WO2022210266A1 - ガス濃度検出システム - Google Patents
ガス濃度検出システム Download PDFInfo
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- WO2022210266A1 WO2022210266A1 PCT/JP2022/014021 JP2022014021W WO2022210266A1 WO 2022210266 A1 WO2022210266 A1 WO 2022210266A1 JP 2022014021 W JP2022014021 W JP 2022014021W WO 2022210266 A1 WO2022210266 A1 WO 2022210266A1
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/416—Systems
- G01N27/417—Systems using cells, i.e. more than one cell and probes with solid electrolytes
- G01N27/4175—Calibrating or checking the analyser
Definitions
- One aspect of the present disclosure is It is arranged and used in an exhaust pipe of an internal combustion engine, and is composed of a sensor electrode and a sensor reference electrode provided on a sensor solid electrolyte body, and is based on the current flowing between the sensor electrode and the sensor reference electrode.
- the catalyst arranged in the exhaust pipe 7 may be a lean NOx trap catalyst (LNT) that detoxifies NOx (nitrogen oxides) in the exhaust gas G.
- LNT lean NOx trap catalyst
- Lean NOx trap catalysts are primarily installed in diesel engines, but may also be installed in gasoline engines.
- the gas concentration detection system 1 may be employed in a lean-burn engine that performs combustion operation on the leaner side of the fuel than the stoichiometric air-fuel ratio.
- the sensor electrode 311A and the sensor reference electrode 312A are arranged in the longitudinal direction L of the sensor element 2 at positions on the front end side L1 exposed to the exhaust gas G so as to overlap in the stacking direction D with the sensor solid electrolyte body 3A interposed therebetween. ing.
- a sensor cell 21A composed of a sensor electrode 311A, a sensor reference electrode 312A, and a portion of the sensor solid electrolyte body 3A sandwiched between the electrodes 311A and 312A is located on the front end side L1 in the longitudinal direction L of the sensor element 2. is formed.
- the pump electrode 311B and the pump reference electrode 312B are arranged in a position overlapping in the stacking direction D via the solid electrolyte body 3B for the pump at a portion on the front end side L1 exposed to the exhaust gas G in the longitudinal direction L of the sensor element 2. ing.
- a pump cell 21B composed of a pump electrode 311B, a pump reference electrode 312B, and a portion of the pump solid electrolyte body 3B sandwiched between the electrodes 311B and 312B is located on the tip side L1 in the longitudinal direction L of the sensor element 2. is formed.
- the gas chamber 35 is formed between the inner surface 301A of the sensor solid electrolyte body 3A and the inner surface 301B of the pump solid electrolyte body 3B. It is formed surrounded by the body 3A and the pump solid electrolyte body 3B.
- the gas chamber 35 is formed at a position on the front end side L1 in the longitudinal direction L of the intermediate insulator 33C to accommodate the sensor electrode 311A.
- the gas chamber 35 is formed as a space closed by the intermediate insulator 33C, the diffusion resistance portion 32, the sensor solid electrolyte body 3A, and the pump solid electrolyte body 3B.
- the exhaust gas G flowing through the exhaust pipe 7 passes through the diffusion resistance portion 32 and is introduced into the gas chamber 35 .
- Atmospheric duct 36 As shown in FIGS. 2 and 3, on the outer surface 302B of the pump solid electrolyte body 3B, there is an atmosphere duct 36 surrounded by the pump-side insulator 33B and the pump solid electrolyte body 3B and into which the atmosphere A is introduced. formed adjacent to each other.
- the atmosphere duct 36 is formed from a portion of the pump-side insulator 33B in the longitudinal direction L that accommodates the pump reference electrode 312B to a base end position in the longitudinal direction L of the sensor element 2 .
- a surface protection layer 38 covering the element detection section 21 is formed on the front end side L1 of the sensor element 2 in the longitudinal direction L.
- the surface protective layer 38 is composed of a plurality of mutually bonded ceramic particles as a ceramic material having pores through which the exhaust gas G can pass.
- the housing 41 is used to fasten the gas sensor 10 to the mounting port 71 of the exhaust pipe 7.
- the housing 41 holds the sensor element 2 via an element holding member 42 and the like.
- the sensor element 2 is held by the element holding material 42 via the glass powder 421
- the element holding material 42 is held by the housing 41 via caulking materials 422 , 423 and 424 .
- a terminal holding member 43 for holding contact terminals 44 is connected to the base end side L2 of the element holding member 42 in the longitudinal direction L. As shown in FIG.
- the terminal holding member 43 is supported by the base end cover 46 by the contact member 431 .
- the tip side cover 45 is provided on the tip side L1 in the longitudinal direction L of the housing 41 and covers the sensor cell 21A of the sensor element 2.
- a gas flow hole 451 through which the exhaust gas G coming into contact with the sensor element 2 can flow is formed in the tip end cover 45 .
- the element detecting portion 21 of the sensor element 2 and the tip side cover 45 are arranged inside the exhaust pipe 7 of the engine. A portion of the exhaust gas G flowing through the exhaust pipe 7 flows into the tip end cover 45 through the gas flow holes 451 of the tip end cover 45 . Then, the exhaust gas G inside the front end cover 45 passes through the surface protective layer 38 of the sensor element 2 and the diffusion resistance portion 32 and is guided into the gas chamber 35 .
- the base end cover 46 is provided on the base end side L2 in the longitudinal direction L of the housing 41, and covers the wiring portion located on the base end side L2 in the longitudinal direction L of the gas sensor 10 to protect the wiring portion from the atmosphere A. It is for protecting from water etc. inside.
- the wiring part is configured by the contact terminal 44 as a part electrically connected to the sensor element 2, a connecting part (connecting fitting 441) between the contact terminal 44 and the lead wire 48, and the like.
- the sensor control device 5 of this embodiment includes a sensor detection unit 51, a NOx concentration calculation unit 52, a pump detection unit 53, an air-fuel ratio calculation unit 54, and a temperature detection unit 57. have.
- the current Is from the sensor detection unit 51 flows from the sensor electrode 311A through the sensor solid electrolyte body 3A to the sensor reference electrode 312A as NOx is decomposed in the sensor electrode 311A. Oxide ions migrate to and are detected on the positive side.
- the current Is from the sensor detection unit 51 is applied from the sensor reference electrode 312A to the sensor solid electrolyte body 3A in order to react the unburned gas at the sensor electrode 311A. Oxide ions move to the sensor electrode 311A through the sensor electrode 311A and are detected on the negative side.
- the NOx concentration calculator 52 calculates the concentration of NOx in the exhaust gas G based on the positive current Is detected by the sensor detector 51 .
- the higher the positive current Is the higher the calculated NOx concentration.
- the NOx concentration calculator 52 may be built in the engine control device 6 .
- the pump detector 53 detects the current Ip on the positive side.
- the oxygen in the atmosphere duct 36 is used to burn the unburned gas in contact with the pump electrode 311B. is ionized and moves from the pump reference electrode 312B to the pump electrode 311B via the pump solid electrolyte body 3B, whereby the pump detector 53 detects the current Ip on the negative side.
- the air-fuel ratio detector 55 of the present embodiment detects whether or not the air-fuel ratio of the engine by the pump cell 21B is in the specific rich state R or not. More specifically, the air-fuel ratio detector 55 of the present embodiment detects whether the air-fuel ratio of the engine calculated by the air-fuel ratio calculator 54 is in the specific rich state R or not. Since the air-fuel ratio detector 55 uses the pump cell 21B and the air-fuel ratio calculator 54, there is no need to obtain air-fuel ratio information from another gas sensor or the like, and the configuration of the gas concentration detection system 1 can be simplified. Note that the air-fuel ratio detection unit 55 may detect whether the air-fuel ratio is in the specific rich state R using the air-fuel ratio detected by an air-fuel ratio sensor as another gas sensor.
- the air-fuel ratio which is the mass ratio of combustion air to fuel, is stoichiometric when 14.7 (or 14.5), and becomes smaller than 14.7 on the rich side.
- the air-fuel ratio becomes richer, the amount of unburned gas contained in the exhaust gas G increases. Therefore, as the air-fuel ratio becomes richer, the amount of oxygen required to burn the unburned gas introduced into the gas chamber 35 also increases, and more oxygen is required in the atmosphere duct 36. .
- the short circuit monitoring unit 56 detects that a short circuit (ground short circuit) occurs in the sensor cell 21A when the current flowing through the sensor cell 21A becomes more negative than the negative short circuit determination reference value H1. It has a function to detect that The short circuit determination reference value H1 in FIGS. 6 and 7 is an example. The short circuit determination reference value H1 is appropriately set to an appropriate value.
- the short-circuit monitor 56 has a function of monitoring the current or voltage of the sensor electrode 311A or the sensor reference electrode 312A of the sensor cell 21A.
- the pump cell 21B when the exhaust gas G after being burned in a lean state in the engine reaches the pump electrode 311B in the gas chamber 35, the application of voltage causes the oxygen contained in the exhaust gas G in the gas chamber 35 to flow into the atmospheric duct. 36. At this time, the positive current Ip is detected in the pump detector 53 .
- the pump cell 21B when the exhaust gas G after being burned in a rich state in the engine reaches the pump electrode 311B in the gas chamber 35, a reverse current Ip is generated, causing oxygen to flow from the atmosphere duct 36 into the gas chamber 35. is taken in. At this time, the pump detector 53 detects the current Ip on the negative side.
- the specific rich state R of this embodiment is the air flowing into the air duct 36 that can be supplied from the air duct 36 into the gas chamber 35 in order to react the unburned gas contained in the exhaust gas G flowing into the gas chamber 35. It is determined based on the supply limit amount of oxygen contained in A. With this configuration, the specific rich state R can be determined appropriately.
- the specific rich state R indicates the air-fuel ratio of the engine when the combustion reaction between the unburned gas contained in the exhaust gas G flowing into the gas chamber 35 and the oxygen contained in the atmosphere A within the atmosphere duct 36 is in equilibrium.
- the specific rich state R may be regarded as a limit air-fuel ratio on the rich side that can be detected by the pump cell 21B and the pump detection section 53 .
- Unburned gases such as hydrocarbons and carbon monoxide in the gas chamber 35 react with oxygen and are converted into water, carbon dioxide, and the like.
- the limit amount of oxygen supplied by the air duct 36 is determined by the volume, flow passage cross-sectional area, shape, and the like of the air duct 36 .
- the sensor control device 5 is provided with a temperature detection section 57 for detecting the temperature of the sensor element 2 .
- the temperature detection unit 57 has a temperature detection circuit 571 that detects the resistance value or impedance of the pump cell 21B, and obtains the temperature of the sensor element 2 based on this resistance value or impedance.
- the temperature detection circuit 571 may detect the resistance value or impedance of the sensor cell 21A or the heating element 34.
- the sensor control device 5 is configured to detect the concentration of NOx, the air-fuel ratio, etc. when the temperature detected by the temperature detection unit 57 is equal to or higher than the activation temperature of the sensor element 2 .
- the air-fuel ratio detection unit 55 detects the specific rich state R. detected. Then, as shown in FIG. 6(c), the short-circuit monitoring unit 56 is prohibited from monitoring the detection or determination of the short-circuit state of the sensor cell 21A.
- the specific rich state R is detected after a predetermined time t1 after the current Ip detected by the pump detection unit 53 becomes less than or equal to the negative pump current threshold value P1.
- the amount of oxygen supplied from the atmospheric duct 36 to the pump electrode 311B is restricted by the oxygen supply limit amount of the atmospheric duct 36.
- the current Ip detected by the pump detection unit 53 is maintained at a second negative value Ip2 that is larger than the first negative value Ip1, that is, returned from the first negative value Ip1 to the zero side.
- the amount of oxygen supplied from the atmosphere duct 36 to the pump electrode 311B is limited, unburned gas remaining in the exhaust gas G reaches the sensor electrode 311A.
- the specific rich state R detected by the air-fuel ratio detector 55 may be identified by combining the current Is detected by the sensor detector 51 and the current Ip detected by the pump detector 53 . More specifically, in the specific rich state R, as shown in FIG. 7A, the current Ip flowing between the pump electrode 311B and the pump reference electrode 312B, which is detected by the pump detection unit 53, is at a predetermined negative side. The current Is flowing between the sensor electrode 311A and the sensor reference electrode 312A, which drops below the pump current threshold value P1 and is detected by the sensor detection unit 51 as shown in FIG. 7B, indicates a short circuit state.
- the current Ip detected by the pump detector 53 starts after falling below a predetermined negative sensor current threshold value S1, and then rises to exceed the pump current threshold value P1, and the pump current becomes as shown in FIG. It may end when the threshold value P1 is exceeded and maintained for a predetermined time t3.
- Control method of gas concentration detection system 1 An example of the control method of the gas concentration detection system 1 will be described below with reference to the flowchart of FIG.
- the heating element 34 heats the sensor element 2 (step S101), and the sensor control device 5 determines whether the temperature of the sensor element 2 is equal to or higher than the activation temperature. It is determined whether or not (step S102).
- the normal state N is detected by the air-fuel ratio detection section 55, and the short-circuit state determination by the short-circuit monitoring section 56 is permitted (step S103).
- the current Ip flowing through the pump cell 21B is detected by the pump detection unit 53 (step S104), and the current Is flowing through the sensor cell 21A is detected by the sensor detection unit 51 (step S105).
- the NOx concentration calculator 52 starts calculating the concentration of NOx in the exhaust gas G
- the air-fuel ratio calculator 54 starts calculating the air-fuel ratio of the engine. In the following description, these calculations are omitted, and the control of monitoring whether or not the sensor cell 21A is in a short-circuited state by the short-circuit monitoring unit 56 will be described.
- the air-fuel ratio detection unit 55 determines whether or not the current Ip of the pump cell 21B detected by the pump detection unit 53 has dropped below the negative pump current threshold value P1 indicating the specific rich state R (step S106).
- the short circuit monitoring unit 56 monitors the short circuit state of the sensor cell 21A. Specifically, it is determined whether or not the current Is of the sensor cell 21A detected by the sensor detection unit 51 has become equal to or less than the short-circuit determination reference value H1 (step S108).
- step S109 When the current of the sensor cell 21A becomes equal to or less than the short-circuit determination reference value H1, the short-circuit state of the sensor cell 21A is detected by the short-circuit monitoring unit 56 (step S109). When the current Is of the sensor cell 21A exceeds the short circuit determination reference value H1, the short circuit state of the sensor cell 21A is not detected. Then, the process is executed again from step S103.
- step S110 the specific rich state R is detected by the air-fuel ratio detection unit 55, and the short circuit is detected by the short circuit monitoring unit 56. State determination is prohibited (step S110).
- step S111 the current Ip flowing through the pump cell 21B is detected by the pump detector 53 (step S111).
- the air-fuel ratio detection unit 55 determines whether or not the current Ip of the pump cell 21B detected by the pump detection unit 53 has risen to a pump current recovery value P2 indicating recovery of the air-fuel ratio to the normal state N or more.
- the pump current recovery value P2 is a current that is greater than the pump current threshold value P1 and less than 0 [A]. If the current Is of the pump cell 21B has not risen to the pump current recovery value P2 or more, steps S110 to S112 are repeatedly executed.
- step S112 when the current Ip of the pump cell 21B rises to the pump current recovery value P2 or more, the short-circuit monitoring unit 56 determines whether or not this rising state has been maintained continuously for the predetermined time t2. (step S113). Steps S110 to S113 are repeated until this rising state is maintained for the predetermined time t2.
- step S103 the normal state N is detected by the air-fuel ratio detector 55, and the short-circuit monitor 56 Determination of the short-circuit state is permitted (step S103). Then, steps S103 to S109 are repeatedly executed. In this manner, the short-circuit monitoring unit 56 is prohibited from determining the short-circuit state of the sensor cell 21A in each time period during which the specific rich state R is detected. Determination of the short-circuit state continues (permitted).
- the gas concentration detection system 1 of the present embodiment prohibits the short-circuit monitor 56 from determining whether or not the sensor cell 21A is short-circuited while the air-fuel ratio detector 55 is detecting the specific rich state R. is.
- the specific rich state R since sufficient oxygen is not supplied to the sensor reference electrode 312A, a change in current similar to that in the short circuit state of the sensor cell 21A occurs. Therefore, by not determining the short-circuit state in the specific rich state R, erroneous determination of the short-circuit state can be prevented.
- the air-fuel ratio detection unit 55 detects the specific rich state R, the detection of the short-circuit state may be permitted instead of permitting the determination of the short-circuit state. Further, when the air-fuel ratio detection unit 55 detects the normal state N, the detection of the short-circuit state may be permitted instead of permitting the determination of the short-circuit state. Determination and detection of a short-circuit state need not be clearly distinguished, and both may be regarded as monitoring of a short-circuit state.
- this embodiment shows the case where the sensor element 2 has one solid electrolyte body by providing the pump cell 21B in the sensor solid electrolyte body 3A.
- the gas sensor 10 of the present embodiment has a pump cell 21B configured using a pump electrode 311B and a pump reference electrode 312B provided on the sensor solid electrolyte body 3A.
- the pump cell 21B is used to obtain the air-fuel ratio of the engine based on the exhaust gas G based on the current Ip flowing between the pump electrode 311B and the pump reference electrode 312B.
- the pump reference electrode 312B of this embodiment is integrated with the sensor reference electrode 312A.
- the air-fuel ratio detection unit 55 of this embodiment also detects whether the air-fuel ratio of the engine by the pump cell 21B is in the specific rich state R or not.
- a sensor electrode 311A and a pump electrode 311B are accommodated on the first surface 301 of the sensor solid electrolyte body 3A of the present embodiment, and a gas chamber 35 into which the exhaust gas G is introduced via the diffusion resistance portion 32 is adjacent to the first surface 301. formed.
- a sensor reference electrode 312A and a pump reference electrode 312B are accommodated on the second surface 302 of the sensor solid electrolyte body 3A, which is located on the side opposite to the side on which the gas chamber 35 is located, and the atmosphere A is introduced.
- An atmospheric duct 36 is formed adjacently.
- the sensor electrode 311A is arranged at a position downstream of the arrangement position of the pump electrode 311B in the gas chamber 35 in the flow of the exhaust gas G.
- the configurations of the air-fuel ratio detector 55, the short-circuit monitor 56, and the like are the same as those of the first embodiment.
- the specific rich state R detected by the air-fuel ratio detection unit 55 of this embodiment can be supplied from the air duct 36 into the gas chamber 35 in order to react the unburned gas contained in the exhaust gas G flowing into the gas chamber 35. It is determined based on the oxygen supply limit.
- This embodiment shows a case where the configuration of the sensor cell 21A is different from the first and second embodiments.
- the sensor cell 21A of this embodiment has a configuration for reducing the influence of oxygen remaining in the gas chamber 35 on the sensor cell 21A after oxygen contained in the exhaust gas G in the gas chamber 35 is removed by the pump cell 21B.
- the sensor electrode 311A provided in the sensor solid electrolyte body 3A of this embodiment is composed of a specific gas electrode 311C and an oxygen electrode 311D.
- 311 C of specific gas electrodes have the catalytic activity with respect to oxygen and NOx like 311 A of sensor electrodes of Embodiment 1.
- the oxygen electrode 311D like the sensor reference electrode 312A of the first embodiment, has catalytic activity with respect to oxygen.
- the sensor cell 21A of this embodiment includes a specific gas cell 21C configured using a specific gas electrode 311C and a sensor reference electrode 312A provided on the sensor solid electrolyte body 3A, and an oxygen electrode 311D provided on the sensor solid electrolyte body 3A. and an oxygen cell 21D constructed using a sensor reference electrode 312A.
- the specific gas cell 21C is used to obtain the concentration of the specific gas after the oxygen contained in the exhaust gas G is reduced by the pump cell 21B based on the current flowing between the specific gas electrode 311C and the sensor reference electrode 312A.
- the oxygen cell 21D is used to obtain the concentration of oxygen in the gas chamber 35 after the oxygen contained in the exhaust gas G is reduced by the pump cell 21B, based on the current flowing between the oxygen electrode 311D and the sensor reference electrode 312A. .
- the sensor detection unit 51 of this embodiment is composed of a sensor detection unit 51C that detects current flowing through the specific gas cell 21C and a sensor detection unit 51D that detects current flowing through the oxygen cell 21D.
- the sensor detection unit 51 is configured to subtract the current flowing through the oxygen cell 21D from the current flowing through the specific gas cell 21C to obtain the output current. With this configuration, it is possible to reduce the influence of residual oxygen as noise on NOx detection.
- the short-circuit monitoring unit 56 of this embodiment is configured to detect whether or not at least one of the specific gas cell 21C and the oxygen cell 21D has become short-circuited, or to permit or prohibit the determination. In order to appropriately monitor the short-circuit state, the short-circuit monitoring unit 56 should monitor the short-circuit state of both the specific gas cell 21C and the oxygen cell 21D.
- the influence of residual oxygen on NOx detection is reduced, so that the calculation accuracy of the NOx concentration can be improved.
- Other configurations, effects, and the like in the gas concentration detection system 1 of the present embodiment are the same as the configurations, effects, and the like of the first and second embodiments.
- the components indicated by the same reference numerals as those in the first and second embodiments are the same as those in the first and second embodiments.
- This embodiment shows a case where the configurations of the air-fuel ratio detector 55 and the short-circuit monitor 56 are applied to a gas sensor 10 that is further different from the gas sensors 10 of the first to third embodiments.
- the sensor solid electrolyte body 3A, the pump solid electrolyte body 3B, the sensor cell 21A, and the pump cell 21B may have various configurations.
- Each of the sensor solid electrolyte body 3A and the pump solid electrolyte body 3B may be composed of a plurality of solid electrolyte bodies.
- the sensor element 2 of the gas sensor 10 includes a pump solid electrolyte body 3B provided with a pump cell 21B and an oxygen cell 21D for detecting the concentration of residual oxygen in the gas chamber 35.
- a first sensor solid electrolyte body 3A1 and a second sensor solid electrolyte body 3A2 provided with a specific gas cell 21C for detecting the concentration of NOx may be provided.
- the gas chamber 35 is formed between the pump solid electrolyte body 3B and the first sensor solid electrolyte body 3A1, and the pump reference electrode 312B of the pump cell 21B is connected to the exhaust gas through the protective layer 321. exposed to G.
- the gas chamber 35 penetrates the first sensor solid electrolyte body 3A1 and is formed between the first sensor solid electrolyte body 3A1 and the second sensor solid electrolyte body 3A2. It is connected up to the gas chamber 351 . Between the first sensor solid electrolyte body 3A1 and the second sensor solid electrolyte body 3A2, an atmosphere duct 36 into which the atmosphere A is introduced is formed adjacent to the detected gas chamber 351. As shown in FIG.
- a pump electrode 311B of the pump cell 21B and an oxygen electrode 311D of the oxygen cell 21D are arranged in the gas chamber 35.
- the sensor reference electrode 312A of the oxygen cell 21D and the sensor reference electrode 312A of the specific gas cell 21C are located within the air duct 36.
- the specific gas electrode 311C and the sensor reference electrode 312A of the specific gas cell 21C are provided on the surface of the second sensor solid electrolyte body 3A2 on the same side. Also in this case, the specific gas cell 21C and the oxygen cell 21D are monitored for a short circuit state by the short circuit monitor 56.
- the oxygen contained in the exhaust gas G introduced into the gas chamber 35 from the diffusion resistance section 32 is discharged outside by the operation of the pump cell 21B. Further, the concentration of oxygen remaining in the gas chamber 35 is detected by the operation of the oxygen cell 21D, and the operation of the pump cell 21B is controlled so as to eliminate the residual oxygen. Then, in the specific gas cell 21C, a plus side current corresponding to the concentration of NOx contained in the exhaust gas G introduced into the detection gas chamber 351 is detected.
- the unburned gas contained in the exhaust gas G introduced from the diffusion resistance portion 32 into the gas chamber 35 is supplied from the outside through the pump solid electrolyte body 3B to the gas chamber. 35 and oxygen taken into the gas chamber 35 from the atmosphere duct 36 via the first sensor solid electrolyte body 3A1.
- the exhaust gas G flowing into the detected gas chamber 351 contains water, carbon dioxide, etc. produced by the reaction between the unburned gas and oxygen, but contains almost no NOx. almost no current flows.
- the unburned gas contained in the exhaust gas G introduced from the diffusion resistance portion 32 into the gas chamber 35 cannot completely react with the oxygen introduced into the gas chamber 35. , flows into the detection gas chamber 351 .
- the amount of oxygen supplied by the atmosphere duct 36 reaches its limit, and oxygen moves from the atmosphere duct 36 into the detection gas chamber 351 in order to react the unburned gas in the detection gas chamber 351 .
- a negative current is detected in the specific gas cell 21C.
- the negative current that flows through the specific gas cell 21C in the specific rich state R cannot be distinguished from the negative current that flows when the specific gas cell 21C is short-circuited. Therefore, by using the gas concentration detection system 1 having the air-fuel ratio detection unit 55 and the short-circuit monitoring unit 56 and prohibiting the monitoring of the short-circuit state in the specific rich state R, erroneous detection or erroneous determination of the short-circuit state can be prevented. can.
- the sensor element 2 of the gas sensor 10 includes a main pump cell 21B1 provided in the pump solid electrolyte body 3B and the sensor solid electrolyte body 3A, and the pump solid electrolyte body 3B and the sensor solid electrolyte body 3B.
- a configuration including the auxiliary pump cell 21B2 provided in the electrolyte body 3A and the sensor cell 21A provided in the sensor solid electrolyte body 3A may be employed.
- the pump electrodes 311B of the main pump cell 21B1 and the auxiliary pump cell 21B2 are provided across the pump solid electrolyte body 3B and the sensor solid electrolyte body 3A.
- the pump reference electrodes 312B of the main pump cell 21B1 and the auxiliary pump cell 21B2 are exposed to the external exhaust gas G through the surface protection layer 38. As shown in FIG.
- the portion of the insulator is small, and portions other than the pump solid electrolyte body 3B and the sensor solid electrolyte body 3A are also formed of the fixed electrolyte body.
- the solid electrolyte body 3B for the pump and the solid electrolyte body 3A for the sensor are appropriately conducted, and they are combined to generate oxide ion conductivity.
- a sensor electrode 311A of the sensor cell 21A is arranged in the gas chamber 35, and a sensor reference electrode 312A of the sensor cell 21A is arranged in an atmosphere introduction layer 361 connected to the atmosphere duct 36. Also in this case, the sensor cell 21A is monitored for a short-circuit state by the short-circuit monitoring unit 56 .
- the oxygen contained in the exhaust gas G introduced into the gas chamber 35 from the diffusion resistance section 32 is discharged outside by the operation of the main pump cell 21B1 and the auxiliary pump cell 21B2. Further, the operation of the auxiliary pump cell 21B2 adjusts the oxygen partial pressure in the gas chamber 35 to a low partial pressure that does not substantially affect NOx detection. Then, in the sensor cell 21A, a plus side current corresponding to the concentration of NOx contained in the exhaust gas G introduced into the gas chamber 35 is detected.
- the unburned gas contained in the exhaust gas G introduced from the diffusion resistance portion 32 into the gas chamber 35 is supplied from the outside through the pump solid electrolyte body 3B to the gas chamber. 35, and oxygen introduced into the gas chamber 35 from the atmosphere duct 36 via the atmosphere introduction layer 361 and the sensor solid electrolyte body 3A.
- the exhaust gas G reaching the sensor electrode 311A contains water, carbon dioxide, etc. produced by the reaction between the unburned gas and oxygen, but hardly contains NOx. Current cannot flow.
- the unburned gas contained in the exhaust gas G introduced from the diffusion resistance portion 32 into the gas chamber 35 cannot completely react in the main pump cell 21B1 and the auxiliary pump cell 21B2. , reaches the sensor electrode 311A.
- the amount of oxygen supplied by the air duct 36 reaches its limit, and in order to react the unburned gas reaching the sensor electrode 311A, the oxygen is supplied from the sensor reference electrode 312A to the sensor electrode 311A via the sensor solid electrolyte 3A. Oxygen moves. As a result, the negative current is detected in the sensor cell 21A.
- the negative current that flows through the sensor cell 21A in the specific rich state R cannot be distinguished from the negative current that flows when the sensor cell 21A is short-circuited. Therefore, by using the gas concentration detection system 1 having the air-fuel ratio detection unit 55 and the short-circuit monitoring unit 56 and prohibiting the monitoring of the short-circuit state in the specific rich state R, erroneous detection or erroneous determination of the short-circuit state can be prevented. can.
- present disclosure is not limited to only each embodiment, and further different embodiments can be configured without departing from the gist thereof.
- the present disclosure includes various modifications, modifications within the equivalent range, and the like.
- the technical idea of the present disclosure includes combinations of various constituent elements, forms, and the like assumed from the present disclosure.
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Abstract
Description
内燃機関の排気管に配置されて使用されるものであって、センサ用固体電解質体に設けられたセンサ電極及びセンサ基準電極によって構成され、前記センサ電極及び前記センサ基準電極間に流れる電流に基づいて、前記排気管を流れる排ガスに含まれる特定ガスの濃度を求めるためのセンサセルを有する、ガスセンサと、
前記排ガスに基づく前記内燃機関の空燃比が、特定値以下に小さいことを示す特定リッチ状態にあるか否かを検知する空燃比検知部と、
前記空燃比検知部が前記特定リッチ状態を検知していない間には、前記センサセルが短絡状態になったか否かの検出又は判定を許可する一方、前記空燃比検知部が前記特定リッチ状態を検知している間には、前記センサセルが短絡状態になったか否かの検出又は判定を禁止する短絡監視部と、を備えるガス濃度検出システムにある。
<実施形態1>
本形態のガス濃度検出システム1は、図1~図5に示すように、ガスセンサ10と、空燃比検知部55及び短絡監視部56を有するセンサ制御装置5とを備える。ガスセンサ10は、内燃機関としてのエンジンの排気管7に配置されて使用されるものである。ガスセンサ10は、センサ用固体電解質体3Aに設けられたセンサ電極311A及びセンサ基準電極312Aによって構成されたセンサセル21Aを有する。センサセル21Aは、センサ電極311A及びセンサ基準電極312A間に流れる電流に基づいて、排気管7を流れる排ガスGに含まれる特定ガスの濃度を求めるために用いられる。
(ガスセンサ10)
図1に示すように、ガスセンサ10は、車両の内燃機関(エンジン)の排気管7の取付口71に配置され、排気管7を流れる排ガスGを検出対象ガスとして、検出対象ガスにおける特定ガスの濃度を検出するために用いられる。本形態のガスセンサ10のセンサセル21Aは、排ガスGに含まれる特定ガスとしてのNOx(窒素酸化物)の濃度を求めるためのものである。エンジンは、ディーゼルエンジンでもよく、ガソリンエンジンでもよい。
図1~図4に示すように、本形態のガスセンサ10は、センサ用固体電解質体3Aに積層されたポンプ用固体電解質体3Bに設けられたポンプ電極311B及びポンプ基準電極312Bを用いて構成されたポンプセル21Bをさらに有する。ポンプセル21Bは、ポンプ電極311B及びポンプ基準電極312B間に流れる電流Ipに基づいて、排ガスGに基づくエンジンの空燃比を求めるために使用される。センサ素子2の長手方向Lの先端側L1の部分には、センサセル21A及びポンプセル21Bによる素子検知部21が形成されている。
本形態において、センサ素子2の長手方向Lとは、センサ素子2が長尺形状に延びる方向のことをいう。また、長手方向Lに直交し、センサ用固体電解質体3A、ポンプ用固体電解質体3B及び各絶縁体33A,33B,33Cが積層された方向を、積層方向Dという。また、長手方向Lと積層方向Dとに直交する方向を、幅方向Wという。また、センサ素子2の長手方向Lにおいて、排ガスGに晒される側を先端側L1といい、先端側L1の反対側を基端側L2という。ガスセンサ10においても、センサ素子2の長手方向Lと同じ方向のことを長手方向Lという。
図2及び図3に示すように、センサ用固体電解質体3A及びポンプ用固体電解質体3Bは、所定の活性温度において、酸化物イオン(O2-)の伝導性を有するものである。センサ用固体電解質体3Aの内側表面301Aには、排ガスGに晒されるセンサ電極311Aが設けられており、センサ用固体電解質体3Aの外側表面302Aには、大気Aに晒されるセンサ基準電極312Aが設けられている。
図2~図4に示すように、ガス室35は、センサ用固体電解質体3Aの内側表面301Aとポンプ用固体電解質体3Bの内側表面301Bとの間において、中間絶縁体33Cとセンサ用固体電解質体3Aとポンプ用固体電解質体3Bとに囲まれて形成されている。ガス室35は、中間絶縁体33Cの長手方向Lの先端側L1の部位において、センサ電極311Aを収容する位置に形成されている。ガス室35は、中間絶縁体33Cと拡散抵抗部32とセンサ用固体電解質体3Aとポンプ用固体電解質体3Bとによって閉じられた空間部として形成されている。排気管7内を流れる排ガスGは、拡散抵抗部32を通過してガス室35内に導入される。
図2及び図4に示すように、本形態の拡散抵抗部(ガス導入部)32は、ガス室35の長手方向Lの先端側L1の部位に設けられている。拡散抵抗部32は、中間絶縁体33Cに形成された導入口内に、酸化アルミニウム(アルミナ)等の金属酸化物の多孔質体を配置することによって形成されている。ガス室35に導入される排ガスGの拡散速度(流量)は、排ガスGが拡散抵抗部32における多孔質体の気孔を通過する速度が制限されることによって決定される。なお、拡散抵抗部32は、ガス室35の幅方向Wの両側の部位に設けてもよい。
図2及び図3に示すように、ポンプ用固体電解質体3Bの外側表面302Bには、ポンプ側絶縁体33Bとポンプ用固体電解質体3Bとに囲まれ、大気Aが導入される大気ダクト36が隣接して形成されている。大気ダクト36は、ポンプ側絶縁体33Bにおける、ポンプ基準電極312Bを収容する長手方向Lの部位から、センサ素子2の長手方向Lにおける基端位置まで形成されている。
図2及び図3に示すように、センサ用固体電解質体3Aの外側表面302Aには、センサ側絶縁体33Aとセンサ用固体電解質体3Aとに囲まれ、大気Aが導入される補助大気ダクト37が隣接して形成されている。補助大気ダクト37は、センサ側絶縁体33Aにおける、センサ基準電極312Aを収容する長手方向Lの部位から、センサ素子2の長手方向Lにおける基端位置まで形成されている。なお、補助大気ダクト37内には、酸化アルミニウム等の金属酸化物の多孔質体による保護層を設けてもよい。
図2及び図3に示すように、センサ側絶縁体33Aは、補助大気ダクト37を形成するものであり、中間絶縁体33Cは、ガス室35を形成するものであり、ポンプ側絶縁体33Bは、大気ダクト36を形成するとともに発熱体34を埋設するものである。各絶縁体33A,33B,33Cは、酸化アルミニウム等の金属酸化物によって形成されている。各絶縁体33A,33B,33Cは、排ガスG又は大気Aである気体が透過することができない緻密体として形成されている。
図2~図4に示すように、発熱体34は、大気ダクト36を形成するポンプ側絶縁体33B内に埋設されている。発熱体34は、通電によって発熱する発熱部341と、発熱部341の、長手方向Lの基端側L2に繋がる発熱体リード部342とを有する。発熱部341は、積層方向Dにおいて、少なくとも一部がセンサ電極311A、センサ基準電極312A、ポンプ電極311B及びポンプ基準電極312Bに重なる位置に配置されている。発熱体34は、導電性を有する金属材料によって構成されている。発熱体リード部342の長手方向Lの基端側L2の端部には、端子接続部22が形成されている。
図1に示すように、センサ素子2の長手方向Lの先端側L1には、素子検知部21を覆う表面保護層38が形成されている。表面保護層38は、排ガスGが通過可能な気孔を有するセラミックス材料としての、互いに結合された複数のセラミックス粒子によって構成されている。
図1に示すように、ガスセンサ10は、センサ素子2を排気管7に配置して、センサ制御装置5に電気配線するために、ハウジング41、素子保持材42、端子保持材43、接触部材431、接点端子44、先端側カバー45、基端側カバー46、ブッシュ47、リード線48等を有する。
図1に示すように、ガスセンサ10におけるリード線48は、ガスセンサ10におけるガス検出の制御を行うセンサ制御装置5に電気接続されている。センサ制御装置5は、エンジンにおける燃焼運転を制御するエンジン制御装置6と連携してガスセンサ10における電気制御を行うものである。センサ制御装置5は、各種制御回路、コンピュータ等を用いて構成されている。なお、センサ制御装置5は、エンジン制御装置6内に構築してもよい。
図2に示すように、センサ検出部51は、排気管7を流れる排ガスGに含まれる特定ガスとしてのNOxの濃度を算出するために用いられ、センサ電極311Aとセンサ基準電極312Aとの間に流れる電流Isを検出する。センサ検出部51は、センサ電極311Aとセンサ基準電極312Aとの間に直流電圧を印加する電圧印加回路511と、センサ電極311Aとセンサ基準電極312Aとの間に流れる電流Isを検出する電流検出回路512とを有する。電圧印加回路511は、センサセル21Aに限界電流特性が生じる大きさの直流電圧を各電極311A,312A間に印加する。直流電圧は、センサ基準電極312Aをプラス側として印加される。
図2及び図5に示すように、NOx濃度算出部52は、センサ検出部51によって検出されるプラス側の電流Isに基づいて、排ガスGにおけるNOxの濃度を算出する。NOx濃度算出部52においては、プラス側の電流Isが大きいほど、NOxの濃度が高く算出される。NOx濃度算出部52は、エンジン制御装置6内に構築されていてもよい。
図2及び図5に示すように、ポンプ検出部53は、ポンプ電極311Bとポンプ基準電極312Bとの間に直流電圧を印加する電圧印加回路531と、ポンプ電極311Bとポンプ基準電極312Bとの間に流れる電流Ipを検出する電流検出回路532とを有する。電圧印加回路531は、排ガスGがガス室35内に流入するときの拡散抵抗部32による拡散抵抗によってポンプセル21Bに限界電流特性が生じる大きさの直流電圧を各電極311B,312B間に印加する。直流電圧は、ポンプ基準電極312Bをプラス側として印加され、直流電圧の印加によって、ガス室35内の酸素が大気ダクト36へ排出される。
図2及び図5に示すように、空燃比算出部54は、ポンプ検出部53によって検出される電流Ipに基づいて、排ガスGの組成に基づくエンジンの空燃比を算出する。ポンプ検出部53がプラス側の電流Ipを検出するときには、空燃比算出部54によってリーン側の空燃比が算出される。ポンプ検出部53がマイナス側の電流Ipを検出するときには、空燃比算出部54によってリッチ側の空燃比が算出される。空燃比算出部54は、エンジン制御装置6内に構築されていてもよい。
図2及び図5に示すように、本形態の空燃比検知部55は、ポンプセル21Bによるエンジンの空燃比が特定リッチ状態Rにあるか否かを検知する。より具体的には、本形態の空燃比検知部55は、空燃比算出部54によって算出されるエンジンの空燃比が、特定リッチ状態Rにあるか否かを検知する。空燃比検知部55がポンプセル21B及び空燃比算出部54を利用することにより、他のガスセンサ等から空燃比の情報を得る必要がなくなり、ガス濃度検出システム1の構成を簡単にすることができる。なお、空燃比検知部55は、他のガスセンサとしての空燃比センサによって検出された空燃比を利用して、空燃比が特定リッチ状態Rにあるか否かを検知してもよい。
図5及び図6に示すように、短絡監視部56は、センサセル21Aに流れる電流が、マイナス側の短絡判定基準値H1よりもマイナス側になったときには、センサセル21Aに短絡(グランドショート)が生じていることを検出する機能を有する。図6及び図7における短絡判定基準値H1は一例である。短絡判定基準値H1は、適切な値に適宜設定される。短絡監視部56は、センサセル21Aのセンサ電極311A又はセンサ基準電極312Aの電流又は電圧を監視する機能を有する。ただし、短絡監視部56は、空燃比検知部55が特定リッチ状態Rを検知している間には、センサセル21Aが短絡状態になったか否かの検出、又は短絡状態になったか否かの判定を禁止する。エンジンの空燃比は、特定リッチ状態Rとなるリッチ側の空燃比に一時的になったとしても、その後、特定リッチ状態Rではない通常状態Nに復帰する。
図2及び図5に示すように、センサ制御装置5には、センサ素子2の温度を検知するための温度検知部57が設けられている。温度検知部57は、ポンプセル21Bの抵抗値又はインピーダンスを検出する温度検出回路571を有しており、この抵抗値又はインピーダンスに基づいて、センサ素子2の温度を求める。温度検出回路571は、センサセル21A又は発熱体34の抵抗値又はインピーダンスを検出してもよい。センサ制御装置5は、温度検知部57によって検知される温度が、センサ素子2の活性温度以上である場合に、NOxの濃度の検出、空燃比の検出等を行うよう構成されている。
図6(a),(b)には、エンジンにおいてリッチの状態で燃焼した後の排ガスGがガス室35内に導入されるときの、ポンプセル21Bにおける電流Ipの変化、及びセンサセル21Aにおける電流Isの変化を示す。図6(a)に示すように、ガス室35内に未燃ガスを含む排ガスGが導入されるときには、ポンプ検出部53によってマイナス側の電流Ipが検出される。このとき、大気ダクト36内の酸素が、ポンプ基準電極312Bにおいてイオン化してポンプ用固体電解質体3Bを介してポンプ電極311Bへ移動できるイオン伝導能力に応じて、ポンプ検出部53によって検出される電流が所定の第1マイナス値Ip1に維持される。
エンジンの空燃比がリーン側に変化したときには、排ガスGに含まれる未燃ガス又は酸素が、ポンプ電極311Bに到達する時点から、センサ電極311Aに到達する時点までには時間遅れが生じる。そのため、ポンプ検出部53によって検出される電流Ipが変化する時点から、センサ検出部51によって検出される電流Isが変化する時点までには時間遅れが生じる。
以下に、ガス濃度検出システム1の制御方法の一例について、図8のフローチャートを参照して説明する。
車両のエンジン、エンジン制御装置6及びセンサ制御装置5の起動後、発熱体34によってセンサ素子2が加熱され(ステップS101)、センサ制御装置5によって、センサ素子2の温度が活性温度以上であるか否かが判定される(ステップS102)。次いで、センサ素子2の温度が活性温度以上である場合には、空燃比検知部55によって通常状態Nが検知され、短絡監視部56による短絡状態の判定が許可される(ステップS103)。次いで、ポンプ検出部53によってポンプセル21Bに流れる電流Ipが検出され(ステップS104)、センサ検出部51によってセンサセル21Aに流れる電流Isが検出される(ステップS105)。
本形態のガス濃度検出システム1は、空燃比検知部55が特定リッチ状態Rを検知している間は、短絡監視部56による、センサセル21Aが短絡状態になったか否かの判定を禁止するものである。特定リッチ状態Rにおいては、センサ基準電極312Aに十分な酸素が供給されないために、センサセル21Aが短絡状態になった場合と同様の電流の変化が生じる。そのため、特定リッチ状態Rにおいて、短絡状態の判定を行わないことにより、短絡状態の誤判定を防ぐことができる。
本形態は、図9及び図10に示すように、ポンプセル21Bをセンサ用固体電解質体3Aに設けることにより、センサ素子2が1枚の固体電解質体を有する場合について示す。本形態のガスセンサ10は、センサ用固体電解質体3Aに設けられたポンプ電極311B及びポンプ基準電極312Bを用いて構成されたポンプセル21Bを有する。ポンプセル21Bは、ポンプ電極311B及びポンプ基準電極312B間に流れる電流Ipに基づいて、排ガスGに基づくエンジンの空燃比を求めるために用いられる。本形態のポンプ基準電極312Bは、センサ基準電極312Aと一体化されている。
本形態は、センサセル21Aの構成が実施形態1,2の場合と異なる場合について示す。本形態のセンサセル21Aは、ポンプセル21Bによって、ガス室35内の排ガスGに含まれる酸素が除去された後にガス室35内に残留する酸素がセンサセル21Aに与える影響を少なくするための構成を有する。
本形態は、空燃比検知部55及び短絡監視部56の構成を、実施形態1~3のガスセンサ10とはさらに異なるガスセンサ10に適用する場合について示す。センサ用固体電解質体3A、ポンプ用固体電解質体3B、センサセル21A及びポンプセル21Bは、種々の構成を有していてもよい。センサ用固体電解質体3A及びポンプ用固体電解質体3Bは、それぞれ複数の固体電解質体によって構成してもよい。
また、図13に示すように、ガスセンサ10のセンサ素子2は、ポンプ用固体電解質体3B及びセンサ用固体電解質体3Aに設けられた主ポンプセル21B1と、及びポンプ用固体電解質体3B及びセンサ用固体電解質体3Aに設けられた補助ポンプセル21B2と、センサ用固体電解質体3Aに設けられたセンサセル21Aとを有する構成としてもよい。主ポンプセル21B1及び補助ポンプセル21B2のポンプ電極311Bは、ポンプ用固体電解質体3B及びセンサ用固体電解質体3Aに跨って設けられている。主ポンプセル21B1及び補助ポンプセル21B2のポンプ基準電極312Bは、表面保護層38を介して外部の排ガスGに晒されている。
Claims (8)
- 内燃機関の排気管(7)に配置されて使用されるものであって、センサ用固体電解質体(3A)に設けられたセンサ電極(311A)及びセンサ基準電極(312A)によって構成され、前記センサ電極及び前記センサ基準電極間に流れる電流(Is)に基づいて、前記排気管を流れる排ガス(G)に含まれる特定ガスの濃度を求めるためのセンサセル(21A)を有する、ガスセンサ(10)と、
前記排ガスに基づく前記内燃機関の空燃比が、特定値以下に小さいことを示す特定リッチ状態(R)にあるか否かを検知する空燃比検知部(55)と、
前記空燃比検知部が前記特定リッチ状態を検知していない間には、前記センサセルが短絡状態になったか否かの検出又は判定を許可する一方、前記空燃比検知部が前記特定リッチ状態を検知している間には、前記センサセルが短絡状態になったか否かの検出又は判定を禁止する短絡監視部(56)と、を備えるガス濃度検出システム(1)。 - 前記ガスセンサは、前記センサ用固体電解質体に積層されたポンプ用固体電解質体(3B)に設けられたポンプ電極(311B)及びポンプ基準電極(312B)によって構成され、前記ポンプ電極及び前記ポンプ基準電極間に流れる電流(Ip)に基づいて、前記排ガスに基づく前記内燃機関の空燃比を求めるためのポンプセル(21B)をさらに有しており、
前記空燃比検知部は、前記ポンプセルによる前記内燃機関の空燃比が前記特定リッチ状態にあるか否かを検知する、請求項1に記載のガス濃度検出システム。 - 前記センサ用固体電解質体の内側表面(301A)と前記ポンプ用固体電解質体の内側表面(301B)との間には、前記ポンプ電極及び前記センサ電極が収容されるとともに、拡散抵抗部(32)を介して前記排ガスが導入されるガス室(35)が形成されており、
前記ポンプ用固体電解質体の外側表面(302B)には、前記ポンプ基準電極が収容されるとともに、大気(A)が導入される大気ダクト(36)が隣接して形成されており、
前記特定リッチ状態は、前記ガス室内に流入する前記排ガスに含まれる未燃ガスを反応させるために、前記大気ダクトから前記ガス室内へ供給可能な、前記大気ダクトに流入する大気に含まれる酸素の供給限界量に基づいて定められる、請求項2に記載のガス濃度検出システム。 - 前記ガスセンサは、前記センサ用固体電解質体に設けられたポンプ電極(311B)及びポンプ基準電極(312B)によって構成され、前記ポンプ電極及び前記ポンプ基準電極間に流れる電流(Ip)に基づいて、前記排ガスに基づく前記内燃機関の空燃比を求めるためのポンプセル(21B)をさらに有しており、
前記空燃比検知部は、前記ポンプセルによる前記内燃機関の空燃比が前記特定リッチ状態にあるか否かを検知する、請求項1に記載のガス濃度検出システム。 - 前記センサ用固体電解質体には、前記センサ電極及び前記ポンプ電極が収容されるとともに、拡散抵抗部(32)を介して前記排ガスが導入されるガス室(35)が隣接して形成されており、
前記センサ用固体電解質体の、前記ガス室が位置する側とは反対側には、前記センサ基準電極及び前記ポンプ基準電極が収容されるとともに、大気(A)が導入される大気ダクト(36)が隣接して形成されており、
前記特定リッチ状態は、前記ガス室内に流入する前記排ガスに含まれる未燃ガスを反応させるために、前記大気ダクトから前記ガス室内へ供給可能な、前記大気ダクトに流入する大気に含まれる酸素の供給限界量に基づいて定められる、請求項4に記載のガス濃度検出システム。 - 前記センサ電極は、特定ガス電極(311C)と酸素電極(311D)とによって構成されており、
前記センサセルは、
前記センサ用固体電解質体に設けられた前記特定ガス電極及び前記センサ基準電極によって構成され、前記特定ガス電極及び前記センサ基準電極間に流れる電流に基づいて、前記ポンプセルによって前記排ガスに含まれる酸素が減らされた後の前記ガス室内の前記特定ガスの濃度を求めるための特定ガスセル(21C)と、
前記センサ用固体電解質体に設けられた前記酸素電極及び前記センサ基準電極によって構成され、前記酸素電極及び前記センサ基準電極間に流れる電流に基づいて、前記ポンプセルによって前記排ガスに含まれる酸素が減らされた後の前記ガス室内の酸素の濃度を求めるための酸素セル(21D)と、によって構成されており、
前記短絡監視部は、前記特定ガスセル及び前記酸素セルの少なくとも一方が短絡状態になったか否かの検出の許可及び禁止を行うよう構成されている、請求項3又は5に記載のガス濃度検出システム。 - 前記特定リッチ状態は、前記ポンプ電極及び前記ポンプ基準電極間に流れる電流が、所定のマイナス側のポンプ電流閾値(P1)以下に低下して、前記ポンプ電流閾値以下に所定時間(t1)維持された後から始まり、前記ポンプ電流閾値超過に上昇して、前記ポンプ電流閾値超過に所定時間(t2)維持されたときに終わる、請求項2~6のいずれか1項に記載のガス濃度検出システム。
- 前記特定リッチ状態は、前記ポンプ電極及び前記ポンプ基準電極間に流れる電流が、所定のマイナス側のポンプ電流閾値(P1)以下に低下し、かつ前記センサ電極及び前記センサ基準電極間に流れる電流が、所定のマイナス側のセンサ電流閾値(S1)以下に低下した後から始まり、前記ポンプ電極及び前記ポンプ基準電極間に流れる電流が、前記ポンプ電流閾値超過に上昇して、又は前記センサ電極及び前記センサ基準電極間に流れる電流が、前記センサ電流閾値超過に上昇して、所定時間(t3)維持されたときに終わる、請求項2~6のいずれか1項に記載のガス濃度検出システム。
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