embodiment of the invention, the value set as the sub-feedback update amount DSFBG is changed in accordance with the amount of divergence.
[Concrete Processings in Third Embodiment]
In the routine shown in
When the result of the aforementioned determination is positive, namely, when it is determined that the output of the ammonia sensor 18 is located in the neighborhood of the target value, the processings starting from step 102 are thereafter performed. In this case, the sub-feedback update amount DSFBG is set to −0.01 or 0.01 depending on whether or not the output of the ammonia sensor 18 is smaller than the target value. The sub-feedback learning value SFBG is corrected with the width between those set values.
On the other hand, when the result of the determination in the aforementioned step 130 is negative, the processings starting from step 132 are thereafter performed. In this case, the sub-feedback update amount DSFBG is set to −0.03 or 0.03 depending on whether or not the output of the ammonia sensor 18 is smaller than the target value (steps 134 and 136). Then, through the processings starting from step 108, the sub-feedback learning value SFBG is corrected with the width between those set values.
According to the aforementioned processings, when the output of the ammonia sensor 18 is located in the neighborhood of the target value, accurate air-fuel ratio control can be realized by correcting the sub-feedback learning value SFBG with a very small width. Further, when the output of the ammonia sensor 18 greatly diverges from the target value, the air-fuel ratio of exhaust gas can be swiftly made close to the target air-fuel ratio by correcting the sub-feedback learning value SFBG with a large width. Thus, according to the system of this embodiment of the invention, the control accuracy of the air-fuel ratio of exhaust gas can further be enhanced.
[Configuration of Fourth Embodiment] Next, the fourth embodiment of the invention will be described with reference to
As shown in
[Features of Fourth Embodiment]
In the system according to this embodiment of the invention, the control point of the air-fuel ratio can be set to a range richer than the aforementioned “CONTROL POINT ACCORDING TO COMPARATIVE EXAMPLE” by performing the sub-feedback control on the basis of the output of the ammonia sensor 18. Further, when the criterial value to be compared with the output of the oxygen sensor 40 is set to a sufficiently small value, the control point based on the output of the oxygen sensor 40 can also be shifted to a range leaner than the “CONTROL POINT ACCORDING TO COMPARATIVE EXAMPLE”. Thus, according to the system of this embodiment of the invention, the control point can be set within a sufficiently wider range than a control point generally realized by a system having only an oxygen sensor disposed downstream of a catalyst (see a range indicated as “CONTROL POINT ACCORDING TO THIS EMBODIMENT OF THE INVENTION (VARIABLE)” in
The wider the settable range of the control point of the air-fuel ratio becomes, the higher the degree of freedom regarding the air-fuel ratio control of the internal combustion engine 10 becomes. Accordingly, the system according to this embodiment of the invention makes it possible to perform the sub-feedback control of the air-fuel ratio with a higher degree of freedom than the system equipped with only the oxygen sensor downstream of the catalyst.
As described in the foregoing second embodiment of the invention, in the low-load low-rotation range, it is desirable to set the AF target value of the sub-feedback control on the lean side in consideration of a decrease in the purification capacity for HC 10, and CO. On the other hand, in the high-load high-rotation range, the AF target value may be shifted to the rich side, giving priority to the suppression of the discharge of NOx.
In the system according to this embodiment of the invention, the output of the oxygen sensor 40 and the output of the ammonia sensor 18 can be utilized as base data of the sub-feedback control. The oxygen sensor 40 inverts one of a rich output and a lean output to the other in the neighborhood of the stoichiometric air-fuel ratio, and the output of the oxygen sensor 40 converges to the lean output in a range slightly leaner than the stoichiometric air-fuel ratio. Thus, when the sub-feedback control is performed on the basis of the output of the oxygen sensor 40, the AF target value can be set on the lean side. On the other hand, the ammonia sensor 18 is sensitive to the air-fuel ratio in the rich range. Thus, when the sub-feedback control is performed on the basis of the output of the ammonia sensor 18, the AF target value can be set on the rich side.
Further, in the first intermediate-load intermediate-rotation range, the sub-feedback control is performed on the basis of the output of the oxygen sensor 40, with the criterial value set to 0.5 V. Since the criterial value is set to 0.5 V, the AF target value is slightly returned to the rich side in this range in comparison with the AF target value in the low-load low-rotation range.
In the range where the load or the rotational speed is slightly higher than in the first intermediate-load intermediate-rotation range, namely, in the second intermediate-load intermediate-rotation range, the sub-feedback control is performed on the basis of the output of the ammonia sensor 18, with the criterial value of NH3 set to 20 ppm. NH3 is generated in the rich range. Thus, in this range, the sub-feedback control can be performed with the AF target value set slightly on the rich side with respect to the stoichiometric air-fuel ratio.
In the high-load high-rotation range, the sub-feedback control is performed on the basis of the output of the ammonia sensor 18 with the criterial value for NH3 set to 30 ppm. Since the criterial value has been increased to 30 ppm, the sub-feedback control can be performed in this range using the AF target value that is still richer than the AF target value set in the second intermediate-load intermediate-rotation range.
As described above, the system according to this embodiment of the invention changes over the sensor output and criterial value that are utilized to perform the sub-feedback control, in accordance with the operation state of the internal combustion engine 10. According to this method, the AF target value can be changed over a wider range. Thus, according to the system of this embodiment of the invention, the degree of freedom in the air-fuel ratio control can further be enhanced.
Further, as described with reference to
Further, as described with reference to
Due to the reason described above, the system according to this embodiment of the invention can ensure a higher degree of freedom as to air-fuel ratio control. Further, according to this system, more excellent emission properties can be realized in the entire operation range of the internal combustion engine 10.
[Concrete Processings in Fourth Embodiment]
In the routine shown in
It is then determined whether the selected output is the output of the oxygen sensor 40 or the output of the ammonia sensor 18 (step 142). As a result, when it is determined that the output of the ammonia sensor 18 is selected (when the result of the determination is No), the AF target value is thereafter subjected to feedback control through the performance of the processings of steps 100 to 110.
On the other hand, when it is determined in step 142 that the selected output is the output of the oxygen sensor 40, the processings for proceeding with the sub-feedback control based on that output are thereafter performed. More specifically, the output of the oxygen sensor 40 is first read (step 144). It is then determined whether or not the output of the oxygen sensor 40 is smaller than the target value set in the aforementioned step 140 (step 146).
As a result, when it is determined that the output of the oxygen sensor 40 is smaller than the target value, it can be determined that the air-fuel ratio downstream of the three-way catalyst 14 is deviant from the target air-fuel ratio to the lean side. In this case, the sub-feedback update amount DSFBG is set to −0.01 (step 148).
On the other hand, when it is determined that the output of the oxygen sensor 40 is not smaller than the target value, it can be determined that the air-fuel ratio of exhaust gas downstream of the three-way catalyst 14 is deviant from the target air-fuel ratio to the rich side. In this case, the sub-feedback update amount DSFBG is set to 0.01 (step 150).
After that, a corrective processing for the AF target value based on the sub-feedback update amount DSFBG is performed through the processings of steps 108 and 110. As a result, when the air-fuel ratio of exhaust gas downstream of the catalyst is deviant to the lean side, the AF target value is corrected to the rich side, and as a result, the air-fuel ratio of exhaust gas is made close to the target thereof. On the other hand, when the air-fuel ratio of exhaust gas is deviant to the rich side, the AF target value is corrected to the lean side, and the air-fuel ratio of exhaust gas is made close to the target thereof.
According to the processing described above, the sensor and the target value as the base of the sub-feedback control can be changed over as shown in
In the foregoing fourth embodiment of the invention, the sub-feedback control is performed on the basis of only the output of the oxygen sensor 40 in the range on the low-load low-rotation side. However, the invention is not limited to this configuration. That is, the sub-feedback control may be performed on the basis of both the output of the oxygen sensor 40 and the output of the ammonia sensor 18 in the range on the low-load low-rotation side.
In the foregoing fourth embodiment of the invention, “the third feedback means” is realized through the performance of the processings of steps 144 to 150 and steps 108 and 110 by the ECU 30. Further, “the second feedback selection means” is realized through the performance of the processing of step 140 by the ECU 30. Furthermore, in this case, “the operation state detection means” is realized through the performance of the processings of steps 120 and 122 by the ECU 30.
[Features of Fifth Embodiment] Next, the fifth embodiment of the invention will be described with reference to
As is the case with the system according to the fourth embodiment of the invention, the system according to this embodiment of the invention is equipped with the oxygen sensor 40 as well as the ammonia sensor 18 downstream of the three-way catalyst 14.
In the system according to this embodiment of the invention, as shown in
In the lean range, NOx are likely to be generated. Further, as described with reference to
In the system according to this embodiment of the invention, as shown in
According to this setting, it is possible to reduce the frequency with which the air-fuel ratio enters the lean range, and create a situation where NOx are unlikely to be produced. Further, the output of the ammonia sensor 18 has linearity for the air-fuel ratio. Therefore, according to the control based on the output of the ammonia sensor 18, the deviation amount of the air-fuel ratio can be fed back with accuracy. Thus, according to the system of this embodiment of the invention, the air-fuel ratio can be accurately controlled while suppressing the production of NOx in the rich range.
Due to the reason described above, according to the system of this embodiment of the invention, when the air-fuel ratio of exhaust gas enters the lean range, the deviation of the air-fuel ratio to the lean side can be swiftly canceled. Further, while the air-fuel ratio of exhaust gas belongs to the rich range, it is possible to perform control with accuracy such that the air-fuel ratio of exhaust gas becomes equal to the AF target value shifted from the stoichiometric air-fuel ratio to the rich side. Thus, according to the system of this embodiment of the invention, the emission properties of the internal combustion engine 10 can be comprehensively improved.
[Concrete Processings in Fifth Embodiment]
In the routine shown in
In the routine shown in
The output of the oxygen sensor 40 abruptly changes across the stoichiometric air-fuel ratio, and decreases as the air-fuel ratio of exhaust gas is shifted to the lean side in the range where the output of the oxygen sensor 40 abruptly changes. Thus, an air-fuel ratio by which it is determined whether or not the condition of the aforementioned step 164 is fulfilled (hereinafter referred to as “a rich-lean threshold”) is shifted to the lean side as the sub-feedback target value decreases, and is shifted to the rich side as the target value increases. The maps shown in
When the fulfillment of the condition of the aforementioned step 164 is recognized, it can be determined that the air-fuel ratio of exhaust gas is located on the lean side with respect to the rich-lean threshold. In this case, the ECU 30 sets the sub-feedback update value DSFBG to −0.01 (step 166). As a result, the AF target value thereafter shifts to the rich side through the performance of the processings of steps 108 and 100.
The oxygen sensor 40 has excellent responsiveness for the ammonia sensor. Thus, the aforementioned shift of the AF target value to the rich side is swiftly carried out after the air-fuel ratio of exhaust gas exceeds the rich-lean threshold. As a result, the deviation of the air-fuel ratio of exhaust gas to the lean side is swiftly canceled, and the discharge of NOx is suppressed.
Further, the rich-lean threshold shifts to the rich side as the engine rotational speed and the engine load rise as described above. Therefore, the air-fuel ratio of exhaust gas realized as a result of the aforementioned processings also shifts to the rich side as the engine rotational speed and the engine load rise. As described in the second embodiment of the invention, when the control center of the air-fuel ratio is shifted to the rich side as the engine load and the engine rotational speed rise, the emission properties of the internal combustion engine 10 can be comprehensively improved. Thus, according to the system of this embodiment of the invention, the effect thereof also makes it possible to improve the emission properties of the internal combustion engine 10.
When the air-fuel ratio of exhaust gas belongs to the lean range, namely, the range on the lean side with respect to the rich-lean threshold, it is determined in the aforementioned step 164 that the output of the oxygen sensor 40 is not smaller than the sub-feedback target value for the output. In this case, the AF target value is thereafter corrected such that the output of the ammonia sensor 18 coincides with the sub-feedback target value for the output, through the processings of steps 100 to 110. As a result, excellent emission properties are realized (see
As described above, according to the routine shown in
In the foregoing fifth embodiment of the invention, “the direction determination means” may be realized through the performance of the processing of step 164 by the ECU 30. Further, “the second feedback selection means” may be realized through the selective performance of either the processing of step 166 or the processings of steps 100 to 106 by the ECU 30 in accordance with the result of the determination in step 164.
Further, in the foregoing fifth embodiment of the invention, “the second feedback means” may be realized through the performance of the processings of steps 100 to 106 by the ECU 30. Furthermore, “the third feedback means” may be realized through the performance of the processings of steps 164 and 166 by the ECU 30.
[Features of Sixth Embodiment] Next, the sixth embodiment of the invention will be described with reference to
The system according to the foregoing fifth embodiment of the invention performs feedback control for making the output of the oxygen sensor 40 close to the target value thereof with a certain gain when the air-fuel ratio of exhaust gas belongs to the lean range. Further, the system according to the fifth embodiment of the invention performs feedback control for making the output of the ammonia sensor 18 close to the target value thereof with a certain gain when the air-fuel ratio of exhaust gas belongs to the rich range. The system according to this embodiment of the invention is characterized in that this feedback method is combined with the processing of reflecting the amount of divergence of the sensor output from the target value on the gain.
[Concrete Processings in Sixth Embodiment]
In steps 130 to 136, which constitute the aforementioned third difference, are identical to the processings included in the routine executed in the third embodiment of the invention (see
In the routine shown in
The output of the ammonia sensor 18 and the output of the oxygen sensor 40 are then sequentially read (steps 170 and 162). It is then determined in step 164 whether or not the output of the oxygen sensor 40 is smaller than the target value for the output.
The condition of step 164 is fulfilled when the air-fuel ratio of exhaust gas belongs to the lean range. Accordingly, when the fulfillment of this condition is denied, it can be determined that the air-fuel ratio of exhaust gas belongs to the rich range. In this case, the sub-feedback update amount DSFBG for making the output of the ammonia sensor 18 close to the target value thereof is thereafter calculated through the processings starting from step 130.
Especially, when it is determined in step 130 that the output of the ammonia sensor 18 is not in the neighborhood of the target value, the sub-feedback update amount DSFBG is calculated in the routine shown in
When it is determined in step 164 that the output of the oxygen sensor 40 is smaller than the target value, it can be determined that the air-fuel ratio of exhaust gas belongs to the lean range. In the routine shown in
As described with reference to
When it is determined in step 172 that the output of the ammonia sensor 18 is smaller than the criterial value, the ECU 30 determines that the air-fuel ratio of exhaust gas is not greatly deviant to the lean side. In this case, with a view to correcting the air-fuel ratio slightly to the rich side, the sub-feedback update amount DSFBG is thereafter set to −0.01 in step 166. On the other hand, when it is determined in step 172 that the output of the ammonia sensor 18 is larger than the criterial value, the ECU 30 determines that the air-fuel ratio is greatly deviant to the lean side. In this case, with a view to correcting the air-fuel ratio of exhaust gas greatly to the rich side, the sub-feedback update amount DSFBG is set to −0.03.
As described above, according to the routine shown in
In the foregoing sixth embodiment of the invention, “the third feedback means”, namely, “the control parameter setting means” and “the gain setting means” may be realized through the performance of the processings of steps 172, 166, and 174 by the ECU 30.
While the invention has been described with reference to what are considered to be preferred embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments or constructions. On the contrary, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the disclosed invention are shown in various combinations and configurations, which are exemplary, other combinations and configurations, including more, less or only a single element, are also within the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-275974 | Oct 2007 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB2008/002814 | 10/22/2008 | WO | 00 | 1/22/2010 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2009/053814 | 4/30/2009 | WO | A |
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