US20140373512A1 - Emission gas cleaning device of internal combustion engine - Google Patents
Emission gas cleaning device of internal combustion engine Download PDFInfo
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- US20140373512A1 US20140373512A1 US14/376,179 US201314376179A US2014373512A1 US 20140373512 A1 US20140373512 A1 US 20140373512A1 US 201314376179 A US201314376179 A US 201314376179A US 2014373512 A1 US2014373512 A1 US 2014373512A1
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- F01N11/00—Monitoring or diagnostic devices for exhaust-gas treatment apparatus, e.g. for catalytic activity
- F01N11/007—Monitoring or diagnostic devices for exhaust-gas treatment apparatus, e.g. for catalytic activity the diagnostic devices measuring oxygen or air concentration downstream of the exhaust apparatus
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- B01D53/34—Chemical or biological purification of waste gases
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- B01D53/34—Chemical or biological purification of waste gases
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- B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
- B01D53/9459—Removing one or more of nitrogen oxides, carbon monoxide, or hydrocarbons by multiple successive catalytic functions; systems with more than one different function, e.g. zone coated catalysts
- B01D53/9477—Removing one or more of nitrogen oxides, carbon monoxide, or hydrocarbons by multiple successive catalytic functions; systems with more than one different function, e.g. zone coated catalysts with catalysts positioned on separate bricks, e.g. exhaust systems
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Abstract
In a system having an oxygen sensor arranged downstream of a NOx storage-reduction catalyst, a constant current is made to flow between sensor electrodes by a constant current circuit provided in the outside of the oxygen sensor, which makes it possible to change an output characteristic of the oxygen sensor. Further, during a lean combustion control of an engine, a sensing responsiveness to a lean component of the oxygen sensor is improved. In this way, when NOx (lean component) is emitted to the downstream of the catalyst, the NOx can be quickly sensed by the oxygen sensor. Meanwhile, during a rich combustion control of the engine, the sensing responsiveness to a rich component of the oxygen sensor is improved. In this way, when HC and CO (rich components) are emitted to the downstream of the catalyst, the HC and the CO can be quickly sensed by the oxygen sensor.
Description
- This application is based on Japanese Patent Applications No. 2012-22261 filed on Feb. 3, 2012, and No. 2012-221944 filed on Oct. 4, 2012, the disclosures of which are incorporated herein by reference.
- The present disclosure relates to an emission gas cleaning device of an internal combustion engine which has a catalyst for cleaning an emission gas of the internal combustion engine and which has an emission gas sensor arranged downstream of the catalyst or in the catalyst.
- In an emission gas cleaning system of an internal combustion engine, for example, as described in Patent Literature 1 (Japanese Patent No. 399759), there is proposed the following emission gas cleaning system: that is, an exhaust pipe has a catalyst (for example, a three-way catalyst or a NOx storage-reduction catalyst) arranged therein and has an emission gas sensor (an air-fuel ratio sensor or an oxygen sensor) arranged upstream or downstream of the catalyst, the catalyst cleaning an emission gas, and the emission gas sensor. The emission gas sensor senses an air-fuel ratio of an emission gas or senses whether the air-fuel ratio of the emission gas is rich or lean. The air-fuel ratio is fed back on the basis of an output of the emission gas sensor to thereby increase an emission gas cleaning rate of the catalyst.
- In the emission gas sensor such as the oxygen sensor, when the air-fuel ratio of the emission gas is changed from a rich value to a lean value or vice versa, the output of the emission gas sensor causes a delay in a change in a sensor output to a change in an actual air-fuel ratio. Hence, it is necessary for improving a sensing responsiveness.
- For embodiment, as described in Patent Literature 2 (JP-H8-20414 B), there is proposed the following emission gas cleaning device: that is, a gas sensor such as an oxygen sensor has at least one auxiliary electrochemical cell built therein and the auxiliary electrochemical cell is connected to one electrode of the gas sensor; and an impressed current is applied to the auxiliary electrochemical cell to thereby perform an ion pumping, whereby an output characteristic of the gas sensor can be changed according to the impressed current and hence the sensing responsiveness of the gas sensor can be improved.
- Further, as described in Patent Literature 3 (JP-S56-89051 A), there is proposed also the following emission gas cleaning device: that is, in an oxygen sensor having a sensor element constructed of a barrier film layer, a reference-electrode electronic-conductive layer, a solid electrolyte layer, and a measurement-electrode electronic-conductive layer, which are laminated on each other, oxygen ions are moved from a measurement electrode to a reference electrode by current supplied from a DC power source to thereby make an oxygen partial pressure on the measurement electrode lower than an oxygen partial pressure in an emission gas (gas to be sensed), which makes it possible to sense an air-fuel ratio leaner than a stoichiometric air-fuel ratio [see a column (A) in
FIG. 11 ]. -
- [Patent Literature 1] Japanese Patent No. 3997599
- [Patent Literature 2] JP-H8-20414 B
- [Patent Literature 3] JP-S56-89051 A
- An air-fuel ratio of an emission gas flowing into a catalyst is changed by an operating state or the like of an internal combustion engine, and also an air-fuel ratio of the emission gas downstream of the catalyst and in the catalyst is changed accordingly. However, the emission gas cleaning system of the
Patent Literature 1 described above does not have a function of changing an output characteristic of the emission gas sensor and hence suffers the effect of delay in a change in a sensor output to a change in the air-fuel ratio of the emission gas downstream of the catalyst and in the catalyst and cannot effectively utilize the catalyst in some cases, so that the emission gas cleaning system cannot effectively reduce an exhaust emission. - In the Patent Literature 2 described above is disclosed a technique for changing the output characteristic of the gas sensor. In this technique, however, the gas sensor needs to have the auxiliary electrochemical cell built therein and hence needs to have a sensor structure greatly changed as compared with an ordinary gas sensor not having the auxiliary electrochemical cell built therein. Hence, when the technique described in the Patent Literature 2 is put into practical use, the design of the gas sensor needs to be changed. As a result, the manufacturing cost of the gas sensor is increased.
- In the technique of Patent Literature 3, an output E of the oxygen sensor can be expressed by the following fundamental equation (Nernst Equation).
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E=(R×T)/(4×F)×ln(P1/P2) - Here, “R” is a gas constant; “T” is an absolute temperature; “F” is Farady constant; “P1” is an oxygen partial pressure on an atmosphere (reference electrode); and “P2” is an oxygen partial pressure on an exhaust (measurement electrode).
- Hence, in order to decrease variations in the output “E” of the oxygen sensor to thereby stabilize the output “E”, it is important to stabilize an oxygen concentration on the reference electrode to thereby stabilize the oxygen partial pressure “P1” on the reference electrode.
- However, the oxygen sensor of Patent Literature 3 described above has the following construction: the reference electrode is not exposed to the atmosphere, so that oxygen is supplied to the reference electrode from the measurement electrode. Hence, there is a possibility that the oxygen sensor suffers the effect of an oxygen concentration on the measurement electrode and hence cannot keep the oxygen concentration on the reference electrode constant. For embodiment, in the case where the oxygen sensor is arranged downstream of the catalyst, the oxygen concentration of the emission gas sensed by the oxygen sensor is extremely decreased in some case. In this case, the oxygen concentration on the measurement electrode is extremely decreased and hence the oxygen can hardly be supplied to the reference electrode from the measurement electrode, so that the oxygen concentration on the reference electrode might not be kept constant [see a column (B) in
FIG. 11 ]. In this way, an output on a rich of the oxygen sensor might become unstable and hence the sensing accuracy of the oxygen sensor might be decreased. - In the oxygen sensor of the Patent Literature 3 described above, the current is made to flow in such a way as to supply oxygen to the reference electrode from the measurement electrode, whereby an output characteristic curve of the oxygen sensor can be shifted to a lean. However, the reference electrode is not exposed to the atmosphere and hence the oxygen can hardly be supplied to the measurement electrode from the reference electrode, so that an output characteristic curve of the oxygen sensor can hardly be shifted to a rich [see a column (C) in
FIG. 11 ]. - Hence, an object of the present disclosure is to solve the problem described above.
- According to one aspect of the present disclosure, an emission gas cleaning device is applied to an internal combustion engine having a catalyst which cleans an emission gas of an internal combustion engine, and an emission gas sensor which is arranged on a downstream of the catalyst or in the catalyst and senses a concentration of a specified component in the emission gas by a sensor element. The sensor element has a solid electrolyte material provided between a pair of sensor electrodes. One of the sensor electrodes is exposed to the atmosphere. The emission gas cleaning device of the internal combustion engine has a constant current supply portion for making a constant current flow between the sensor electrodes to thereby change an output characteristic of the emission gas sensor. Further, the emission gas cleaning device of the internal combustion engine has a current control portion for determining a direction of the constant current made to flow between the sensor electrodes according to a change request for changing the output characteristic of the emission gas sensor or according to an operating state of the internal combustion engine. The current control portion controls the constant current supply portion in such a way that the constant current flows in the direction determined.
- In this configuration, the output characteristic of the emission gas sensor can be changed by making the constant current flow between the sensor electrodes by the constant current supply portion. In this case, the emission gas sensor does not need to have the auxiliary electrochemical cell or the like built therein, so that the output characteristic of the emission gas sensor can be changed without causing a significant design change and a large increase in cost of the emission gas sensor.
- Further, the direction of the constant current made to flow between the sensor electrodes is determined according to the change request for changing the output characteristic of the emission gas sensor or according to the operating state of the internal combustion engine and the constant current supply portion is controlled in such a way that the constant current flows in the direction determined. Hence, even if a state of the emission gas flowing into the catalyst is changed by the operating state or the like of the internal combustion engine and hence the state of the emission gas downstream of the catalyst or in the catalyst is changed, the output characteristic of the emission gas sensor can be changed accordingly and hence the sensing responsiveness of the emission gas sensor can be improved. In this way, the catalyst can be effectively utilized without being much affected by a delay in a change in the sensor output to a change in the state of the emission gas downstream of the catalyst or in the catalyst and hence the exhaust emission can be effectively reduced.
- Still further, one sensor electrode (atmosphere sensor electrode) is exposed to the atmosphere, so an oxygen concentration on the atmosphere sensor electrode can be kept at a constant value (corresponding to the atmosphere) regardless of the oxygen concentration on the other sensor electrode (exhaust sensor electrode). Hence, even in the case where the emission gas sensor is arranged downstream of the catalyst, in other words, even in the case where the oxygen concentration of the emission gas sensed by the emission gas sensor is extremely decreased in some case, variations in the output of the emission gas sensor can be decreased and hence the output of the emission gas sensor can be stabilized.
- Still further, by making the current flow in such a way that oxygen is supplied to the atmosphere sensor electrode from the exhaust sensor electrode, the output characteristic curve of the emission gas sensor can be shifted to a lean, whereas by making the current flow in such a way that the oxygen is supplied to the exhaust sensor electrode from the atmosphere sensor electrode, the output characteristic curve of the emission gas sensor can be shifted to a rich. Hence, there is presented also an advantage that the output characteristic curve of the emission gas sensor can be shifted to both of the lean and the rich.
- According to a second aspect of the present disclosure, an emission gas cleaning device is applied to a system having a NOx storage-reduction catalyst as the catalyst described above, the NOx storage-reduction catalyst adsorbing NOx in the emission gas when an air-fuel ratio of the emission gas flowing into the catalyst is lean and reducing, cleaning, discharging the NOx adsorbed by the catalyst when the air-fuel ratio of the emission gas flowing into the catalyst becomes rich. In this way, the NOx storage-reduction catalyst can be effectively utilized and hence the exhaust emission can be reduced.
- In a system in which an emission gas sensor is arranged downstream of the NOx storage-reduction catalyst or in the NOx storage-reduction catalyst, during a lean combustion control in which an air-fuel ratio of an air-fuel mixture to be supplied to an internal combustion engine is controlled to a lean value, it is recommended to control a constant current supply portion in such a way that a constant current flows in a direction in which a sensing responsiveness to a lean component of the emission gas sensor is improved, whereas during a rich combustion control in which the air-fuel ratio of the air-fuel mixture to be supplied to the internal combustion engine is controlled to a rich value, it is recommended to control the constant current supply portion in such a way that the constant current flows in a direction in which a sensing responsiveness to a rich component of the emission gas sensor is improved.
- During the lean combustion control, the air-fuel ratio of the emission gas flowing into the NOx storage-reduction catalyst becomes lean and NOx (lean component) in the emission gas is adsorbed by the NOx storage-reduction catalyst, but when the amount of the NOx adsorbed by the NOx storage-reduction catalyst is increased, there is brought about a state in which the NOx in the emission gas is passed through the NOx storage-reduction catalyst and is emitted to the downstream of the NOx storage-reduction catalyst. For this reason, if the lean responsiveness of the emission gas sensor (sensing responsiveness of the emission gas sensor to the lean component) is improved during the lean combustion control, when a state in which the amount of the NOx adsorbed by the NOx storage-reduction catalyst is increased and in which the NOx (lean component) is emitted to the downstream of the NOx storage-reduction catalyst is brought about during the lean combustion control, the state can be quickly sensed by the emission gas sensor. In this way, when the state in which the NOx is emitted to the downstream of the NOx storage-reduction catalyst is brought about after the lean combustion control is started, the lean combustion control can be quickly stopped and hence the amount of emission of the NOx can be reduced.
- During the rich combustion control, the air-fuel ratio of the emission gas flowing into the NOx storage-reduction catalyst becomes rich and the NOx adsorbed by the NOx storage-reduction catalyst is reduced, cleaned, and discharged by HC and CO (rich components) in the emission gas, but when the amount of the NOx adsorbed by the NOx storage-reduction catalyst is decreased, there is brought about a state in which the HC and the CO in the emission gas is passed through the NOx storage-reduction catalyst and is emitted to the downstream of the NOx storage-reduction catalyst. For this reason, if the rich responsiveness of the emission gas sensor (sensing responsiveness of the emission gas sensor to the rich component) is improved during the rich combustion control, when a state in which the amount of the NOx adsorbed by the NOx storage-reduction catalyst is decreased and in which the HC and the CO (rich components) are emitted to the downstream of the NOx storage-reduction catalyst is brought about during the rich combustion control, the state can be quickly sensed by the emission gas sensor. In this way, when a state in which the HC and the CO are emitted to the downstream of the NOx storage-reduction catalyst is brought about after the rich combustion control is started, the rich combustion control can be quickly stopped and hence the amount of emission of the HC and the CO can be reduced.
- The present disclosure may be applied to a system having a three-way catalyst for cleaning CO, HC, and NOx in an emission gas as the catalyst described above. In this way, the three-way catalyst can be effectively utilized and the exhaust emission can be reduced.
- The above-mentioned object, other objects, features, and advantages of the present disclosure will be made clearer by the following detailed description with reference to the accompanying drawings.
-
FIG. 1 is a diagram to show a general configuration of an engine control system in anembodiment 1 of the present disclosure. -
FIG. 2 is a section view to show a sectional construction of a sensor element. -
FIG. 3 is an electromotive characteristic graph to show a relationship between an air-fuel ratio (excess air ratio λ) of an emission gas and an electromotive force of a sensor element. -
FIG. 4A is a schematic diagram to show a state of a gas component around a sensor element. -
FIG. 4B is a schematic diagram to show a state of a gas component around a sensor element. -
FIG. 5 is a time chart to illustrate a behavior of a sensor output. -
FIG. 6A is a schematic diagram to show a state of a gas component around a sensor element. -
FIG. 6B is a schematic diagram to show a state of a gas component around a sensor element. -
FIG. 7 is an output characteristic graph of an oxygen sensor in the case where a lean responsiveness and a rich responsiveness are improved. -
FIG. 8 is a time chart to show an embodiment of performing a catalyst utilizing control. -
FIG. 9 is a flow chart to show a processing flow of a catalyst utilizing control routine. -
FIG. 10 is a drawing to illustrate an effect of theembodiment 1. -
FIG. 11 is a drawing to illustrate a conventional technique. -
FIG. 12 is a diagram to show a general configuration of an engine control system of an embodiment 2 of the present invention. -
FIG. 13 is a flow chart to show a processing flow of a sensor responsiveness control routine. - Hereinafter, embodiments in which a mode for carrying out the present disclosure is embodied will be described.
- An
embodiment 1 of the present disclosure will be described on the basis ofFIG. 1 toFIG. 10 . - First, a general configuration of an entire engine control system will be described on the basis of
FIG. 1 . - An
intake pipe 12 of anengine 11 is provided with athrottle valve 13, the opening of which is controlled by a motor or the like, and athrottle opening sensor 14, which senses an opening of the throttle valve 13 (throttle position). Further, each of cylinders of theengine 11 is provided with afuel injection valve 15 for performing a direct injection or an intake port injection, whereas a cylinder head of theengine 11 has anignition plug 16 fixed on each of the cylinders. An air-fuel mixture in each of the cylinders is ignited by a spark discharge of eachignition plug 16. - On the other hand, an
exhaust pipe 17 of theengine 11 has a three-way catalyst 18, which cleans CO, HC, and NOx in an emission gas, provided therein and has a NOx storage-reduction catalyst 19 provided downstream of the three-way catalyst 18. The NOx storage-reduction catalyst 19 has the following characteristic: that is, when an air-fuel ratio of the emission gas flowing into the NOx storage-reduction catalyst 19 is lean, the NOx storage-reduction catalyst 19 adsorbs NOx in the emission gas, whereas when the air-fuel ratio of the emission gas flowing into the NOx storage-reduction catalyst 19 becomes rich, the NOx storage-reduction catalyst 19 reduces, cleans, and discharges NOx adsorbed by the NOx storage-reduction catalyst 19. - Further, the
exhaust pipe 17 hasemission gas sensors catalyst 18. As each of theemission gas sensors exhaust pipe 17 has an oxygen sensor (O2 sensor) 28, arranged as an emission gas sensor downstream of the NOx storage-reduction catalyst 19. The output voltage of the oxygen sensor is reversed depending on whether the air-fuel ratio of the emission gas is rich or lean with respect to the stoichiometric air-fuel ratio. - Still further, the present system has various sensors such as a
crank angle sensor 22 for outputting a pulse signal every time a crankshaft (not shown in the drawing) of theengine 11 is rotated by a specified crank angle, an air-flow sensor 23 for sensing an intake air volume of theengine 11, and acoolant temperature sensor 24 for sensing a coolant temperature of theengine 11. A crank angle and an engine rotation speed are sensed on the basis of an output signal of thecrank angle sensor 22. - The outputs of these various sensors are inputted to an electronic control unit (hereinafter denoted by “ECU”) 25. The
ECU 25 is mainly constructed of a microcomputer and executes various programs, which are stored in a built-in ROM (memory medium) and are used for controlling the engine, to thereby control a fuel injection quantity, an ignition timing, a throttle opening (intake air volume), and the like according to an engine operating state. - Next, the construction of the
oxygen sensor 28 will be described on the basis ofFIG. 2 . - The
oxygen sensor 28 has asensor element 31 of a cup type structure. In reality, thesensor element 31 is constructed in such a way that the whole of the element is housed in a housing or an element cover not shown in the drawing and is arranged in theexhaust pipe 17 of theengine 11. - In the
sensor element 31, a solid electrolyte layer 32 (solid electrolyte material) is formed in the shape of a cup when viewed in a cross section and has anexhaust electrode layer 33 fixed on its outer surface and has anatmosphere electrode layer 34 fixed on its inner surface. Thesolid electrolyte layer 32 is formed of an oxygen ion conductive oxide sintered material in which CaO, MgO, Y2O3, or Yb2O3 is dissolved as a stabilizer in ZrO2, HfO2, ThO2, or Bi2O3. Further, each of the electrode layers 33, 34 is formed of a noble metal such as platinum having an enhanced catalytic activity and has porous chemical plating or the like applied to its surface. These electrode layers 33, 34 form a pair of opposite electrodes (sensor electrodes). An inner space surrounded by thesolid electrolyte layer 32 becomes anatmosphere chamber 35 and theatmosphere chamber 35 has aheater 36 housed therein. Theheater 36 has a heating capacity sufficient for activating thesensor element 31 and the whole of thesensor element 31 is heated by the heating energy of theheater 36. An activation temperature of theoxygen sensor 28 is, for example, approximately 350 to 400° C. Here, theatmosphere chamber 35 has the atmosphere introduced thereinto and hence has its interior held at a specified oxygen concentration, whereby theatmosphere electrode layer 34 is exposed to the atmosphere in theatmosphere chamber 35. - In the
sensor element 31, the outside (electrode layer 33) of thesolid electrolyte layer 32 is in an exhaust atmosphere and the inside (electrode layer 34) of thesolid electrolyte layer 32 is in the atmosphere, whereby an electromotive force is generated between the electrode layers 33, 34 according to a difference in the oxygen concentration (a difference in an oxygen partial pressure) between these atmospheres. In other words, in thesensor element 31, a different electromotive force is generated according to whether the air-fuel ratio is rich or lean. In this way, theoxygen sensor 28 outputs an electromotive force signal corresponding to the oxygen concentration (that is, the air-fuel ratio) of the emission gas. - As shown in
FIG. 3 , thesensor element 31 generates a different electromotive force according to whether the air-fuel ratio is rich or lean with respect to a stoichiometric air-fuel ratio (excess air ratio λ=1) and has a characteristic such that the electromotive force is suddenly changed near the stoichiometric air-fuel ratio (excess air ratio λ=1). Specifically, when the air-fuel ratio is rich, the electromotive force generated by thesensor element 31 is approximately 0.9 V, whereas when the air-fuel ratio is lean, the electromotive force generated by thesensor element 31 is approximately 0 V. - As shown in
FIG. 2 , thesensor element 31 has theexhaust electrode layer 33 grounded to the earth and has theatmosphere electrode layer 34 connected to amicrocomputer 26. When thesensor element 31 generates an electromotive force according to the air-fuel ratio (the oxygen concentration) of the emission gas, a sensor sensing signal corresponding to the electromotive force is outputted to themicrocomputer 26. Themicrocomputer 26 is built in, for example, theECU 25 and calculates the air-fuel ratio on the basis of the sensor sensing signal. Here, themicrocomputer 26 may calculate an engine rotation speed or an intake air volume on the basis of the sensed results of the various sensors described above. - By the way, when the
engine 11 is operated, an actual air-fuel ratio of the emission gas is successively varied and, in some cases, is repeatedly varied between a rich value and a lean value. When the actual air-fuel ratio is varied in this way, if the sensing responsiveness of theoxygen sensor 28 is low, it is concerned that the low sensing responsiveness will cause a bad effect on the performance of theengine 11. For embodiment, it is concerned that when theengine 11 is operated at a high load, the amount of NOx in the emission gas will be increased more than expected. - The sensing responsiveness of the
oxygen sensor 28 when the actual air-fuel ratio is varied between the rich value and the lean value will be described. When the actual air-fuel ratio (actual air-fuel ratio downstream of the NOx storage-reduction catalyst 19) is varied between the rich value and the lean value in the emission gas emitted from theengine 11, the component composition of the emission gas is changed. At this time, when the component of the emission gas just before the component composition of the emission gas being changed remains, a change in the output of theoxygen sensor 28 to the air-fuel ratio after the component composition of the emission gas being changed (that is, the responsiveness of the sensor output) becomes slow. Specifically, when the actual air-fuel ratio is changed from the rich value to the lean value, as shown inFIG. 4A , just after the actual air-fuel ratio is changed to the lean value, HC or the like that is a rich component remains near theexhaust electrode layer 33 and hence the reaction of a lean component (NOx or the like) at the sensor electrode is prevented by the rich component. As a result, theoxygen sensor 28 is lowered in the responsiveness of a lean output. On the other hand, when the actual air-fuel ratio is changed from the lean value to the rich value, as shown inFIG. 4B , just after the actual air-fuel ratio is changed to the rich value, NOx or the like which is a lean component remains near theexhaust electrode layer 33 and hence the reaction of a rich component (HC or the like) at the sensor electrode is prevented by the lean component. As a result, theoxygen sensor 28 is lowered in the responsiveness of a rich output. - A change in the output of the
oxygen sensor 21 will be described by the use of a time chart shown inFIG. 5 . InFIG. 5 , when the actual air-fuel ratio is changed between a rich value and a lean value, a sensor output (output of the oxygen sensor 28) is changed between a rich gas sensing value (0.9 V) and a lean gas sensing value (0 V) according to a change in the actual air-fuel ratio. However, in this case, the sensor output is changed with a delay to the change in the actual air-fuel ratio. InFIG. 5 , when the actual air-fuel ratio is changed from the rich value to the lean value, the sensor output is changed with a delay of TD1 to the change in the actual air-fuel ratio, whereas when the actual air-fuel ratio is changed from the lean value to the rich value, the sensor output is changed with a delay of TD2 to the change in the actual air-fuel ratio. - Hence, in the present embodiment, as shown in
FIG. 2 , a constantcurrent circuit 27 as a constant current supply portion is connected to theatmosphere electrode layer 34 and themicrocomputer 26 controls the supply of a constant current “Ics” by the constantcurrent circuit 27 to thereby make the current flow in a specified direction between the pair of sensor electrodes (exhaust electrode layer 33 and the atmosphere electrode layer 34), which in turn changes the output characteristic of theoxygen sensor 28 to thereby change the sensing responsiveness of theoxygen sensor 28. In this case, themicrocomputer 26 sets a direction and a quantity of the constant current “Ics” flowing between the pair of sensor electrodes and controls the constantcurrent circuit 27 in such a way that the constant current “Ics” having the direction and the quantity set flows. - In more detail, the constant
current circuit 27 is a circuit that supplies theatmosphere electrode layer 34 with the constant current “Ics” in either of a forward direction or a reverse direction and that can variably adjust the flow rate of the constant current “Ics”. In other words, themicrocomputer 26 variably controls the constant current “Ics” by a PWM control. In this case, in the constantcurrent circuit 27, the constant current “Ics” is adjusted according to a duty signal outputted from themicrocomputer 26 and the constant current “Ics” having its flow rate controlled is made to flow between the sensor electrodes (between theexhaust electrode layer 33 and the atmosphere electrode layer 34). - In the present embodiment, the constant current “Ics” flowing in the direction from the
exhaust electrode layer 33 to theatmosphere electrode layer 34 is assumed to be a negative constant current (−“Ics”), whereas the constant current “Ics” flowing in the direction from theatmosphere electrode layer 34 to theexhaust electrode layer 33 is assumed to be a positive constant current (+“Ics”). - For embodiment, in the case where the sensing responsiveness (lean sensitivity) when the actual air-fuel ratio is changed from the rich value to the lean value is improved, as shown in
FIG. 6A , the constant current “Ics” (negative constant current “Ics”) is made to flow in such a way that oxygen is supplied from theatmosphere electrode layer 34 to theexhaust electrode layer 33 through thesolid electrolyte layer 32. In this case, the oxygen is supplied to the exhaust from the atmosphere, whereby an oxidation reaction of the rich component (HO) existing (remaining) around theexhaust electrode layer 33 is accelerated and hence the rich component can be quickly removed by the accelerated oxidation reaction. In this way, the lean component (NOx) can be easily reacted in theexhaust electrode layer 33, which results in improving the responsiveness of the lean output of theoxygen sensor 28. - On the other hand, in the case where the sensing responsiveness (rich sensitivity) when the actual air-fuel ratio is changed from the lean value to the rich value is improved, as shown in
FIG. 6B , the constant current “Ics” (positive constant current “Ics”) is made to flow in such a way that oxygen is supplied from theexhaust electrode layer 33 to theatmosphere electrode layer 34 through thesolid electrolyte layer 32. In this case, the oxygen is supplied to the atmosphere from the exhaust, whereby a reduction reaction of the lean component (NOx) existing (remaining) around theexhaust electrode layer 33 is accelerated and hence the lean component can be quickly removed by the accelerated reduction reaction. In this way, the rich component (HC) can be easily reacted in theexhaust electrode layer 33, which results in improving the responsiveness of the rich output of theoxygen sensor 28. -
FIG. 7 is a graph to show an output characteristic (electromotive force characteristic) of theoxygen sensor 28 in the case where the sensing responsiveness (lean sensitivity) when the actual air-fuel ratio is changed from the rich value to the lean value and in the case where the sensing responsiveness (rich sensitivity) when the actual air-fuel ratio is changed from the lean value to the rich value. - In order to improve the sensing responsiveness (lean sensitivity) in a case where the actual air-fuel ratio is changed from the rich value to the lean value as described above, when the negative constant current “Ics” is made to flow in such a way that the oxygen is supplied from the
atmosphere electrode layer 34 to theexhaust electrode layer 33 through the solid electrolyte layer 32 (seeFIG. 6A ), an output characteristic curve is shifted to a rich (in more detail, to the rich and to the in which the electromotive force is decreased) as shown by a single dot and dash line (a) inFIG. 7 . In this case, even if the actual air-fuel ratio is in a rich region near the stoichiometric air-fuel ratio, the sensor output becomes a lean output. The output characteristic of theoxygen sensor 28 is improved in the sensing responsiveness (lean sensitivity) when the actual air-fuel ratio is changed from the rich value to the lean value. - On the other hand, in order to improve the sensing responsiveness (rich sensitivity) in a case where the actual air-fuel ratio is changed from the lean value to the rich value as described above, when the positive constant current “Ics” is made to flow in such a way that the oxygen is supplied from the
exhaust electrode layer 33 to theatmosphere electrode layer 34 through the solid electrolyte layer 32 (seeFIG. 6B ), the output characteristic curve is shifted to a lean (in more detail, the output characteristic curve is shifted to the lean and to the in which the electromotive force is increased) as shown by a single dot and dash line (b) inFIG. 7 . In this case, even if the actual air-fuel ratio is within a lean region near the stoichiometric air-fuel ratio, the sensor output becomes a rich output. That is, the output characteristic of theoxygen sensor 28 is improved in the sensing responsiveness (lean sensitivity) when the actual air-fuel ratio is changed from the lean value to the rich value. - In the
present embodiment 1, the ECU 25 (or the microcomputer 26) performs a catalyst utilizing control routine shown inFIG. 9 , which will be described later, thereby determining the direction of the constant current “Ics” flowing between the sensor electrodes (between theexhaust electrode layer 33 and the atmosphere electrode layer 34) according to the operating state of theengine 11 and controlling the constantcurrent circuit 27 in such a way that the constant current “Ics” flows in the determined direction. In this way, even if a state of the emission gas flowing into the NOx storage-reduction catalyst 19 is changed by the operating state of theengine 11 to thereby cause a change in the state of the emission gas downstream of the NOx storage-reduction catalyst 19, the ECU 25 (or the microcomputer 26) changes the output characteristic of theoxygen sensor 28 according to the change in the state of the emission gas and hence can improve the sensing responsiveness of theoxygen sensor 28. - Specifically, as shown by a time chart in
FIG. 8 , when a specified lean operation performance condition is met while theengine 11 is being operated, a lean combustion control for controlling the air-fuel ratio of an air-fuel mixture to be supplied to theengine 11 to a leaner value than the stoichiometric air-fuel ratio (λ=1) to thereby combust the air-fuel mixture at a lean air-fuel ratio is performed. At a timing t1 when the output of theoxygen sensor 28 becomes not more than a specified lean determination threshold value (for example, 0.45 V) during the lean combustion control, it is determined that NOx (lean component) starts to be emitted to the downstream of the NOx storage-reduction catalyst 28. Then, the lean combustion control is stopped and a rich combustion control for controlling the air-fuel ratio of the air-fuel mixture to be supplied to theengine 11 to a richer value than the stoichiometric air-fuel ratio (λ=1) to thereby combust the air-fuel mixture at a rich air-fuel ratio is performed. At a timing t2 when the output of theoxygen sensor 28 becomes not less than a specified rich determination threshold value (for example, 0.45 V) during the rich combustion control, it is determined that HC and CO (rich components) start to be emitted to the downstream of the NOx storage-reduction catalyst 28. Then, the rich combustion control is stopped and the lean combustion control is performed. In this way, the lean combustion control and the rich combustion control are alternately performed. - At that time, during the lean combustion control, the constant
current circuit 27 is controlled in such a way that the constant current “Ics” flows in the direction in which the lean sensitivity of theoxygen sensor 28 is improved to thereby improve the lean responsiveness (sensing responsiveness to the lean component). In this case, the constantcurrent circuit 27 is controlled in such a way that the constant current “Ics” (negative constant current “Ics”) flows in the direction in which the oxygen is supplied from theatmosphere electrode layer 34 to theexhaust electrode layer 33. On the other hand, during the rich combustion control, the constantcurrent circuit 27 is controlled in such a way that the constant current “Ics” flows in the direction in which the rich sensitivity of theoxygen sensor 28 is improved to thereby improve the rich responsiveness (sensing responsiveness to the rich component). In this case, the constantcurrent circuit 27 is controlled in such a way that the constant current “Ics” (positive constant current “Ics”) flows in the direction in which the oxygen is supplied from theexhaust electrode layer 33 to theatmosphere electrode layer 34. - During the lean combustion control, the air-fuel ratio of the emission gas flowing into the NOx storage-
reduction catalyst 19 becomes lean and NOx (lean component) in the emission gas is adsorbed by the NOx storage-reduction catalyst 19. However, when the amount of NOx adsorbed by the NOx storage-reduction catalyst 19 is increased, NOx in the emission gas passes through the NOx storage-reduction catalyst 19 and is emitted to the downstream of the NOx storage-reduction catalyst 19. For this reason, if the lean responsiveness (sensing responsiveness to the lean component) of theoxygen sensor 28 is improved during the lean combustion control, when the amount of NOx adsorbed by the NOx storage-reduction catalyst 19 is increased during the lean combustion control to thereby bring about a state in which the NOx (lean component) is emitted to the downstream of the NOx storage-reduction catalyst 19, the state can be quickly sensed by theoxygen sensor 28. In this way, when there is brought about the state in which the NOx is emitted to the downstream of the NOx storage-reduction catalyst 19 after the lean combustion control is started, the lean combustion control can be quickly stopped. Hence, the amount of emission of NOx can be reduced as compared with a conventional system not having a function of changing a sensor output characteristic (see broken lines inFIG. 8 ). - On the other hand, during the rich combustion control, the air-fuel ratio of the emission gas flowing into the NOx storage-
reduction catalyst 19 becomes rich and the NOx adsorbed by the NOx storage-reduction catalyst 19 is reduced, cleaned, and discharged by HC and CO (rich components) in the emission gas. However, when the amount of NOx adsorbed by the NOx storage-reduction catalyst 19 is decreased, the HC and the CO in the emission gas pass through the NOx storage-reduction catalyst 19 and are emitted to the downstream of the NOx storage-reduction catalyst 19. For this reason, if the rich responsiveness (sensing responsiveness to the rich component) of theoxygen sensor 28 is improved during the rich combustion control, when the amount of NOx adsorbed by the NOx storage-reduction catalyst 19 is decreased during the rich combustion control to thereby bring about a state in which the HC and the CO (rich components) are emitted to the downstream of the NOx storage-reduction catalyst 19, the state can be quickly sensed by theoxygen sensor 28. In this way, when there is brought about the state in which the HC and the CO are emitted to the downstream of the NOx storage-reduction catalyst 19 after the rich combustion control is started, the rich combustion control can be quickly stopped. Hence, the amount of emission of the HC and the CO can be reduced as compared with the conventional system not having the function of changing the sensor output characteristic (see broken lines inFIG. 8 ). - Hereinafter, processing contents of the catalyst utilizing control routine shown in
FIG. 9 performed by the ECU 25 (or the microcomputer 26) in the present embodiment will be described. - The catalyst utilizing control routine shown in
FIG. 9 is repeatedly performed at a specified period during a period in which the power of theECU 25 is on, thereby playing a role as a current control portion. First, instep 101, it is determined whether or not a lean operation performance condition is met. The lean operation performance condition is to satisfy, for example, all of the following conditions (1) to (3). - (1) A coolant temperature of the
engine 11 is not less than a specified temperature. - (2) The NOx storage-
reduction catalyst 19 is in an active state (for example, an estimated temperature or a sensed temperature of thecatalyst 19 is not less than an active temperature, or time which passes after the engine is started is not less than a specified time.) - (3) Each portion of the system (for example, fuel system and exhaust system) is not abnormal.
- If all of these conditions (1) to (3) are satisfied, the lean operation performance condition is met. However, if any one of the conditions (1) to (3) is not satisfied, the lean operation performance condition is not met.
- In the case where it is determined in this
step 101 that the lean operation performance condition is met, pieces of processing insteps 102 to 108 are repeatedly performed. First, the routine proceeds to step 102 in which the lean combustion control for controlling the air-fuel ratio of the air-fuel mixture to be supplied to theengine 11 to a leaner value than the stoichiometric air-fuel ratio (λ=1) to thereby combust the air-fuel mixture at the lean air-fuel ratio is performed. - Then, the routine proceeds to step 103 in which the constant
current circuit 27 is controlled during the lean combustion control in such a way that the constant current “Ics” flows in the direction in which the lean responsiveness of theoxygen sensor 28 is improved. In other words, the constantcurrent circuit 27 is controlled in such a way that the constant current “Ics” (negative constant current “Ics”) flows in a direction in which the oxygen is supplied from theatmosphere electrode layer 34 to theexhaust electrode layer 33. In this way, the lean responsiveness of theoxygen sensor 28 is improved. - Then, the routine proceeds to step 104 in which it is determined whether or not the output of the
oxygen sensor 28 is not more than the lean determination threshold value (for example, 0.45 V). In the case where it is determined that the output of theoxygen sensor 28 is more than the lean determination threshold value, the routine returns to step 102. Then, the lean combustion control is continuously performed and a control for increasing the lean responsiveness of theoxygen sensor 28 is continuously performed (steps 102, 103). - Then, at a timing when it is determined in the
step 104 that the output of theoxygen sensor 28 is not more than the lean determination threshold value, it is determined that the NOx (lean component) starts to be emitted to the downstream of the NOx storage-reduction catalyst 19. Then, the routine proceeds to step 105 in which the lean combustion control is stopped and the rich combustion control for controlling the air-fuel ratio of the air-fuel mixture to be supplied to theengine 11 to a richer value than the stoichiometric air-fuel ratio (λ=1) to thereby combust the air-fuel mixture at the rich air-fuel ratio is performed. - Then, the routine proceeds to step 106 in which the constant
current circuit 27 is controlled during the rich combustion control in such a way that the constant current “Ics” flows in the direction in which the rich responsiveness of theoxygen sensor 28 is improved. In other words, the constantcurrent circuit 27 is controlled in such a way that the constant current “Ics” (positive constant current “Ics”) flows in the direction in which the oxygen is supplied to theatmosphere electrode layer 34 from theexhaust electrode layer 33. In this way, the rich responsiveness of theoxygen sensor 28 is improved. - Then, the routine proceeds to step 107. Then, if it is determined by whether or not the output of the
oxygen sensor 28 is not less than the rich determination value (for example, 0.45 V) that the output of theoxygen sensor 28 is less than the rich determination threshold value, the routine returns to thestep 105 in which the rich combustion control is continuously performed and a control for increasing the rich responsiveness of theoxygen sensor 28 is continuously performed (steps 105, 106). - Then, at a timing when it is determined in
step 107 that the output of theoxygen sensor 28 is not less than the rich determination threshold value, it is determined that HC and CO (rich components) start to be emitted to the downstream of the NOx storage-reduction catalyst 19 and then the routine proceeds to step 108 in which the rich combustion control is stopped. - On the other hand, in the case where it is determined in the
step 101 that the lean operation performance condition is not met, the routine proceeds to step 109 in which a stoichiometric air-fuel ratio combustion control for controlling the air-fuel ratio of the air-fuel mixture to be supplied to theengine 11 to a stoichiometric air-fuel ratio to thereby combust the air-fuel mixture at the stoichiometric air-fuel ratio is performed. Then, the routine proceeds to step 110 in which a control for not changing the sensing responsiveness of theoxygen sensor 28 with respect to a reference responsiveness, that is, a control for controlling the constant current “Ics” to “0” is performed. - In the
present embodiment 1 described above, in the system having theoxygen sensor 28 arranged downstream of the NOx storage-reduction catalyst 19, the constant current is made to flow between the sensor electrodes by the constantcurrent circuit 27 provided in the outside of theoxygen sensor 28, whereby the output characteristic of theoxygen sensor 28 can be changed and hence the lean responsiveness and the rich responsiveness of theoxygen sensor 28 can be improved. In addition, theoxygen sensor 28 does not need to have the auxiliary electrochemical cell or the like built therein, so that the output characteristic of theoxygen sensor 28 can be changed without causing a significant design change and an increase in cost of theoxygen sensor 28. - Further, during the lean combustion control, the constant
current circuit 27 is controlled in such a way that the constant current “Ics” flows in the direction in which the lean responsiveness of theoxygen sensor 28 is improved. Hence, when there is brought about a state in which the NOx (lean component) is emitted to the downstream of the NOx storage-reduction catalyst 19, the state can be quickly sensed by theoxygen sensor 28 and the lean combustion control can be quickly stopped, whereby the amount of emission of the NOx can be reduced. On the other hand, during the rich combustion control, the constantcurrent circuit 27 is controlled in such a way that the constant current “Ics” flows in the direction in which the rich responsiveness of theoxygen sensor 28 is improved. Hence, when there is brought about a state in which the HC and the CO (rich components) are emitted to the downstream of the NOx storage-reduction catalyst 19, the state can be quickly sensed by theoxygen sensor 28 and the rich combustion control can be quickly stopped, whereby the amount of emission of the HC and the CO can be reduced. In this way, the NOx storage-reduction catalyst 19 can be effectively utilized without being much affected by the delay of a change in the output of theoxygen sensor 28 to a change of the state of the emission gas downstream of the NOx storage-reduction catalyst 19 and hence the exhaust emission can be effectively reduced. - By the way, the output E of the
oxygen sensor 28 can be expressed by the following fundamental equation (Nernst Equation). -
E=(R×T)/(4×F)×ln(P1/P2) - Here, “R” is a gas constant; “T” is an absolute temperature; “F” is Farady constant; “P1” is an oxygen partial pressure on the
atmosphere electrode layer 34; and “P2” is an oxygen partial pressure on anexhaust electrode layer 33. - Hence, in order to decrease variations in the output E of the
oxygen sensor 28 to thereby stabilize the output E, it is important to stabilize an oxygen concentration on theatmosphere electrode layer 34 to thereby stabilize the oxygen partial pressure P1 on theatmosphere electrode layer 34. - In this regard, the
oxygen sensor 28 of thepresent embodiment 1, as shown inFIG. 10 , has theatmosphere electrode layer 34 exposed to the atmosphere, so that theoxygen sensor 28 can always keep the oxygen concentration on theatmosphere electrode layer 34 at a constant value (corresponding to the atmosphere) regardless of the oxygen concentration on theexhaust electrode layer 33. Hence, even in the case where theoxygen sensor 28 is arranged downstream of thecatalyst 19, in other words, even in the case where the oxygen concentration of the emission gas sensed by theoxygen sensor 28 is significantly decreased, the output of theoxygen sensor 28 can be stabilized. - Further, the output characteristic curve of the
oxygen sensor 28 can be shifted to the lean by making the current flow in such a way that the oxygen is supplied to theatmosphere electrode layer 34 from theexhaust electrode layer 33, whereas the output characteristic curve of theoxygen sensor 28 can be shifted to the rich by making the current flow in such a way that the oxygen is supplied to theexhaust electrode layer 33 from theatmosphere electrode layer 34. In other words, there is presented also an advantage that the output characteristic curve of theoxygen sensor 28 can be shifted to either of the lean and the rich. - In this regard, the
embodiment 1 employs the configuration in which theoxygen sensor 28 is arranged downstream of the NOx storage-reduction catalyst 19. However, it is also recommended to employ a configuration in which that theoxygen sensor 28 is arranged at a position in the NOx storage-reduction catalyst 19 (for example, at a middle position between an inlet and an outlet of the catalyst 19). - Next, an embodiment 2 of the present disclosure will be described by the use of
FIG. 12 andFIG. 13 . However, descriptions of the parts substantially identical to those in theembodiment 1 will be omitted or simplified and parts different from those in theembodiment 1 will be mainly described. - In the present embodiment 2, a three-
way catalyst 37 for cleaning CO, HC, and NOx in the emission gas is arranged also downstream of the three-way catalyst 18. Further, an emission gas sensor 20 (air-fuel ratio sensor or oxygen sensor) for sensing an air-fuel ratio of an emission gas or sensing whether an air-fuel ratio of an emission gas is rich or lean is arranged upstream of the three-way catalyst 18, and anoxygen sensor 28, the output voltage of which is reversed depending on whether the air-fuel ratio of the emission gas is rich or lean with respect to a stoichiometric air-fuel ratio, is arranged downstream of the three-way catalyst 18 (between the three-way catalyst 18 and the three-way catalyst 37). - Further, in the present embodiment 2, an ECU 25 (or microcomputer 26) performs a sensor responsiveness control routine shown in
FIG. 13 , which will be described later. - The sensor responsiveness control routine shown in
FIG. 13 is repeatedly performed at a specified period during a period in which the power of theECU 25 is on. In the sensor responsiveness control routine, it is determined insteps 201 to 203 whether or not a change request for changing a responsiveness of theoxygen sensor 28 is made, and insteps 204 to 207, a constant current control is performed on the basis of a determination result of the change request to thereby change the responsiveness of theoxygen sensor 28. - In
step 201, it is determined whether anengine 11 is in a cold state according to whether or not any one of the following conditions (1) to (3) is satisfied. - (1) A coolant temperature of the
engine 11 is not more than a specified temperature. - (2) An oil temperature (temperature of lubricating oil) of the
engine 11 is not more than a specified temperature. - (3) A fuel temperature in a fuel passage is not more than a specified temperature.
- In the case where it is determined in this
step 201 that theengine 11 is in the clod state, it is determined that a change request for increasing a rich responsiveness (sensing responsiveness when the air-fuel ratio of the emission gas is changed to a rich value) is made. In this case, the routine proceeds to step 204 in which the supply of a constant current “Ics” is controlled on the basis of the change request for increasing the rich responsiveness. Specifically, “a positive constant current Ics” is set as a constant current of a constantcurrent circuit 27. At this time, the constantcurrent circuit 27 is controlled by themicrocomputer 26 and the constant current “Ics” (positive constant current “Ics”) flows in the direction in which oxygen is supplied to theatmosphere electrode layer 34 from theexhaust electrode layer 33. In this way, in the case where theengine 11 is in the cold state, the rich responsiveness of theoxygen sensor 28 is improved. Here, it is recommended that the amount of the constant current be a specified value determined previously. - On the other hand, in the case where it is determined in
step 201 that theengine 11 is not in the cold state, the routine proceeds to step 202 in which it is determined whether or not theengine 11 is in a high load operating state according to whether or not any one of the following conditions (4) to (6) is satisfied. - (4) An air volume introduced into a cylinder is not less than a specified volume.
- (5) A combustion pressure in a cylinder is not less than a specified value.
- (6) An accelerator opening is not less than a specified value.
- In the case where it is determined in this
step 202 that theengine 11 is in the high load operating state, it is determined that a change request for increasing the lean responsiveness (sensing responsiveness when the air-fuel ratio of the emission gas is changed to a lean value) is made. In this case, the routine proceeds to step 205 in which the supply of the constant current “Ics” is controlled on the basis of the change request for increasing the lean responsiveness. Specifically, “a negative constant current “Ics” is set as the constant current of the constantcurrent circuit 27. At this time, the constantcurrent circuit 27 is controlled by themicrocomputer 26, whereby the constant current “Ics” (negative constant current “Ics”) flows in the direction in which the oxygen is supplied to theexhaust electrode layer 33 fromatmosphere electrode layer 34. In this way, in the case where theengine 11 is in the high load operating state, the lean responsiveness of theoxygen sensor 28 is improved. Here, it is recommended that the amount of the constant current be a specified value determined previously. - When a high load operating period in which the
engine 11 is operated in the high load operating state is considered, the high load operating period includes a transient period in which an engine load is changed on an increase and a high-load steady period in which theengine 11 is increased in load increased and is brought into a high load state. In this case, the lean responsiveness is improved in both of the transient period and the high-load steady period, and at the time of increasing the sensing responsiveness, it is recommended to make a responsiveness level required as the sensing responsiveness different between in the transient period and in the high-load steady period. - Specifically, the responsiveness level in the transient period is made higher than the responsiveness level in the high-load steady period. In other words, in the case where it is determined that the
engine 11 is in the high-load operating state, that is, in the high-load operating period, it is further determined whether the high-load operating period is the transient period or the high-load steady period. A determination that the high-load operating period is the transient period corresponds to a determination that a change request for increasing the lean responsiveness and for comparatively decreasing the responsiveness level (decreasing the responsiveness level as compared with the responsiveness level when the high-load operating period is the high-load steady period) is made. On the other hand, a determination that the high-load operating period is the high-load steady period corresponds to a determination that a change request for increasing the lean responsiveness and for comparatively increasing the responsiveness level (increasing the responsiveness level as compared with the responsiveness when the high-load operating period is the transient period) is made. In each of the case where the high-load operating period is the transient period and the case where high-load operating period is the high-load steady period, the supply of the constant current “Ics” is controlled on the basis of the change request. - On the other hand, in the case where it is determined in the
step 202 that theengine 11 is not in the high-load operating state, the routine proceeds to step 203 in which it is determined whether or not the present timing is just after theengine 11 is returned to a fuel injecting operation from a fuel cutting operation and whether or not a rich injection control for neutralizing bothcatalysts catalysts oxygen sensor 28 when theengine 11 is returned from the fuel cutting operation. In the rich injection control, the atmospheres of bothcatalysts oxygen sensor 28 is shifted from a lean value to a rich value after theengine 11 is returned from the fuel cutting operation, the rich injection control is finished. In the present embodiment, in the case where the rich injection control is performed, the sensing responsiveness when the air-fuel ratio of the emission gas is changed to the rich value is decreased. - In the case where it is determined in this
step 203 that the rich injection control is performed, it is determined that a change request for decreasing the rich responsiveness (sensing responsiveness when the air-fuel ratio of the emission gas is changed to the rich value) is made. In this case, the routine proceeds to step 206 in which the supply of the constant current “Ics” is controlled on the basis of the change request for deteriorating the rich responsiveness. Specifically, “a negative constant current Ics” is set as the constant current of the constantcurrent circuit 27. At this time, the constantcurrent circuit 27 is controlled by themicrocomputer 26, whereby the constant current “Ics” (negative constant current “Ics”) flows in the direction in which the oxygen is supplied from theatmosphere electrode layer 34 to theexhaust electrode layer 33. In this way, in the case where the rich injection control is performed, the rich responsiveness is deteriorated. In this regard, it is recommended that the amount of the constant current be a specified value determined previously. - Further, in the case where a determination result in all of the
steps 201 to 203 is “NO”, the routine proceeds to step 207 in which a control not changing the sensing responsiveness of theoxygen sensor 28 with respect to the reference responsiveness, that is, a control for controlling the constant current “Ics” to “0” is performed. - In the routine shown in
FIG. 13 , all pieces of the processing (steps 201, 204) of increasing the rich responsiveness of theoxygen sensor 28 in the case where theengine 11 is in the cold state, the pieces of processing (steps 202, 205) of increasing the lean responsiveness of theoxygen sensor 28 in the case where theengine 11 is in the high-load operating state, and the pieces of processing (steps 203, 206) of deteriorating the rich responsiveness of theoxygen sensor 28 in the case where the rich injection control is performed are performed. However, the routine is not limited to this but any one or two of these pieces of processing may be performed. - In the present embodiment 2 described above, in the system having the
oxygen sensor 28 arranged downstream of the three-way catalyst 18, it is determined whether or not the change request for changing the sensing responsiveness of theoxygen sensor 28 is made and the constant current control is performed on the basis of a determination result of the change request to thereby change the sensing responsiveness of theoxygen sensor 28. Hence, the exhaust emission can be reduced by effectively utilizing the three-way catalyst 18. - In the embodiment 2 described above, the
oxygen sensor 28 is arranged downstream of the three-way catalyst 18. However, theoxygen sensor 28 is arranged at a middle position in the three-way catalyst 18 (for example, at a middle position between an inlet and an outlet of the catalyst 18). - Further, in the
respective embodiments 1, 2 described above, the constantcurrent circuit 27 is connected to theatmosphere electrode layer 34 of the oxygen sensor 28 (sensor element 31), but the configuration is not limited to this. For embodiment, the constantcurrent circuit 27 is connected to theexhaust electrode layer 33 of the oxygen sensor 28 (sensor element 31) or the constantcurrent circuit 27 is connected to both of theexhaust electrode layer 33 and theatmosphere electrode layer 34 of the oxygen sensor 28 (sensor element 31). - Still further, in the
respective embodiments 1, 2 described above, the present disclosure is applied to the system using theoxygen sensor 28 having thesensor element 31 of the cup type structure but a system to which the present disclosure is applied is not limited to this. For embodiment, the present disclosure may be applied to a system using an oxygen sensor having a sensor element of a laminated structure. - Still further, the present disclosure may be applied not only to the oxygen sensor but also to a gas sensor other than the oxygen sensor, for example, an air-fuel sensor for outputting a linear air-fuel ratio signal according to an air-fuel ratio, an HC sensor for sensing an HC concentration, and a NOx sensor for sensing a NOx concentration.
Claims (4)
1. An emission gas cleaning device of an internal combustion engine having a catalyst which cleans an emission gas of an internal combustion engine, and an emission gas sensor which is arranged on a downstream of the catalyst or in the catalyst and senses a concentration of a specified component in the emission gas by a sensor element having a solid electrolyte material provided between a pair of sensor electrodes one of which is exposed to the atmosphere, the emission gas cleaning device of an internal combustion engine comprising:
a constant current supply portion making a constant current flow between the sensor electrodes to change an output characteristic of the emission gas sensor; and
a current control portion determining a direction of the constant current flowing between the sensor electrodes according to a change request for changing the output characteristic of the emission gas sensor or according to an operating state of the internal combustion engine, the current control portion controlling the constant current supply portion in such a way that the constant current flows in the direction.
2. The emission gas cleaning device of an internal combustion engine as claimed in claim 1 , wherein
the catalyst is a NOx storage-reduction catalyst for adsorbing NOx in the emission gas when an air-fuel ratio of the emission gas flowing into the catalyst is lean and for reducing, cleaning, and discharging the NOx adsorbed by the catalyst when the air-fuel ratio of the emission gas flowing into the catalyst becomes rich.
3. The emission gas cleaning device of an internal combustion engine as claimed in claim 2 , wherein
during a lean combustion control in which an air-fuel ratio of an air-fuel mixture to be supplied to the internal combustion engine is controlled to a lean value, the current control portion controls the constant current supply portion in such a way that the constant current flows in a direction in which a sensing responsiveness to a lean component of the emission gas sensor is improved, and
during a rich combustion control in which the air-fuel ratio of the air-fuel mixture to be supplied to the internal combustion engine is controlled to a rich value, the current control portion controls the constant current supply portion in such a way that the constant current flows in a direction in which a sensing responsiveness to a rich component of the emission gas sensor is improved.
4. The emission gas cleaning device of an internal combustion engine as claimed in claim 1 , wherein
the catalyst is a three-way catalyst for cleaning CO, HC, and NOx in the emission gas.
Applications Claiming Priority (5)
Application Number | Priority Date | Filing Date | Title |
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JP2012-022261 | 2012-02-03 | ||
JP2012022261 | 2012-02-03 | ||
JP2012221944A JP5867357B2 (en) | 2012-02-03 | 2012-10-04 | Exhaust gas purification device for internal combustion engine |
JP2012-221944 | 2012-10-04 | ||
PCT/JP2013/000284 WO2013114814A1 (en) | 2012-02-03 | 2013-01-22 | Exhaust gas purification device for internal combustion engine |
Publications (1)
Publication Number | Publication Date |
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US20140373512A1 true US20140373512A1 (en) | 2014-12-25 |
Family
ID=48904866
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Application Number | Title | Priority Date | Filing Date |
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US14/376,179 Abandoned US20140373512A1 (en) | 2012-02-03 | 2013-01-22 | Emission gas cleaning device of internal combustion engine |
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US (1) | US20140373512A1 (en) |
JP (1) | JP5867357B2 (en) |
DE (1) | DE112013000824T5 (en) |
WO (1) | WO2013114814A1 (en) |
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2015068698A (en) * | 2013-09-27 | 2015-04-13 | 株式会社デンソー | Gas sensor control device |
US9845719B2 (en) | 2013-08-09 | 2017-12-19 | Denso Corporation | Gas sensor control device |
US20180216512A1 (en) * | 2015-08-05 | 2018-08-02 | Cummins Emission Solutions Inc. | Oxygen correction for engine-out nox estimates using a nox sensor of an aftertreatment system |
US10302588B2 (en) | 2013-08-09 | 2019-05-28 | Denso Corporation | Gas sensor control method |
Families Citing this family (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP5748180B2 (en) * | 2012-02-10 | 2015-07-15 | 株式会社デンソー | Catalyst deterioration diagnosis device |
JP5904173B2 (en) | 2013-08-09 | 2016-04-13 | 株式会社デンソー | Gas sensor control device |
JP5904171B2 (en) | 2013-08-09 | 2016-04-13 | 株式会社デンソー | Gas sensor control device |
JP5904172B2 (en) | 2013-08-09 | 2016-04-13 | 株式会社デンソー | Gas sensor control device |
JP6398866B2 (en) * | 2015-05-19 | 2018-10-03 | 株式会社デンソー | Oxygen sensor control method |
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JPS6034065B2 (en) * | 1979-12-20 | 1985-08-06 | 日産自動車株式会社 | Air fuel ratio detection method |
FR2494445A1 (en) * | 1980-11-17 | 1982-05-21 | Socapex | ELECTROCHEMICAL SENSOR OF SPECIES CONCENTRATIONS IN A FLUID MIXTURE AND SYSTEM FOR REGULATING THE WEALTH OF AN AIR-FUEL MIXTURE USING SUCH A SENSOR |
JPS57200641A (en) * | 1981-06-01 | 1982-12-08 | Nippon Denso Co Ltd | Controlling device for air-fuel ratio |
JPS61104137A (en) * | 1984-10-27 | 1986-05-22 | Mazda Motor Corp | Control device for air-fuel ratio of engine |
JPS61118653A (en) * | 1984-11-14 | 1986-06-05 | Ngk Insulators Ltd | Method for controlling current of electrochemical element |
JP3997599B2 (en) * | 1998-04-27 | 2007-10-24 | 株式会社デンソー | Air-fuel ratio control device for internal combustion engine |
JP4379595B2 (en) * | 2004-06-08 | 2009-12-09 | トヨタ自動車株式会社 | Air-fuel ratio control device for internal combustion engine |
JP5126388B2 (en) * | 2010-08-19 | 2013-01-23 | 株式会社デンソー | Gas sensor control device |
-
2012
- 2012-10-04 JP JP2012221944A patent/JP5867357B2/en not_active Expired - Fee Related
-
2013
- 2013-01-22 DE DE112013000824.6T patent/DE112013000824T5/en not_active Withdrawn
- 2013-01-22 WO PCT/JP2013/000284 patent/WO2013114814A1/en active Application Filing
- 2013-01-22 US US14/376,179 patent/US20140373512A1/en not_active Abandoned
Cited By (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US9845719B2 (en) | 2013-08-09 | 2017-12-19 | Denso Corporation | Gas sensor control device |
US10302588B2 (en) | 2013-08-09 | 2019-05-28 | Denso Corporation | Gas sensor control method |
EP2837786B1 (en) * | 2013-08-09 | 2020-06-17 | Denso Corporation | Gas sensor control apparatus and gas sensor control method |
JP2015068698A (en) * | 2013-09-27 | 2015-04-13 | 株式会社デンソー | Gas sensor control device |
US10234418B2 (en) | 2013-09-27 | 2019-03-19 | Denso Corporation | Gas sensor control device |
US20180216512A1 (en) * | 2015-08-05 | 2018-08-02 | Cummins Emission Solutions Inc. | Oxygen correction for engine-out nox estimates using a nox sensor of an aftertreatment system |
US10539058B2 (en) * | 2015-08-05 | 2020-01-21 | Cummins Emission Solutions Inc. | Oxygen correction for engine-out NOx estimates using a NOx sensor of an aftertreatment system |
Also Published As
Publication number | Publication date |
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JP5867357B2 (en) | 2016-02-24 |
WO2013114814A1 (en) | 2013-08-08 |
DE112013000824T5 (en) | 2014-10-16 |
JP2013177884A (en) | 2013-09-09 |
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