JP3589872B2 - Method and apparatus for detecting exhaust gas concentration - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas concentration detection method for measuring the concentration of a harmful gas component contained in gas discharged from an internal combustion engine and a device therefor, and more particularly to a method and a device for calibrating a zero point of an output of a NOx gas sensor.
[0002]
[Prior art]
With the tightening of exhaust gas regulations, there is a strong demand for sensors capable of directly measuring the concentrations of CO, HC and NOx, which are harmful gas components in exhaust gas. Therefore, an oxide semiconductor type or ZrO₂Development of a limiting current type gas sensor using an oxygen ion conductor such as the above has been advanced. An oxide semiconductor gas sensor is a sensor that utilizes a fact that a change in electric resistance of an oxide semiconductor is proportional to an amount of a predetermined gas component adsorbed on the oxide semiconductor. On the other hand, as a limiting current type gas sensor (NOx sensor), for example, an electrode having NOx dissociation catalytic ability is arranged on an oxygen ion conductor to constitute an oxygen ion pump cell, and the oxygen ion pump cell faces a space facing the oxygen ion pump cell. A sensor that diffuses a gas whose oxygen concentration is controlled, decomposes NOx in the space, pumps out dissociated oxygen ions using the oxygen ion pump cell, and obtains a NOx gas concentration from a current flowing through the oxygen ion pump cell. Proposed.
[0003]
[Problems to be solved by the invention]
However, oxide semiconductor type gas sensors have a problem in reproducibility. On the other hand, in the limiting current type sensor, although there is no problem in reproducibility and repetition accuracy, there is a problem that the current to be detected in principle (the current flowing in the oxygen ion pump cell) is as small as about several microamps. . In addition, since the decomposition of harmful gas components (for example, NOx) is controlled or suppressed by the catalytic action on the electrode surface, the catalytic activity changes over a long period of use and the zero point (the concentration of the predetermined component is substantially reduced). There is a problem that the detection output of the gas sensor indicating zero is shifted. For this reason, the use environment of any type of gas sensor greatly changes like a sensor attached to an internal combustion engine, particularly an exhaust gas system of a vehicle, and has not been used as a sensor used for a long time.
[0004]
In view of the above circumstances, an object of the present invention is to provide a method and apparatus for detecting an exhaust gas concentration using a gas sensor capable of performing highly accurate gas concentration measurement over a long period of time, in particular, a zero point of a detection output of a NOx gas sensor. And a method for calibrating the same.
[0005]
[Means for Solving the Problems]
In order to solve the above problem, a first means of the present invention is a method for detecting an exhaust gas concentration using a NOx sensor attached to an exhaust pipe of an internal combustion engine and detecting a NOx concentration in gas exhausted from the internal combustion engine. The method,Atmospheric atmosphere is introduced into the NOx sensor, and the concentration of oxygen in the gas introduced into the NOx sensor is measured from the current flowing through the first oxygen pump cell, and the measured oxygen concentration corresponds to the concentration of oxygen in the atmosphere. WhenMeans or a step of calibrating a zero point of the detection output of the NOx sensor indicating that the NOx concentration is zero, based on the detection output of the NOx sensor, and calculating the NOx concentration based on the calibrated detection output. Detecting means or step. The second means of the present invention cuts off the fuel supply to the internal combustion engine to make the NOx concentration in the gas introduced into the NOx sensor substantially zero or substantially the same level as the atmosphere,A means or a step of measuring the oxygen concentration in the gas introduced into the NOx sensor from the current flowing in the first oxygen pump cell, and a method for measuring the oxygen concentration when the measured oxygen concentration corresponds to the oxygen concentration in the atmosphere.Means or a step of calibrating a zero point of the detection output of the NOx sensor indicating that the NOx concentration is zero, based on the detection output of the NOx sensor, and calculating the NOx concentration based on the calibrated detection output. Detecting means or step.
[0006]
The third means is a means or a step of reducing a predetermined component in the exhaust gas by enriching the air-fuel ratio of the internal combustion engine, and the concentration of the predetermined component is reduced to substantially zero or substantially the same level as the atmosphere by this reduction. Based on the detected output of the gas sensor at the time of, based on the means or process for calibrating the zero point of the detected output of the gas sensor indicating that the concentration of the predetermined component is zero, based on the calibrated detected output Means or steps for detecting the concentration of the predetermined component. The fourth means is that the gas discharged from the internal combustion engineNOxMeans or steps for operating the internal combustion engine under conditions where the concentration can be estimated or known;NOxBased on the detection output of the sensor.NOxMeans or a step of calibrating the detection output of the sensor, and based on the calibrated detection output,NOxAnd means or steps for detecting the concentration.
[0007]
The fifth means isThe NOx sensor includes first and second gaps, first and second diffusion resistance sections, and first and second oxygen ion pump cells, and the gas flows through the first gap through the first diffusion resistance section. The first oxygen ion pump cell diffuses oxygen through the first diffusion resistance portion, and diffuses oxygen from the first void portion so that the oxygen concentration in the gas diffused into the first void portion becomes a predetermined concentration. Pumping out, the gas having an oxygen concentration of the predetermined concentration diffuses from the first gap through the second diffusion resistor to the second gap, decomposes NOx in the second gap, It is characterized in that oxygen ions dissociated by a two oxygen ion pump cell are pumped out and the NOx concentration is detected from a current flowing through the second oxygen ion pump cell.
Sixth means,The NOx sensor is attached downstream of the NOx storage type catalyst, and the NOx sensor is mounted on the basis of the detection output of the NOx sensor when the air-fuel ratio is temporarily made rich to purify the NOx stored in the NOx storage type catalyst. It is characterized by performing zero point calibration.
[0008]
A seventh means is an exhaust gas concentration detecting method which is attached to an exhaust pipe of an internal combustion engine and uses a NOx sensor for detecting a NOx concentration in gas exhausted from the internal combustion engine, wherein the NOx concentration can be estimated. Alternatively, the internal combustion engine is operated under known conditions,Measuring the oxygen concentration in the gas introduced into the NOx sensor from the current flowing in the first oxygen pump cell, and measuring the oxygen concentration in the gas when the measured oxygen concentration corresponds to the oxygen concentration in the atmosphere.The detection output of the NOx sensor is calibrated based on the detection output of the NOx sensor, and the NOx concentration is detected based on the calibrated detection output.
Eighth means is a NOx sensor attached to an exhaust pipe of the internal combustion engine for detecting a NOx concentration in gas exhausted from the internal combustion engine, and detects a NOx concentration in gas exhausted from the internal combustion engine. A NOx sensor, operating condition setting means for setting operating conditions of the internal combustion engine at which the NOx concentration can be estimated or known, and under the operating conditions set by the operating condition setting means.The oxygen concentration in the gas introduced into the NOx sensor is measured from the current flowing in the first oxygen pump cell, and when the measured oxygen concentration corresponds to the oxygen concentration in the atmosphere.And a calibration means for calibrating the detection output of the NOx sensor based on the detection output of the NOx sensor.
[0009]
The calibration method of the detection output of the gas sensor according to the present invention performs the calibration (calibration) of the gas sensor based on the detection output of the gas sensor under the condition that the concentration of the harmful exhaust gas component can be estimated among the operating conditions of the internal combustion engine. It is characterized by: Generally, in an internal combustion engine of a vehicle having an electronic control type fuel supply device, for example, harmful gases such as NOx, HC, and CO in exhaust gas are used to cut off fuel supply when output becomes unnecessary such as during deceleration. The concentrations of the components are at about the same level as the atmosphere. On the other hand, under normal operating conditions, the concentration of harmful gas components emitted from the internal combustion engine is significantly higher than the level in the atmosphere. Therefore, by calibrating the gas sensor during the fuel cut, the concentration of the harmful exhaust gas component can be accurately detected even after long-term use. Further, as described above, since the zero point (offset) of the detection output changes due to long-term use of the gas sensor, the zero point may be corrected. That is, the detection output when the fuel cut is activated may be set to, for example, a level indicating zero NOx concentration.
[0010]
If the offset value of the detection output of the gas sensor (the detection output when the concentration of the detected component is zero, the detection output at the zero point) has oxygen concentration dependency (when the offset value changes depending on the oxygen concentration), All offsets (for each oxygen concentration) may be corrected based on the detected output value at the time of the fuel cut in which the concentration of the detected component and the oxygen concentration are known. For example, the difference between the initial value of the offset (OF1) corresponding to the predetermined oxygen concentration stored in the memory and the detection output value (OF2) corresponding to the predetermined oxygen concentration at the time of the fuel cut, "OF1-OF2" The offset value OF [O corresponding to each oxygen concentration stored in the memory₂] And subtract that value from the new offset value OF [O₂] May be stored in the memory. In a sensor capable of measuring the oxygen concentration, a gas having an oxygen concentration almost the same as that in the atmosphere, that is, a gas having an oxygen concentration of 20.9% is supplied to the sensor at the time of fuel cut, so that the sensitivity (gain) can be calibrated. For example, by applying the detection method of the present invention to a NOx sensor described later, the sensitivity of the first oxygen pump current can be calibrated, and the oxygen concentration can be accurately measured even after endurance use.
[0011]
When the gas sensor is a NOx sensor, and this NOx sensor is installed downstream of the NOx storage catalyst, a spike having a rich atmosphere is provided to reduce the stored NOx. At this timing, since there is almost no NOx emission, the zero point can be calibrated in the same manner as described above. Further, in this case, by comparing the detection output of the NOx sensor before and after the spike of the rich atmosphere is applied, it is possible to detect the deterioration of the catalyst (reduction of the NOx storage amount) without having to consider the change in the offset.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described. A gas sensor to which the present invention is preferably applied is a gas sensor capable of detecting the concentration of harmful components in exhaust gas of an internal combustion engine, for example, flammable CO, HC, and NOx components. As a CO sensor, for example, In₂O₃A gas sensor using an oxide semiconductor element such as the above is applied. Further, each of the HC sensors includes an oxygen pump element and an oxygen concentration cell element exposed to a test gas, and the oxygen pump element when an electromotive force generated in the oxygen concentration cell element reaches a predetermined value or less. A gas sensor for obtaining a combustible gas component concentration from a current value flowing through the gas sensor is applied. In addition, a gas sensor including an oxygen pump cell, an oxygen sensor cell, and a combustible gas component concentration detector made of an oxide semiconductor is applied. Further, as the NOx sensor, a NOx sensor having two sets of diffusion resistance parts, an oxygen ion pump cell, and a gap is applied. The measurement principle of this NOx sensor is as follows.
[0013]
(1) Exhaust gas flows into the first void portion through the first diffusion resistance portion having diffusion resistance. (2) The first oxygen ion pump cell pumps out oxygen in the first gap to such an extent that all NOx is not decomposed (the oxygen partial pressure in the first gap is controlled by a signal output from the oxygen partial pressure detection electrode) Do). (3) The gas in the first gap (the gas whose oxygen concentration is controlled) flows into the second gap through the second diffusion resistor. (4) The NOx in the second void is reduced to N by pumping out oxygen further by the second oxygen ion pump cell.₂Gas and O₂Decomposed into gas. (5) At this time, since there is a linear relationship between the second oxygen pump current Ip2 flowing through the second oxygen ion pump cell and the NOx gas concentration, the NOx gas concentration can be detected by detecting Ip2. (6) Also, the oxygen concentration in the exhaust gas can be measured from the first oxygen pump current Ip1 flowing through the first oxygen ion pump cell when the first oxygen ion pump cell pumps out the oxygen in the first gap. Using the measured value of the oxygen concentration, the NOx decomposition rate in the first void portion can be obtained, and the NOx gas concentration can be corrected.
[0014]
Next, a preferred method of using the NOx sensor in an exhaust gas purification system for a gasoline engine or a diesel engine will be described. Referring to FIG. 7A, in an exhaust gas purification system of a gasoline engine (particularly, a lean burn engine), an oxygen sensor (1) and a NOx storage type three-way catalyst are provided in an exhaust pipe from a gasoline engine to a downstream side. And an oxygen sensor {circle around (2)} (the above-described NOx sensor also serving as an oxygen sensor) are sequentially mounted. The oxygen sensor {circle around (1)} is a sensor for controlling the air-fuel ratio of the engine, and controls the fuel, air and the like supplied to the engine based on the detection output. On the other hand, the NOx sensor serving also as an oxygen sensor disposed downstream of the NOx storage type three-way catalyst is a sensor for detecting the NOx concentration and determining the operating state of the three-way catalyst and its deterioration. The engine and the like are controlled so that the three-way catalyst operates optimally based on the detected output. This NOx storage type three-way catalyst is obtained by imparting a NOx storage effect to the three-way catalyst. When the excess air ratio λ = 1 (stoichiometric point), the three-way catalyst operates as a normal three-way catalyst, and temporarily stores NOx in a lean state. , And the temporarily stored NOx is purified by periodically adding a rich spike. Generally, the material of the NOx storage type three-way catalyst is Pt to which Ba or the like having a NOx storage effect is added.
[0015]
Further, the degree of deterioration of the NOx storage type catalyst can be detected by using the NOx sensor arranged downstream of the NOx storage type catalyst. That is, when a spike in a rich atmosphere (preferably, an air-fuel ratio of 14 to 14.5 for about 3 seconds) is introduced to reduce the NOx stored in the NOx storage type catalyst, the detection output of the NOx sensor before and after this spike is applied. Changes. If not deteriorated, the output of the NOx sensor when returning to the lean state after the spike is lower than before the spike. On the other hand, in the case of deterioration, NOx is not purified when returning to the lean state after the spike, and the output of the NOx sensor remains high. Therefore, the deterioration of the catalyst can be determined from the change in the output of the NOx sensor before and after the rich spike. Further, when the spike is applied, almost no NOx is generated, so that the zero point of the NOx sensor can be calibrated.
[0016]
Referring to FIG. 7 (b), in the exhaust gas purification system for a diesel engine, a light oil injection valve for injecting light oil as an HC source into the exhaust gas from the diesel engine to the exhaust pipe into the exhaust pipe, An HC sensor (not shown), a NOx selective reduction catalyst, and a NOx sensor described in detail above are sequentially mounted. The NOx selective reduction catalyst converts NOx to nitrogen and CO using HC added by light oil injection as a reducing agent.₂, H₂It decomposes into O to purify it. The HC sensor is arranged on the upstream side of the NOx selective reduction catalyst, and performs a function of monitoring the HC concentration in the exhaust gas after light oil injection in order to feedback-control the amount of light oil to be injected into the exhaust gas. is there. Further, the deterioration of the NOx selective reduction catalyst can be detected from the output change of the NOx sensor before and after the addition of HC. That is, according to the catalyst having the NOx purifying ability, the addition of HC reduces the NOx concentration downstream of the catalyst and decreases the NOx sensor output, whereas the catalyst having the deteriorated purifying ability has the HC Does not decrease the NOx concentration, so that the output of the NOx sensor does not decrease.
[0017]
FIG. 8 is a diagram for explaining a control configuration of the exhaust gas concentration detection system using the NOx sensor according to one embodiment of the present invention. Referring to FIG. 8, the detection system includes an internal combustion engine, a catalyst installed in an exhaust system, a NOx sensor installed downstream of the catalyst, an engine control unit (ECU), and a NOx sensor controller. Be composed. The engine control unit sets the operating conditions (such as the air-fuel ratio) of the internal combustion engine and determines the deterioration of the catalyst. The NOx sensor controller stores means for controlling the NOx sensor, means for detecting and outputting the first and second oxygen pump currents Ip1 and Ip2 flowing through the NOx sensor, and a map showing the relationship between the oxygen concentration and the Ip2 offset value. A memory, an operation unit that reads an offset of Ip2 from the memory according to the oxygen concentration (for example, Ip1), executes a predetermined operation based on this and an output of the detection unit, and outputs an operation result to the memory; A signal indicating operating conditions is input from the control unit, an output signal of the Ip1 and Ip2 detecting means is input, an offset correction signal is output to the memory, and the offset correction signal is output to the memory based on the signal output from the arithmetic unit to the memory. Offset correction means for storing a new offset value.
[0018]
The operation of this system will be described. The detection means of the NOx sensor controller detects the second oxygen pump current Ip2 of the NOx sensor and outputs it to the calculation unit, which outputs this to the memory. Here, the engine control unit sets an operating condition for setting the NOx concentration in the exhaust gas to substantially zero or substantially the same level as the atmosphere. As an example, this operating condition is set at the time of fuel cut, that is, the NOx concentration is zero and the oxygen concentration is 20.9%. When the signal indicating the condition output from the engine control unit and the Ip1 and Ip2 signals corresponding to the condition output from the Ip1 and Ip2 detecting means are input to the offset correcting means, the offset correcting means stores a predetermined value in the memory. Is output, and Ip2 detected under the above condition is stored in the memory in association with the oxygen concentration of 20.9%. This stored value becomes the calibrated new offset value of the NOx sensor detection output corresponding to the oxygen concentration of 20.9%. Further, the calculation unit reads out each offset value corresponding to each oxygen concentration stored in the memory, and converts each read value, Ip2 under the above-described conditions, and the oxygen concentration 20.9% stored in the memory. A predetermined operation is performed based on the corresponding offset value. Each offset value corresponding to each oxygen concentration is calibrated based on the calculation result and stored in the memory. The calibration of the detection output of the gas sensor is preferably performed periodically during the operation of the internal combustion engine. It is also possible to perform it at idling.
[0019]
【Example】
An embodiment of the present invention will be described below with reference to the drawings. As the gas sensor, a NOx sensor having the structure shown in FIG. 1 was used. The NOx sensor of FIG. 1 includes a first oxygen ion pump cell 6 including a pair of electrodes 6a and 6b provided with a solid electrolyte layer 5-1 therebetween, and a pair of electrodes provided with a solid electrolyte layer 5-2 therebetween. Oxygen concentration measuring cell 7 provided with oxygen partial pressure detecting electrodes 7a, 7b, second oxygen ion pump cell provided with solid electrolyte layer 5-3, and a pair of electrodes 8a, 8b provided on the surface of solid electrolyte layer 5-4 8 in that order. Insulating layers 11-1, 11-2, and 11-3 are formed between the solid electrolyte layers 5-1, 5-2, 5-3, and 5-4, respectively. Between the first oxygen ion pump cell 6 and the oxygen concentration measurement cell 7, a first measurement chamber (a gap portion) is formed by left and right insulating layers 11-1 and upper and lower solid electrolyte layers 5-1 and 5-2 in the figure. 2), and similarly, a second measurement chamber (gap) 4 is defined above the second oxygen ion pump cell 8 by the insulating layer 11-3 and the solid electrolyte layers 5-3 and 5-4. I have. Further, first diffusion holes (diffusion resistance portions) 1 having diffusion resistance are provided on both sides (front and back in FIG. 1) of the sensor in the lateral direction of the sensor in the first measurement chamber 2, respectively. On the other hand, an opening of the second diffusion hole (diffusion resistance portion) 3 is provided separately from the first diffusion hole 1. The second diffusion hole 3 penetrates through the oxygen concentration measurement cell 7 and the solid electrolyte layer 5-3 to communicate the first and second measurement chambers 2, 4 with a diffusion resistance.
[0020]
In this sensor, both electrodes 8a and 8b of a porous metal (Pt, Rh alloy, etc.) are formed on the same surface of the solid electrolyte 5-4 constituting the second oxygen ion pump cell 8. Although the electrodes 8a and 8b are separated from each other by the insulating layer 11-3, oxygen ions are conducted through the solid electrolyte layer 5-4, and the second oxygen pump current Ip2 flows. The electrode 8b is prevented from being in direct contact with the outside air of the sensor by the solid electrolyte layer 5-4, the insulating layer 11-3, and the lead portion 8d, and via the porous lead portion 8d having diffusion resistance. The oxygen pumped by the second oxygen ion pump cell 8 can be led out. Further, lead portions (lines) 8c (see FIG. 2) and 8d are electrically connected to the electrodes 8a and 8b, respectively, and the lead portion 8d electrically connected to the outer electrode 8b of the second measurement chamber 4 is porous. It is capable of diffusing oxygen ions. Therefore, oxygen decomposed from the NOx gas and pumped to the electrodes 8a to 8b by the second oxygen ion pump cell 8 is released through the lead 8d. FIG. 2 corresponds to a plan cross-sectional view indicated by the arrow A line in FIG. Referring to FIG. 2, it can be seen that the lead portion 8d is in contact with the outside air (in the atmosphere or the atmosphere of the gas to be measured), and communicates the outside air with the electrode 8b via the diffusion resistance.
[0021]
The measurement principle of the NOx sensor shown in FIG. 1 is as described above in the section of the embodiment, and the terminal of the controller is electrically connected to each electrode of the NOx sensor via a lead portion, and the first diffusion is performed. An electromotive force corresponding to the oxygen concentration in the exhaust gas introduced into the first measurement chamber 2 through the hole 1 is generated between the pair of electrodes 7a and 7b of the oxygen concentration measurement cell 7, and the voltage due to the electromotive force is constant. The voltage applied to the first oxygen ion pump cell 6 is controlled such that the control is performed by digital control using a microcomputer or by analog control. Excess oxygen is pumped from the first measurement chamber 2 by the first oxygen ion pump cell 6, and the gas to be measured whose oxygen concentration is controlled to a certain level is diffused into the second measurement chamber 4 through the second diffusion holes 3. Then, a voltage is applied to the pair of electrodes 8a and 8b of the second oxygen ion pump cell 8, and the remaining oxygen is further pumped out, and the catalytic action of the Pt alloy (or Rh alloy) electrode causes NOx is N₂And O₂Is decomposed into₂Becomes ions and conducts through the solid electrolyte layer 5-4 of the second oxygen ion pump cell 8, so that a pair of electrodes 8 a and 8 b of the second oxygen ion pump cell 8 provided inside and outside the second measurement chamber 4 is formed. A second oxygen pump current Ip2 flows in accordance with the amount of NOx gas decomposed. By measuring this Ip2, the NOx gas concentration can be measured.
[0022]
According to this NOx sensor, since the electrode 8b, which is the opposite electrode to the electrode 8a of the second oxygen ion pump cell 8 in the second measurement chamber 4, is installed inside the element (between the stacked solid electrolytes), The electrolyte layer 5-4 and the insulating layer 11-3 serve as protection means for the electrode 8b, and the lead portion 8d serves as diffusion resistance means, so that the electrode 8b is cut off from the atmosphere of the gas to be measured (exhaust gas) and directly contacts the outside air. Oxygen pumped around the electrode 8b is pooled, the oxygen concentration around (near) the electrode 8b is stabilized, and the pair of electrodes 8a, The electromotive force generated between 8b is stabilized. Further, since the generated electromotive force is stabilized, the effective pump voltage (Vp2−electromotive force) of the pump voltage Vp2 applied to the second oxygen ion pump cell 8 is stabilized, and the NOx gas concentration measurement depends on the oxygen concentration. Sex is reduced.
[0023]
[Production example]
Next, an example of manufacturing the NOx sensor shown in FIG. 1 will be described. FIG. 3 is a layout diagram of the NOx sensor shown in FIG. Although the sheet and paste shown in FIG. 3 are in a green state, the same reference numerals are given to the reference numerals assigned to the NOx sensor shown in FIG. In FIG. 3, ZrO is from the upper left to the lower left and from the upper right to the lower right₂A green sheet, an electrode paste, and the like are stacked, dried, and fired to produce an integrated sensor. Paste materials such as insulating coats and electrodes₂The screen is printed on the green sheet to form a laminate. Next, ZrO₂A production example of each component such as a green sheet will be described.
[0024]
[ZrO₂Sheet (5-1 layer to 5-4 layer) molding]: ZrO₂The powder was calcined in an atmospheric furnace at 600 ° C. for 2 hours. Calcined ZrO₂30 kg of powder, 150 g of dispersant, and 10 kg of organic solvent are placed in a trommel together with 60 kg of cobblestone, mixed and dispersed for about 50 hours, and a solution obtained by dissolving 4 kg of organic binder in 10 kg of organic solvent is added thereto and mixed for 20 hours. Thus, a slurry having a viscosity of about 10 Pa · s was obtained. From this slurry, ZrO having a thickness of about 0.4 mm was obtained by a doctor blade method.₂A green sheet was prepared and dried at 100 ° C. × 1 hour.
[0025]
[Printing paste]
(1) For the first oxygen ion pump electrode 6a, oxygen partial pressure detection electrode (oxygen reference electrode) 7b, and second oxygen ion pump electrodes 8a and 8b: Pt powder 20g, ZrO₂2.8 g of powder and an appropriate amount of an organic solvent are placed in a grinder (or pot mill), mixed and dispersed for 4 hours, and a solution obtained by dissolving 2 g of an organic binder in 20 g of an organic solvent is added thereto. 5 g of the agent was added and mixed for 4 hours to prepare a paste having a viscosity of about 150 Pa · s.
[0026]
(2) First oxygen ion pump electrode 6b, oxygen partial pressure detection electrode (oxygen reference electrode) 7a: 19.8 g of Pt powder, ZrO₂2.8 g of powder, 0.2 g of Au powder, and an appropriate amount of an organic solvent were placed in a grinder (or pot mill), mixed for 4 hours and dispersed, and 2 g of an organic binder was dissolved in 20 g of an organic solvent. Then, 5 g of a viscosity modifier was further added and mixed for 4 hours to prepare a paste having a viscosity of about 150 Pa · s.
[0027]
(3) For insulation coating and protection coating: 50 g of alumina powder and an appropriate amount of an organic solvent are put in a grinder (or pot mill), mixed and dissolved for 12 hours, further added with 20 g of a viscosity modifier, and mixed for 3 hours. Thus, a paste having a viscosity of about 100 Pa · s was prepared.
[0028]
(4) Pt-containing porous material (for lead wire): 10 g of alumina powder, 1.5 g of Pt powder, 2.5 g of organic binder, and 20 g of organic solvent are put in a grinder (or pot mill) and mixed for 4 hours. Further, 10 g of a viscosity modifier was added and mixed for 4 hours to prepare a paste having a viscosity of about 100 Pa · s.
[0029]
(5) For the first diffusion hole: 10 g of alumina powder having an average particle size of about 2 μm, 2 g of an organic binder, and 20 g of an organic solvent are put into a grinder (or pot mill), mixed, dispersed, and further, 10 g of a viscosity modifier is added. The mixture was added and mixed for 4 hours to prepare a paste having a viscosity of about 400 pa · s.
[0030]
(6) For carbon coating: 4 g of a carbon powder, 2 g of an organic binder, and 40 g of an organic solvent are put into a grinder (or pot mill), mixed and dispersed, further added with 5 g of a viscosity modifier, and mixed for 4 hours. A paste was made. In addition, by forming a carbon coat by printing, for example, contact between the first oxygen ion pump electrode 6b and the oxygen reference electrode 7a is prevented. The carbon coat is used for forming the first measurement chamber 2 and the second measurement chamber 4. Since carbon is burned off during firing, the carbon coat layer does not exist in the fired body.
[0031]
[Pellets]
(7) For second diffusion hole: 20 g of alumina powder having an average particle size of about several μm, 8 g of an organic binder, and 20 g of an organic solvent are put into a grinder (or a pot mill), mixed for 1 hour, granulated, and then molded. About 2t / cm by press²A pressure was applied to produce a cylindrical press-formed body (green state) having a diameter of 1.3 mm and a thickness of 0.8 mm. This green-state press-formed body is formed into a second or third layer of ZrO.₂The second diffusion hole 3 is formed in the sensor by inserting it into a predetermined portion of the green sheet, pressing and integrating and firing.
[0032]
[ZrO₂Lamination method]
After the second and third layers are pressed, a portion (diameter: 1.3 mm) through which the second diffusion hole 3 penetrates is punched. After the punching, a green cylindrical shaped body to be the second diffusion hole 3 is buried, and 1 to 4 layers of ZrO₂Green sheet pressure: 5kg / cm²Pressing time: 1 minute.
[0033]
[Binder removal and firing]
The pressed compact is debindered at 400 ° C. × 2 hours and baked at 1500 ° C. × 1 hour.
[0034]
[Example of use]
The thus manufactured NOx sensor having the structure shown in FIG. 1 was applied to a real machine and a 500-hour durability test was performed. The configuration of the NOx concentration detecting device is the same as that shown in FIG. 8, and the mounting position of the NOx sensor is the same as that shown in FIG. Further, the controller that controls the NOx sensor determines the gain value ((standard NOx concentration−0) / (current generation amount) of the detection output (second oxygen pump current) of the NOx sensor set using the model gas evaluation device described later. Offset)) and the offset value are stored in the memory. In particular, offset values corresponding to oxygen concentrations from 0% to 20.9% (21%) are stored in a memory for the purpose of canceling the oxygen concentration dependency of the offset. A predetermined offset value is read out based on the oxygen concentration obtained from the oxygen pump current, and the offset value used for calculating the NOx gas concentration is optimally set.
[0035]
Two sets of the controller and the NOx sensor are prepared, and the initial characteristics of the NOx sensors are measured by a model gas evaluation device. When the analyzer output indicates that the NOx concentration is zero, the controller based on the second oxygen pump current is used. Each controller was adjusted so that the detection output of was zero. Next, these NOx sensors were attached to the exhaust pipe of a gasoline engine with a displacement of 3000 cc, respectively, and a durability test was performed for 500 hours in the mode shown in FIG. 4 while controlling the NOx sensors with the respective controllers (rotation in the figure). The number after the number indicates the relative accelerator opening). One controller executed the method of using the gas sensor according to one embodiment of the present invention, and calibrated the offset (zero point) at the time of fuel cut in the endurance mode. The other controller did not calibrate the zero point. The calibration method by one controller is as follows.
[0036]
That is, referring to FIG. 5, when a fuel cut signal output from an ECU (engine control unit) of a gasoline engine is input, one controller detects a detection output of the controller proportional to the second oxygen pump current. Value is O₂= 20.9% as an offset value (OF2). Next, the O stored in the memory₂= 20.9% is read, and the difference between OF1 and OF2 is calculated. This “OF1-OF2” is stored in a memory as an offset value OF [O corresponding to each oxygen concentration.₂] And the value (OF [O₂]-(OF1-OF2)) to the new calibrated offset value OF [O₂] In the memory.
[0037]
FIG. 6 shows the results of the durability test. Referring to the results of the durability test shown in FIG. 6, according to the system according to the example in which the calibration was performed, the NOx concentration detection output of the controller hardly changed even after the 500-hour durability test. In contrast, the output of the system of the comparative example in which the calibration was not performed increased by about 400 ppm.
[0038]
【The invention's effect】
According to the present invention, the shift of the detection output of the gas sensor after the durable use is offset by performing the calibration of the gas sensor when the concentration of the component to be detected can be estimated or known under the operating conditions of the internal combustion engine. However, the concentration of the component to be detected can be accurately detected. The gas sensor to which the present invention is applied may be an HC sensor or a CO sensor in addition to the NOx sensor, or a sensor capable of measuring the oxygen concentration, for example, when the fuel cut, the oxygen concentration is not zero and the oxygen concentration is 20.9% Is introduced, the sensitivity of oxygen concentration can be calibrated. In addition, since the calibration of the present invention can be performed when the fuel is cut or when the air-fuel ratio is rich, there is no need to set special operating conditions for the calibration. In particular, the present invention is applied to NOx sensors and enables accurate measurement of NOx concentration on the order of ppm over a long period of time..In particular, when a NOx sensor that detects the NOx concentration in the gas exhausted from the internal combustion engine is attached downstream of the NOx storage catalyst, there is a mode in which the air-fuel ratio is set to a rich atmosphere in order to reduce the stored NOx. The calibration can be performed using this mode,,The deterioration state of the NOx storage catalyst can also be detected..Also,The deterioration state of the NOx selective reduction catalyst disposed in the exhaust pipe of a system using a diesel engine that cannot make the air-fuel ratio rich can also be detected.
[Brief description of the drawings]
FIG. 1 is a schematic diagram for explaining a structure of a NOx sensor used in one embodiment of the present invention.
FIG. 2 is a view for explaining a plane cross section indicated by an arrow A line in FIG. 1;
FIG. 3 is a diagram for explaining a layout of the NOx sensor shown in FIG. 1;
FIG. 4 is a view for explaining a durability test mode performed using the NOx sensor shown in FIG.
FIG. 5 is a diagram for explaining a method of calibrating the detection output of the NOx sensor according to one embodiment of the present invention.
FIG. 6 is a diagram for explaining the results of the durability test, in which square plots indicate data in the example and triangular plots indicate data in the comparative example.
7A and 7B are diagrams for explaining an exhaust gas concentration detection device using a NOx sensor according to one embodiment of the present invention, and FIG. 7A is a diagram illustrating a gasoline engine (particularly, a lean engine). FIG. 2B is a diagram for explaining an exhaust gas concentration detection device applied to an exhaust gas purification system of a burn engine), and FIG.
FIG. 8 is a diagram for explaining an exhaust gas concentration detection system using a NOx sensor according to one embodiment of the present invention.
[Explanation of symbols]
1: 1st diffusion hole (diffusion resistance part)
2: First measurement chamber (gap)
3: Second diffusion hole (diffusion resistance part)
4: Second measurement chamber (gap)
5-1 ... 5-4: Solid electrolyte layer
6: First oxygen ion pump cell
6a, 6b: electrode
6c: Lead part
7: Oxygen concentration measurement cell
7a, 7b: electrodes
8: Second oxygen ion pump cell
8a, 8b: electrodes
8c, 8d: lead part
11-1,..., 11-3: insulating layer

Claims (8)

An exhaust gas concentration detection method using a NOx sensor attached to an exhaust pipe of an internal combustion engine and detecting a NOx concentration in gas exhausted from the internal combustion engine,
The NOx sensor includes first and second void portions, first and second diffusion resistance portions, first and second oxygen ion pump cells,
The gas diffuses into the first gap through the first diffusion resistor, and the oxygen in the gas diffuses into the first gap through the first oxygen ion pump cell through the first diffusion resistor. Oxygen is pumped out of the first gap so that the concentration becomes a predetermined concentration, and a gas having an oxygen concentration of the predetermined concentration flows from the first gap to the second gap through the second diffusion resistor. Diffusing, decomposing NOx in the second void, pumping out oxygen ions dissociated by the second oxygen ion pump cell, and detecting NOx concentration from a current flowing through the second oxygen ion pump cell;
Atmospheric atmosphere is introduced into the NOx sensor, and the concentration of oxygen in the gas introduced into the NOx sensor is measured from the current flowing through the first oxygen pump cell, and the measured oxygen concentration corresponds to the concentration of oxygen in the atmosphere. The zero point of the detection output of the NOx sensor, which indicates that the NOx concentration is zero, is calibrated based on the detection output of the NOx sensor when the NOx concentration is zero, and the NOx concentration is detected based on the calibrated detection output. Exhaust gas concentration detection method using a NOx sensor. An exhaust gas concentration detection method using a NOx sensor attached to an exhaust pipe of an internal combustion engine and detecting a NOx concentration in gas exhausted from the internal combustion engine,
The NOx sensor includes first and second void portions, first and second diffusion resistance portions, first and second oxygen ion pump cells,
The gas diffuses into the first gap through the first diffusion resistor, and the oxygen in the gas diffuses into the first gap through the first oxygen ion pump cell through the first diffusion resistor. Oxygen is pumped out of the first gap so that the concentration becomes a predetermined concentration, and a gas having an oxygen concentration of the predetermined concentration flows from the first gap to the second gap through the second diffusion resistor. Diffusing, decomposing NOx in the second void, pumping out oxygen ions dissociated by the second oxygen ion pump cell, and detecting NOx concentration from a current flowing through the second oxygen ion pump cell;
Cutting the fuel supply to the internal combustion engine so that the NOx concentration in the gas introduced to the NOx sensor is substantially zero or substantially the same level as the atmosphere, and the current flowing through the first oxygen pump cell Measuring the oxygen concentration in the gas introduced into the NOx sensor, and based on the detection output of the NOx sensor when the measured oxygen concentration corresponds to the oxygen concentration in the atmosphere, the NOx concentration is zero. A method for detecting an exhaust gas concentration, comprising: calibrating a zero point of a detection output of the NOx sensor indicating that the NOx sensor is present, and detecting the NOx concentration based on the calibrated detection output. An exhaust gas concentration detection method using a gas sensor that detects the concentration of a predetermined component in gas exhausted from an internal combustion engine,
By reducing the predetermined component by making the air-fuel ratio of the internal combustion engine rich, based on the detection output of the gas sensor when the concentration of the predetermined component is substantially zero or substantially the same level as the atmosphere, Exhaust gas concentration detection, wherein the zero point of the detection output of the gas sensor indicating that the concentration of the predetermined component is zero is calibrated, and the concentration of the predetermined component is detected based on the calibrated detection output. Method. 4. The exhaust gas concentration detecting method according to claim 3 , wherein the gas sensor is a NOx sensor. The NOx sensor includes first and second void portions, first and second diffusion resistance portions, first and second oxygen ion pump cells,
The gas diffuses into the first gap through the first diffusion resistor, and the oxygen in the gas diffuses into the first gap through the first oxygen ion pump cell through the first diffusion resistor. Oxygen is pumped out of the first gap so that the concentration becomes a predetermined concentration, and a gas having an oxygen concentration of the predetermined concentration flows from the first gap to the second gap through the second diffusion resistor. It diffuses and decomposes NOx in the second void, pumps out oxygen ions dissociated by the second oxygen ion pump cell, and detects NOx concentration from a current flowing through the second oxygen ion pump cell. The exhaust gas concentration detection method according to claim 4, wherein The NOx sensor is attached downstream of the NOx storage type catalyst, and the NOx sensor is mounted on the basis of the detection output of the NOx sensor when the air-fuel ratio is temporarily made rich to purify the NOx stored in the NOx storage type catalyst. The exhaust gas concentration detection method according to claim 1, wherein zero point calibration is performed. An exhaust gas concentration detection method using a NOx sensor attached to an exhaust pipe of an internal combustion engine and detecting a NOx concentration in gas exhausted from the internal combustion engine,
The NOx sensor includes first and second void portions, first and second diffusion resistance portions, first and second oxygen ion pump cells,
The gas diffuses into the first gap through the first diffusion resistor, and the oxygen in the gas diffuses into the first gap through the first oxygen ion pump cell through the first diffusion resistor. Oxygen is pumped out of the first gap so that the concentration becomes a predetermined concentration, and a gas having an oxygen concentration of the predetermined concentration flows from the first gap to the second gap through the second diffusion resistor. Diffusing, decomposing NOx in the second void, pumping out oxygen ions dissociated by the second oxygen ion pump cell, and detecting NOx concentration from a current flowing through the second oxygen ion pump cell;
The internal combustion engine is operated under conditions where the NOx concentration can be estimated or known, and under the operating conditions , the concentration of oxygen in the gas introduced into the NOx sensor is measured from the current flowing through the first oxygen pump cell. The detected output of the NOx sensor is calibrated based on the detected output of the NOx sensor when the measured oxygen concentration corresponds to the oxygen concentration in the atmosphere, and the NOx concentration is detected based on the calibrated detected output. A method for detecting an exhaust gas concentration, comprising: A NOx sensor attached to an exhaust pipe of an internal combustion engine and detecting a NOx concentration in gas exhausted from the internal combustion engine, the NOx sensor comprising: a first and a second gap; a first and a second diffusion resistance; A second oxygen ion pump cell, wherein the gas is diffused into the first gap through the first diffusion resistance portion, and the first oxygen ion pump cell is connected to the first diffusion resistance portion through the first diffusion resistance portion. Oxygen is pumped from the first gap so that the oxygen concentration in the gas diffused into the gap becomes a predetermined concentration, and the gas having the oxygen concentration set to the predetermined concentration flows from the first gap to the second diffusion resistance section. And diffuses into the second gap through the second gap, decomposes NOx in the second gap, pumps out oxygen ions dissociated by the second oxygen ion pump cell, and obtains NOx from a current flowing through the second oxygen ion pump cell. N to detect concentration And x sensor,
And operating condition setting means for setting the operating conditions of the internal combustion engine in which the NOx concentration of the estimable or known, from the current flowing through the Oite the first oxygen pumping cell to the operating conditions set by the operation condition setting unit The oxygen concentration in the gas introduced into the NOx sensor is measured, and the detection output of the NOx sensor is calibrated based on the detection output of the NOx sensor when the measured oxygen concentration corresponds to the oxygen concentration in the atmosphere. And a calibration means for performing the following.

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