WO2014118893A1 - 内燃機関の制御装置 - Google Patents
内燃機関の制御装置 Download PDFInfo
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- WO2014118893A1 WO2014118893A1 PCT/JP2013/051912 JP2013051912W WO2014118893A1 WO 2014118893 A1 WO2014118893 A1 WO 2014118893A1 JP 2013051912 W JP2013051912 W JP 2013051912W WO 2014118893 A1 WO2014118893 A1 WO 2014118893A1
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- fuel ratio
- air
- exhaust
- output current
- reference cell
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D45/00—Electrical control not provided for in groups F02D41/00 - F02D43/00
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D41/00—Electrical control of supply of combustible mixture or its constituents
- F02D41/02—Circuit arrangements for generating control signals
- F02D41/14—Introducing closed-loop corrections
- F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
- F02D41/1444—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases
- F02D41/1454—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being an oxygen content or concentration or the air-fuel ratio
- F02D41/1455—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being an oxygen content or concentration or the air-fuel ratio with sensor resistivity varying with oxygen concentration
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/403—Cells and electrode assemblies
- G01N27/406—Cells and probes with solid electrolytes
- G01N27/407—Cells and probes with solid electrolytes for investigating or analysing gases
- G01N27/41—Oxygen pumping cells
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D41/00—Electrical control of supply of combustible mixture or its constituents
- F02D41/02—Circuit arrangements for generating control signals
- F02D41/021—Introducing corrections for particular conditions exterior to the engine
- F02D41/0235—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D41/00—Electrical control of supply of combustible mixture or its constituents
- F02D41/02—Circuit arrangements for generating control signals
- F02D41/14—Introducing closed-loop corrections
- F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
- F02D41/1473—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the regulation method
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D41/00—Electrical control of supply of combustible mixture or its constituents
- F02D41/02—Circuit arrangements for generating control signals
- F02D41/14—Introducing closed-loop corrections
- F02D41/1401—Introducing closed-loop corrections characterised by the control or regulation method
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D41/00—Electrical control of supply of combustible mixture or its constituents
- F02D41/02—Circuit arrangements for generating control signals
- F02D41/14—Introducing closed-loop corrections
- F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
- F02D41/1439—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the position of the sensor
- F02D41/1441—Plural sensors
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D41/00—Electrical control of supply of combustible mixture or its constituents
- F02D41/02—Circuit arrangements for generating control signals
- F02D41/14—Introducing closed-loop corrections
- F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
- F02D41/1444—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases
- F02D41/1454—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being an oxygen content or concentration or the air-fuel ratio
- F02D41/1456—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being an oxygen content or concentration or the air-fuel ratio with sensor output signal being linear or quasi-linear with the concentration of oxygen
Definitions
- the present invention relates to a control device for an internal combustion engine that controls the internal combustion engine in accordance with the output of an air-fuel ratio sensor.
- Such air-fuel ratio sensors are roughly classified into a one-cell type air-fuel ratio sensor (for example, Patent Documents 2 and 4) and a two-cell type air-fuel ratio sensor (for example, Patent Documents 1, 3, and 5).
- a one-cell type air-fuel ratio sensor only one cell including a solid electrolyte layer capable of passing oxygen ions and two electrodes provided on both side surfaces thereof is provided. One of the electrodes is exposed to the atmosphere, and the other electrode is exposed to the exhaust gas through the diffusion rate controlling layer.
- a voltage is applied between two electrodes arranged on both side surfaces of the solid electrolyte layer, and accordingly, between both side surfaces of the solid electrolyte layer.
- exhaust air-fuel ratio the air-fuel ratio of exhaust gas (hereinafter also referred to as “exhaust air-fuel ratio”) is detected (for example, Patent Document 2).
- the two-cell type air-fuel ratio sensor two cells each having a solid electrolyte layer capable of passing oxygen ions and two electrodes provided on both side surfaces thereof are provided.
- One of these cells (reference cell) is configured such that the detection voltage (electromotive force) changes according to the oxygen concentration in the exhaust gas in the measured gas chamber.
- the other cell pumps oxygen in and out of the exhaust gas in the measured gas chamber according to the pump current.
- the pump current of the pump cell is set so that oxygen is pumped in and pumped out so that the detected voltage detected in the reference cell matches the target voltage value. By detecting this pump current, the exhaust air-fuel ratio is reduced. Detected.
- the air-fuel ratio sensors described in Patent Documents 1 to 5 are generally configured to have output characteristics indicated by a solid line A in FIG. That is, in such an air-fuel ratio sensor, the output current from the air-fuel ratio sensor increases as the exhaust air-fuel ratio increases (that is, as the exhaust air-fuel ratio becomes leaner).
- such an air-fuel ratio sensor is configured such that the output current becomes zero when the exhaust air-fuel ratio is the stoichiometric air-fuel ratio.
- the slope in FIG. 2, that is, the ratio of the increase amount of the output current to the increase amount of the exhaust air-fuel ratio (hereinafter referred to as “output current change rate”) is not necessarily the same even through the same production process. Even a type of air-fuel ratio sensor will vary among individuals. In addition, even in the same air-fuel ratio sensor, the output current change rate changes due to deterioration over time. As a result, even if the same type of sensor is used, the rate of change in the output current decreases as shown by the broken line B in FIG. The rate of current change will increase.
- the output current of the air-fuel ratio sensor varies depending on the sensor used, the period of use, and the like. For example, when the air-fuel ratio sensor has output characteristics as indicated by the solid line A, the output current when measuring the exhaust gas having an air-fuel ratio of af 1 is I 2 . However, when the air-fuel ratio sensor has output characteristics as indicated by the broken line B or the alternate long and short dash line C, the output currents when measuring the exhaust gas having an air-fuel ratio of af 1 are I 1 and I, respectively. 3 , resulting in an output current different from I 2 described above.
- such an air-fuel ratio sensor can accurately detect that the stoichiometric air-fuel ratio and the stoichiometric air-fuel ratio are rich and lean.
- the air-fuel ratio of the exhaust gas is not the stoichiometric air-fuel ratio, its absolute The value (that is, the rich degree or the lean degree) could not be accurately detected.
- an object of the present invention is to provide an internal combustion engine using an air-fuel ratio sensor that can detect the absolute value of the air-fuel ratio of the exhaust gas even when the air-fuel ratio of the exhaust gas is not the stoichiometric air-fuel ratio. It is to provide an engine control device.
- the first invention includes an air-fuel ratio sensor provided in an exhaust passage of the internal combustion engine, and an engine control device that controls the internal combustion engine based on a sensor output current of the air-fuel ratio sensor.
- the air-fuel ratio sensor includes a measured gas chamber into which an exhaust gas that is an air-fuel ratio detection target is allowed to flow, and a reference cell according to the air-fuel ratio of the exhaust gas in the measured gas chamber A reference cell in which an output current changes; and a pump cell that pumps oxygen into and out of the exhaust gas in the measured gas chamber in accordance with a pump current, and the reference cell is in the measured gas chamber.
- the applied voltage at which the reference cell output current becomes zero changes according to the air-fuel ratio of the exhaust gas, and the applied voltage in the reference cell is changed when the air-fuel ratio of the exhaust gas in the measured gas chamber is the stoichiometric air-fuel ratio.
- the applied voltage in the reference cell is fixed at a constant voltage.
- the pump current control device controls the pump current so that the reference cell output current is zero when the reference cell output current is zero when the air-fuel ratio is different from the stoichiometric air-fuel ratio.
- a pump current detection device that detects the pump current as the sensor output current.
- the reference cell in a second invention, includes a first electrode exposed to the exhaust gas in the measured gas chamber, a second electrode exposed to a reference atmosphere, and the first electrode.
- the diffusion rate controlling layer is arranged such that exhaust gas in the measured gas chamber reaches the first electrode through the diffusion rate controlling layer.
- the reference cell has a limit current region that is a voltage region in which the reference cell output current becomes a limit current for each exhaust air-fuel ratio.
- the constant voltage is a voltage within the limit current region when the exhaust air-fuel ratio is the stoichiometric air-fuel ratio.
- the reference cell is proportional to the increase of the applied voltage with respect to the relationship between the applied voltage and the reference cell output current for each exhaust air-fuel ratio. Proportional to the voltage region in which the reference cell output current increases, and the water decomposition region in which the reference cell output current changes according to the change in applied voltage due to the occurrence of water decomposition.
- An intermediate region that is a voltage region between the region and the water splitting region, and the constant voltage is a voltage within the intermediate region when the exhaust air-fuel ratio is the stoichiometric air-fuel ratio.
- the constant voltage is a voltage at which a reference cell output current becomes zero when the exhaust air-fuel ratio is 1% higher than the stoichiometric air-fuel ratio
- the air-fuel ratio of the exhaust gas in the measured gas chamber is 1% lower than the stoichiometric air-fuel ratio, it is set to a voltage between the voltage at which the reference cell output current becomes zero.
- the reference cell increases the applied voltage with respect to the relationship between the applied voltage and the reference cell output current for each exhaust air-fuel ratio.
- the reference cell output current increases to the first inflection point, and as the applied voltage increases from the first inflection point, the reference cell output current increases to the second inflection point, and the applied voltage increases from the second inflection point.
- the increase in the reference cell output current relative to the increase in applied voltage is smaller in the voltage region between the first and second bending points than in the other voltage regions.
- the constant voltage is a voltage between the first bending point and the second bending point when the exhaust air-fuel ratio is the stoichiometric air-fuel ratio.
- the reference cell includes a current increasing region that is a voltage region in which the reference cell output current increases as the applied voltage increases for each exhaust air-fuel ratio;
- a current slightly increasing region that is a voltage region in which the amount of increase in the reference cell output current with respect to the amount of increase in the applied voltage is smaller than that in the current increasing region. This is the voltage within the current slightly increasing region when the fuel ratio is the stoichiometric air-fuel ratio.
- the diffusion-controlling layer is made of alumina, and the constant voltage is 0.1 V or more and 0.9 V or less.
- the engine control device has an exhaust air / fuel ratio different from a stoichiometric air / fuel ratio when a sensor output current of the air / fuel ratio sensor becomes zero. It is determined that the air-fuel ratio is determined in advance.
- the internal combustion engine is an exhaust purification device capable of storing oxygen provided in the exhaust passage upstream of the air-fuel ratio sensor in the exhaust flow direction.
- the constant voltage is set so that the reference cell output current becomes zero when the exhaust air-fuel ratio is a predetermined rich determination air-fuel ratio that is richer than the stoichiometric air-fuel ratio.
- the engine control device can control the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst, and the sensor output current of the air-fuel ratio sensor becomes zero or less.
- the target air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst is made leaner than the stoichiometric air-fuel ratio.
- the engine control apparatus according to the twelfth aspect of the present invention, wherein the oxygen storage amount of the exhaust purification catalyst is greater than the maximum oxygen storage amount when the sensor output current of the air-fuel ratio sensor becomes zero or less.
- Oxygen storage amount increasing means for continuously or intermittently making the target air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst leaner than the stoichiometric air-fuel ratio until the predetermined storage amount decreases, and oxygen of the exhaust purification catalyst
- the target air-fuel ratio is continuously or intermittently stoichiometrically reduced so that the oxygen occlusion amount decreases toward zero without reaching the maximum oxygen occlusion amount.
- Oxygen storage amount reducing means for making the fuel richer than the fuel ratio.
- the difference is larger than the difference between the target air-fuel ratio and the stoichiometric air-fuel ratio during a period in which the oxygen storage amount reducing means is continuously or intermittently made richer than the stoichiometric air-fuel ratio.
- the internal combustion engine control device includes an upstream air-fuel ratio provided in the engine exhaust passage upstream of the exhaust purification catalyst in the exhaust flow direction.
- a sensor is provided, and the engine control device controls the exhaust air-fuel ratio based on the output of the upstream air-fuel ratio sensor so that the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst becomes the target air-fuel ratio.
- the upstream air-fuel ratio sensor is configured such that the applied voltage at which the sensor output current becomes zero changes according to the exhaust air-fuel ratio and the exhaust air-fuel ratio is the stoichiometric air-fuel ratio.
- the applied voltage in the upstream air-fuel ratio sensor is increased, the sensor output current increases accordingly.
- the applied voltage in the upstream air-fuel ratio sensor is greater than the applied voltage of the air-fuel ratio sensor. Is also low.
- the applied voltage in the upstream air-fuel ratio sensor is fixed at a constant voltage
- the constant voltage is The voltage at which the sensor output current becomes zero when the air-fuel ratio of the exhaust gas in the gas measurement chamber is the stoichiometric air-fuel ratio.
- a control device for an internal combustion engine using an air-fuel ratio sensor capable of detecting an absolute value of an air-fuel ratio of exhaust gas even when the air-fuel ratio of the exhaust gas is not a stoichiometric air-fuel ratio.
- FIG. 1 is a diagram schematically showing an internal combustion engine in which a control device according to a first embodiment of the present invention is used.
- FIG. 2 is a diagram showing output characteristics of the air-fuel ratio sensor.
- FIG. 3 is a schematic cross-sectional view of the air-fuel ratio sensor.
- FIG. 4 is a diagram schematically showing the operation of the air-fuel ratio sensor.
- FIG. 5 is a diagram showing output characteristics of the air-fuel ratio sensor.
- FIG. 6 is a diagram schematically showing the operation of the reference cell.
- FIG. 7 is a diagram showing the relationship between the sensor applied voltage and the reference cell output current at each exhaust air-fuel ratio.
- FIG. 8 is a diagram showing the relationship between the exhaust air-fuel ratio and the reference cell output current at each sensor applied voltage.
- FIG. 1 is a diagram schematically showing an internal combustion engine in which a control device according to a first embodiment of the present invention is used.
- FIG. 2 is a diagram showing output characteristics of the air-fuel ratio sensor.
- FIG. 9 is a diagram showing the relationship between the sensor applied voltage and the reference cell output current in the air-fuel ratio sensor.
- FIG. 10 is a diagram showing the relationship between the exhaust air-fuel ratio and the reference cell output current in the air-fuel ratio sensor.
- FIG. 11 is a diagram illustrating the relationship between the sensor applied voltage and the reference cell output current.
- FIG. 12 is a view similar to FIG. 8 showing the relationship between the exhaust air-fuel ratio and the reference cell output current at each sensor applied voltage, and shows a wider range than FIG.
- FIG. 13 is a diagram illustrating an example of a specific circuit constituting the voltage application device and the reference cell output current detection device.
- FIG. 14 shows the relationship between the oxygen storage amount of the exhaust purification catalyst and the concentrations of NOx and unburned gas in the exhaust gas flowing out from the exhaust purification catalyst.
- FIG. 15 is a time chart of the oxygen storage amount of the exhaust purification catalyst.
- FIG. 16 is a time chart of the oxygen storage amount of the exhaust purification catalyst.
- FIG. 17 is a functional block diagram of the control device.
- FIG. 18 is a flowchart showing a control routine of calculation control of the air-fuel ratio correction amount.
- FIG. 19 is a time chart of the oxygen storage amount of the exhaust purification catalyst.
- FIG. 20 is a cross-sectional view similar to FIG. 3, schematically showing the configuration of the air-fuel ratio sensor of the third embodiment.
- FIG. 1 is a diagram schematically showing an internal combustion engine in which a control device according to a first embodiment of the present invention is used.
- 1 is an engine body
- 2 is a cylinder block
- 3 is a piston that reciprocates in the cylinder block
- 4 is a cylinder head fixed on the cylinder block
- 5 is a piston 3 and a cylinder head 4.
- a combustion chamber formed therebetween 6 is an intake valve
- 7 is an intake port
- 8 is an exhaust valve
- 9 is an exhaust port.
- the intake valve 6 opens and closes the intake port 7, and the exhaust valve 8 opens and closes the exhaust port 9.
- a spark plug 10 is disposed at the center of the inner wall surface of the cylinder head 4, and a fuel injection valve 11 is disposed around the inner wall surface of the cylinder head 4.
- the spark plug 10 is configured to generate a spark in response to the ignition signal.
- the fuel injection valve 11 injects a predetermined amount of fuel into the combustion chamber 5 according to the injection signal.
- the fuel injection valve 11 may be arranged so as to inject fuel into the intake port 7.
- gasoline having a theoretical air-fuel ratio of 14.6 in the exhaust purification catalyst is used as the fuel.
- the internal combustion engine of the present invention may use other fuels.
- the intake port 7 of each cylinder is connected to a surge tank 14 via a corresponding intake branch pipe 13, and the surge tank 14 is connected to an air cleaner 16 via an intake pipe 15.
- the intake port 7, the intake branch pipe 13, the surge tank 14, and the intake pipe 15 form an intake passage.
- a throttle valve 18 driven by a throttle valve drive actuator 17 is disposed in the intake pipe 15. The throttle valve 18 is rotated by a throttle valve drive actuator 17 so that the opening area of the intake passage can be changed.
- the exhaust port 9 of each cylinder is connected to an exhaust manifold 19.
- the exhaust manifold 19 has a plurality of branches connected to the exhaust ports 9 and a collective part in which these branches are assembled.
- a collecting portion of the exhaust manifold 19 is connected to an upstream casing 21 containing an upstream exhaust purification catalyst 20.
- the upstream casing 21 is connected to a downstream casing 23 containing a downstream exhaust purification catalyst 24 via an exhaust pipe 22.
- the exhaust port 9, the exhaust manifold 19, the upstream casing 21, the exhaust pipe 22, and the downstream casing 23 form an exhaust passage.
- An electronic control unit (ECU) 31 comprises a digital computer, and is connected to each other via a bidirectional bus 32, a RAM (Random Access Memory) 33, a ROM (Read Only Memory) 34, a CPU (Microprocessor) 35, and an input.
- a port 36 and an output port 37 are provided.
- An air flow meter 39 for detecting the flow rate of air flowing through the intake pipe 15 is disposed in the intake pipe 15, and the output of the air flow meter 39 is input to the input port 36 via the corresponding AD converter 38.
- an upstream air-fuel ratio sensor 40 that detects the air-fuel ratio of the exhaust gas flowing through the exhaust manifold 19 (that is, the exhaust gas flowing into the upstream exhaust purification catalyst 20) is disposed at the collecting portion of the exhaust manifold 19.
- the downstream side that detects the air-fuel ratio of the exhaust gas that flows in the exhaust pipe 22 (that is, the exhaust gas that flows out of the upstream side exhaust purification catalyst 20 and flows into the downstream side exhaust purification catalyst 24).
- An air-fuel ratio sensor 41 is arranged. The outputs of these air-fuel ratio sensors 40 and 41 are also input to the input port 36 via the corresponding AD converter 38. The configuration of these air-fuel ratio sensors 40 and 41 will be described later.
- a load sensor 43 that generates an output voltage proportional to the amount of depression of the accelerator pedal 42 is connected to the accelerator pedal 42, and the output voltage of the load sensor 43 is input to the input port 36 via the corresponding AD converter 38.
- the crank angle sensor 44 generates an output pulse every time the crankshaft rotates 15 degrees, and this output pulse is input to the input port 36.
- the CPU 35 calculates the engine speed from the output pulse of the crank angle sensor 44.
- the output port 37 is connected to the spark plug 10, the fuel injection valve 11, and the throttle valve drive actuator 17 via the corresponding drive circuit 45.
- the ECU 31 functions as an engine control device that controls the internal combustion engine based on outputs from various sensors and the like.
- FIG. 3 is a schematic cross-sectional view of the air-fuel ratio sensors 40 and 41.
- the air-fuel ratio sensors 40 and 41 in the present embodiment are two-cell type air-fuel ratio sensors having two cells each composed of a solid electrolyte layer and a pair of electrodes.
- the air-fuel ratio sensors 40 and 41 include a measured gas chamber 51, a reference gas chamber 52, and two solid electrolyte layers 53 and 54 disposed on both sides of the measured gas chamber 51. It has.
- the reference gas chamber 52 is provided on the opposite side of the measured gas chamber 51 with the second solid electrolyte layer 54 interposed therebetween.
- a gas chamber side electrode (third electrode) 55 is disposed on the side surface of the first solid electrolyte layer 53 on the measured gas chamber 51 side, and an exhaust side electrode is disposed on the side surface of the first solid electrolyte layer 53 on the exhaust gas side. (Fourth electrode) 56 is arranged.
- the first solid electrolyte layer 53, the gas chamber side electrode 55 and the exhaust side electrode 56 constitute a pump cell 60.
- a gas chamber side electrode (first electrode) 57 is disposed on the side surface of the second solid electrolyte layer 54 on the measured gas chamber 51 side, and on the side surface of the second solid electrolyte layer 54 on the reference gas chamber 52 side.
- a reference side electrode (second electrode) 58 is disposed.
- the second solid electrolyte layer 54, the gas chamber side electrode 57 and the reference side electrode 58 constitute a reference cell 61.
- a diffusion rate controlling layer 63 is provided so as to surround the gas chamber side electrode 55 of the pump cell 60 and the gas chamber side electrode 57 of the reference cell 61. Therefore, the measured gas chamber 51 is defined by the first solid electrolyte layer 53, the second solid electrolyte layer 54, and the diffusion-controlling layer 63. Exhaust gas is allowed to flow into the measured gas chamber 51 via the diffusion-controlling layer 63. Therefore, the electrodes arranged in the measured gas chamber 51, that is, the gas chamber side electrode 55 of the pump cell 60 and the gas chamber side electrode 57 of the reference cell 61 are exposed to the exhaust gas through the diffusion control layer 63. Become.
- the diffusion control layer 63 is not necessarily provided so that the exhaust gas flowing into the measured gas chamber 51 passes through. As long as the exhaust gas that reaches the gas chamber side electrode 57 of the reference cell 61 becomes the exhaust gas that has passed through the diffusion control layer, the diffusion control layer may be arranged in any manner.
- a heater portion 64 is provided on the side surface of the second solid electrolyte layer 54 on the side of the reference gas chamber 52 so as to surround the reference gas chamber 52. Therefore, the reference gas chamber 52 is defined by the second solid electrolyte layer 54 and the heater unit 64. A reference gas is introduced into the reference gas chamber 52. In the present embodiment, the reference gas chamber 52 is open to the atmosphere, and thus the atmosphere is introduced into the reference gas chamber 52 as the reference gas.
- the heater section 64 is provided with a plurality of heaters 65, and the heaters 65 can control the temperature of the air-fuel ratio sensors 40 and 41, particularly the temperature of the solid electrolyte layers 53 and 54.
- the heater 65 has a heat generation capacity sufficient to heat the solid electrolyte layers 53 and 54 until they are activated.
- a protective layer 66 is provided on the side surface of the first solid electrolyte layer 53 on the exhaust gas side.
- the protective layer 66 is formed of a porous material so that the exhaust gas reaches the exhaust side electrode 56 while preventing liquid or the like in the exhaust gas from directly adhering to the exhaust side electrode 56.
- the solid electrolyte layers 53 and 54 are oxygen ion conductive materials obtained by distributing CaO, MgO, Y 2 O 3 , Yb 2 O 3 or the like as stabilizers to ZrO 2 (zirconia), HfO 2 , ThO 2 , Bi 2 O 3 or the like. It is formed of an oxide sintered body. Further, the diffusion control layer 63 is formed of a porous sintered body of a heat resistant inorganic material such as alumina, magnesia, silica, spinel, mullite or the like. Further, the electrodes 55 to 58 are made of a noble metal having high catalytic activity such as platinum.
- a sensor application voltage Vr is applied between the gas chamber side electrode 57 and the reference side electrode 58 of the reference cell 61 by a reference cell voltage application device 70 mounted on the ECU 31.
- the ECU 31 has a reference cell for detecting a reference cell output current Ir flowing between the electrodes 57 and 58 via the second solid electrolyte layer 54 when the sensor application voltage Vr is applied by the reference cell voltage application device 70.
- An output current detection device 71 is provided.
- a pump voltage Vp is applied between the gas chamber side electrode 55 and the exhaust side electrode 56 of the pump cell 60 by a pump voltage application device 72 mounted on the ECU 31.
- the pump voltage Vp applied by the pump voltage application device 72 is set according to the reference cell output current Ir detected by the reference cell output current detection device 71.
- the pump voltage Vp is set according to the difference between the reference cell output current Ir detected by the reference cell output current detection device 71 and a preset target current (for example, zero).
- the ECU 31 includes a pump current detection device 73 that detects a pump current Ip flowing between the electrodes 55 and 56 via the first solid electrolyte layer 53 when the pump voltage Vp is applied by the pump voltage application device 72. Provided.
- the pump voltage application device 72 changes the pump voltage Vp
- the pump current Ip flowing between the electrodes 85 and 86 changes.
- the pump voltage application device 72 controls the pump current Ip. Therefore, the pump voltage application device 72 functions as a pump current control device that controls the pump current Ip.
- the pump current Ip can also be changed by, for example, arranging a variable resistor in series with the pump voltage applying device 72 and changing the variable resistor. Therefore, means other than the pump voltage applying device 72 such as a variable resistor can be used as the pump current control device.
- FIG. 4 is a diagram schematically showing the operation of the air-fuel ratio sensors 40 and 41.
- the air-fuel ratio sensors 40 and 41 are arranged so that the outer peripheral surfaces of the protective layer 66 and the diffusion-controlling layer 63 are exposed to the exhaust gas. Air is introduced into the reference gas chamber 52 of the air-fuel ratio sensors 40 and 41.
- the solid electrolyte layers 53 and 54 are formed of a sintered body of an oxygen ion conductive oxide. For this reason, when a difference in oxygen concentration occurs between both side surfaces of the solid electrolyte layers 53 and 54 in a state activated by high temperature, the oxygen ions try to move from the side surface having a high concentration to the side surface having a low concentration.
- the electromotive force E is generated (oxygen battery characteristics).
- oxygen ion movement will be caused so that an oxygen concentration ratio is generated between both side surfaces of the solid electrolyte layer in accordance with the potential difference. It has the characteristic (oxygen pump characteristic). Specifically, when a potential difference is applied between both side surfaces, the oxygen concentration on the side surface provided with positive polarity is a ratio corresponding to the potential difference with respect to the oxygen concentration on the side surface provided with negative polarity. The movement of oxygen ions is caused to increase.
- the reference cell 61 of the present embodiment has a predetermined air-fuel ratio in which the air-fuel ratio of the exhaust gas in the measured gas chamber 51 is slightly richer than the stoichiometric air-fuel ratio by a mechanism described later. For example, in the case of 14.55), the reference cell output current flowing between the electrodes 57 and 58 becomes zero. On the other hand, when the air-fuel ratio of the exhaust gas in the measured gas chamber 51 is richer than the rich determination air-fuel ratio, the reference cell output current flowing between the electrodes 57 and 58 becomes a negative current, and the magnitude is determined from the rich determination air-fuel ratio. Is proportional to the difference.
- the pump voltage application device 72 applies the pump voltage to the electrodes 55 and 56 of the pump cell 60 based on this.
- a pump voltage is applied using the exhaust side electrode 56 as a positive electrode and the gas chamber side electrode 55 as a negative electrode.
- the pump voltage application device 72 applies the pump voltage to the electrodes 55 and 56 of the pump cell 60, in the first solid electrolyte layer 53 of the pump cell 60, from the negative electrode to the positive electrode, that is, from the gas chamber side electrode 55 to the exhaust side electrode 56.
- the movement of oxygen ions occurs. For this reason, oxygen in the measured gas chamber 51 is pumped into the exhaust gas around the air-fuel ratio sensors 40 and 41.
- the flow rate of oxygen pumped from the measured gas chamber 51 into the exhaust gas around the air-fuel ratio sensors 40 and 41 is proportional to the pump voltage, and the pump voltage is detected by the reference cell output current detector 71. Is proportional to the magnitude of the reference cell output current. Therefore, the greater the degree of leanness of the exhaust air / fuel ratio in the measured gas chamber 51, that is, the higher the oxygen concentration in the measured gas chamber 51, the more the exhaust around the air / fuel ratio sensors 40 and 41 from the measured gas chamber 51. The flow rate of oxygen pumped into the gas increases.
- the flow rate of oxygen flowing into the measured gas chamber 51 via the diffusion rate controlling layer 63 and the flow rate of oxygen pumped out by the pump cell 60 basically coincide with each other, and the measured gas chamber 51 is basically almost rich.
- the determination air-fuel ratio is maintained.
- the oxygen flow rate pumped out by the pump cell 60 is equal to the flow rate of oxygen ions that have moved through the first solid electrolyte layer 53 of the pump cell 60.
- the flow rate of this oxygen ion is equal to the current flowing between the electrodes 55 and 56 of the pump cell 60. Therefore, the pump current flowing between the electrodes 55 and 56 is detected by the pump current detection device 73 as the output current (hereinafter referred to as “sensor output current”) of the air-fuel ratio sensors 40 and 41, so that the The flow rate of oxygen flowing into the measured gas chamber 51 and, therefore, the lean air-fuel ratio of the exhaust gas around the measured gas chamber 51 can be detected.
- Rich air-fuel ratio exhaust gas flows in.
- rich air-fuel ratio exhaust gas containing a large amount of unburned gas HC, CO, etc.
- a negative reference cell output current flows in proportion, and the reference cell output current is detected by the reference cell output current detector 71.
- the pump voltage application device 72 applies a pump voltage between the electrodes 55 and 56 of the pump cell 60 based on this.
- a pump voltage is applied using the gas chamber side electrode 55 as a positive electrode and the exhaust side electrode 56 as a negative electrode.
- the flow rate of oxygen pumped from the exhaust gas around the air-fuel ratio sensors 40 and 41 into the measured gas chamber 51 is proportional to the pump voltage, and the pump voltage is a negative voltage detected by the reference cell output current detector 71. Is proportional to the magnitude of the reference cell output current. Therefore, the greater the richness of the exhaust air / fuel ratio in the measured gas chamber 51, that is, the higher the concentration of unburned gas in the measured gas chamber 51, the more the exhaust gas around the air / fuel ratio sensors 40 and 41 is covered. The flow rate of oxygen pumped into the gas measuring chamber 51 increases.
- the flow rate of the unburned gas flowing into the measured gas chamber 51 via the diffusion rate controlling layer 63 and the oxygen flow rate pumped by the pump cell 60 become a chemical equivalence ratio. Therefore, the rich determination air-fuel ratio is maintained.
- the flow rate of oxygen pumped by the pump cell 60 is equal to the flow rate of oxygen ions that have moved through the first solid electrolyte layer 53 in the pump cell 60.
- the flow rate of this oxygen ion is equal to the current flowing between the electrodes 55 and 56 of the pump cell 60. Therefore, by detecting the pump current flowing between the electrodes 55 and 56 as the sensor output current by the pump current detecting device 73, the flow rate of the unburned gas flowing into the measured gas chamber 51 via the diffusion rate controlling layer 63 is determined accordingly.
- the rich air-fuel ratio of the exhaust gas around the measured gas chamber 51 can be detected.
- the rich determination air-fuel ratio is provided in the measured gas chamber 51 via the diffusion rate limiting layer 63.
- Exhaust gas flows in.
- the reference cell output current flowing between the electrodes 57 and 58 of the reference cell 61 becomes zero by a mechanism described later, and the reference cell output current is the reference cell output current. It is detected by the detection device 71.
- the pump voltage applied by the pump voltage application device 72 is also zero. For this reason, oxygen ions do not move in the first solid electrolyte layer 53 of the pump cell 60, so that the measured gas chamber 51 is basically maintained at a substantially rich judgment air-fuel ratio. And since the movement of oxygen ion has not arisen in the 1st solid electrolyte layer 53 of the pump cell 60, the pump current (namely, sensor output current) detected by the pump current detection apparatus 73 also becomes zero. Therefore, when the pump current detected by the pump current detection device 73 is zero, it can be seen that the air-fuel ratio of the exhaust gas around the measured gas chamber 51 is equal to the rich determination air-fuel ratio.
- the air-fuel ratio sensors 40 and 41 configured in this way have the output characteristics shown in FIG. That is, in the air-fuel ratio sensors 40 and 41, the pump current (sensor output current) Ip increases as the exhaust air-fuel ratio increases (that is, the leaner the exhaust air-fuel ratio). In addition, in the present embodiment, the air-fuel ratio sensors 40 and 41 are configured such that the pump current (sensor output current) Ip becomes zero when the exhaust air-fuel ratio matches the rich determination air-fuel ratio.
- FIG. 6 is a diagram schematically showing the operation of the reference cell 61.
- the reference side electrode 58 is fixed between the electrodes 57 and 58 so that the reference side electrode 58 is positive and the gas chamber side electrode 57 is negative.
- the sensor applied voltage Vr is applied.
- the ratio of the oxygen concentration between both side surfaces of the second solid electrolyte layer 54 is not so large.
- the sensor applied voltage Vr is set to an appropriate value, the actual oxygen concentration ratio becomes smaller between the two side surfaces of the second solid electrolyte layer 54 than the oxygen concentration ratio corresponding to the sensor applied voltage Vr. Therefore, as shown in FIG. 6A, the gas chamber side electrode is set so that the oxygen concentration ratio between both side surfaces of the second solid electrolyte layer 54 increases toward the oxygen concentration ratio corresponding to the sensor applied voltage Vr. Oxygen ions move from 57 to the reference electrode 58.
- the magnitude of the current (reference cell output current) Ir flowing at this time flows into the measured gas chamber 51 from the exhaust gas through the diffusion rate controlling layer 63 if the sensor applied voltage Vr is set to an appropriate value. Proportional to oxygen flow rate. Therefore, by detecting the magnitude of the current Ir by the reference cell output current detector 71, the oxygen concentration in the measured gas chamber 51 can be known, and as a result, the air-fuel ratio in the lean region can be known.
- the unburned gas flows into the measured gas chamber 51 from the exhaust gas through the diffusion rate controlling layer 63. Even if oxygen is present on the side electrode 57, it reacts with the unburned gas and is removed. For this reason, the oxygen concentration in the measured gas chamber 51 becomes extremely low, and as a result, the ratio of the oxygen concentration between both side surfaces of the second solid electrolyte layer 54 becomes large. For this reason, if the sensor applied voltage Vr is set to an appropriate value, the actual oxygen concentration ratio becomes larger between the two side surfaces of the second solid electrolyte layer 54 than the oxygen concentration ratio corresponding to the sensor applied voltage Vr.
- the reference-side electrode 58 is formed so that the oxygen concentration ratio between both side surfaces of the second solid electrolyte layer 54 decreases toward the oxygen concentration ratio corresponding to the sensor applied voltage Vr.
- the oxygen ions move from the gas toward the gas chamber side electrode 57.
- a current flows from the reference side electrode 58 to the gas chamber side electrode 57 through the reference cell voltage application device 70 that applies the sensor application voltage Vr.
- the magnitude of the current flowing at this time (reference cell output current) Ir moves in the second solid electrolyte layer 54 from the reference side electrode 58 to the gas chamber side electrode 57 if the sensor applied voltage Vr is set to an appropriate value. It depends on the flow rate of oxygen ions.
- the oxygen ions react (combust) on the gas chamber side electrode 57 with the unburned gas that flows into the measured gas chamber 51 through the diffusion rate-determining layer 63 from the exhaust gas. Therefore, the moving flow rate of oxygen ions corresponds to the concentration of unburned gas in the exhaust gas flowing into the measured gas chamber 51. Therefore, by detecting the magnitude of the current Ir by the reference cell output current detection device 71, it is possible to know the unburned gas concentration in the measured gas chamber 51, and thus the air-fuel ratio in the rich region. .
- the exhaust air-fuel ratio in the measured gas chamber 51 matches the rich determination air-fuel ratio
- the amounts of oxygen and unburned gas in the measured gas chamber 51 are the chemical equivalent ratio.
- both of them are completely burned by the catalytic action of the gas chamber side electrode 57, and the concentration of oxygen and unburned gas in the measured gas chamber 51 does not change.
- the oxygen concentration ratio between both side surfaces of the second solid electrolyte layer 54 is not changed and is maintained as the oxygen concentration ratio corresponding to the sensor applied voltage Vr.
- the movement of oxygen ions due to the oxygen pump characteristics does not occur, and as a result, no current flows through the circuit.
- FIG. 7 is a diagram showing the relationship between the sensor applied voltage Vr and the reference cell output current Ir in the reference cell.
- the reference cell has a limit current region in which the reference cell output current Ir hardly increases even when the sensor applied voltage Vr is increased.
- the reference cell output current Ir also increases slightly as the sensor applied voltage Vr increases. For example, taking the case where the exhaust air-fuel ratio is the stoichiometric air-fuel ratio (14.6) as an example, when the sensor applied voltage Vr is about 0.45 V, the reference cell output current Ir becomes zero.
- the reference cell output current Ir when the sensor applied voltage Vr is somewhat lower than 0.45 V (for example, 0.2 V), the reference cell output current Ir becomes a value lower than 0. On the other hand, when the sensor applied voltage Vr is higher than 0.45V (for example, 0.7V), the reference cell output current Ir has a value higher than 0.
- FIG. 8 is a diagram showing the relationship between the exhaust air-fuel ratio and the reference cell output current Ir.
- FIG. 8 shows that the reference cell output current Ir for the same exhaust air-fuel ratio is slightly different for each sensor applied voltage Vr in the region near the theoretical air-fuel ratio.
- the reference cell output current Ir becomes 0 when the sensor applied voltage Vr is 0.45 V.
- the reference cell output current Ir is also increased.
- the sensor applied voltage Vr is smaller than 0.45V, the reference cell output current Ir is also decreased.
- FIG. 8 shows that the exhaust air / fuel ratio when the reference cell output current Ir becomes 0 (hereinafter referred to as “exhaust air / fuel ratio at zero current”) differs for each sensor applied voltage Vr.
- the reference cell output current Ir when the sensor applied voltage Vr is 0.45 V, the reference cell output current Ir becomes 0 when the exhaust air-fuel ratio is the stoichiometric air-fuel ratio.
- the sensor applied voltage Vr is larger than 0.45 V, the reference cell output current Ir becomes 0 when the exhaust air-fuel ratio is richer than the stoichiometric air-fuel ratio, and the sensor applied voltage Vr becomes large.
- the exhaust air-fuel ratio at zero current becomes smaller.
- the reference cell output current Ir becomes 0 when the exhaust air-fuel ratio is leaner than the stoichiometric air-fuel ratio, and the current decreases as the sensor applied voltage Vr decreases.
- the exhaust air-fuel ratio at zero becomes large. That is, by changing the sensor applied voltage Vr, the exhaust air-fuel ratio at the time of zero current can be changed.
- the output current change rate varies among the individual air-fuel ratio sensors, and even in the same air-fuel ratio sensor, it varies due to deterioration over time. Such a tendency also applies to the reference cell 61.
- the ratio of the increase amount of the reference cell output current to the increase amount of the exhaust air-fuel ratio (hereinafter referred to as “reference cell output current change rate”) does not necessarily become the same even after the same production process. In other words, even if the same type of air-fuel ratio sensor is used, variations occur between individuals. In addition, even in the same air-fuel ratio sensor, the reference cell output current change rate changes due to deterioration over time.
- the exhaust air-fuel ratio at zero current (FIG. 2).
- the stoichiometric air-fuel ratio hardly changes. That is, when the reference cell output current Ir takes a value other than zero, the absolute value of the exhaust air-fuel ratio at that time is not necessarily constant, but when the reference cell output current Ir becomes zero, the exhaust air-fuel ratio at that time The absolute value (the theoretical air fuel ratio in the example of FIG. 17) is constant.
- the air-fuel ratio sensors 40 and 41 can change the exhaust air-fuel ratio at zero current by changing the sensor applied voltage Vr.
- the reference cell output current detected by the reference cell output current detection device 71 is zero
- the pump voltage applied by the pump voltage application device 72 is also zero
- the pump current (sensor output current) Ip is also zero. Become. Therefore, according to the air-fuel ratio sensors 40 and 41, the absolute value of the exhaust air-fuel ratio other than the stoichiometric air-fuel ratio can be accurately detected by changing the sensor applied voltage Vr.
- the exhaust air / fuel ratio at zero current is only slightly (for example, ⁇ 1) with respect to the theoretical air / fuel ratio (14.6).
- % Range (within about 14.45 to about 14.75) can be adjusted. Therefore, by appropriately setting the sensor applied voltage Vr, it becomes possible to accurately detect the absolute value of the air-fuel ratio slightly different from the theoretical air-fuel ratio.
- the exhaust air-fuel ratio at the time of zero current can be changed by changing the sensor applied voltage Vr.
- the sensor applied voltage Vr is made larger than a certain upper limit voltage or made smaller than a certain lower limit voltage, the amount of change in the exhaust air / fuel ratio at zero current with respect to the amount of change in the sensor applied voltage Vr becomes larger. Therefore, in such a voltage region, if the sensor applied voltage Vr slightly shifts, the exhaust air-fuel ratio at the time of zero current changes greatly. Therefore, in such a voltage region, in order to accurately detect the absolute value of the exhaust air / fuel ratio, it is necessary to precisely control the sensor applied voltage Vr, which is not practical. For this reason, from the viewpoint of accurately detecting the absolute value of the exhaust air-fuel ratio, the sensor applied voltage Vr needs to be a value within a “specific voltage region” between a certain upper limit voltage and a certain lower limit voltage. Become.
- Such a specific voltage region can be defined in various ways. Hereinafter, some examples of definitions will be described with reference to FIGS.
- the reference cell 61 is a voltage region where the reference cell output current Ir increases as the sensor applied voltage Vr increases for each exhaust air-fuel ratio.
- a current increasing region and a current slightly increasing region which is a voltage region in which the increase amount of the reference cell output current Ir with respect to the increasing amount of the sensor applied voltage Vr is smaller than the current increasing region due to the provision of the diffusion rate limiting layer (FIG. 9).
- (A) shows the current increasing region and the current slightly increasing region only when the exhaust air-fuel ratio is the stoichiometric air-fuel ratio).
- the current slightly increasing region when the exhaust air-fuel ratio is the stoichiometric air-fuel ratio is set as the “specific voltage region”.
- the reference cell 61 has a limit current region that is a voltage region in which the reference cell output current Ir becomes a limit current for each exhaust air-fuel ratio (FIG. 9).
- 9 (B) shows the limit current region only when the exhaust air-fuel ratio is the stoichiometric air-fuel ratio).
- the limit current region when the exhaust air-fuel ratio is the stoichiometric air-fuel ratio is set as the “specific voltage region”.
- the reference cell 61 is a proportional voltage region in which the reference cell output current Ir increases in proportion to an increase in applied voltage for each exhaust air-fuel ratio.
- An area, a water decomposition area that is a voltage area in which the reference cell output current Ir changes according to a change in applied voltage due to the occurrence of decomposition of water and the solid electrolyte layers 53 and 54, and a proportional area and a water decomposition area, (FIG. 9C shows the proportional region, the water splitting region, and the intermediate region only when the exhaust air-fuel ratio is the stoichiometric air-fuel ratio).
- the intermediate region when the exhaust air-fuel ratio is the stoichiometric air-fuel ratio is set as the “specific voltage region”.
- the exhaust air / fuel ratio at zero current changes according to the sensor applied voltage Vr.
- the exhaust air / fuel ratio at the time of zero current is, for example, 0.5% to 2% of the theoretical air / fuel ratio AFst.
- the air-fuel ratio becomes low (preferably about 1%).
- the exhaust air-fuel ratio at the time of zero current becomes an air-fuel ratio that is, for example, about 0.5 to 2% (preferably about 1%) higher than the theoretical air-fuel ratio AFst.
- the upper limit voltage value the voltage value at which the exhaust air-fuel ratio at zero current is 1% lower than the stoichiometric air-fuel ratio AFst, for example
- the lower limit voltage value exhaust air-fuel ratio at zero current. Is a voltage range between the stoichiometric air-fuel ratio AFst, for example, a voltage value that is 1% higher than the stoichiometric air-fuel ratio AFst).
- FIG. 11 shows the change of current with respect to voltage.
- the reference cell output current Ir increases to the first inflection point B 1 as the sensor applied voltage Vr increases from the negative state.
- the reference cell output current Ir increases from the first bending point B 1 to the second bending point B 2 as the sensor application voltage Vr increases, and the reference cell output increases as the sensor application voltage Vr increases from the second bending point B 2.
- the current Ir increases.
- the increase amount of the applied current Ir with respect to the increase amount of the sensor applied voltage Vr is smaller than in the other voltage regions.
- the voltage between the first inflection point and the second inflection point when the exhaust air-fuel ratio is the stoichiometric air-fuel ratio is set as the “specific voltage region”.
- the upper limit voltage value and the lower limit voltage value of the “specific voltage region” are specified by specific numerical values.
- the “specific voltage region” is 0.05 V or more and 0.95 V or less, preferably 0.1 V or more and 0.9 V or less, more preferably 0.15 V or more and 0.8 V or less.
- FIG. 12 is a diagram showing the relationship between the exhaust air-fuel ratio and the reference cell output current Ir at each sensor applied voltage Vr, as in FIG. FIG. 8 microscopically shows the relationship only in the vicinity of the theoretical air-fuel ratio, whereas FIG. 12 macroscopically shows the relationship for a wider range of air-fuel ratio.
- the reference cell output current Ir hardly changes even if the exhaust air-fuel ratio changes.
- This constant exhaust air-fuel ratio changes according to the sensor applied voltage Vr, and is higher as the sensor applied voltage Vr is higher.
- the sensor applied voltage Vr is increased to a certain value (maximum voltage) or more
- the reference cell output current Ir becomes equal to whatever value the exhaust air / fuel ratio is, as shown by the one-dot chain line in the figure. It will not become zero.
- the reference cell output current Ir hardly changes even if the exhaust air / fuel ratio changes.
- This constant exhaust air-fuel ratio also changes according to the sensor applied voltage Vr, and is lower as the sensor applied voltage Vr is lower. For this reason, when the sensor applied voltage Vr is lowered below a certain value (minimum voltage), the reference cell output current Ir becomes whatever the exhaust air / fuel ratio is, as indicated by a two-dot chain line in the figure. (For example, when the sensor applied voltage Vr is set to 0 V, the reference cell output current Ir does not become 0 regardless of the exhaust air-fuel ratio).
- the sensor applied voltage Vr is a voltage between the maximum voltage and the minimum voltage, there exists an exhaust air / fuel ratio at which the reference cell output current becomes zero. Conversely, if the sensor applied voltage Vr is higher than the maximum voltage or lower than the minimum voltage, there is no exhaust air / fuel ratio at which the reference cell output current becomes zero. Therefore, the sensor applied voltage Vr is at least a voltage at which the reference cell output current becomes zero when the exhaust air-fuel ratio is any air-fuel ratio, that is, a voltage between the maximum voltage and the minimum voltage. It will be necessary.
- the above-described “specific voltage region” is a voltage region between the maximum voltage and the minimum voltage.
- the sensor applied voltage Vrupp in the upstream air-fuel ratio sensor 40 is theoretically the exhaust air-fuel ratio.
- the reference cell output current (and sensor output current) is fixed at a constant voltage (for example, 0.45 V) so that the air-fuel ratio (14.6 in the present embodiment) is zero.
- the sensor applied voltage Vrup is set so that the exhaust air-fuel ratio at zero current becomes the stoichiometric air-fuel ratio.
- the sensor applied voltage Vr in the downstream air-fuel ratio sensor 41 is determined in advance so that the exhaust air-fuel ratio is slightly richer than the stoichiometric air-fuel ratio.
- the reference cell output current (and sensor output current) is fixed at a constant voltage (for example, 0.7 V) so that the rich determination air-fuel ratio (for example, 14.55) is zero.
- the sensor applied voltage Vrdwn is set so that the exhaust air-fuel ratio at the time of zero current becomes a rich determination air-fuel ratio that is slightly richer than the theoretical air-fuel ratio.
- the sensor applied voltage Vrdwn in the downstream air-fuel ratio sensor 41 is set to a voltage higher than the sensor applied voltage Vrup in the upstream air-fuel ratio sensor 40.
- the ECU 31 connected to both the air-fuel ratio sensors 40, 41 has the stoichiometric air-fuel ratio around the upstream air-fuel ratio sensor 40 when the sensor output current Iupp of the upstream air-fuel ratio sensor 40 becomes zero. Judge that there is. On the other hand, the ECU 31 determines that the exhaust air-fuel ratio around the downstream air-fuel ratio sensor 41 is different from the rich determination air-fuel ratio, that is, the stoichiometric air-fuel ratio, when the sensor output current Ipdwn of the downstream air-fuel ratio sensor 41 becomes zero. It is determined that the air / fuel ratio is high.
- the air-fuel ratio of the exhaust gas is detected by the air-fuel ratio sensor, for example, when fuel cut control described later is not executed, or the air-fuel ratio detected by the air-fuel ratio sensor becomes a high value of 18 or more. When not.
- FIG. 13 shows an example of a specific circuit constituting the reference cell voltage application device 70 and the reference cell output current detection device 71.
- E is an electromotive force generated by oxygen battery characteristics
- Ri is an internal resistance of the second solid electrolyte layer 54
- Vs is a potential difference between both electrodes 57 and 58.
- the reference cell voltage application device 70 basically performs negative feedback control so that the electromotive force E generated by the oxygen battery characteristics matches the sensor applied voltage Vr.
- the reference cell voltage application device 70 applies the potential difference Vs to the sensor. Negative feedback control is performed so that the voltage Vr is obtained.
- the second solid electrolyte layer 54 The oxygen concentration ratio between the two side surfaces is an oxygen concentration ratio corresponding to the sensor applied voltage Vr.
- the electromotive force E coincides with the sensor applied voltage Vr, and the potential difference Vs between the electrodes 57 and 58 is also the sensor applied voltage Vr. As a result, the current Ir does not flow.
- the reference cell voltage application device 70 substantially applies the sensor application voltage Vr between the electrodes 57 and 58.
- the electric circuit of the reference cell voltage application device 70 does not necessarily have to be as shown in FIG. 13, and any mode can be used as long as the sensor application voltage Vr can be substantially applied between the electrodes 57 and 58.
- the apparatus may be used.
- the reference cell output current detector 71 is actually a current rather than detecting, and calculates the current from the voltage E 0 by detecting the voltage E 0.
- E 0 can be expressed as the following formula (1).
- E 0 Vr + V 0 + IrR (1)
- V 0 is an offset voltage (a voltage to be applied so that E 0 does not become a negative value, for example, 3 V)
- R is a resistance value shown in FIG.
- the sensor applied voltage Vr, the offset voltage V 0 and the resistance value R are constant, so that the voltage E 0 changes according to the current Ir. Therefore, if the voltage E 0 is detected, the current Ir can be calculated from the voltage E 0 .
- the reference cell output current detection device 71 substantially detects the current Ir flowing between the electrodes 57 and 58.
- the electric circuit of the reference cell output current detection device 71 does not necessarily have to be as shown in FIG. 13. Any device can be used as long as the current Ir flowing between the electrodes 57 and 58 can be detected. There may be.
- the upstream side exhaust purification catalyst 20 is a three-way catalyst having an oxygen storage capacity. Specifically, the upstream side exhaust purification catalyst 20 supports a noble metal having a catalytic action (for example, platinum (Pt)) and a substance having an oxygen storage capacity (for example, ceria (CeO 2 )) on a carrier made of ceramic. It has been made. When the upstream exhaust purification catalyst 20 reaches a predetermined activation temperature, the upstream exhaust purification catalyst 20 exhibits oxygen storage capacity in addition to the catalytic action of simultaneously purifying unburned gas (HC, CO, etc.) and nitrogen oxides (NOx).
- HC, CO, etc. hydrogen oxides
- the upstream side exhaust purification catalyst 20 is such that the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 is leaner than the stoichiometric air-fuel ratio (lean air-fuel ratio). Sometimes it stores oxygen in the exhaust gas. On the other hand, the upstream side exhaust purification catalyst 20 releases oxygen stored in the upstream side exhaust purification catalyst 20 when the air-fuel ratio of the inflowing exhaust gas is richer than the stoichiometric air-fuel ratio (rich air-fuel ratio).
- the “air-fuel ratio of exhaust gas” means the ratio of the mass of fuel to the mass of air supplied until the exhaust gas is generated. Normally, combustion is performed when the exhaust gas is generated. It means the ratio of the mass of fuel to the mass of air supplied into the chamber 5.
- the upstream side exhaust purification catalyst 20 has a catalytic action and an oxygen storage capacity, and thus has a NOx and unburned gas purification action according to the oxygen storage amount.
- FIG. 14 shows the relationship between the oxygen storage amount of the upstream side exhaust purification catalyst 20 and the concentrations of NOx and unburned gas (HC, CO, etc.) in the exhaust gas flowing out from the upstream side exhaust purification catalyst 20.
- FIG. 14A shows the oxygen storage amount and the NOx concentration in the exhaust gas flowing out from the upstream side exhaust purification catalyst 20 when the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 is a lean air-fuel ratio. The relationship is shown.
- FIG. 14 shows the relationship between the oxygen storage amount of the upstream side exhaust purification catalyst 20 and the concentrations of NOx and unburned gas (HC, CO, etc.) in the exhaust gas flowing out from the upstream side exhaust purification catalyst 20.
- FIG. 14A shows the oxygen storage amount and the NOx concentration in the exhaust
- 14B shows the oxygen occlusion amount and the exhaust gas in the exhaust gas flowing out from the upstream side exhaust purification catalyst 20 when the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 is a rich air-fuel ratio. The relationship with the concentration of fuel gas is shown.
- the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 is a rich air-fuel ratio (that is, the exhaust gas includes unburned gas).
- the oxygen stored in the upstream side exhaust purification catalyst 20 is released.
- the unburned gas in the exhaust gas flowing into the upstream side exhaust purification catalyst 20 is oxidized and purified.
- the exhaust gas flowing out from the upstream side exhaust purification catalyst 20 contains almost no unburned gas.
- the exhaust purification catalysts 20 and 24 used in the present embodiment NOx and unburned gas in the exhaust gas according to the air-fuel ratio and oxygen storage amount of the exhaust gas flowing into the exhaust purification catalysts 20 and 24.
- the exhaust purification catalysts 20 and 24 may be different from the three-way catalyst as long as they have a catalytic action and an oxygen storage capacity.
- the sensor output current of the upstream air-fuel ratio sensor 40 (that is, the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20) Iupp is set based on the sensor output current Iupup of the upstream air-fuel ratio sensor 40. Feedback control is performed so that the value corresponds to the air-fuel ratio.
- the target air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 is set based on the sensor output current Ipdwn of the downstream side air-fuel ratio sensor 41. Specifically, when the sensor output current Ipdwn of the downstream air-fuel ratio sensor 41 becomes zero or less, the target air-fuel ratio is set to the lean set air-fuel ratio and is maintained at that air-fuel ratio. When the sensor output current Ipdwn becomes equal to or less than zero, the air-fuel ratio of the exhaust gas flowing out from the upstream side exhaust purification catalyst 20 is slightly richer than the stoichiometric air-fuel ratio. .55) It means that it became below.
- the lean set air-fuel ratio is a predetermined air-fuel ratio that is somewhat leaner than the stoichiometric air-fuel ratio, and is, for example, 14.65 to 20, preferably 14.68 to 18, and more preferably 14.7. About 16 or so.
- the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20 is estimated.
- the oxygen storage amount OSAsc is estimated by estimating the intake air amount into the combustion chamber 5 calculated based on the sensor output current Iupup of the upstream air-fuel ratio sensor 40 and the air flow meter 39 or the like, or the fuel from the fuel injection valve 11. This is performed based on the injection amount.
- the estimated value of the oxygen storage amount OSAsc becomes equal to or larger than a predetermined determination reference storage amount Cref, the target air-fuel ratio that has been the lean set air-fuel ratio until then becomes the weak rich set air-fuel ratio, and is maintained at that air-fuel ratio.
- the The weak rich set air-fuel ratio is a predetermined air-fuel ratio that is slightly richer than the stoichiometric air-fuel ratio, and is, for example, 13.5 to 14.58, preferably 14 to 14.57, more preferably 14.3. About 14.55. Thereafter, when the sensor output current Ipdwn of the downstream side air-fuel ratio sensor 41 becomes equal to or less than zero again, the target air-fuel ratio is made the lean set air-fuel ratio again, and thereafter the same operation is repeated.
- the target air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 is alternately set to the lean set air-fuel ratio and the weak rich set air-fuel ratio.
- the difference between the lean set air-fuel ratio and the stoichiometric air-fuel ratio is larger than the difference between the weak rich set air-fuel ratio and the stoichiometric air-fuel ratio. Therefore, in this embodiment, the target air-fuel ratio is alternately set to a short-term lean set air-fuel ratio and a long-term weak rich set air-fuel ratio.
- FIG. 15 shows the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20, the sensor output current Ipdwn of the downstream side air-fuel ratio sensor 41, and the air-fuel ratio correction amount when air-fuel ratio control is performed in the control apparatus for an internal combustion engine of the present invention.
- 4 is a time chart of AFC, sensor output current Iupup of an upstream air-fuel ratio sensor 40, and NOx concentration in exhaust gas flowing out from an upstream side exhaust purification catalyst 20.
- the sensor output current Iupup of the upstream side air-fuel ratio sensor 40 becomes zero when the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 is the stoichiometric air-fuel ratio, and the exhaust gas of the exhaust gas A negative value is obtained when the air-fuel ratio is a rich air-fuel ratio, and a positive value is obtained when the air-fuel ratio of the exhaust gas is a lean air-fuel ratio.
- the sensor output current Iupp of the upstream air-fuel ratio sensor 40 increases as the difference from the stoichiometric air-fuel ratio increases. The absolute value increases.
- the sensor output current Ipdwn of the downstream side air-fuel ratio sensor 41 becomes zero when the air-fuel ratio of the exhaust gas flowing out from the upstream side exhaust purification catalyst 20 is a rich determination air-fuel ratio (slightly richer than the theoretical air-fuel ratio). Therefore, a negative value is obtained when the air-fuel ratio of the exhaust gas is richer than the rich determination air-fuel ratio, and a positive value is obtained when the air-fuel ratio of the exhaust gas is leaner than the rich determination air-fuel ratio.
- the sensor output of the downstream-side air-fuel ratio sensor 41 increases as the difference from the rich determination air-fuel ratio increases.
- the absolute value of the current Ipdwn increases.
- the air / fuel ratio correction amount AFC is a correction amount related to the target air / fuel ratio.
- the target air-fuel ratio is the stoichiometric air-fuel ratio.
- the air-fuel ratio correction amount AFC is a positive value
- the target air-fuel ratio is a lean air-fuel ratio
- the air-fuel ratio correction amount AFC is a negative value. In some cases, the target air-fuel ratio becomes a rich air-fuel ratio.
- the air-fuel ratio correction amount AFC is set to the weak rich set correction amount AFCrich before the time t 1 .
- the weak rich set correction amount AFCrich is a value corresponding to the weak rich set air-fuel ratio, and is a value smaller than zero. Accordingly, the target air-fuel ratio is set to a rich air-fuel ratio, and accordingly, the sensor output current Iupp of the upstream air-fuel ratio sensor 40 becomes a negative value. Since the exhaust gas flowing into the upstream side exhaust purification catalyst 20 contains unburned gas, the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20 gradually decreases.
- the unburned gas contained in the exhaust gas is purified by the upstream side exhaust purification catalyst 20, and the air-fuel ratio of the exhaust gas flowing out from the upstream side exhaust purification catalyst 20 becomes substantially the stoichiometric air-fuel ratio.
- the sensor output current Ipdwn of the downstream air-fuel ratio sensor has a positive value (corresponding to the theoretical air-fuel ratio).
- the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 is a rich air-fuel ratio, the NOx emission amount from the upstream side exhaust purification catalyst 20 is suppressed.
- the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20 gradually decreases, the oxygen storage amount OSAsc decreases beyond the lower limit storage amount (see Crowlim in FIG. 14) at time t 1 .
- the oxygen storage amount OSAsc decreases below the lower limit storage amount, a part of the unburned gas that has flowed into the upstream side exhaust purification catalyst 20 flows out without being purified by the upstream side exhaust purification catalyst 20. Therefore, after time t 1 , the sensor output current Ipdwn of the downstream air-fuel ratio sensor 41 gradually decreases as the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20 decreases. Also at this time, since the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 is a rich air-fuel ratio, the NOx emission amount from the upstream side exhaust purification catalyst 20 is suppressed.
- the air-fuel ratio correction amount AFC is set to the lean set correction amount AFClean so as to suppress the decrease in the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20.
- the lean set correction amount AFClean is a value corresponding to the lean set air-fuel ratio, and is a value larger than zero. Therefore, the target air-fuel ratio is a lean air-fuel ratio.
- the air-fuel ratio correction amount AFC is switched. This is because even if the oxygen storage amount of the upstream side exhaust purification catalyst 20 is sufficient, the air-fuel ratio of the exhaust gas flowing out from the upstream side exhaust purification catalyst 20 may slightly deviate from the stoichiometric air-fuel ratio. is there.
- the oxygen storage amount has decreased beyond the lower limit storage amount only after the air-fuel ratio of the exhaust gas flowing out from the upstream side exhaust purification catalyst 20 reaches the rich determination air-fuel ratio.
- the rich determination air-fuel ratio is such that the air-fuel ratio of the exhaust gas flowing out from the upstream side exhaust purification catalyst 20 does not reach when the oxygen storage amount of the upstream side exhaust purification catalyst 20 is sufficient. It is said.
- the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20 increases. Accordingly, the air-fuel ratio of the exhaust gas flowing out from the upstream side exhaust purification catalyst 20 changes to the stoichiometric air-fuel ratio, and the sensor output current Ipdwn of the downstream side air-fuel ratio sensor 41 is also a positive value corresponding to the stoichiometric air-fuel ratio. Converges to a value. At this time, the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 is a lean air-fuel ratio.
- the oxygen storage capacity of the upstream side exhaust purification catalyst 20 has a sufficient margin, the inflowing exhaust gas The oxygen therein is stored in the upstream side exhaust purification catalyst 20, and NOx is reduced and purified. For this reason, the NOx emission amount from the upstream side exhaust purification catalyst 20 is suppressed.
- the oxygen storage amount OSAsc the upstream exhaust purification catalyst 20 is increased, the oxygen storage amount OSAsc at time t 4 reaches the determination reference storage amount Cref.
- the air-fuel ratio correction amount AFC is set to the weak rich set correction amount AFCrich (less than 0) in order to stop storing oxygen in the upstream side exhaust purification catalyst 20. (Small value). Therefore, the target air-fuel ratio is set to a rich air-fuel ratio.
- the criterion storage amount Cref is the maximum oxygen storage amount Cmax and upper storage amount since it is set sufficiently lower than (see Cuplim in FIG. 14), the oxygen storage amount OSAsc even at time t 5 is the maximum oxygen storage amount Cmax And the upper limit occlusion amount is not reached.
- the determination reference storage amount Cref is equal to the oxygen storage amount OSAsc. The amount is sufficiently small so as not to reach the maximum oxygen storage amount Cmax or the upper limit storage amount.
- the criterion storage amount Cref is 3/4 or less, preferably 1/2 or less, more preferably 1/5 or less of the maximum oxygen storage amount Cmax. Therefore, the NOx emission amount from the upstream side exhaust purification catalyst 20 is also suppressed from time t 4 to t 5 .
- the air-fuel ratio correction amount AFC there is a weak rich set correction amount AFCrich. Accordingly, the target air-fuel ratio is set to a rich air-fuel ratio, and accordingly, the sensor output current Iupp of the upstream air-fuel ratio sensor 40 becomes a negative value. Since the exhaust gas flowing into the upstream exhaust purification catalyst 20 will include unburned gas, the oxygen storage amount OSAsc the upstream exhaust purification catalyst 20 is gradually decreased at time t 6, the time Similar to t 1 , the oxygen storage amount OSAsc decreases beyond the lower limit storage amount. Also at this time, since the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 is a rich air-fuel ratio, the NOx emission amount from the upstream side exhaust purification catalyst 20 is suppressed.
- the control of the air-fuel ratio correction amount AFC is performed by the ECU 31. Therefore, the ECU 31 determines that the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20 is equal to the determination reference storage amount Cref when the air-fuel ratio of the exhaust gas detected by the downstream air-fuel ratio sensor 41 becomes equal to or less than the rich determination air-fuel ratio.
- the oxygen storage amount increasing means for continuously setting the target air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 to the lean set air-fuel ratio and the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20 are determined as the reference storage. When the amount Cref is equal to or greater than the amount Cref, the oxygen storage amount decreases continuously so that the target air-fuel ratio decreases toward zero without exceeding the maximum oxygen storage amount Cmax. Means.
- the NOx emission amount from the upstream side exhaust purification catalyst 20 can always be suppressed. That is, as long as the above-described control is performed, the NOx emission amount from the upstream side exhaust purification catalyst 20 can be basically reduced.
- the oxygen storage amount OSAsc when the oxygen storage amount OSAsc is estimated based on the sensor output current Iupup of the upstream air-fuel ratio sensor 40 and the estimated value of the intake air amount, an error may occur. Also in this embodiment, since the oxygen storage amount OSAsc is estimated from time t 3 to t 4 , the estimated value of the oxygen storage amount OSAsc includes some errors. However, even if such an error is included, if the reference storage amount Cref is set sufficiently lower than the maximum oxygen storage amount Cmax or the upper limit storage amount, the actual oxygen storage amount OSAsc will be the maximum oxygen storage amount. The amount Cmax and the upper limit storage amount are hardly reached. Therefore, the NOx emission amount from the upstream side exhaust purification catalyst 20 can be suppressed also from such a viewpoint.
- the oxygen storage amount of the exhaust purification catalyst is kept constant, the oxygen storage capacity of the exhaust purification catalyst will be reduced.
- the oxygen storage amount OSAsc constantly fluctuates up and down, it is possible to suppress a decrease in the oxygen storage capacity.
- the downstream air-fuel ratio sensor 41 can accurately detect the absolute value at the rich determination air-fuel ratio.
- the conventional air-fuel ratio sensor it is difficult for the conventional air-fuel ratio sensor to accurately detect the absolute value of the air-fuel ratio other than the stoichiometric air-fuel ratio. For this reason, if an error occurs in the sensor output current due to deterioration over time or individual differences in the conventional air-fuel ratio sensor, even if the actual air-fuel ratio of the exhaust gas is different from the rich judgment air-fuel ratio, the sensor output of the air-fuel ratio sensor The current becomes a value corresponding to the rich determination air-fuel ratio.
- the switching timing of the air-fuel ratio correction amount AFC from the weak rich setting correction amount AFCrich to the lean setting correction amount AFClean is delayed, or such switching is performed at a timing that does not require switching.
- the downstream air-fuel ratio sensor 41 can accurately detect the absolute value at the rich determination air-fuel ratio. For this reason, it is possible to suppress a delay in the switching timing of the air-fuel ratio correction amount AFC from the weak rich setting correction amount AFCrich to the lean setting correction amount AFClean or switching at a timing that does not require switching.
- the air-fuel ratio correction amount AFC is maintained at the lean set correction amount AFClean from time t 2 to t 4 .
- the air-fuel ratio correction amount AFC does not necessarily have to be kept constant, and may be set so as to fluctuate, for example, gradually decrease.
- the air-fuel ratio correction amount AFC is maintained at the weak rich set correction amount AFrich.
- the air-fuel ratio correction amount AFC does not necessarily have to be kept constant, and may be set so as to fluctuate, for example, gradually decrease.
- the air-fuel ratio correction amount AFC is at time t 2 ⁇ t 4, the difference between the average value and the stoichiometric air-fuel ratio the target air-fuel ratio in the period, the target air at time t 4 ⁇ t 7 It is set to be larger than the difference between the average value of the fuel ratio and the stoichiometric air-fuel ratio.
- the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20 is estimated based on the sensor output current Iupup of the upstream side air-fuel ratio sensor 40 and the estimated value of the intake air amount into the combustion chamber 5. ing.
- the oxygen storage amount OSAsc may be calculated based on other parameters in addition to these parameters, or may be estimated based on parameters different from these parameters.
- the target air-fuel ratio is switched from the lean set air-fuel ratio to the slightly rich set air-fuel ratio.
- the timing at which the target air-fuel ratio is switched from the lean set air-fuel ratio to the weakly rich set air-fuel ratio is determined by other parameters such as the engine operation time after the target air-fuel ratio is switched from the weak rich set air-fuel ratio to the lean set air-fuel ratio. May be used as a reference.
- the target air-fuel ratio is changed from the lean set air-fuel ratio to the slightly rich set air-fuel ratio while the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20 is estimated to be smaller than the maximum oxygen storage amount. It is necessary to switch.
- a downstream side exhaust purification catalyst 24 is also provided.
- the oxygen storage amount OSAvemc of the downstream side exhaust purification catalyst 24 is set to a value in the vicinity of the maximum storage amount Cmax by fuel cut control performed every certain period. For this reason, even if exhaust gas containing unburned gas flows out from the upstream side exhaust purification catalyst 20, these unburned gas is oxidized and purified in the downstream side exhaust purification catalyst 24.
- the fuel cut control is a control that does not inject fuel from the fuel injection valve 11 even when the crankshaft or the piston 3 is moving, for example, during deceleration of a vehicle equipped with an internal combustion engine. .
- This control is performed, a large amount of air flows into both exhaust purification catalysts 20, 24.
- FIG. 16 is a diagram similar to FIG. 15, and instead of the transition of the NOx concentration in FIG. 15, the oxygen storage amount OSAvemc of the downstream side exhaust purification catalyst 24 and the exhaust gas in the exhaust gas flowing out from the downstream side exhaust purification catalyst 24 are not shown. It shows the transition of the concentration of fuel gas (HC, CO, etc.). In the example shown in FIG. 16, the same control as in the example shown in FIG. 15 is performed.
- fuel cut control is performed before time t 1 .
- the oxygen storage amount OSAvemc the downstream exhaust purifying catalyst 24 has a value of the maximum oxygen storage amount Cmax vicinity.
- the air-fuel ratio of the exhaust gas flowing out from the upstream side exhaust purification catalyst 20 is maintained substantially at the stoichiometric air-fuel ratio. For this reason, the oxygen storage amount OSAvemc of the downstream side exhaust purification catalyst 24 is kept constant.
- unburned gas flows out from the upstream side exhaust purification catalyst 20 at a certain time interval as in the case of time t 1 to t 4 .
- the unburned gas flowing out in this manner is basically reduced and purified by oxygen stored in the downstream side exhaust purification catalyst 24. Therefore, the unburned gas hardly flows out from the downstream side exhaust purification catalyst 24.
- the amount of unburned gas and NOx discharged from the downstream side exhaust purification catalyst 24 is reduced. Always less.
- FIG. 17 which is a functional block diagram
- the control device in the present embodiment is configured to include the functional blocks A1 to A9.
- each functional block will be described with reference to FIG.
- the in-cylinder intake air amount calculation means A1 includes an intake air flow rate Ga measured by the air flow meter 39, an engine speed NE calculated based on the output of the crank angle sensor 44, and a map stored in the ROM 34 of the ECU 31 or Based on the calculation formula, the intake air amount Mc to each cylinder is calculated.
- the basic fuel injection amount calculation means A2 divides the in-cylinder intake air amount Mc calculated by the in-cylinder intake air amount calculation means A1 by the target air-fuel ratio AFT calculated by the target air-fuel ratio setting means A6 described later.
- An injection instruction is issued to the fuel injection valve 11 so that the fuel of the fuel injection amount Qi calculated in this way is injected from the fuel injection valve 11.
- the oxygen storage amount calculation means A4 is an estimated value of the oxygen storage amount of the upstream side exhaust purification catalyst 20 based on the fuel injection amount Qi calculated by the fuel injection amount calculation means A3 and the sensor output current Iupp of the upstream side air-fuel ratio sensor 40. OSAest is calculated. For example, the oxygen storage amount calculation means A4 multiplies the difference between the air-fuel ratio corresponding to the sensor output current Iupup of the upstream air-fuel ratio sensor 40 and the theoretical air-fuel ratio by the fuel injection amount Qi and integrates the obtained value. Is used to calculate an estimated value OSAest of the oxygen storage amount. The estimation of the oxygen storage amount of the upstream side exhaust purification catalyst 20 by the oxygen storage amount calculation means A4 may not always be performed.
- the oxygen storage amount estimated value OSAest reaches the determination reference storage amount Cref (in FIG. 15).
- the oxygen storage amount may be estimated only until the time t 4 ).
- the target air-fuel ratio air- A fuel ratio correction amount AFC is calculated. Specifically, the air-fuel ratio correction amount AFC is set to the lean set correction amount AFClean when the sensor output current Ipdwn of the downstream air-fuel ratio sensor 41 becomes zero (a value corresponding to the rich determination air-fuel ratio) or less. . Thereafter, the air-fuel ratio correction amount AFC is maintained at the lean set correction amount AFClean until the estimated value OSAest of the oxygen storage amount reaches the determination reference storage amount Cref.
- the air-fuel ratio correction amount AFC is set to the weak rich set correction amount AFCrich. Thereafter, the air-fuel ratio correction amount AFC is maintained at the weak rich set correction amount AFCrich until the sensor output current Ipdwn of the downstream air-fuel ratio sensor 41 becomes zero or less.
- the target air-fuel ratio setting means A6 adds the air-fuel ratio correction amount AFC calculated by the target air-fuel ratio correction amount calculation means A5 to the reference air-fuel ratio, in this embodiment, the theoretical air-fuel ratio AFR, so that the target air-fuel ratio is set. AFT is calculated. Therefore, the target air-fuel ratio AFT is a slightly rich set air-fuel ratio that is slightly richer than the stoichiometric air-fuel ratio AFR (when the air-fuel ratio correction amount AFC is the weak rich set correction amount AFCrich) or is somewhat higher than the stoichiometric air-fuel ratio AFR. One of the lean set air-fuel ratios (when the air-fuel ratio correction amount AFC is the lean set correction amount AFClean). The target air-fuel ratio AFT calculated in this way is input to the basic fuel injection amount calculating means A2 and an air-fuel ratio difference calculating means A8 described later.
- FIG. 18 is a flowchart showing a control routine for calculation control of the air-fuel ratio correction amount AFC.
- the illustrated control routine is performed by interruption at regular time intervals.
- step S11 it is determined whether or not a calculation condition for the air-fuel ratio correction amount AFC is satisfied.
- the case where the calculation condition of the air-fuel ratio correction amount is satisfied includes, for example, that fuel cut control is not being performed. If it is determined in step S11 that the target air-fuel ratio calculation condition is satisfied, the process proceeds to step S12.
- step S12 the sensor output current Iupup of the upstream air-fuel ratio sensor 40, the sensor output current Ipdwn of the downstream air-fuel ratio sensor 41, and the fuel injection amount Qi are acquired.
- step S13 an estimated value OSAest of the oxygen storage amount is calculated based on the sensor output current Iupup and the fuel injection amount Qi of the upstream air-fuel ratio sensor 40 acquired in step S12.
- step S14 it is determined whether or not the lean setting flag Fr is set to zero.
- the lean setting flag Fr is set to 1 when the air-fuel ratio correction amount AFC is set to the lean setting correction amount AFClean, and is set to 0 otherwise. If the lean setting flag Fr is set to 0 in step S14, the process proceeds to step S15.
- step S15 it is determined whether or not the sensor output current Ipdwn of the downstream air-fuel ratio sensor 41 is equal to or less than zero. If it is determined that the sensor output current Ipdwn of the downstream air-fuel ratio sensor 41 is greater than zero, the control routine is terminated.
- the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20 decreases and the air-fuel ratio of the exhaust gas flowing out from the upstream side exhaust purification catalyst 20 decreases
- the sensor output current of the downstream side air-fuel ratio sensor 41 in step S15 It is determined that Ipdwn is less than or equal to zero. In this case, the process proceeds to step S16, and the air-fuel ratio correction amount AFC is set to the lean set correction amount AFClean.
- the lean setting flag Fr is set to 1, and the control routine is ended.
- step S14 it is determined in step S14 that the lean setting flag Fr is not set to 0, and the process proceeds to step S18.
- step S18 it is determined whether or not the estimated value OSAest of the oxygen storage amount calculated in step S13 is smaller than the determination reference storage amount Cref.
- the routine proceeds to step S19, where the air-fuel ratio correction amount AFC is continuously set to the lean set correction amount AFClean.
- step S18 when the oxygen storage amount of the upstream side exhaust purification catalyst 20 increases, it is determined in step S18 that the estimated value OSAest of the oxygen storage amount is equal to or greater than the determination reference storage amount Cref, and the process proceeds to step S20.
- step S20 the air-fuel ratio correction amount AFC is set to the weak rich setting correction amount AFCrich.
- step S21 the lean setting flag Fr is reset to 0, and the control routine is ended.
- the numerical value conversion means A7 is based on the sensor output current Iupup of the upstream air-fuel ratio sensor 40 and a map or calculation formula that defines the relationship between the sensor output current Iupup of the air-fuel ratio sensor 40 and the air-fuel ratio.
- An upstream exhaust air-fuel ratio AFup corresponding to is calculated. Therefore, the upstream side exhaust air-fuel ratio AFup corresponds to the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20.
- This air-fuel ratio difference DAF is a value that represents the excess or deficiency of the fuel supply amount with respect to the target air-fuel ratio AFT.
- the F / B correction amount calculation means A9 supplies fuel based on the following equation (1) by subjecting the air-fuel ratio difference DAF calculated by the air-fuel ratio difference calculation means A8 to proportional / integral / differential processing (PID processing). An F / B correction amount DFi for compensating for the excess or deficiency of the amount is calculated. The F / B correction amount DFi calculated in this way is input to the fuel injection amount calculation means A3.
- DFi Kp / DAF + Ki / SDAF + Kd / DDAF (1)
- Kp is a preset proportional gain (proportional constant)
- Ki is a preset integral gain (integral constant)
- Kd is a preset differential gain (differential constant).
- DDAF is a time differential value of the air-fuel ratio difference DAF, and is calculated by dividing the difference between the air-fuel ratio difference DAF updated this time and the air-fuel ratio difference DAF updated last time by the time corresponding to the update interval. Is done.
- the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 is detected by the upstream side air-fuel ratio sensor 40.
- this exhaust gas is based on the fuel injection amount from the fuel injection valve 11 and the output of the air flow meter 39. You may make it estimate the air fuel ratio of gas.
- a control device for an internal combustion engine according to a second embodiment of the present invention will be described with reference to FIG.
- the configuration and control of the internal combustion engine control device according to the second embodiment are basically the same as the configuration and control of the internal combustion engine control device according to the first embodiment.
- the air-fuel ratio correction amount AFC is set to the weak rich set correction amount AFCrich, the air-fuel ratio correction amount AFC is over a short time at certain time intervals.
- the value temporarily corresponds to the lean air-fuel ratio (for example, a lean set correction amount AFClean). That is, in the control device of the present embodiment, even when the target air-fuel ratio is the weak rich set air-fuel ratio, the lean air-fuel ratio is temporarily reduced over a short period of time at a certain time interval.
- the fuel ratio is set.
- FIG. 19 is a diagram similar to FIG. 15, and times t 1 to t 7 in FIG. 19 show the same control timing as times t 1 to t 7 in FIG. Therefore, also in the control shown in FIG. 19, the same control as the control shown in FIG. 15 is performed at each timing from time t 1 to time t 7 .
- the control shown in FIG. 19 during the time t 4 to t 7 , that is, while the air-fuel ratio correction amount AFC is set to the weak rich set correction amount AFCrich, the control is temporarily performed for a plurality of times.
- the fuel ratio correction amount AFC is set to the lean set correction amount AFClean.
- the air-fuel ratio correction amount AFC is a lean set correction amount AFClean over a short time from the time t 8. Since the delays in the change in the air-fuel ratio as described above, the air-fuel ratio of the exhaust gas flowing into the upstream exhaust purification catalyst 20 is a lean air-fuel ratio over a short time from the time t 9. Thus, when the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 becomes the lean air-fuel ratio, the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20 temporarily increases during that time.
- the air-fuel ratio correction amount AFC is a lean set correction amount AFClean even over a short period of time at time t 10. Accordingly, the air-fuel ratio of the exhaust gas flowing into the upstream exhaust purification catalyst 20 is a lean air-fuel ratio over the time t 11 in a short time, during which, the oxygen storage amount OSAsc the upstream exhaust purification catalyst 20 Increases temporarily.
- the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20 is temporarily increased or the oxygen storage amount OSAsc. Can be temporarily reduced. Therefore, according to this embodiment, switch the air-fuel ratio correction quantity AFC weak rich set correction amount AFCrich at time t 4, the sensor output current Ipdwn of the downstream air-fuel ratio sensor 41 is zero at time t 7 (rich It is possible to lengthen the time until it reaches a value corresponding to the determination air-fuel ratio.
- the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20 becomes near zero, and the timing at which unburned gas flows out of the upstream side exhaust purification catalyst 20 can be delayed. Thereby, the outflow amount of unburned gas from the upstream side exhaust purification catalyst 20 can be reduced.
- the air-fuel ratio correction amount AFC is basically set to the weak rich set correction amount AFCrich (time t 4 to t 7 )
- the air-fuel ratio correction amount AFC is temporarily changed to the lean set correction amount.
- AFClean When the air-fuel ratio correction amount AFC is temporarily changed in this way, it is not always necessary to change the air-fuel ratio correction amount AFC to the lean set correction amount AFClean, and any value that is leaner than the weak rich set correction amount AFCrich is used. You may change to an air fuel ratio.
- the air-fuel ratio correction amount AFC is basically set to the lean set correction amount AFClean (time t 2 to t 4 )
- the air-fuel ratio correction amount AFC may be temporarily set to the weak rich set correction amount AFCrich.
- the air-fuel ratio correction amount AFC may be changed to any air-fuel ratio as long as it is richer than the lean set correction amount AFClean.
- the air-fuel ratio correction amount AFC at times t 2 to t 4 is such that the difference between the average value of the target air-fuel ratio and the theoretical air-fuel ratio in the period is the target air-fuel ratio at times t 4 to t 7 . Is set so as to be larger than the difference between the average value and the theoretical air-fuel ratio.
- the ECU 31 detects that the upstream side when the air-fuel ratio of the exhaust gas detected by the downstream side air-fuel ratio sensor 41 becomes equal to or lower than the rich determination air-fuel ratio.
- the oxygen storage is performed to make the target air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 continuously or intermittently the lean set air-fuel ratio.
- the oxygen storage amount OSAsc of the amount increasing means and the upstream side exhaust purification catalyst 20 becomes equal to or larger than the determination reference storage amount Cref
- the oxygen storage amount OSAsc decreases toward zero without reaching the maximum oxygen storage amount Cmax.
- an oxygen storage amount reducing means for continuously or intermittently setting the target air-fuel ratio to a slightly rich set air-fuel ratio.
- control device for an internal combustion engine according to a third embodiment of the present invention will be described with reference to FIG.
- the configuration of the control device for the internal combustion engine according to the third embodiment is basically the same as the configuration and control of the control device for the internal combustion engine according to the above embodiment.
- a diffusion rate limiting layer is provided around the gas chamber side electrode of the reference cell of the air-fuel ratio sensor.
- FIG. 20 is a cross-sectional view similar to FIG. 3, schematically showing the configuration of the upstream air-fuel ratio sensor 80 and the downstream sensor 81 of the third embodiment.
- the air-fuel ratio sensors 80, 81 have a reference cell diffusion rate limiting layer 82 provided in the measured gas chamber 51.
- the reference cell diffusion control layer 82 is disposed so as to surround the gas chamber side electrode 57 of the reference cell 61. Therefore, the gas chamber side electrode 57 is exposed to the gas chamber 51 to be measured via the diffusion limiting layer 82 for the reference cell.
- the exhaust gas flowing around the gas chamber side electrode 57 can be diffusion controlled.
- the relationship among the exhaust air-fuel ratio, the sensor applied voltage Vr, and the reference cell output current Ir is as shown in FIGS.
- the absolute value of the air-fuel ratio different from the stoichiometric air-fuel ratio may not be detected properly.
- the absolute value of the air-fuel ratio different from the stoichiometric air-fuel ratio is more reliably detected by sufficiently diffusion-limiting the exhaust gas flowing around the reference cell diffusion-controlling layer 82 gas chamber side electrode 57. be able to.
- the diffusion limiting layer 82 for the reference cell when the diffusion limiting layer 82 for the reference cell is provided around the gas chamber side electrode 57, the diffusion limiting layer 63 that defines the gas chamber 51 to be measured is not necessarily provided. Therefore, instead of the diffusion-controlling layer 63, a layer or a small hole that restricts the inflow of exhaust gas into the measured gas chamber 51 may be provided. In any case, the diffusion rate-limiting layer may be arranged at any position as long as the exhaust gas reaches the gas chamber side electrode 57 via the diffusion rate-limiting layer.
- the oxygen storage amount of the exhaust purification catalyst is described as changing between the maximum oxygen storage amount and zero. This means that the amount of oxygen that can be further stored by the exhaust purification catalyst varies between zero (when the oxygen storage amount is the maximum oxygen storage amount) and the maximum value (when the oxygen storage amount is zero). Means.
Abstract
Description
図1を参照すると1は機関本体、2はシリンダブロック、3はシリンダブロック2内で往復動するピストン、4はシリンダブロック2上に固定されたシリンダヘッド、5はピストン3とシリンダヘッド4との間に形成された燃焼室、6は吸気弁、7は吸気ポート、8は排気弁、9は排気ポートをそれぞれ示す。吸気弁6は吸気ポート7を開閉し、排気弁8は排気ポート9を開閉する。
次に、図3を参照して、本実施形態における空燃比センサ40、41の構成について説明する。図3は、空燃比センサ40、41の概略的な断面図である。図3から分かるように、本実施形態における空燃比センサ40、41は、固体電解質層及び一対の電極から成るセルが2つである2セル型の空燃比センサである。
次に、図4を参照して、このように構成された空燃比センサ40、41の動作の基本的な概念について説明する。図4は、空燃比センサ40、41の動作を概略的に示した図である。使用時において、空燃比センサ40、41は、保護層66及び拡散律速層63の外周面が排気ガスに曝されるように配置される。また、空燃比センサ40、41の基準ガス室52には大気が導入される。
上述したように、基準セル61では、被測ガス室51内の排気空燃比がリッチ判定空燃比であるときには電極57、58間に流れる基準セル出力電流が零になり、被測ガス室51内の排気空燃比がリッチ判定空燃比とは異なる空燃比となったときにはその排気空燃比に応じて基準セル出力電流が変化する。以下では、図6を参照して基準セル61の動作の基本的な概念について説明する。図6は、基準セル61の動作を概略的に示した図である。使用時においては、上述したように、被測ガス室51には拡散律速層63を介して排気ガスが導入され、基準ガス室52には大気が導入される。また、図3及び図6に示したように、空燃比センサ40、41では、基準側電極58が正極性、ガス室側電極57が負極性となるように、これら電極57、58間に一定のセンサ印加電圧Vrが印加されている。
ところで、本発明者らが鋭意研究を行ったところ、基準セル61におけるセンサ印加電圧Vrと基準セル出力電流Irとの関係や、排気空燃比と基準セル出力電流Irとの関係を理論空燃比近傍で微視的に見ると図7及び図8のようになることを見出した。
ところで、上述したように、センサ印加電圧Vrを変化させることにより、電流零時の排気空燃比を変化させることができる。しかしながら、センサ印加電圧Vrを或る上限電圧よりも大きくするか又は或る下限電圧よりも小さくすると、センサ印加電圧Vrの変化量に対する電流零時の排気空燃比の変化量が大きくなる。したがって、斯かる電圧領域では、センサ印加電圧Vrが僅かにずれると、電流零時の排気空燃比が大きく変化してしまう。したがって、斯かる電圧領域では、排気空燃比の絶対値を正確に検出するためには、センサ印加電圧Vrを精密に制御することが必要になり、あまり実用的ではない。このため、排気空燃比の絶対値を正確に検出する観点からは、センサ印加電圧Vrは或る上限電圧と或る下限電圧との間の「特定電圧領域」内の値とすることが必要になる。
本実施形態では、上述した微視的特性に鑑みて、上流側空燃比センサ40によって排気ガスの空燃比を検出するときには、上流側空燃比センサ40におけるセンサ印加電圧Vrupは、排気空燃比が理論空燃比(本実施形態では14.6)であるときに基準セル出力電流(及びセンサ出力電流)が零となるような一定電圧(例えば、0.45V)に固定される。換言すると、上流側空燃比センサ40では電流零時の排気空燃比が理論空燃比となるようにセンサ印加電圧Vrupが設定される。
図13に、基準セル電圧印加装置70及び基準セル出力電流検出装置71を構成する具体的な回路の一例を示す。図示した例では、酸素電池特性により生じる起電力をE、第二固体電解質層54の内部抵抗をRi、両電極57、58間の電位差をVsと表している。
E0=Vr+V0+IrR …(1)
ここで、V0はオフセット電圧(E0が負値とならないように印加しておく電圧であり、例えば3V)、Rは図13に示した抵抗の値である。
次に、本実施形態で用いられる排気浄化触媒20、24について説明する。上流側排気浄化触媒20及び下流側排気浄化触媒24は、いずれも同様な構成を有する。以下では、上流側排気浄化触媒20についてのみ説明するが、下流側排気浄化触媒24も同様な構成及び作用を有する。
次に、本発明の内燃機関の制御装置における空燃比制御の概要を説明する。本実施形態では、上流側空燃比センサ40のセンサ出力電流Ipupに基づいて上流側空燃比センサ40のセンサ出力電流(すなわち、上流側排気浄化触媒20に流入する排気ガスの空燃比)Ipupが目標空燃比に相当する値となるようにフィードバック制御が行われる。
図15を参照して、上述したような操作について具体的に説明する。図15は、本発明の内燃機関の制御装置における空燃比制御を行った場合における、上流側排気浄化触媒20の酸素吸蔵量OSAsc、下流側空燃比センサ41のセンサ出力電流Ipdwn、空燃比補正量AFC、上流側空燃比センサ40のセンサ出力電流Ipup、及び上流側排気浄化触媒20から流出する排気ガス中のNOx濃度のタイムチャートである。
また、本実施形態では、上流側排気浄化触媒20に加えて下流側排気浄化触媒24も設けられている。下流側排気浄化触媒24の酸素吸蔵量OSAufcは或る程度の期間毎に行われる燃料カット制御によって最大吸蔵量Cmax近傍の値とされる。このため、たとえ上流側排気浄化触媒20から未燃ガスを含んだ排気ガスが流出したとしても、これら未燃ガスは下流側排気浄化触媒24において酸化浄化される。
次に、図17及び図18を参照して、上記実施形態における制御装置について具体的に説明する。本実施形態における制御装置は、機能ブロック図である図17に示したように、A1~A9の各機能ブロックを含んで構成されている。以下、図17を参照しながら各機能ブロックについて説明する。
まず、燃料噴射量の算出について説明する。燃料噴射量の算出に当たっては、筒内吸入空気量算出手段A1、基本燃料噴射量算出手段A2、及び燃料噴射量算出手段A3が用いられる。
次に、目標空燃比の算出について説明する。目標空燃比の算出に当たっては、酸素吸蔵量算出手段A4、目標空燃比補正量算出手段A5、及び目標空燃比設定手段A6が用いられる。
再び図17に戻って、上流側空燃比センサ40のセンサ出力電流Ipupに基づいたF/B補正量の算出について説明する。F/B補正量の算出に当たっては、数値変換手段A7、空燃比差算出手段A8、F/B補正量算出手段A9が用いられる。
DFi=Kp・DAF+Ki・SDAF+Kd・DDAF …(1)
次に、図19を参照して、本発明の第二実施形態に係る内燃機関の制御装置について説明する。第二実施形態に係る内燃機関の制御装置の構成及び制御は、基本的に、第一実施形態に係る内燃機関の制御装置の構成及び制御と同様である。しかしながら、本実施形態の制御装置では、空燃比補正量AFCが弱リッチ設定補正量AFCrichとされている間においても、或る程度の時間間隔毎に、空燃比補正量AFCが短い時間に亘って一時的にリーン空燃比に相当する値(例えば、リーン設定補正量AFClean)とされる。すなわち、本実施形態の制御装置では、目標空燃比が弱リッチ設定空燃比とされている間においても、或る程度の時間間隔毎に、目標空燃比が短い時間に亘って一時的にリーン空燃比とされる。
次に、図20を参照して、本発明の第三実施形態に係る内燃機関の制御装置について説明する。第三実施形態に係る内燃機関の制御装置の構成は、基本的に、上記実施形態に係る内燃機関の制御装置の構成及び制御と同様である。ただし、本実施形態の制御装置では、空燃比センサの基準セルのガス室側電極周りに拡散律速層が設けられる。
6 吸気弁
8 排気弁
10 点火プラグ
11 燃料噴射弁
13 吸気枝管
15 吸気管
18 スロットル弁
19 排気マニホルド
20 上流側排気浄化触媒
21 上流側ケーシング
22 排気管
23 下流側ケーシング
24 下流側排気浄化触媒
31 ECU
39 エアフロメータ
40 上流側空燃比センサ
41 下流側空燃比センサ
Claims (17)
- 内燃機関の排気通路に設けられた空燃比センサと、該空燃比センサのセンサ出力電流に基づいて内燃機関を制御する機関制御装置とを具備する、内燃機関の制御装置において、
前記空燃比センサは、空燃比の検出対象である排気ガスが流入せしめられる被測ガス室と、該被測ガス室内の排気ガスの空燃比に応じて基準セル出力電流が変化する基準セルと、ポンプ電流に応じて前記被測ガス室内の排気ガスに対して酸素の汲み入れ及び汲み出しを行うポンプセルとを具備し、
前記基準セルは、前記被測ガス室内の排気ガスの空燃比に応じて基準セル出力電流が零となる印加電圧が変化すると共に、前記被測ガス室内の排気ガスの空燃比が理論空燃比であるときに当該基準セルにおける印加電圧を増大させるとこれに伴って基準セル出力電流が増大するように構成されており、
前記空燃比センサによって排気空燃比を検出するときには、前記基準セルにおける印加電圧は一定電圧に固定され、該一定電圧は、前記被測ガス室内の排気ガスの空燃比が理論空燃比であるときに基準セル出力電流が零となる電圧とは異なる電圧であって且つ前記被測ガス室内の排気ガスの空燃比が理論空燃比とは異なる空燃比であるときに基準セル出力電流が零となる電圧であり、
前記空燃比センサは、前記基準セル出力電流が零になるようにポンプ電流を制御するポンプ電流制御装置と、該ポンプ電流を前記センサ出力電流として検出するポンプ電流検出装置とを更に具備する、内燃機関の制御装置。 - 前記基準セルは、前記被測ガス室内の排気ガスに曝される第一電極と、基準雰囲気に曝される第二電極と、前記第一電極と前記第二電極との間に配置された固体電解質層とを具備し、
前記空燃比センサは、拡散律速層を更に具備し、該拡散律速層は排気ガスが当該拡散律速層を介して前記第一電極に到達するように配置される、請求項1に記載の内燃機関の制御装置。 - 前記拡散律速層は、前記被測ガス室内の排気ガスが当該拡散律速層を介して前記第一電極に到達するように配置される、請求項2に記載の内燃機関の制御装置。
- 前記基準セルは、各排気空燃比毎に前記基準セル出力電流が限界電流となる電圧領域である限界電流領域を有するように構成されており、
前記一定電圧は、排気空燃比が理論空燃比であるときの前記限界電流領域内の電圧である、請求項1~3のいずれか1項に記載の内燃機関の制御装置。 - 前記基準セルは、各排気空燃比毎に、前記印加電圧と基準セル出力電流との関係について、印加電圧の増大に比例して基準セル出力電流が増大する電圧領域である比例領域と、水の分解が発生したことによって印加電圧の変化に応じて基準セル出力電流が変化する電圧領域である水分解領域と、これら比例領域と水分解領域との間の電圧領域である中間領域とを有するように構成されており、
前記一定電圧は、排気空燃比が理論空燃比であるときの前記中間領域内の電圧である、請求項1~3のいずれか1項に記載の内燃機関の制御装置。 - 前記一定電圧は、排気空燃比が理論空燃比よりも1%高いときに基準セル出力電流が零となる電圧と、前記被測ガス室内の排気ガスの空燃比が理論空燃比よりも1%低いときに基準セル出力電流が零となる電圧との間の電圧とされる、請求項1~3のいずれか1項に記載の内燃機関の制御装置。
- 前記基準セルは、各排気空燃比毎に、前記印加電圧と基準セル出力電流との関係について、印加電圧が増大するにつれて第一の屈曲点まで基準セル出力電流が増大し、第一の屈曲点から印加電圧が増大するにつれて第二の屈曲点まで基準セル出力電流が増大し、第二の屈曲点から印加電圧が増大するにつれて基準セル出力電流が増大すると共に、第一の屈曲点と第二の屈曲点の間における電圧領域においては他の電圧領域よりも印加電圧の増加量に対する基準セル出力電流の増加量が小さくなるように構成されており、
前記一定電圧は、排気空燃比が理論空燃比であるときの前記第一の屈曲点及び第二の屈曲点との間の電圧とされる、請求項1~3のいずれか1項に記載の内燃機関の制御装置。 - 前記基準セルは、各排気空燃比毎に、印加電圧の増大に伴って基準セル出力電流が増大する電圧領域である電流増大領域と、前記拡散律速層を設けたことにより印加電圧の増加量に対する基準セル出力電流の増加量が前記電流増大領域よりも小さくなる電圧領域である電流微増領域とを有し、
前記一定電圧は、排気空燃比が理論空燃比であるときの前記電流微増領域内の電圧である、請求項2又は3に記載の内燃機関の制御装置。 - 前記拡散律速層はアルミナで形成され、
前記一定電圧が、0.1V以上0.9V以下とされる、請求項2又は3に記載の内燃機関の制御装置。 - 前記機関制御装置は、前記空燃比センサのセンサ出力電流が零になったときに排気空燃比が理論空燃比とは異なる予め定められた空燃比であると判断する、請求項1~9のいずれか1項に記載の内燃機関の制御装置。
- 前記内燃機関は、前記空燃比センサよりも排気流れ方向上流側において前記排気通路に設けられた酸素を吸蔵可能な排気浄化触媒を具備し、
前記一定電圧は、排気空燃比が理論空燃比よりもリッチである所定のリッチ判定空燃比であるときに前記基準セル出力電流が零になるような電圧とされる、請求項1~10のいずれか1項に記載の内燃機関の制御装置。 - 前記機関制御装置は、前記排気浄化触媒に流入する排気ガスの空燃比を制御可能であり、前記空燃比センサのセンサ出力電流が零以下になったときには前記排気浄化触媒に流入する排気ガスの目標空燃比が理論空燃比よりもリーンとされる、請求項11に記載の内燃機関の制御装置。
- 前記機関制御装置は、前記空燃比センサのセンサ出力電流が零以下となったときに、前記排気浄化触媒の酸素吸蔵量が最大酸素吸蔵量よりも少ない所定の吸蔵量となるまで、前記排気浄化触媒に流入する排気ガスの目標空燃比を継続的又は断続的に理論空燃比よりもリーンにする酸素吸蔵量増加手段と、前記排気浄化触媒の酸素吸蔵量が前記所定の吸蔵量以上になったときに、該酸素吸蔵量が最大酸素吸蔵量に達することなく零に向けて減少するように、前記目標空燃比を継続的又は断続的に理論空燃比よりもリッチにする酸素吸蔵量減少手段とを具備する、請求項12に記載の内燃機関の制御装置。
- 前記酸素吸蔵量増加手段によって継続的又は断続的に理論空燃比よりもリーンにされている期間における前記目標空燃比の平均値と理論空燃比との差は、前記酸素吸蔵量減少手段によって継続的又は断続的に理論空燃比よりもリッチにされている期間における前記目標空燃比と理論空燃比との差よりも大きい、請求項13に記載の内燃機関の制御装置。
- 当該内燃機関の制御装置は、前記排気浄化触媒よりも排気流れ方向上流側において機関排気通路に設けられた上流側空燃比センサを具備し、
前記機関制御装置は上流側空燃比センサの出力に基づいて前記排気浄化触媒に流入する排気ガスの空燃比が目標空燃比となるように排気空燃比を制御する、請求項11~14のいずれか1項に記載の内燃機関の制御装置。 - 前記上流側空燃比センサは、排気空燃比に応じてセンサ出力電流が零となる印加電圧が変化すると共に、排気空燃比が理論空燃比であるときに当該上流側空燃比センサにおける印加電圧を増大させるとこれに伴ってセンサ出力電流が増大するように構成されており、
前記上流側空燃比センサにおける印加電圧は、前記空燃比センサの印加電圧よりも低い、請求項15に記載の内燃機関の制御装置。 - 前記上流側空燃比センサによって排気空燃比を検出するときには、前記上流側空燃比センサにおける印加電圧は一定電圧に固定され、該一定電圧は、前記被測ガス室内の排気ガスの空燃比が理論空燃比であるときにセンサ出力電流が零となる電圧とされる、請求項16に記載の内燃機関の制御装置。
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US (1) | US10001076B2 (ja) |
EP (1) | EP2952721B1 (ja) |
JP (1) | JP5949959B2 (ja) |
KR (1) | KR20150063555A (ja) |
CN (1) | CN104956058B (ja) |
AU (1) | AU2013376227B2 (ja) |
BR (1) | BR112015017838B1 (ja) |
RU (1) | RU2617423C2 (ja) |
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Families Citing this family (5)
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BR112015017838B1 (pt) | 2013-01-29 | 2021-10-19 | Toyota Jidosha Kabushiki Kaisha | Sistema de controle de motor de combustão interna |
CA2899221C (en) * | 2013-01-29 | 2018-05-15 | Toyota Jidosha Kabushiki Kaisha | Control system of internal combustion engine |
WO2014118894A1 (ja) * | 2013-01-29 | 2014-08-07 | トヨタ自動車株式会社 | 内燃機関の制御装置 |
JP6627396B2 (ja) * | 2015-10-09 | 2020-01-08 | トヨタ自動車株式会社 | 硫黄成分検出方法 |
JP6536341B2 (ja) * | 2015-10-09 | 2019-07-03 | トヨタ自動車株式会社 | 硫黄酸化物検出装置 |
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2013
- 2013-01-29 BR BR112015017838-3A patent/BR112015017838B1/pt not_active IP Right Cessation
- 2013-01-29 US US14/763,022 patent/US10001076B2/en active Active
- 2013-01-29 WO PCT/JP2013/051912 patent/WO2014118893A1/ja active Application Filing
- 2013-01-29 JP JP2014559392A patent/JP5949959B2/ja active Active
- 2013-01-29 AU AU2013376227A patent/AU2013376227B2/en not_active Ceased
- 2013-01-29 RU RU2015131027A patent/RU2617423C2/ru active
- 2013-01-29 EP EP13873938.8A patent/EP2952721B1/en not_active Not-in-force
- 2013-01-29 CN CN201380071606.8A patent/CN104956058B/zh not_active Expired - Fee Related
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Also Published As
Publication number | Publication date |
---|---|
AU2013376227A1 (en) | 2015-07-23 |
US10001076B2 (en) | 2018-06-19 |
BR112015017838B1 (pt) | 2021-10-19 |
US20150369156A1 (en) | 2015-12-24 |
EP2952721B1 (en) | 2018-03-21 |
CN104956058A (zh) | 2015-09-30 |
RU2015131027A (ru) | 2017-03-06 |
BR112015017838A2 (pt) | 2017-07-11 |
AU2013376227B2 (en) | 2016-05-12 |
CN104956058B (zh) | 2017-11-03 |
JPWO2014118893A1 (ja) | 2017-01-26 |
EP2952721A1 (en) | 2015-12-09 |
EP2952721A4 (en) | 2016-01-27 |
KR20150063555A (ko) | 2015-06-09 |
JP5949959B2 (ja) | 2016-07-13 |
RU2617423C2 (ru) | 2017-04-25 |
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