WO2014118888A1 - Dispositif de commande pour moteur à combustion interne - Google Patents

Dispositif de commande pour moteur à combustion interne Download PDF

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Publication number
WO2014118888A1
WO2014118888A1 PCT/JP2013/051907 JP2013051907W WO2014118888A1 WO 2014118888 A1 WO2014118888 A1 WO 2014118888A1 JP 2013051907 W JP2013051907 W JP 2013051907W WO 2014118888 A1 WO2014118888 A1 WO 2014118888A1
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Prior art keywords
fuel ratio
air
storage amount
purification catalyst
exhaust purification
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PCT/JP2013/051907
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English (en)
Japanese (ja)
Inventor
雄士 山口
中川　徳久
岡崎　俊太郎
圭一郎 青木
剛 林下
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トヨタ自動車株式会社
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Priority to PCT/JP2013/051907 priority Critical patent/WO2014118888A1/fr
Publication of WO2014118888A1 publication Critical patent/WO2014118888A1/fr

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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
    • 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
    • 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
    • G01N27/416—Systems
    • G01N27/417—Systems using cells, i.e. more than one cell and probes with solid electrolytes

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.
  • control devices for internal combustion engines are widely known in which an air-fuel ratio sensor is provided in the exhaust passage of the internal combustion engine and the amount of fuel supplied to the internal combustion engine is controlled based on the output of the air-fuel ratio sensor.
  • an upstream air-fuel ratio sensor provided upstream of the exhaust purification catalyst provided in the exhaust passage, and provided downstream of the exhaust purification catalyst in the exhaust flow direction.
  • a device having a downstream air-fuel ratio sensor is known (see, for example, Patent Documents 1 to 4).
  • the fuel injection amount is feedback controlled so that the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst becomes the target air-fuel ratio based on the output of the upstream air-fuel ratio sensor.
  • the target air-fuel ratio in the feedback control of the fuel injection amount is feedback-controlled based on the output of the downstream air-fuel ratio sensor.
  • the air-fuel ratio of the exhaust gas detected by the downstream air-fuel ratio sensor (hereinafter also referred to as “exhaust air-fuel ratio”) is richer than the stoichiometric air-fuel ratio (hereinafter referred to as “rich air-fuel ratio”).
  • the target air-fuel ratio is corrected to the lean side by a predetermined value.
  • the exhaust air-fuel ratio detected by the downstream air-fuel ratio sensor is leaner than the stoichiometric air-fuel ratio (hereinafter also referred to as “lean air-fuel ratio”)
  • the target air-fuel ratio is corrected to the rich side by a predetermined value.
  • the predetermined value is changed according to the catalyst capacity per unit exhaust gas amount, and is set to a smaller value as the exhaust gas amount increases, that is, as the catalyst capacity per unit exhaust gas amount decreases.
  • the control device described in Patent Document 1 when the predetermined value is set as described above, the target air-fuel ratio sensor based on the downstream air-fuel ratio sensor is slowed down when the response of the air-fuel ratio downstream of the catalyst is delayed. It is said that the response speed in the correction of the fuel ratio can be reduced. As a result, according to the control device described in Patent Document 1, the air-fuel ratio can be accurately controlled.
  • JP 2006-153026 A Japanese Patent Laid-Open No. 08-232723 JP 2009-162139 A JP 2001-234787 A
  • the performance required for the upstream air-fuel ratio sensor and the downstream air-fuel ratio sensor are different.
  • the upstream air-fuel ratio sensor is used for feedback control of the fuel injection amount so that the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst becomes the target air-fuel ratio based on the output. If the exhaust air-fuel ratio detection range is narrow at this time, the output of the air-fuel ratio sensor becomes constant when the exhaust air-fuel ratio becomes higher than a certain level or lower than a certain level. On the other hand, since the air-fuel ratio of the exhaust gas flowing out from the engine body and flowing into the exhaust purification catalyst fluctuates to some extent, if the detection range of the exhaust air-fuel ratio in the upstream side air-fuel ratio sensor is narrow, the air-fuel ratio sensor is appropriately The exhaust air / fuel ratio cannot be detected. Therefore, the upstream air-fuel ratio sensor is required to have a wide exhaust air-fuel ratio detection range.
  • the upstream air-fuel ratio sensor is exposed to the exhaust gas before flowing through the exhaust purification catalyst. That is, the upstream air-fuel ratio sensor is exposed to exhaust gas containing a large amount of unburned gas (HC, CO, etc.), NOx, oxygen, and the like. For this reason, the upstream sensor is also required to be resistant to deterioration even when exposed to such exhaust gas, that is, to have high durability.
  • the downstream air-fuel ratio sensor is required to have high detection accuracy of the exhaust air-fuel ratio. That is, NOx and unburned gas in the exhaust gas are basically purified by the exhaust purification catalyst, and oxygen in the exhaust gas is basically stored in the exhaust purification catalyst. For this reason, normally, only the exhaust gas having a substantially stoichiometric air-fuel ratio is discharged from the exhaust purification catalyst.
  • the downstream air-fuel ratio sensor is required to accurately detect when the exhaust gas discharged from the exhaust purification catalyst having such an action slightly deviates from the stoichiometric air-fuel ratio. Therefore, the downstream air-fuel ratio sensor is required to have high detection accuracy of the exhaust air-fuel ratio in the vicinity of a specific air-fuel ratio (in the case of Patent Document 1, near the theoretical air-fuel ratio).
  • an object of the present invention is to provide an internal combustion engine control device configured so that the upstream air-fuel ratio sensor and the downstream air-fuel ratio sensor sufficiently satisfy the requirements for each. .
  • an exhaust purification catalyst provided in an exhaust passage of an internal combustion engine, and an upstream side empty provided in the exhaust passage upstream of the exhaust purification catalyst in the exhaust flow direction.
  • An internal combustion engine based on an output of a fuel ratio sensor, a downstream air-fuel ratio sensor provided in the exhaust passage downstream of the exhaust purification catalyst in the exhaust flow direction, and an upstream air-fuel ratio sensor or downstream air-fuel ratio sensor;
  • the upstream air-fuel ratio sensor includes a measured gas chamber into which an exhaust gas to be detected is allowed to flow, and the measured gas according to a pump current.
  • a two-cell type air-fuel ratio sensor comprising: a pump current control device for controlling the pump current; and a pump current detection device for detecting the pump current as an output current of the upstream air-fuel ratio sensor.
  • the fuel ratio sensor is disposed between the first electrode exposed to the exhaust gas to be detected through the diffusion rate limiting layer, the second electrode exposed to the reference atmosphere, and the first electrode and the second electrode.
  • a solid electrolyte layer a voltage applying device that applies a voltage between the first electrode and the second electrode, and a current flowing between the first electrode and the second electrode that flows the downstream air-fuel ratio
  • a control device for an internal combustion engine which is a one-cell air-fuel ratio sensor including a current detection device that detects the output current of the sensor.
  • the engine control device is configured such that the exhaust gas flowing into the exhaust purification catalyst is emptied so that an output current of the upstream air-fuel ratio sensor becomes a value corresponding to a target air-fuel ratio.
  • the target air-fuel ratio is controlled to be an air-fuel ratio different from the stoichiometric air-fuel ratio.
  • the target air-fuel ratio is alternately switched between an air-fuel ratio richer than the stoichiometric air-fuel ratio and an air-fuel ratio leaner than the stoichiometric air-fuel ratio.
  • the engine control device is configured such that the air-fuel ratio corresponding to the output current of the downstream air-fuel ratio sensor deviates from the stoichiometric air-fuel ratio and a difference from the stoichiometric air-fuel ratio is predetermined.
  • the target air-fuel ratio is set to an air-fuel ratio that deviates from the stoichiometric air-fuel ratio in a direction opposite to the direction in which the air-fuel ratio corresponding to the output current of the downstream air-fuel ratio sensor deviates from the stoichiometric air-fuel ratio To do.
  • the judgment reference difference is a value within 1% of the theoretical air-fuel ratio.
  • the target air-fuel ratio is set such that a difference from the theoretical air-fuel ratio is larger than the determination reference difference.
  • the engine control device is configured such that the air-fuel ratio corresponding to the output current of the downstream air-fuel ratio sensor is richer than the stoichiometric air-fuel ratio by a determination reference difference.
  • the target air-fuel ratio is theoretically or intermittently maintained until the oxygen storage amount of the exhaust purification catalyst becomes a predetermined storage amount smaller than the maximum oxygen storage amount when the air-fuel ratio becomes less than the rich determination air-fuel ratio.
  • the oxygen storage amount of the exhaust purification catalyst becomes equal to or greater than the predetermined storage amount, the oxygen storage amount becomes zero without reaching the maximum oxygen storage amount.
  • the time average value of the target air-fuel ratio and the stoichiometric air-fuel ratio in a period in which the oxygen storage amount increasing means is continuously or intermittently made leaner than the stoichiometric air-fuel ratio. Is larger than the difference between the time average value of the target air-fuel ratio and the stoichiometric air-fuel ratio during a period in which the oxygen storage amount reducing means continuously or intermittently enriches the oxygen storage amount.
  • the engine control device is configured such that an air-fuel ratio corresponding to an output current of the downstream air-fuel ratio sensor is leaner than a stoichiometric air-fuel ratio by a determination reference difference.
  • the oxygen storage amount of the exhaust purification catalyst becomes a predetermined storage amount greater than zero, the target air-fuel ratio is continuously or intermittently reduced from the stoichiometric air-fuel ratio.
  • the oxygen storage amount reducing means for increasing the oxygen storage amount, and when the oxygen storage amount of the exhaust purification catalyst falls below the predetermined storage amount, the oxygen storage amount increases toward the maximum oxygen storage amount without reaching zero.
  • an oxygen storage amount increasing means for making the target air-fuel ratio leaner than the stoichiometric air-fuel ratio continuously or intermittently.
  • the engine control device has a value corresponding to a rich determination air-fuel ratio in which an output current of the downstream air-fuel ratio sensor is richer than a theoretical air-fuel ratio.
  • the air-fuel ratio lean switching means for changing the target air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst to a lean set air-fuel ratio that is leaner than the stoichiometric air-fuel ratio, and the air-fuel ratio lean switching means After the target air-fuel ratio is changed, the target air-fuel ratio is set to the lean setting air-fuel ratio before the output current of the downstream-side air-fuel ratio sensor becomes equal to or greater than the value corresponding to the lean determination air-fuel ratio leaner than the stoichiometric air-fuel ratio.
  • the air-fuel ratio rich switching means for changing the target air-fuel ratio to a rich set air-fuel ratio richer than the stoichiometric air-fuel ratio, and after changing the target air-fuel ratio by the air-fuel ratio rich switching means, A rich air-fuel ratio that changes the target air-fuel ratio to a rich air-fuel ratio in which the difference from the stoichiometric air-fuel ratio is smaller than the rich set air-fuel ratio before the output current of the downstream air-fuel ratio sensor becomes equal to or less than the value corresponding to the rich determination air-fuel ratio.
  • Degree lowering means for changing the target air-fuel ratio to a rich set air-fuel ratio richer than the stoichiometric air-fuel ratio, and after changing the target air-fuel ratio by the air-fuel ratio rich switching means.
  • the reference cell of the upstream air-fuel ratio sensor includes a third electrode exposed to the exhaust gas in the measured gas chamber and a reference atmosphere.
  • the fourth electrode to be exposed, the solid electrolyte layer disposed between the third electrode and the fourth electrode, and the electromotive force between the third electrode and the fourth electrode are detected as the detected value.
  • a reference voltage detecting device a reference voltage detecting device.
  • a control device for an internal combustion engine configured so that the upstream air-fuel ratio sensor and the downstream air-fuel ratio sensor sufficiently satisfy the requirements for each.
  • 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 graph showing 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. 3 is a schematic cross-sectional view of the downstream air-fuel ratio sensor.
  • FIG. 4 is a diagram schematically showing the operation of the downstream air-fuel ratio sensor.
  • FIG. 5 is a diagram illustrating an example of a specific circuit constituting the voltage application device and the current detection device.
  • FIG. 6 is a diagram showing output characteristics of the downstream air-fuel ratio sensor.
  • FIG. 7 is a schematic cross-sectional view of the upstream air-fuel ratio sensor.
  • FIG. 8 is a diagram schematically showing the operation of the upstream air-fuel ratio sensor.
  • FIG. 9 is a diagram showing the relationship between the exhaust air-fuel ratio and the electromotive force in the reference cell.
  • FIG. 10 is a diagram showing the relationship between the control reference voltage and the output current in the upstream air-fuel ratio sensor.
  • FIG. 11 is a diagram for explaining hysteresis in the reference cell.
  • FIG. 12 is a time chart of the oxygen storage amount of the exhaust purification catalyst.
  • FIG. 13 is a time chart of the oxygen storage amount of the exhaust purification catalyst.
  • FIG. 14 is a functional block diagram of the control device.
  • FIG. 15 is a flowchart showing a control routine for calculation control of the air-fuel ratio correction amount.
  • FIG. 16 is a time chart of the oxygen storage amount of the exhaust purification catalyst.
  • FIG. 17 is a time chart of the oxygen storage amount of the exhaust purification catalyst.
  • FIG. 18 is a time chart of the oxygen storage amount of the exhaust purification catalyst.
  • FIG. 19 is a time chart of the oxygen storage amount of the exhaust purification catalyst.
  • 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.
  • the exhaust purification catalysts 20 and 24 are three-way catalysts having an oxygen storage capacity. Specifically, the exhaust purification catalysts 20 and 24 support 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 ceramic support. It has been made. When the exhaust purification catalysts 20 and 24 reach a predetermined activation temperature, the exhaust purification catalysts 20 and 24 exhibit an oxygen storage capability in addition to the catalytic action of simultaneously purifying unburned gas (HC, CO, etc.) and nitrogen oxides (NOx).
  • the exhaust purification catalysts 20, 24 are such that the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalysts 20, 24 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 exhaust purification catalysts 20, 24 release the oxygen stored in the exhaust purification catalysts 20, 24 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 exhaust purification catalysts 20 and 24 have a catalytic action and an oxygen storage capacity, and thus have a NOx and unburned gas purification action according to the oxygen storage amount. That is, as shown in FIG. 2A, when the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalysts 20, 24 is a lean air-fuel ratio, the exhaust gas is exhausted by the exhaust purification catalysts 20, 24 when the oxygen storage amount is small. The oxygen inside is occluded and NOx is reduced and purified. Further, when the oxygen storage amount increases, the concentrations of oxygen and NOx in the exhaust gas flowing out from the exhaust purification catalysts 20, 24 abruptly increase with the upper limit storage amount Cuplim as a boundary.
  • the exhaust purification catalysts 20, 24 store the oxygen when the oxygen storage amount is large. The released oxygen is released and the unburned gas in the exhaust gas is oxidized and purified. Further, when the oxygen storage amount decreases, the concentration of unburned gas in the exhaust gas flowing out from the exhaust purification catalysts 20 and 24 rapidly increases with the lower limit storage amount Clowlim as a boundary.
  • the purification characteristics of 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 are obtained. Change.
  • 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.
  • FIG. 3 is a schematic cross-sectional view of the downstream air-fuel ratio sensor 41.
  • the downstream air-fuel ratio sensor 41 in the present embodiment is a one-cell type air-fuel ratio sensor having one cell composed of a solid electrolyte layer and a pair of electrodes.
  • the downstream air-fuel ratio sensor 41 includes a solid electrolyte layer 51, an exhaust side electrode (first electrode) 52 disposed on one side surface of the solid electrolyte layer 51, and a solid electrolyte layer 51.
  • An atmosphere-side electrode (second electrode) 53 disposed on the other side surface, a diffusion-controlling layer 54 that performs diffusion-controlling the exhaust gas that passes through, a protective layer 55 that protects the diffusion-controlling layer 54, and a downstream space
  • a heater unit 56 that heats the fuel ratio sensor 41.
  • a diffusion-controlling layer 54 is provided on one side surface of the solid electrolyte layer 51, and a protective layer 55 is provided on the side surface of the diffusion-controlling layer 54 opposite to the side surface on the solid electrolyte layer 51 side.
  • a measured gas chamber 57 is formed between the solid electrolyte layer 51 and the diffusion-controlling layer 54.
  • a gas to be detected by the downstream air-fuel ratio sensor 41 that is, exhaust gas is introduced into the measured gas chamber 57 through the diffusion rate controlling layer 54.
  • the exhaust side electrode 52 is disposed in the measured gas chamber 57, and therefore, the exhaust side electrode 52 is exposed to the exhaust gas through the diffusion rate controlling layer 54.
  • the gas chamber 57 to be measured is not necessarily provided, and may be configured such that the diffusion-controlling layer 54 is in direct contact with the surface of the exhaust-side electrode 52.
  • a heater portion 56 is provided on the other side surface of the solid electrolyte layer 51.
  • a reference gas chamber 58 is formed between the solid electrolyte layer 51 and the heater portion 56, and the reference gas is introduced into the reference gas chamber 58.
  • the reference gas chamber 58 is open to the atmosphere, and therefore the atmosphere is introduced into the reference gas chamber 58 as the reference gas.
  • the atmosphere side electrode 53 is disposed in the reference gas chamber 58, and therefore, the atmosphere side electrode 53 is exposed to the reference gas (reference atmosphere). In the present embodiment, since the atmosphere is used as the reference gas, the atmosphere side electrode 53 is exposed to the atmosphere.
  • the heater unit 56 is provided with a plurality of heaters 59, and these heaters 59 can control the temperature of the downstream air-fuel ratio sensor 41, particularly the temperature of the solid electrolyte layer 51.
  • the heater unit 56 has a heat generation capacity sufficient to heat the solid electrolyte layer 51 until it is activated.
  • the solid electrolyte layer 51 is an oxygen ion conductive oxide in which ZrO 2 (zirconia), HfO 2 , ThO 2 , Bi 2 O 3, etc. are distributed with CaO, MgO, Y 2 O 3 , Yb 2 O 3 etc. as stabilizers.
  • the sintered body is formed.
  • the diffusion control layer 54 is formed of a porous sintered body of a heat-resistant inorganic substance such as alumina, magnesia, silica, spinel, mullite or the like.
  • the electrodes 52 and 53 are made of a noble metal having high catalytic activity such as platinum.
  • a sensor application voltage Vr is applied between the exhaust side electrode 52 and the atmosphere side electrode 53 by the voltage application device 60 mounted on the ECU 31.
  • the ECU 31 is provided with a current detection device 61 that detects a current (output current) flowing between the electrodes 52 and 53 via the solid electrolyte layer 51 when the sensor application voltage Vr is applied by the voltage application device 60. It is done.
  • the current detected by the current detector 61 is the output current of the downstream air-fuel ratio sensor 41.
  • FIG. 4 is a diagram schematically showing the operation of the downstream air-fuel ratio sensor 41.
  • the downstream air-fuel ratio sensor 41 is arranged so that the outer peripheral surfaces of the protective layer 55 and the diffusion-controlling layer 54 are exposed to the exhaust gas. Further, the atmosphere is introduced into the reference gas chamber 58 of the downstream air-fuel ratio sensor 41.
  • the solid electrolyte layer 51 is formed of a sintered body of an oxygen ion conductive oxide. Therefore, when a difference in oxygen concentration occurs between both side surfaces of the solid electrolyte layer 51 in a state activated by high temperature, an electromotive force E that attempts to move oxygen ions from the high concentration side surface to the low concentration side surface. Has a property (oxygen battery characteristics).
  • oxygen ions move so that an oxygen concentration ratio is generated between both side surfaces of the solid electrolyte layer according to the potential difference.
  • Characteristics oxygen pump characteristics. 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. Further, as shown in FIGS. 3 and 4, in the downstream air-fuel ratio sensor 41, a constant value is provided between the electrodes 52 and 53 so that the atmosphere-side electrode 53 is positive and the exhaust-side electrode 52 is negative. A sensor applied voltage Vr is applied.
  • the ratio of oxygen concentration between both side surfaces of the solid electrolyte layer 51 is small.
  • the sensor applied voltage Vr is set to an appropriate value, the actual oxygen concentration ratio becomes smaller between the both side surfaces of the solid electrolyte layer 51 than the oxygen concentration ratio corresponding to the sensor applied voltage Vr. Therefore, as shown in FIG. 4A, the oxygen concentration ratio between the both side surfaces of the solid electrolyte layer 51 increases from the exhaust side electrode 52 to the atmosphere so as to increase toward the oxygen concentration ratio corresponding to the sensor applied voltage Vr. Oxygen ions move toward the side electrode 53. As a result, a current flows from the positive electrode of the voltage application device 60 that applies the sensor application voltage Vr to the negative electrode of the voltage application device 60 via the atmosphere side electrode 53, the solid electrolyte layer 51, and the exhaust side electrode 52.
  • the magnitude of the current (output current) Ir flowing at this time is the amount of oxygen flowing into the measured gas chamber 57 from the exhaust gas through the diffusion rate controlling layer 54 if the sensor applied voltage Vr is set to an appropriate value. Is proportional to Therefore, by detecting the magnitude of the current Ir by the current detector 61, it is possible to know the oxygen concentration and thus the air-fuel ratio in the lean region.
  • the sensor applied voltage Vr is set to an appropriate value, the actual oxygen concentration ratio between the both side surfaces of the solid electrolyte layer 51 becomes larger than the oxygen concentration ratio corresponding to the sensor applied voltage Vr.
  • the exhaust gas is exhausted from the atmosphere side electrode 53 so that the oxygen concentration ratio between the both side surfaces of the solid electrolyte layer 51 decreases toward the oxygen concentration ratio corresponding to the sensor applied voltage Vr.
  • Oxygen ions move toward the side electrode 52.
  • a current flows from the atmosphere side electrode 53 to the exhaust side electrode 52 through the voltage application device 60 that applies the sensor application voltage Vr.
  • the magnitude of the current (output current) Ir flowing at this time is that of oxygen ions that can be moved from the atmosphere side electrode 53 to the exhaust side electrode 52 in the solid electrolyte layer 51 if the sensor applied voltage Vr is set to an appropriate value. It depends on the flow rate.
  • the oxygen ions react (combust) on the exhaust-side electrode 52 with the unburned gas that flows into the measured gas chamber 57 from the exhaust gas through the diffusion-controlling layer 54 by diffusion. 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 57. Therefore, by detecting the magnitude of the current Ir by the current detection device 61, it is possible to know the unburned gas concentration and thus the air-fuel ratio in the rich region.
  • the exhaust air-fuel ratio around the downstream air-fuel ratio sensor 41 is the stoichiometric air-fuel ratio
  • the amount of oxygen and unburned gas flowing into the measured gas chamber 57 is the chemical equivalent ratio.
  • both of them are completely combusted by the catalytic action of the exhaust side electrode 52, and the concentration of oxygen and unburned gas in the measured gas chamber 57 does not change.
  • the oxygen concentration ratio between the both side surfaces of the solid electrolyte layer 51 is not changed and is maintained as the oxygen concentration ratio corresponding to the sensor applied voltage Vr.
  • oxygen ions do not move due to the oxygen pump characteristics, and as a result, no current flows through the circuit.
  • FIG. 5 shows an example of a specific circuit constituting the voltage application device 60 and the current detection device 61.
  • E is an electromotive force generated by oxygen battery characteristics
  • Ri is an internal resistance of the solid electrolyte layer 51
  • Vs is a potential difference between the electrodes 52 and 53.
  • the voltage application device 60 basically performs negative feedback control so that the electromotive force E generated by the oxygen battery characteristics matches the sensor applied voltage Vr.
  • the voltage application device 60 becomes the sensor applied voltage Vr. Negative feedback control is performed.
  • the oxygen concentration ratio between the both side surfaces of the solid electrolyte layer 51 is determined by sensor application.
  • the oxygen concentration ratio corresponds to the voltage Vr.
  • the electromotive force E coincides with the sensor applied voltage Vr, and the potential difference Vs between the electrodes 52 and 53 is also the sensor applied voltage Vr. As a result, the current Ir does not flow.
  • the electromotive force E has a value different from the sensor applied voltage Vr. Therefore, by negative feedback control, a potential difference Vs is applied between the electrodes 52 and 53 in order to move oxygen ions between both side surfaces of the solid electrolyte layer 51 so that the electromotive force E matches the sensor applied voltage Vr. The And current Ir flows with the movement of oxygen ions at this time. As a result, the electromotive force E converges on the sensor applied voltage Vr, and when the electromotive force E converges on the sensor applied voltage Vr, the potential difference Vs eventually converges on the sensor applied voltage Vr.
  • the voltage application device 60 substantially applies the sensor application voltage Vr between the electrodes 52 and 53.
  • the electric circuit of the voltage applying device 60 is not necessarily as shown in FIG. 5, and any device can be used as long as the sensor applied voltage Vr can be substantially applied between the electrodes 52 and 53. It may be.
  • the current detector 61 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 value of the resistance 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 current detection device 61 substantially detects the current Ir flowing between the electrodes 52 and 53.
  • the electric circuit of the current detection device 61 does not necessarily have to be as shown in FIG. 5, and any device can be used as long as the current Ir flowing between the electrodes 52 and 53 can be detected. Good.
  • the downstream air-fuel ratio sensor 41 configured and operating as described above has a sensor applied voltage-current (VI) characteristic as shown in FIG. As can be seen from FIG. 6, when the sensor applied voltage Vr is gradually increased from a negative value when the exhaust air-fuel ratio is constant in the region where the sensor applied voltage Vr is 0 or less and in the vicinity of 0, As a result, the output current Ir increases.
  • Vr sensor applied voltage-current
  • the flow rate of oxygen ions that can move through the solid electrolyte layer 51 is small. For this reason, the flow rate of oxygen ions that can move through the solid electrolyte layer 51 is smaller than the inflow rate of the exhaust gas through the diffusion-controlling layer 54, so that the output current Ir can move through the solid electrolyte layer 51. It changes according to the flow rate of oxygen ions. Since the flow rate of oxygen ions that can move through the solid electrolyte layer 51 changes according to the sensor applied voltage Vr, the output current increases as the sensor applied voltage Vr increases. The reason why the output current Ir takes a negative value when the sensor applied voltage Vr is 0 is that an electromotive force E corresponding to the oxygen concentration ratio between the both side surfaces of the solid electrolyte layer 51 is generated due to oxygen battery characteristics.
  • the output current Ir changes according to the oxygen concentration or the unburned gas concentration in the exhaust gas flowing into the measured gas chamber 57 via the diffusion rate controlling layer 54. Even if the sensor applied voltage Vr is changed with the exhaust air-fuel ratio being constant, the oxygen concentration and the unburned gas concentration in the exhaust gas flowing into the measured gas chamber 57 via the diffusion-controlling layer 54 should basically not change. Therefore, the output voltage Ir does not change.
  • the output current Ir depends on the exhaust air / fuel ratio. Change. As can be seen from FIG. 6, the flow direction of the limit current is reversed between the lean air-fuel ratio and the rich air-fuel ratio, and the air-fuel ratio increases when the lean air-fuel ratio is increased, and the air-fuel ratio decreases when the air-fuel ratio is rich. The absolute value of the limit current increases.
  • the output current Ir begins to increase again accordingly.
  • the moisture contained in the exhaust gas is decomposed on the exhaust-side electrode 52, and a current flows accordingly. If the sensor applied voltage Vr is further increased, the solid electrolyte layer 51 is decomposed this time.
  • FIG. 7 is a schematic cross-sectional view of the upstream air-fuel ratio sensor 40.
  • the upstream air-fuel ratio sensor 40 in the present embodiment is a two-cell air-fuel ratio sensor having two cells each composed of a solid electrolyte layer and a pair of electrodes.
  • the upstream air-fuel ratio sensor 40 includes a measured gas chamber 81, a reference gas chamber 82, and two solid electrolyte layers 83 and 84 disposed on both sides of the measured gas chamber 81. It has.
  • the reference gas chamber 82 is provided on the opposite side of the measured gas chamber 81 with the second solid electrolyte layer 84 interposed therebetween.
  • a gas chamber side electrode (fifth electrode) 85 is disposed on the side surface of the first solid electrolyte layer 83 on the measured gas chamber 81 side, and an exhaust side electrode is disposed on the side surface of the first solid electrolyte layer 83 on the exhaust gas side. (Sixth electrode) 86 is arranged.
  • the first solid electrolyte layer 83, the gas chamber side electrode 85, and the exhaust side electrode 86 constitute a pump cell 90.
  • a gas chamber side electrode (third electrode) 87 is disposed on the side surface of the second solid electrolyte layer 84 on the measured gas chamber 81 side, and on the side surface of the second solid electrolyte layer 84 on the reference gas chamber 82 side.
  • a reference side electrode (fourth electrode) 88 is disposed.
  • the second solid electrolyte layer 84, the gas chamber side electrode 87 and the reference side electrode 88 constitute a reference cell 91.
  • a diffusion control layer 93 is provided so as to surround the gas chamber side electrode 85 of the pump cell 90 and the gas chamber side electrode 87 of the reference cell 91.
  • the measured gas chamber 81 is defined by the first solid electrolyte layer 83, the second solid electrolyte layer 84, and the diffusion-controlling layer 93. Exhaust gas is allowed to flow into the measured gas chamber 81 via the diffusion-controlling layer 93. Therefore, the electrodes arranged in the measured gas chamber 81, that is, the gas chamber side electrode 85 of the pump cell 90 and the gas chamber side electrode 87 of the reference cell 91 are exposed to the exhaust gas through the diffusion control layer 93. Become.
  • the diffusion control layer 93 is not necessarily provided so that the exhaust gas flowing into the measured gas chamber 81 passes therethrough. As long as the exhaust gas reaching the gas chamber side electrode 87 of the reference cell 91 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 94 is provided on the side surface of the second solid electrolyte layer 84 on the side of the reference gas chamber 82 so as to surround the reference gas chamber 82. Therefore, the reference gas chamber 82 is defined by the second solid electrolyte layer 84 and the heater unit 94.
  • a reference gas is introduced into the reference gas chamber 82.
  • the reference gas chamber 82 is filled with air.
  • the reference gas chamber 82 is not opened to the atmosphere, but may be opened to the atmosphere, or a gas different from the gas in the atmosphere may be used as the reference gas.
  • the heater unit 94 is provided with a plurality of heaters 95, and the heaters 95 can control the temperature of the upstream air-fuel ratio sensor 40, particularly the temperature of the solid electrolyte layers 83 and 84.
  • the heater section 94 has a heat generation capacity sufficient to heat the solid electrolyte layers 83 and 84 until they are activated.
  • a protective layer 96 is provided on the side surface of the first solid electrolyte layer 83 on the exhaust gas side.
  • the protective layer 96 is formed of a porous material so that the exhaust gas reaches the exhaust side electrode 86 while preventing liquid or the like in the exhaust gas from directly attaching to the exhaust side electrode 86.
  • the solid electrolyte layers 83 and 84 are formed of the same material as the solid electrolyte layer 51 of the downstream air-fuel ratio sensor 41.
  • the diffusion rate controlling layer 93 is also formed of the same material as the diffusion rate controlling layer 54 of the downstream air-fuel ratio sensor 41.
  • the electrodes 85 to 88 are also made of the same material as the electrodes 52 and 53 of the downstream air-fuel ratio sensor 41. Note that the diffusion-controlling layer 93 of the upstream air-fuel ratio sensor 40 does not necessarily have the same rate-controlling effect as the diffusion-controlling layer 54 (an effect that the speed of the exhaust gas flowing into the measured gas chamber becomes substantially constant). It does not have to be.
  • the ECU 31 includes an electromotive force detection device 100 connected to the gas chamber side electrode 87 and the reference side electrode 88.
  • the electromotive force detection device 100 detects an electromotive force generated between the electrodes 87 and 88.
  • a pump voltage Vp is applied between the gas chamber side electrode 85 and the exhaust side electrode 86 of the pump cell 90 by the pump voltage application device 101 mounted on the ECU 31.
  • the pump voltage Vp applied by the pump voltage application device 101 is set according to the electromotive force Ve detected by the electromotive force detection device 100.
  • the pump voltage Vp is set according to the difference between the electromotive force Ve detected by the electromotive force detection device 100 and a preset control reference voltage (0.45 V in this embodiment). .
  • the ECU 31 has a pump current detection device 102 that detects a pump current Ip flowing between the electrodes 85 and 86 via the first solid electrolyte layer 83 when the pump voltage Vp is applied by the pump voltage application device 101. Provided.
  • the pump voltage application device 101 changes the pump voltage Vp
  • the pump current Ip flowing between the electrodes 85 and 86 changes.
  • the pump voltage application device 101 controls the pump current Ip. Therefore, the pump voltage application device 101 functions as a pump current control device that controls the pump current Ip.
  • the pump current Ip is also changed by, for example, arranging a variable resistor in series with the pump voltage application device 101 and changing the variable resistor. Therefore, means other than the pump voltage application device 101 such as a variable resistor can be used as the pump current control device.
  • FIG. 8 is a diagram schematically showing the operation of the upstream air-fuel ratio sensor 40.
  • the upstream air-fuel ratio sensor 40 is arranged so that the outer peripheral surfaces of the protective layer 96 and the diffusion-controlling layer 93 are exposed to the exhaust gas. Further, the atmosphere is introduced into the reference gas chamber 82 of the upstream air-fuel ratio sensor 40.
  • the solid electrolyte layers 83 and 84 have oxygen battery characteristics and oxygen pump characteristics. Therefore, in the pump cell 90, when the pump voltage application device 101 applies the pump voltage Vp between the gas chamber side electrode 85 and the exhaust side electrode 86, oxygen ions move accordingly. Accompanying such movement of oxygen ions, oxygen is pumped into or pumped from the exhaust gas into the measured gas chamber 81.
  • the electromotive force Ve changes according to the oxygen concentration in the measured gas chamber 81. More precisely, in the reference cell 91, an electromotive force Ve corresponding to the ratio between the oxygen partial pressure in the measured gas chamber 81 and the oxygen partial pressure in the reference gas chamber 82 is generated. As a result, the relationship between the exhaust air-fuel ratio in the measured gas chamber 81 and the electromotive force Ve is as shown in FIG. That is, the electromotive force Ve changes greatly in the vicinity of the stoichiometric air-fuel ratio.
  • the electromotive force Ve increases, and conversely, the exhaust air in the measured gas chamber 81 increases.
  • the electromotive force Ve decreases. Therefore, for example, when the electromotive force Ve is higher than a predetermined voltage (for example, 0.45 V, hereinafter referred to as “control reference voltage”), the exhaust air-fuel ratio in the measured gas chamber 81 is the rich air-fuel ratio.
  • control reference voltage for example, 0.45 V, hereinafter referred to as “control reference voltage
  • the exhaust air-fuel ratio in the measured gas chamber 81 is the rich air-fuel ratio.
  • the electromotive force Ve is lower than the control reference voltage, it can be determined that the exhaust air-fuel ratio in the measured gas chamber 81 is a lean air-fuel ratio.
  • a pump voltage is applied to the electrodes 85 and 86 of the pump cell 90 by the pump voltage application device 101 based on this.
  • a pump voltage is applied using the exhaust side electrode 86 as a positive electrode and the gas chamber side electrode 85 as a negative electrode.
  • the flow rate of oxygen pumped from the measured gas chamber 81 into the exhaust gas around the upstream air-fuel ratio sensor 40 is proportional to the pump voltage, and the pump voltage is the electromotive force Ve detected by the electromotive force detection device 100. Is proportional to the difference from the control reference voltage. Therefore, the upstream air-fuel ratio sensor from the measured gas chamber 81 increases as the exhaust air-fuel ratio in the measured gas chamber 81 deviates greatly from the stoichiometric air-fuel ratio, that is, the oxygen concentration in the measured gas chamber 81 increases. The flow rate of oxygen pumped into the exhaust gas around 40 increases.
  • the flow rate of oxygen flowing into the measured gas chamber 81 through the diffusion rate controlling layer 93 and the flow rate of oxygen pumped out by the pump cell 90 basically coincide with each other, and the inside of the measured gas chamber 81 is basically the control standard.
  • the air-fuel ratio corresponding to the voltage, that is, the stoichiometric air-fuel ratio is maintained.
  • the flow rate of oxygen pumped out by the pump cell 90 is equal to the flow rate of oxygen ions that have moved through the first solid electrolyte layer 83 of the pump cell 90.
  • the flow rate of this oxygen ion is equal to the current flowing between the electrodes 85 and 86 of the pump cell 90. Therefore, the current flowing between the electrodes 85 and 86 is detected by the pump current detection device 102, so that the flow rate of oxygen flowing into the measured gas chamber 81 via the diffusion rate controlling layer 93, and hence the surroundings of the measured gas chamber 81, is increased.
  • the lean air-fuel ratio of the exhaust gas can be detected.
  • a pump voltage is applied between the electrodes 85 and 86 of the pump cell 90 by the pump voltage application device 101 based on this.
  • a pump voltage is applied using the gas chamber side electrode 85 as a positive electrode and the exhaust side electrode 86 as a negative electrode.
  • the flow rate of oxygen pumped from the exhaust gas around the upstream air-fuel ratio sensor 40 into the measured gas chamber 81 is proportional to the pump voltage, and the pump voltage is the electromotive force Ve detected by the electromotive force detection device 100. Is proportional to the difference from the control reference voltage. Accordingly, the exhaust gas around the upstream air-fuel ratio sensor 40 increases as the exhaust air-fuel ratio in the measured gas chamber 81 is far from the stoichiometric air-fuel ratio richly, that is, as the unburned gas concentration in the measured gas chamber 81 is higher.
  • the flow rate of oxygen pumped into the measured gas chamber 81 from the inside increases.
  • the flow rate of the unburned gas flowing into the measured gas chamber 81 via the diffusion rate controlling layer 93 and the oxygen flow rate pumped by the pump cell 90 become a chemical equivalence ratio, and thus the measured gas chamber 81 has a basic structure. Therefore, the air-fuel ratio corresponding to the control reference voltage, that is, the stoichiometric air-fuel ratio is maintained.
  • the oxygen flow rate pumped by the pump cell 90 is equal to the flow rate of oxygen ions that have moved through the first solid electrolyte layer 83 in the pump cell 90.
  • the flow rate of this oxygen ion is equal to the current flowing between the electrodes 85 and 86 of the pump cell 90. Therefore, the current flowing between the electrodes 85 and 86 is detected by the pump current detection device 102, so that the flow rate of the unburned gas flowing into the measured gas chamber 81 via the diffusion rate controlling layer 93, and therefore the measured gas chamber.
  • the rich air-fuel ratio of the exhaust gas around 81 can be detected.
  • the stoichiometric air-fuel ratio is exhausted into the measured gas chamber 81 via the diffusion rate-limiting layer 93 as shown in FIG. Gas flows in.
  • exhaust gas having an air fuel ratio (theoretical air fuel ratio) corresponding to the control reference voltage flows in this way, an electromotive force voltage Ve substantially equal to the control reference voltage is generated between the electrodes 87 and 88 of the reference cell 91.
  • the electromotive force Ve is detected by the electromotive force detection device 100.
  • the pump voltage applied by the pump voltage application device 101 is made zero accordingly. For this reason, oxygen ions do not move in the first solid electrolyte layer 83 of the pump cell 90, and thus the measured gas chamber 81 is basically maintained at the air-fuel ratio corresponding to the control reference voltage. Further, since no movement of oxygen ions occurs in the first solid electrolyte layer 83 of the pump cell 90, the pump current detected by the pump current detection device 102 is also zero. Therefore, when the pump current detected by the pump current detection device 102 is zero, it can be seen that the air-fuel ratio of the exhaust gas around the measured gas chamber 81 is the air-fuel ratio corresponding to the reference voltage Vr.
  • the output is performed when the exhaust air-fuel ratio around the upstream air-fuel ratio sensor 40 matches the air-fuel ratio corresponding to the control reference voltage (that is, the theoretical air-fuel ratio).
  • the pump current which is the current, becomes zero.
  • the pump current that is the output current becomes positive, and the absolute value of the pump current increases according to the degree of lean.
  • the pump current that is the output current becomes negative, and the absolute value of the pump current increases according to the richness.
  • the upstream air-fuel ratio sensor 40 has the diffusion-controlling layer 93
  • the upstream-side air-fuel ratio sensor 40 may not necessarily have the diffusion-controlling layer 93 as long as the exhaust gas flowing into the measured gas chamber 81 can be limited. .
  • the upstream air-fuel ratio sensor (two-cell type air-fuel ratio sensor) 40 configured and operated as described above has a control reference voltage-current (VI) characteristic as shown in FIG.
  • the “limit current region” in FIG. 10 indicates the limit current region when the exhaust air-fuel ratio is the stoichiometric air-fuel ratio.
  • the relationship between the control reference voltage Ve and the output current Ip is the relationship between the sensor applied voltage Vr and the output current Ir in the downstream air-fuel ratio sensor 41 (see FIG. 6). ).
  • the exhaust air-fuel ratio becomes an air-fuel ratio that is a certain level or higher (upper limit air-fuel ratio) and an air-fuel ratio that is a certain level or lower (lower limit air-fuel ratio). Even if the exhaust air-fuel ratio changes, the output current Ir does not change. In the example shown in FIG. 6, for example, when the sensor applied voltage Vr is about 0.1 V, the output current Ir becomes a substantially constant value when the exhaust air-fuel ratio becomes 16.6 or more. Therefore, if the sensor applied voltage Vr is constant in the downstream side air-fuel ratio sensor 41, the detectable air-fuel ratio range is limited.
  • the upstream air-fuel ratio sensor 40 can detect the air-fuel ratio in a wide range by keeping the control reference voltage Ve constant.
  • the upstream air-fuel ratio sensor 40 can detect the air-fuel ratio in a wider range than the downstream air-fuel ratio sensor 41.
  • the reference cell 91 of the upstream air-fuel ratio sensor 40 has a relationship between the exhaust air-fuel ratio in the measured gas chamber 81 and the electromotive force Ve as shown in FIG.
  • the electromotive force depends on the direction of change of the air-fuel ratio. Have different values. FIG.
  • FIG. 11 is a diagram showing the situation, where a solid line A is a relationship when the air-fuel ratio is changed from the rich side to the lean side, and a solid line B is when the air-fuel ratio is changed from the lean side to the rich side. The relationship is shown respectively.
  • the electromotive force remains high near the theoretical air-fuel ratio even if the actual air-fuel ratio becomes the lean air-fuel ratio.
  • the solid line B in FIG. 11 when the air-fuel ratio is changed from the lean side to the rich side, the electromotive force remains low near the theoretical air-fuel ratio even when the actual air-fuel ratio becomes rich. It becomes.
  • the reference cell 91 has hysteresis according to the direction of change of the air-fuel ratio. As a result, even if the exhaust air-fuel ratio in the measured gas chamber 81 is the same, the electromotive force of the reference cell 91 may be different, and an error occurs in the output current of the upstream air-fuel ratio sensor 40. Cheap.
  • the downstream air-fuel ratio sensor 41 changes its output current when the internal resistance of the solid electrolyte layer 51 changes even if the exhaust air-fuel ratio is the same. For this reason, the detection accuracy of the air-fuel ratio decreases due to aging.
  • the pump cell 90 of the upstream air-fuel ratio sensor 40 the relationship between the pumping current and the pumping current of oxygen into the gas chamber 81 to be measured and the pumping current is constant even if the internal resistance changes. It is. For this reason, the pump cell 90 has little influence on the output even if the internal resistance of the first solid electrolyte layer 83 changes.
  • the upstream air-fuel ratio sensor 40 can detect the air-fuel ratio with higher accuracy than the downstream air-fuel ratio sensor even if the internal resistance changes due to aging degradation or the like.
  • the exhaust gas before purification by the upstream side exhaust purification catalyst 20 flows into the upstream side air-fuel ratio sensor 40.
  • the upstream air-fuel ratio sensor 40 is exposed to exhaust gas containing a large amount of unburned gas, NOx, etc., and therefore, compared with the downstream air-fuel ratio sensor 41, the internal resistance of the solid electrolyte layer due to aging degradation or the like. Changes are likely to occur.
  • the upstream air-fuel ratio sensor 40 is a two-cell type air-fuel ratio sensor in which the detection accuracy hardly changes even if the internal resistance changes, the influence of aging degradation or the like is minimized. be able to.
  • this output current Iupp is based on the output current Iupp of the upstream side air-fuel ratio sensor 40 (corresponding to the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 and corresponding to the above-mentioned Ip). Feedback control is performed so that becomes a value corresponding to the target air-fuel ratio.
  • the target air-fuel ratio is set based on the output current of the downstream air-fuel ratio sensor 41. Specifically, when the output current Irdwn (corresponding to Ir described above) of the downstream side air-fuel ratio sensor 41 becomes equal to or less than the rich determination reference value Iref, the target air-fuel ratio is set to the lean set air-fuel ratio, Maintained.
  • the rich determination reference value Iref is a value corresponding to a predetermined rich determination air-fuel ratio (for example, 14.55) that is slightly richer than the theoretical air-fuel ratio.
  • 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 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 output current Irdwn of the downstream air-fuel ratio sensor 41 again becomes equal to or less than the rich determination reference value Iref, the target air-fuel ratio is again set to the lean set air-fuel ratio, 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.
  • the air-fuel ratio corresponding to the output current Irdwn of the downstream air-fuel ratio sensor 41 deviates from the stoichiometric air-fuel ratio
  • the difference from the stoichiometric air-fuel ratio is determined in advance as a reference difference (that is, (The difference between the rich determination air-fuel ratio and the stoichiometric air-fuel ratio) becomes equal to or greater than the target air-fuel ratio in the direction in which the air-fuel ratio corresponding to the output current Irdwn of the downstream air-fuel ratio sensor 41 deviates from the stoichiometric air-fuel ratio (rich direction).
  • the air / fuel ratio (in this embodiment, the lean set air / fuel ratio) is set.
  • the reference difference is within 1% of the theoretical air-fuel ratio, preferably within 0.5%, more preferably within 0.35%. Therefore, when the theoretical air-fuel ratio is 14.6, the reference difference is 0.15 or less, preferably 0.073 or less, more preferably 0.051 or less. Further, the difference between the target air-fuel ratio (for example, the weak rich set air-fuel ratio and the lean set air-fuel ratio) from the theoretical air-fuel ratio is set to be larger than the reference difference.
  • FIG. 12 shows the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20, the output current Irdwn of the downstream side air-fuel ratio sensor 41, and the air-fuel ratio correction amount AFC 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 the output current Iupup of the upstream air-fuel ratio sensor 40 and the NOx concentration in the exhaust gas flowing out from the upstream side exhaust purification catalyst 20.
  • the 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 air-fuel ratio of the exhaust gas is rich air-fuel ratio. Is a negative value, and a positive value when the air-fuel ratio of the exhaust gas is a lean air-fuel ratio. Further, when the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 is the rich air-fuel ratio or the lean air-fuel ratio, the absolute value of the output current Iupp of the upstream air-fuel ratio sensor 40 increases as the difference from the stoichiometric air-fuel ratio increases. The value increases.
  • the output current Irdwn of the downstream side air-fuel ratio sensor 41 also changes in the same manner as the output current Iupp of the upstream side air-fuel ratio sensor 40 according to the air-fuel ratio of the exhaust gas flowing out from the upstream side exhaust purification catalyst 20.
  • the air-fuel ratio correction amount AFC is a correction amount related to the target air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20.
  • 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.
  • 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 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 output current Irdwn of the downstream side air-fuel ratio sensor becomes substantially 0 (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 decreases beyond the lower limit storage amount (see Clowlim in FIG. 2) 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 output current Irdwn 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 output current Irdwn of the downstream air-fuel ratio sensor 41 reaches the rich determination reference value Iref corresponding to the rich determination air-fuel ratio.
  • the air-fuel ratio correction amount AFC is set to be lean so as to suppress the decrease in the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20.
  • the correction amount is switched to AFClean.
  • 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.
  • 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 output current Irdwn of the downstream side air-fuel ratio sensor 41 converges to zero.
  • 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. 2), 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 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 reaching 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 output current Iupp of the upstream air-fuel ratio sensor 40, the estimated value of the intake air amount, and the like, 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 detects whether or not the air-fuel ratio of the exhaust gas flowing out from the upstream side exhaust purification catalyst 20 is equal to or less than the rich determination air-fuel ratio.
  • the air-fuel ratio is an air-fuel ratio that is slightly deviated from the stoichiometric air-fuel ratio. Therefore, the range of the air-fuel ratio that can be detected by the downstream air-fuel ratio sensor 41 may be narrow. However, when the air-fuel ratio of the exhaust gas flowing out from the upstream side exhaust purification catalyst 20 becomes equal to or lower than the rich determination air-fuel ratio, it is necessary to quickly switch the target air-fuel ratio. Accuracy is required.
  • the upstream air-fuel ratio sensor 40 is used for feedback control so that the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 becomes the target air-fuel ratio.
  • the range of the air-fuel ratio that can be detected by the upstream air-fuel ratio sensor 40 is required to be wide.
  • the upstream air-fuel ratio sensor 40 a two-cell type air-fuel ratio sensor having a wide range of detectable air-fuel ratio is used as the upstream air-fuel ratio sensor 40, and the downstream air-fuel ratio sensor 41 has high detection accuracy.
  • a one-cell air-fuel ratio sensor is used. Therefore, according to the present embodiment, the upstream air-fuel ratio sensor 40 and the downstream air-fuel ratio sensor 41 can sufficiently satisfy the requirements for each.
  • 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 at the times t 2 to t 4 is the difference between the time average value of the target air-fuel ratio and the theoretical air-fuel ratio in the period, and the target at the times t 4 to t 7 . It is set to be larger than the difference between the time average value of the air-fuel ratio and the theoretical air-fuel ratio.
  • the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20 is estimated based on the 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. Yes.
  • 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. 13 is a diagram similar to FIG. 12, and instead of the transition of the NOx concentration in FIG. 12, 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.). Moreover, in the example shown in FIG. 13, the same control as the example shown in FIG. 12 is performed.
  • the 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 emitted from the downstream side exhaust purification catalyst 24 Will always be less.
  • FIG. 14 which is a functional block diagram
  • the control device in the present embodiment is configured to include each of 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 OSAest 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 output current Iupp of the upstream side air-fuel ratio sensor 40. Is calculated. For example, the oxygen storage amount calculating means A4 multiplies the difference between the air-fuel ratio corresponding to the output current Iupp 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. An estimated value OSAest of the oxygen storage amount is calculated. 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. 12).
  • the oxygen storage amount may be estimated only until the time t 4 ).
  • the air-fuel ratio of the target air-fuel ratio is calculated based on the estimated value OSAest of the oxygen storage amount calculated by the oxygen storage amount calculation means A4 and the output current Irdwn of the downstream air-fuel ratio sensor 41.
  • a correction amount AFC is calculated. Specifically, the air-fuel ratio correction amount AFC is the lean set correction amount AFClean when the output current Irdwn of the downstream air-fuel ratio sensor 41 becomes equal to or less than the rich determination reference value Iref (value corresponding to the rich determination air-fuel ratio). It is said.
  • 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.
  • the air-fuel ratio correction amount AFC is maintained at the weak rich set correction amount AFCrich until the output current Irdwn of the downstream air-fuel ratio sensor 41 reaches the rich determination reference value Iref (a value corresponding to the rich determination air-fuel ratio).
  • 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 (when the air-fuel ratio correction amount AFC is a weak rich set correction amount AFCrich) slightly richer than the stoichiometric air-fuel ratio AFR, or is more than the stoichiometric air-fuel ratio AFR.
  • Any lean set air-fuel ratio (in the case where the air-fuel ratio correction amount AFC is the lean set correction amount AFClean) that is lean to some extent.
  • 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. 15 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 the 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 output current Iupup of the upstream side air-fuel ratio sensor 40, the output current Irdwn of the downstream side air-fuel ratio sensor 41, and the fuel injection amount Qi are acquired.
  • step S13 the estimated value OSAest of the oxygen storage amount is calculated based on the 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 output current Irdwn of the downstream air-fuel ratio sensor 41 is equal to or less than the rich determination reference value Iref. When it is determined that the output current Irdwn of the downstream air-fuel ratio sensor 41 is larger than the rich determination reference value Iref, the control routine is ended.
  • the output current Irdwn of the downstream side air-fuel ratio sensor 41 in step S15 Is determined to be less than or equal to the rich determination reference value Iref.
  • 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 corresponds to the output current Iupup based on the output current Iupup of the upstream air-fuel ratio sensor 40 and a map or calculation formula that defines the relationship between the output current Iupup of the air-fuel ratio sensor 40 and the air-fuel ratio.
  • An upstream exhaust air-fuel ratio AFup 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. 16 is a diagram similar to FIG. 12, and the times t 1 to t 7 in FIG. 16 show the same control timing as the times t 1 to t 7 in FIG. Therefore, also in the control shown in FIG. 16, the same control as the control shown in FIG. 7 is performed at each timing from time t 1 to time t 7 .
  • the control shown in FIG. 16 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 output current Irdwn rich determination reference value of the downstream air-fuel ratio sensor 41 at time t 7 The time required to reach Iref can be increased. That is, 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 is at time t 2 ⁇ t 4, the difference between the time 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 time average value of the fuel ratio and the stoichiometric 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.
  • a 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 and control of the control device for the internal combustion engine according to the third embodiment are basically the same as the configuration and control of the control device for the internal combustion engine according to the above embodiment.
  • the air-fuel ratio is controlled so that the exhaust gas flowing out from the upstream side exhaust purification catalyst 20 does not include unburned gas.
  • the target air-fuel ratio is set based on the output current of the downstream air-fuel ratio sensor 41. Specifically, when the output current Irdwn of the downstream air-fuel ratio sensor 41 becomes equal to or greater than the lean determination reference value Iref, the target air-fuel ratio is set to the rich set air-fuel ratio and is maintained at that air-fuel ratio.
  • the lean determination reference value Iref is a value corresponding to a predetermined lean determination air-fuel ratio (for example, 14.65) that is slightly leaner than the theoretical air-fuel ratio.
  • the rich set air-fuel ratio is a predetermined air-fuel ratio that is somewhat richer than the theoretical air-fuel ratio, and is, for example, 10 to 14.55, preferably 12 to 14.52, more preferably 13 to 14.5. It is said to be about.
  • 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 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. Then, when the estimated value of the oxygen storage amount OSAsc becomes equal to or less than a predetermined determination reference storage amount Cref, the target air-fuel ratio that has been the rich set air-fuel ratio until then becomes the weak lean set air-fuel ratio, and is maintained at that air-fuel ratio.
  • the weak lean set air-fuel ratio is a predetermined air-fuel ratio that is slightly leaner than the stoichiometric air-fuel ratio, and is, for example, 14.62 to 15.5, preferably 14.63 to 15, and more preferably 14.65. About 14.8. Thereafter, when the output current Irdwn of the downstream side air-fuel ratio sensor 41 again becomes equal to or greater than the lean determination reference value Iref, the target air-fuel ratio is again set to the rich set air-fuel ratio, 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 rich set air-fuel ratio and the weak lean set air-fuel ratio.
  • the difference between the rich set air-fuel ratio and the stoichiometric air-fuel ratio is larger than the difference between the weak lean set air-fuel ratio and the stoichiometric air-fuel ratio. Therefore, in the present embodiment, the target air-fuel ratio is alternately set to the short-time rich set air-fuel ratio and the long-term weak lean set air-fuel ratio.
  • the air-fuel ratio corresponding to the output current Irdwn of the downstream air-fuel ratio sensor 41 deviates from the stoichiometric air-fuel ratio
  • the difference from the stoichiometric air-fuel ratio is determined in advance as a reference difference (that is, (The difference between the lean determination air-fuel ratio and the stoichiometric air-fuel ratio) becomes equal to or greater than the target air-fuel ratio in the direction in which the air-fuel ratio corresponding to the output current Irdwn of the downstream air-fuel ratio sensor 41 deviates from the stoichiometric air-fuel ratio (lean direction).
  • the air-fuel ratio (in this embodiment, the rich set air-fuel ratio) is set.
  • the reference difference is set in the same manner as in the first embodiment. Further, the difference between the target air-fuel ratio (for example, the weak lean set air-fuel ratio and the rich set air-fuel ratio) from the theoretical air-fuel ratio is set to be larger than the reference difference.
  • the target air-fuel ratio for example, the weak lean set air-fuel ratio and the rich set air-fuel ratio
  • FIG. 17 is a time chart similar to FIG. 12 when the air-fuel ratio control is performed in the present embodiment.
  • the air-fuel ratio correction amount AFC is set to the weak lean set correction amount AFClean.
  • the weak lean set correction amount AFClean is a value corresponding to the weak lean set air-fuel ratio, and is a value larger than zero. Accordingly, the target air-fuel ratio is set to a lean air-fuel ratio, and accordingly, the output current Iupp of the upstream air-fuel ratio sensor 40 becomes a positive value. Since the exhaust gas flowing into the upstream side exhaust purification catalyst 20 contains oxygen, the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20 gradually increases.
  • the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20 gradually increases, the oxygen storage amount OSAsc increases beyond the upper limit storage amount (see Cuplim in FIG. 2) at time t 1 .
  • the oxygen storage amount OSAsc increases above the upper limit storage amount, part of the oxygen in the exhaust gas flowing into the upstream side exhaust purification catalyst 20 flows out without being stored in the upstream side exhaust purification catalyst 20. Therefore, after time t 1 , the output current Irdwn of the downstream air-fuel ratio sensor 41 gradually increases as the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20 increases. Also at this time, since the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 is a lean air-fuel ratio, the amount of unburned gas discharged from the upstream side exhaust purification catalyst 20 is suppressed.
  • the output current Irdwn of the downstream air-fuel ratio sensor 41 reaches the lean determination reference value Iref corresponding to the lean determination air-fuel ratio.
  • the air-fuel ratio correction amount AFC is set to be rich so as to suppress an increase in the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20.
  • the correction amount is switched to AFCrich.
  • the rich set correction amount AFCrich is a value corresponding to the rich set air-fuel ratio, and is a value larger than zero. Therefore, the target air-fuel ratio is set to a rich air-fuel ratio.
  • the air-fuel ratio correction amount AFC is switched. This is the same as in the first embodiment when the air-fuel ratio correction amount AFC is switched 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. This is for a reason.
  • the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 does not immediately become the rich air-fuel ratio, and some delay occurs.
  • the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 changes from the lean air-fuel ratio to the rich air-fuel ratio at time t 3 .
  • the air-fuel ratio of the exhaust gas flowing out from the upstream side exhaust purification catalyst 20 is the lean air-fuel ratio, so this exhaust gas contains oxygen and NOx. .
  • the amount of unburned gas discharged from the upstream side exhaust purification catalyst 20 is suppressed.
  • the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20 decreases.
  • 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 output current Irdwn of the downstream side air-fuel ratio sensor 41 converges to zero.
  • the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 is a rich air-fuel ratio.
  • the upstream side exhaust purification catalyst 20 stores a large amount of oxygen, The fuel gas is purified by the upstream side exhaust purification catalyst 20. For this reason, the amount of unburned gas discharged from the upstream side exhaust purification catalyst 20 is suppressed.
  • the oxygen storage amount OSAsc the upstream exhaust purification catalyst 20 is reduced, 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 lean set correction amount AFCrich (less than 0) in order to stop the release of oxygen from the upstream side exhaust purification catalyst 20. Switch to a large value). Therefore, the target air-fuel ratio is a lean air-fuel ratio.
  • the criterion occlusion amount Cref because it is set sufficiently higher than zero and lower absorption amount (see Clowlim in FIG. 2), the oxygen storage amount OSAsc even at time t 5 does not reach the zero or lower storage amount .
  • the determination reference storage amount Cref is equal to the oxygen storage amount OSAsc.
  • the amount is sufficiently large so as not to reach zero or the lower limit storage amount.
  • the criterion storage amount Cref is set to 1 ⁇ 4 or more, preferably 1 ⁇ 2 or more, more preferably 4/5 or more of the maximum oxygen storage amount Cmax. Accordingly, the amount of unburned gas discharged 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 is a slightly lean set correction amount AFCrich. Accordingly, the target air-fuel ratio is set to a lean air-fuel ratio, and accordingly, the output current Iupp of the upstream air-fuel ratio sensor 40 becomes a positive value. Since the exhaust gas flowing into the upstream side exhaust purification catalyst 20 contains oxygen, the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20 gradually increases, and at time t 6 , at time t 1 Similarly, the oxygen storage amount OSAsc decreases beyond the upper 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 lean air-fuel ratio, the amount of unburned gas discharged 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 greater than the lean determination air-fuel ratio.
  • the oxygen storage amount reducing means for continuously or intermittently setting the target air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 to the rich set air-fuel ratio and the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20 are When the oxygen storage amount OSAsc does not reach zero, the target air-fuel ratio is continuously or intermittently slightly lean set air-fuel ratio so that the oxygen storage amount OSAsc increases toward the maximum oxygen storage amount Cmax when the reference storage amount Cref is equal to or less than the determination reference storage amount Cref. It can be said that it comprises oxygen storage amount increasing means.
  • the amount of unburned gas discharged from the upstream side exhaust purification catalyst 20 can be suppressed. That is, as long as the above-described control is performed, the amount of unburned gas discharged from the upstream side exhaust purification catalyst 20 can be basically reduced.
  • the air-fuel ratio correction amount AFC is maintained at the rich set correction amount AFCrich 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 to vary, for example, by gradually increasing it.
  • the air-fuel ratio correction amount AFC is maintained at the weak lean set correction amount AFlean.
  • the air-fuel ratio correction amount AFC does not necessarily have to be kept constant, and may be set to vary, for example, by gradually increasing it.
  • the air-fuel ratio correction amount AFC at the times t 2 to t 4 is the difference between the time average value of the target air-fuel ratio and the theoretical air-fuel ratio in the period, and the target at the times t 4 to t 7 . It is set to be larger than the difference between the time average value of the air-fuel ratio and the theoretical air-fuel ratio.
  • control device for an internal combustion engine according to a fourth 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 fourth embodiment is basically the same as the configuration of the control device for the internal combustion engine according to the above embodiment.
  • the control device of this embodiment performs air-fuel ratio control different from the control in the above embodiment.
  • the target air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 is set based on the output current Irdwn of the downstream side air-fuel ratio sensor 41 and the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20. . Specifically, when the output current Irdwn of the downstream air-fuel ratio sensor 41 becomes equal to or less than the rich determination reference value Irrich, the air-fuel ratio of the exhaust gas detected by the downstream air-fuel ratio sensor 41 becomes the rich air-fuel ratio. To be judged. In this case, the target air-fuel ratio is made the lean set air-fuel ratio by the lean switching means, and is maintained at that air-fuel ratio.
  • the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20 reaches a predetermined storage amount larger than zero with the target air-fuel ratio set to the lean set air-fuel ratio, the target air-fuel ratio is weakened by the lean degree reducing means.
  • the lean set air-fuel ratio is switched to (the oxygen storage amount at this time is referred to as “lean degree change reference storage amount”).
  • the lean degree change reference storage amount is the storage amount whose difference from zero is the predetermined change reference difference ⁇ .
  • the target air-fuel ratio is set to the rich set air-fuel ratio by the rich switching means.
  • the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20 reaches a predetermined storage amount smaller than the maximum storage amount with the target air-fuel ratio set to the rich set air-fuel ratio
  • the target air-fuel ratio is reduced by the rich degree reducing means.
  • the oxygen storage amount at this time is referred to as “rich degree change reference storage amount”.
  • the rich degree change reference storage amount is the storage amount whose difference from the maximum oxygen storage amount is the predetermined change reference difference ⁇ .
  • the target air-fuel ratio is first set to the lean set air-fuel ratio, and then the oxygen storage amount OSAsc is When it increases to a certain extent, it is set to a slightly lean set air-fuel ratio. Thereafter, when the output current Irdwn of the downstream air-fuel ratio sensor 41 becomes equal to or greater than the lean determination reference value Irlean, first, the target air-fuel ratio is set to the rich set air-fuel ratio, and then the oxygen storage amount OSAsc is reduced to some extent to weakly rich set-empty. The fuel ratio is set and the same operation is repeated.
  • FIG. 18 is a time chart of the oxygen storage amount OSAsc and the like of the upstream side exhaust purification catalyst 20 when air-fuel ratio control is performed in the control device for an internal combustion engine according to the present embodiment.
  • the air-fuel ratio correction amount AFC of the target air-fuel ratio is set to the weak rich set correction amount AFCsrich.
  • the weak rich set correction amount AFCsrich is a value corresponding to the weak rich set air-fuel ratio, and is a value smaller than zero. Therefore, the target air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 is set to a rich air-fuel ratio, and accordingly, the output current Iupp of the upstream side 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 in the exhaust gas flowing into the upstream side exhaust purification catalyst 20 is oxidized and purified by oxygen stored in the upstream side exhaust purification catalyst 20. For this reason, not only the amount of oxygen (and NOx) discharged from the upstream side exhaust purification catalyst 20 but also the amount of unburned gas discharged is suppressed.
  • the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20 gradually decreases, at time t 1 , the oxygen storage amount OSAsc decreases beyond the lower limit storage amount (see Crowlim in FIG. 2).
  • 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 output current Irdwn 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.
  • the unburned gas contained in the exhaust gas flowing out from the upstream side exhaust purification catalyst 20 is oxidized and purified by the downstream side exhaust purification catalyst 24.
  • the output current Irdwn of the downstream air-fuel ratio sensor 41 is gradually decreased, reaches the rich determination reference value Irrich corresponding to rich determination air-fuel ratio at time t 2.
  • the air-fuel ratio correction amount AFC is made lean so as to suppress the decrease in the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20. It is switched to the set correction amount AFCgreen.
  • the lean set correction amount AFCgreen is a value corresponding to the lean set air-fuel ratio, and is a value larger than zero.
  • the air-fuel ratio of the exhaust gas flowing into the upstream exhaust purification catalyst 20 is changed to the lean air-fuel ratio at time t 2, the output current Ipup of the upstream air-fuel ratio sensor 40 with a positive value, the upstream exhaust purification catalyst 20
  • the oxygen storage amount OSAsc begins to increase.
  • the output current Iupp of the upstream side air-fuel ratio sensor 40 changes simultaneously with the switching of the air-fuel ratio correction amount AFC in order to make the explanation easy to understand. So that a delay occurs.
  • the output current Irdwn of the downstream air-fuel ratio sensor 41 decreases. This is because there is a delay from when the target air-fuel ratio is switched until the exhaust gas reaches the upstream side exhaust purification catalyst 20, and the unburned gas still flows out of the upstream side exhaust purification catalyst 20.
  • 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 output of the downstream side air-fuel ratio sensor 41
  • the current Irdwn also increases. Therefore, the output current Irdwn of the downstream air-fuel ratio sensor 41 is larger than the rich determination reference value Irrich at time t 3 or later. Also during this time, the air-fuel ratio correction amount AFC of the target air-fuel ratio is maintained at the lean set correction amount AFCglan, and the output current Iupup of the upstream side air-fuel ratio sensor 40 is maintained at a positive value.
  • the upstream exhaust purification catalyst 20 When increase of the oxygen storage amount OSAsc the upstream exhaust purification catalyst 20 continues to reach the degree of leanness change reference occlusion amount Clean at time t 4.
  • the air-fuel ratio correction is performed so as to slow down the increase rate of the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20.
  • the amount AFC is switched to the weak lean set correction amount AFCslen.
  • the weak lean set correction amount AFCslen is a value corresponding to the weak lean set air-fuel ratio, and is a value smaller than AFCgreen and larger than zero.
  • the target air-fuel ratio is switched to the slightly lean set air-fuel ratio at time t 4 , the difference between the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 and the stoichiometric air-fuel ratio is also reduced. Along with this, the value of the output current Iupp of the upstream side air-fuel ratio sensor 40 decreases, and the increase rate of the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20 decreases. Note that oxygen and NOx in the exhaust gas flowing into the upstream side exhaust purification catalyst 20 are occluded and purified by the upstream side exhaust purification catalyst 20. For this reason, not only the amount of unburned gas discharged from the upstream side exhaust purification catalyst 20 but also the amount of NOx discharged is suppressed.
  • the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20 gradually increases although its increase rate is slow.
  • the oxygen storage amount OSAsc the upstream exhaust purification catalyst 20 gradually increases, at time t 5, the oxygen storage amount OSAsc increases beyond the upper limit storage amount (see Cuplim in FIG. 2).
  • the output current Irdwn of the downstream air-fuel ratio sensor 41 gradually increases as the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20 increases. Note that NOx is not reduced or purified as part of the oxygen is not occluded in the upstream side exhaust purification catalyst 20, but this NOx is reduced and purified by the downstream side exhaust purification catalyst 24.
  • the output current Irdwn of the downstream air-fuel ratio sensor 41 is gradually increased, at time t 6 reaches the lean determination reference value Irlean corresponding to lean determination air-fuel ratio.
  • the air-fuel ratio correction amount AFC is set to be rich so as to suppress an increase in the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20.
  • the correction amount is switched to AFCgrich.
  • the rich set correction amount AFCgrich is a value corresponding to the rich set air-fuel ratio, and is a value smaller than zero.
  • 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 output of the downstream side air-fuel ratio sensor 41
  • the current Irdwn is also reduced.
  • the output current Irdwn of the downstream air-fuel ratio sensor 41 becomes zero or less after time t 7 .
  • the air-fuel ratio correction amount AFC of the target air-fuel ratio is maintained at the rich set correction amount AFCgrich, and the output current Iupup of the upstream air-fuel ratio sensor 40 is maintained at a negative value.
  • the upstream exhaust purification catalyst 20 When reduction of the oxygen storage amount OSAsc the upstream exhaust purification catalyst 20 continues to reach the degree of richness change reference occlusion amount Crich at time t 8.
  • the air-fuel ratio correction is performed so as to slow down the decrease rate of the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20.
  • the amount AFC is switched to the weak rich set correction amount AFCsrich.
  • the weak rich set correction amount AFCsrich is a value corresponding to the weak rich set air-fuel ratio, and is a value larger than AFCgrich and smaller than 0.
  • the oxygen storage amount OSAsc of the upstream side exhaust purification catalyst 20 gradually decreases although its decrease rate is slow, and as a result, unburned gas flows out of the upstream side exhaust purification catalyst 20.
  • the output current Irdwn of the downstream air-fuel ratio sensor 41 reaches the rich determination reference value Irrich. Thereafter, an operation similar to the operation at times t 1 to t 8 is repeated.
  • the target air-fuel ratio is a rich air-fuel ratio immediately after being changed from the rich air-fuel ratio to the lean air-fuel ratio, and the target air-fuel ratio at time t 6 from the lean air-fuel ratio at time t 2 Immediately after the change to, the difference from the stoichiometric air-fuel ratio is made large (that is, the rich degree or lean degree is made large). Therefore, it is possible to reduce the NOx that has been flowing from the upstream exhaust purification catalyst 20 in the unburnt gas and the time t 6 that was flowing out of the upstream exhaust purification catalyst 20 at time t 2 quickly. Therefore, the outflow of unburned gas and NOx from the upstream side exhaust purification catalyst 20 can be suppressed.
  • the target air-fuel ratio is switched to the weak lean set air-fuel ratio at time t 4.
  • the target air-fuel ratio is switched to the weak lean set air-fuel ratio at time t 4.
  • the outflow amount of NOx and unburned gas from the upstream side exhaust purification catalyst 20 per unit time can be reduced. Furthermore, according to the air-fuel ratio control, at time t 5, it can be suppressed to be small the outflow even when the NOx flows out of the upstream exhaust purification catalyst 20. Therefore, the outflow of NOx from the upstream side exhaust purification catalyst 20 can be suppressed.
  • the target air-fuel ratio control of the present embodiment after setting the target air-fuel ratio to a rich set air-fuel ratio at time t 6, it stops the outflow of NOx (oxygen) from the upstream exhaust purification catalyst 20 and the upstream side from reduced oxygen storage amount OSAsc of the exhaust purification catalyst 20 to some extent, the target air-fuel ratio is switched to the weak rich set air-fuel ratio at time t 8.
  • NOx oxygen
  • OSAsc oxygen storage amount
  • the outflow amount of NOx and unburned gas from the upstream side exhaust purification catalyst 20 per unit time can be reduced. Furthermore, according to the above air-fuel ratio control, even when unburned gas flows out from the upstream side exhaust purification catalyst 20 at time t 1 , the outflow amount can be reduced. Therefore, the outflow of unburned gas from the upstream side exhaust purification catalyst 20 can be suppressed.
  • the target air-fuel ratio is changed so that the difference from the stoichiometric air-fuel ratio becomes small.
  • the timing for changing the target air-fuel ratio so that the difference from the stoichiometric air-fuel ratio becomes small may be any time between the times t 2 and t 6 .
  • the target air-fuel ratio is changed so as to reduce the difference from the stoichiometric air-fuel ratio. May be.
  • the target air-fuel ratio is changed so that the difference from the stoichiometric air-fuel ratio becomes small. I am letting.
  • the timing for changing the target air-fuel ratio so that the difference from the stoichiometric air-fuel ratio becomes small may be any time between the times t 6 and t 2 . For example, as shown in FIG.
  • the target air-fuel ratio is fixed to the weak lean set air-fuel ratio or the weak rich set air-fuel ratio between time t 4 and t 6 and between time t 8 and t 2 .
  • the target air-fuel ratio may be set so that the difference becomes smaller in steps, or may be set so that the difference becomes smaller continuously.
  • the ECU 31 An air-fuel ratio lean switching means for changing the target air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 20 to a lean set air-fuel ratio, and a downstream air-fuel ratio sensor after the target air-fuel ratio is changed by the air-fuel ratio lean switching means
  • the target air-fuel ratio is set to a lean air-fuel ratio (weak lean setting) in which the difference from the stoichiometric air-fuel ratio is smaller than the lean air-fuel ratio before the output current 41 becomes equal to or greater than the lean determination air-fuel ratio that is leaner than the stoichiometric air-fuel ratio.
  • the target air-fuel ratio is reduced.
  • 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.

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Abstract

La présente invention concerne un dispositif de commande destiné à un moteur à combustion interne, équipé des éléments suivants : un catalyseur (20) de purification d'échappement, prévu dans le passage d'échappement ; un capteur (40) amont de rapport air sur carburant et un capteur (41) aval de rapport air sur carburant, respectivement prévus en amont et en aval du catalyseur de purification d'échappement ; et un dispositif de commande de moteur, qui commande le moteur à combustion interne en réponse à la sortie de ces capteurs de rapport entre air et carburant. Le capteur (40) amont de rapport entre air et carburant est un capteur bicellulaire de rapport entre air et carburant, équipé des éléments suivants : une chambre (81) de mesure de gaz, dans laquelle un gaz d'échappement peut être amené à circuler ; une cellule (90) de pompage, qui pompe l'oxygène vers l'intérieur ou vers l'extérieur par rapport au gaz d'échappement de la chambre de mesure de gaz, en réponse au courant de pompe ; et une cellule (91) standard, dont la valeur de détection change en réponse à la concentration en oxygène dans la chambre de mesure de gaz. Le capteur (41) aval de rapport entre air et carburant est un capteur unicellulaire de rapport entre air et carburant équipé des éléments suivants : une première électrode (52) exposée aux gaz d'échappement à travers une couche de commande de diffusion ; une seconde électrode (53) exposée à une atmosphère standard ; une couche (51) d'électrolyte solide, agencée entre les deux électrodes ; un dispositif (60) d'application de tension, qui applique une tension entre les deux électrodes ; et un dispositif (61) de détection de courant, qui détecte le courant circulant entre les deux électrodes.
PCT/JP2013/051907 2013-01-29 2013-01-29 Dispositif de commande pour moteur à combustion interne WO2014118888A1 (fr)

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JP2016125982A (ja) * 2015-01-08 2016-07-11 株式会社デンソー 酸素センサ
JP2017057760A (ja) * 2015-09-15 2017-03-23 トヨタ自動車株式会社 内燃機関の制御装置
CN111412044A (zh) * 2019-01-08 2020-07-14 丰田自动车株式会社 电化学反应器

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JPH1082760A (ja) * 1996-07-19 1998-03-31 Denso Corp 空燃比制御方法
JPH10246139A (ja) * 1997-03-04 1998-09-14 Unisia Jecs Corp 内燃機関の空燃比制御装置
JP2000356620A (ja) * 1999-06-14 2000-12-26 Nippon Soken Inc ガス濃度検出装置
JP2002202285A (ja) * 2000-10-31 2002-07-19 Denso Corp ガス濃度検出装置
JP2005127259A (ja) * 2003-10-24 2005-05-19 Hitachi Ltd エンジンの制御装置
JP2010236450A (ja) * 2009-03-31 2010-10-21 Denso Corp 内燃機関の排気浄化装置
WO2012120676A1 (fr) * 2011-03-10 2012-09-13 トヨタ自動車株式会社 Appareil de commande pour moteur à combustion interne

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Publication number Priority date Publication date Assignee Title
JPH1082760A (ja) * 1996-07-19 1998-03-31 Denso Corp 空燃比制御方法
JPH10246139A (ja) * 1997-03-04 1998-09-14 Unisia Jecs Corp 内燃機関の空燃比制御装置
JP2000356620A (ja) * 1999-06-14 2000-12-26 Nippon Soken Inc ガス濃度検出装置
JP2002202285A (ja) * 2000-10-31 2002-07-19 Denso Corp ガス濃度検出装置
JP2005127259A (ja) * 2003-10-24 2005-05-19 Hitachi Ltd エンジンの制御装置
JP2010236450A (ja) * 2009-03-31 2010-10-21 Denso Corp 内燃機関の排気浄化装置
WO2012120676A1 (fr) * 2011-03-10 2012-09-13 トヨタ自動車株式会社 Appareil de commande pour moteur à combustion interne

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2016125982A (ja) * 2015-01-08 2016-07-11 株式会社デンソー 酸素センサ
JP2017057760A (ja) * 2015-09-15 2017-03-23 トヨタ自動車株式会社 内燃機関の制御装置
CN111412044A (zh) * 2019-01-08 2020-07-14 丰田自动车株式会社 电化学反应器

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