GAS SENSOR

Abstract

Gas sensor (100), including: an element body (1, 2, 3, 4, 5, 6) which has an oxygen ion-conducting solid electrolyte layer and which contains a sample gas flow section into which a sample gas is introduced for flow around; a pre-pump cell (15) that pumps oxygen into a pre-chamber (12) of the measuring object gas flow section; a main pump cell (21) that sets an oxygen concentration in a first interior space (20) of the sample gas flow section located downstream of the prechamber (12); an auxiliary pump cell (50) which adjusts the oxygen concentration in a second interior space (40) of the sample gas flow section, which is located downstream of the first interior space (20); a measuring electrode (44) which is arranged in a measuring chamber (61) of the object gas flow section which is located downstream of the second interior space (40); a reference electrode (42) which is arranged in the element body (1, 2, 3, 4, 5, 6) and which comes into contact with a reference gas which serves as a reference for detecting a concentration of a specific gas in the gas of the object being measured; a measuring voltage acquisition unit (82) that acquires a measuring voltage (V2) between the reference electrode (42) and the measuring electrode (44); a unit for measuring the concentration of a specific gas (92) which performs a first control process which determines a measurement value depending on oxygen, which is generated in the measuring chamber (61) and originates from the specific gas, is based on the measuring voltage (V2) while the first control process is carried out, and which detects the concentration of a specific gas in the gas of the object being measured based on the detection value, wherein the first control process is a pre-pump control process of controlling the pre-pump cell (15) such that a constant pre-pump current (Ip0s) flows through the pre-pump cell (15), an auxiliary pump control process of controlling the auxiliary pump cell (50) such that the oxygen concentration in the second interior space (40) becomes a target concentration, and a main pump control process of controlling the main pump cell (21) such that an auxiliary pump current (Ip1) which flows when the auxiliary pump cell (50) sets the oxygen concentration in the second interior space (40) becomes a target value; a storage unit (94) which stores information regarding a zero point at which an oxygen concentration of zero and a main pumping current (Ip0) are relevant to each other in a first correspondence relationship, wherein the first correspondence relationship is a linear correspondence relationship between the oxygen concentration in the gas of measurement and the main pumping current (Ip0) flowing through the main pumping cell (21) while the first control operation is carried out; an oxygen concentration detection unit (92) which detects the oxygen concentration in the gas being measured based on a measured value p of the main pump flow (Ip0) flowing during the execution of the first control operation and the zero-point information stored in the storage unit (94); and a unit for obtaining a measured value (92) which performs a second control operation and which obtains a measured value b1 at a measuring point B1, where a known value of the oxygen concentration and the main pump flow (Ip0) are relevant to each other, by measuring the main pump flow (Ip0) flowing during the execution of the second control operation, at a measurement time where the oxygen concentration in the gas of the object being measured around the element body (1, 2, 3, 4, 5, 6) is considered to be the known value, wherein the second control operation comprises a pre-pump stop operation of stopping the operation of the pre-pump cell (15), the auxiliary pump control operation and the main pump control operation, wherein the oxygen concentration detection unit (92) performs a zero-point correction to correct the measured value p or the information relating to the zero point such that any deviation of the zero point from the first correspondence relation based on the measured value b1 at the measuring point B1 is corrected.

Description

Technical field

[0001] The present invention relates to a gas sensor. State of the art

[0002] A known gas sensor detects the concentration of a specific gas, such as NOx, in a sample gas, such as the exhaust gas of a motor vehicle. For example, PTL 1 discloses a gas sensor comprising a sensor element having oxygen-ion-conducting solid electrolyte layers, a main pump cell, an auxiliary pump cell, and a measuring electrode arranged in the solid electrolyte layers. When an NOx concentration is detected using the gas sensor, the main pump cell and the auxiliary pump cell pump oxygen in or out of a sample gas flow section within the sensor element and a location outside the sensor element, and an oxygen concentration is established in the sample gas flow section. After the oxygen concentration is established, the NOx in the sample gas around the measuring electrode is reduced.The NOx concentration in the gas being measured is determined based on a pump current that flows when oxygen is pumped around the measuring electrode. Furthermore, PTL 2 describes a method for correcting the output of a NOx sensor. PTL 3 further discloses a method and a device for determining the concentration of an emitted gas. Document listPatent documents [PTL 1] JP 2016 - 166 871 A [PTL 2] US 2008 / 0 237 064 A1 [PTL 3] JP H11 - 148 910 A Summary of the invention: Technical problem

[0003] A main pumping current, which flows through the main pumping cell when the oxygen concentration in the sample gas flow section is set, correlates with the oxygen concentration in the sample gas around the sensor element. It is therefore assumed that the oxygen concentration in the sample gas around the sensor element is detected based on the main pumping current. However, the present inventors have conducted investigations and found that the relationship between the oxygen concentration and the main pumping current changes during the use of the gas sensor, and the accuracy of the detection of the oxygen concentration based on the main pumping current decreases in some cases. Regarding the detection of the oxygen concentration in the sample gas, there is a particular need for precise detection of zero oxygen concentration.

[0004] The present invention was made to solve this problem, and a main objective of the present invention is to prevent a decrease in the accuracy of the detection of the oxygen concentration during the use of the gas sensor when the oxygen concentration in the gas of the object being measured is zero. Solution to the problem

[0005] In the present invention, the measure described below is taken to solve the main problem described above.

[0006] A gas sensor according to the present invention comprises an element body having an oxygen-ion-conducting solid electrolyte layer and containing a sample gas flow section into which a sample gas is introduced for flow, a pre-pump cell that pumps oxygen into a pre-chamber of the sample gas flow section, a main pump cell that sets an oxygen concentration in a first interior space of the sample gas flow section located downstream of the pre-chamber, an auxiliary pump cell that sets the oxygen concentration in a second interior space of the sample gas flow section located downstream of the first interior space, a measuring electrode arranged in a measuring chamber of the sample gas flow section located downstream of the second interior space, and a reference electrode.which is arranged in the element body and which comes into contact with a reference gas which serves as a reference for detecting a concentration of a specific gas in the gas of the object being measured, a measuring voltage detection unit which detects a measuring voltage between the reference electrode and the measuring electrode, a unit for detecting the concentration of a specific gas which performs a first control operation which obtains a detection value dependent on oxygen which is generated in the measuring chamber and originates from the specific gas, based on the measuring voltage while the first control operation is carried out, and which detects the concentration of a specific gas in the gas of the object being measured based on the detection value, wherein the first control operation comprises a pre-pump control operation of controlling the pre-pump cell such that a constant pre-pump current flows through the pre-pump cell, an auxiliary pump control operation of controlling the auxiliary pump cell such thatthat the oxygen concentration in the second interior space becomes a target concentration, and a main pump control operation of controlling the main pump cell such that an auxiliary pump flow which flows when the auxiliary pump cell sets the oxygen concentration in the second interior space becomes a target value, comprising a storage unit which stores information regarding a zero point at which an oxygen concentration of zero and a main pump flow are relevant to each other in a first correspondence relationship, wherein the first correspondence relationship is a linear correspondence relationship between the oxygen concentration in the gas of measurement and the main pump flow which flows through the main pump cell while the first control operation is carried out, an oxygen concentration sensing unit which measures the oxygen concentration in the gas of measurement on the basis of a measured value p of the main pump flow,which flows during the execution of the first control operation, and which records information regarding the zero point that is stored in the storage unit, and a unit for obtaining a measured value, which performs a second control operation and which obtains a measured value b1 at a measuring point B1, where a known value of the oxygen concentration and the main pump flow are relevant to each other, by measuring the main pump flow that flows during the execution of the second control operation, at a measuring time where the oxygen concentration in the gas of the object being measured around the element body is considered to be the known value, wherein the second control operation is a pre-pump stop operation of stopping the operation of the pre-pump cell,The auxiliary pump control process and the main pump control process are included. The oxygen concentration detection unit performs a zero-point correction to correct the measured value p or the information regarding the zero point such that any deviation of the zero point from the first correspondence relationship based on the measured value b1 at measuring point B1 is corrected.

[0007] The gas sensor performs the first control operation, including the pre-pump control operation (controlling the pre-pump cell) to maintain a constant pre-pump flow; the auxiliary pump control operation (controlling the auxiliary pump cell) to ensure the oxygen concentration in the second chamber reaches the target concentration; and the main pump control operation (controlling the main pump cell) to ensure the auxiliary pump flow, which occurs when the auxiliary pump cell adjusts the oxygen concentration in the second chamber, reaches the target value. The unit for detecting the concentration of a specific gas detects the concentration of that specific gas in the sample gas while the first control operation is being performed.The oxygen concentration sensing unit also detects the oxygen concentration in the sample gas based on the measured value p of the main pump flow during the first control operation and information regarding the zero point of the linear first correspondence relationship between the oxygen concentration in the sample gas and the main pump flow during the first control operation. If, during the use of the gas sensor, a foreign substance, such as soot, accumulates in the sample gas flow section, the correspondence relationship between the actual oxygen concentration and the main pump flow after accumulation will differ from the first correspondence relationship before accumulation. In particular, the slope of the correspondence relationship after accumulation will be less than that of the first correspondence relationship, and the zero point will deviate.The slope is the ratio of an increase in the main pump flow rate to an increase in the oxygen concentration, and the zero point is the point at which the oxygen concentration is zero and the main pump flow rate are relevant to each other. The following reason can be assumed: It is likely that the foreign substance accumulates near the inlet of the sample gas flow section. The more foreign substance accumulates near the inlet, the greater the diffusion resistance near the inlet of the sample gas flow section, and the smaller the amount of sample gas flowing into the sample gas flow section. Consequently, even if the oxygen concentration in the sample gas remains constant, the amount of oxygen flowing into the sample gas flow section from outside decreases, and the main pump flow rate decreases.For this reason, it is assumed that the more foreign substance accumulates, the lower the slope of the correspondence relationship after accumulation becomes compared to the slope of the first correspondence relationship before accumulation. Oxygen pumped into the pre-pump cell does not flow entirely downstream towards the first interior space; rather, a portion of it moves upstream, flowing from the element body through the inlet of the sample gas flow section to the outside. The proportion of oxygen pumped into the pre-pump cell that flows downstream changes as foreign substance accumulates near the inlet. Specifically, the more foreign substance accumulates near the inlet, the greater the proportion of oxygen flowing downstream, and the overall value of the main pump flow increases.For this reason, it is assumed that the zero point of the correspondence relationship deviates after accumulation in the direction in which the main pump flow increases, compared to the zero point of the first correspondence relationship before accumulation. In particular, the zero point changes from the first correspondence relationship, and consequently, the accuracy of the oxygen concentration measurement decreases when the oxygen concentration in the gas being measured is zero.In the gas sensor according to the present invention, however, the unit for obtaining a measured value carries out the second control process, which includes the pre-pump stop process of stopping the operation of the pre-pump cell, the auxiliary pump control process and the main pump control process, at the measurement time when the oxygen concentration in the gas of the object being measured around the element body is considered to be the known value, and measures the main pump current flowing during the second control process, so that the measured value b1 is obtained at the measurement point B1 where the known value of the oxygen concentration and the main pump current are relevant to each other.The second control process includes the pre-pump stop process; oxygen is not pumped into the pre-pump cell, and consequently, the zero point of the relationship between oxygen concentration and main pump flow remains unchanged during the second control process, even if the foreign substance has accumulated as described above. The second control process incorporates the main pump control process and the auxiliary pump control process, just as in the first control process, and therefore, the slope of the relationship between oxygen concentration and main pump flow during the first control process is the same as during the second control process.If the slope of the correspondence relationship changes during the first control operation due to the accumulation of foreign substance described above, the slope of the correspondence relationship also changes during the second control operation. Therefore, the measured value b1 at measuring point B1, which is measured during the second control operation, is not affected by the change in the zero point described above, but rather by the change in the slope described above, and the measured value b1 correlates with the degree of change in the slope described above. The degree of change in the slope correlates with the degree of accumulation of foreign substance near the inlet of the gas flow section containing the sample., the degree of increase in diffusion resistance near the input, and thus correlates with the extent of the zero point's deviation from the first correspondence relationship. For this reason, the measured value b1 at measuring point B1 also correlates with the extent of the zero point's deviation from the first correspondence relationship. Accordingly, in the gas sensor according to the present invention, the oxygen concentration detection unit causes the zero point correction to correct the measured value p, or the zero point information, such that the zero point's deviation from the first correspondence relationship described above is corrected based on the measured value b1 at measuring point B1.Consequently, the deviation of the zero point from the first correspondence relationship can be corrected at least during the use of the gas sensor, and it can be prevented that the accuracy of the detection of the oxygen concentration decreases when the oxygen concentration in the gas being measured is zero during the use of the gas sensor.

[0008] In this case, the storage unit can store a second correspondence relationship, which represents a linear correspondence between the oxygen concentration in the gas being measured and the main pump flow during the second control operation. The oxygen concentration sensing unit can then perform zero-point correction based on the difference between the second correspondence relationship stored in the storage unit and the measurement point B1. Regarding the correspondence relationship between the oxygen concentration and the main pump flow during the second control operation, only the slope changes, and the zero point remains unchanged even if the foreign substance accumulates, as described above.For this reason, the difference between the second correspondence relationship, which is stored in advance, and the measurement point B1 is not affected by the change in the zero point described above and correlates with the degree of the change in the slope described above. Therefore, the zero point correction can be performed based on the difference between the second correspondence relationship and the measurement point B1.

[0009] In the gas sensor according to the present invention, the unit for obtaining a measured value can obtain a measured value a1 at a measuring point A1, where the known values ​​of the oxygen concentration and the main pump flow are relevant to each other, by measuring the main pump flow flowing while the first control operation is being carried out at the measurement time. The oxygen concentration detection unit can then perform the zero-point correction based on the measured value b1 and the measured value a1. The measured value b1 at measuring point B1 correlates with the degrees of change in the slope of the correspondence relationship during the first control operation and during the second control operation due to the accumulation of the foreign substance described above. The measured value a1 is a value taken during the first control operation and is influenced by both the change in slope and the change in zero point, as described above.For this reason, the deviation of the zero point from the zero point of the first correspondence relationship due to the accumulation of foreign substance can be determined on the basis of the measured value b1 and the measured value a1, and the zero point correction can consequently be carried out in a suitable manner.

[0010] In this case, the oxygen concentration detection unit can derive a slope K1, which is a value that has changed from the slope of a straight line representing the first correspondence relationship, based on measurement point B1; it can derive a modified zero point, corresponding to a zero point after the zero point of the first correspondence relationship has deviated, based on a straight line passing through the first measurement point A1 and having a slope equal to slope K1; and it can perform the zero point correction based on the modified zero point. In this way, the zero point correction can be carried out appropriately by differentiating the modified zero point.In this case, the oxygen concentration detection unit can derive an extent of deviation from the zero point corresponding to the extent of deviation of the changed zero point from the zero point of the first correspondence relation and can perform the zero point correction based on the extent of deviation from the zero point.

[0011] In this case, the oxygen concentration sensing unit can derive the slope K1 as the slope of a straight line passing through the measuring point B1 and a point where the oxygen concentration and the main pump flow are zero. The storage unit can store the second correspondence relationship, which represents the linear correspondence between the oxygen concentration in the gas being measured and the main pump flow flowing while the second control operation is performed. The oxygen concentration sensing unit can then derive the slope K1 based on the difference between the second correspondence relationship stored in the storage unit and the measurement point B1.

[0012] In the gas sensor according to the present invention, which receives the measured value a1 at the measuring point A1, the storage unit can store the first correspondence relationship, and the oxygen concentration detection unit can derive the slope K1, which is a value that changes starting from the slope of the straight line which represents the first correspondence relationship, on the basis of the measuring point B1, can derive the straight line which passes through the measuring point A1 and which has the slope which is equal to the slope K1, as a corrected first correspondence relationship, and can detect the oxygen concentration in the gas of the object being measured on the basis of the measured value p and the corrected first correspondence relationship.In this way, not only is the zero-point correction performed, but the change in the slope of the first correspondence relationship can also be corrected by using the corrected first correspondence relationship, and this improves not only the accuracy of the detection of the oxygen concentration when the oxygen concentration in the gas being measured is zero, but also the accuracy of the detection of the oxygen concentration when the oxygen concentration is not zero.

[0013] In the gas sensor according to the present invention, which receives the measured value a1 at the measuring point A1, the storage unit can store the second correspondence relationship, which represents the linear correspondence relationship between the oxygen concentration in the gas being measured and the main pump flow flowing while the second control process is carried out, and the oxygen concentration detection unit can store a degree of deviation from zero corresponding to a degree of deviation of zero from the first correspondence relationship based on a difference between a degree of deviation between a reference value b0, which is a value of the main pump flow relevant to the known value of the oxygen concentration in the second correspondence relationship, and the measured value b1, and a degree of deviation between a reference value a0, which is a value of the main pump flow,which is relevant for the known value of the oxygen concentration in the first correspondence relationship, and derive from the measured value a1,and can perform zero-point correction based on the magnitude of the deviation from zero. The magnitude of the deviation between the reference value b0 and the measured value b1 correlates with the change in the slope of the first correspondence relationship and the second correspondence relationship due to the accumulation of foreign substance, and the magnitude of the deviation between the reference value a0 and the measured value a1 correlates with the change in the slope and the change in zero point from the first correspondence relationship described above. Therefore, a difference (for example, a difference or a ratio) between these magnitudes of deviation correlates with the change in zero point from the first correspondence relationship. Accordingly, the magnitude of the deviation from zero can be derived based on the difference between these magnitudes of deviation.and the zero-point correction can be carried out in a suitable manner using the extent of the deviation from the zero point.

[0014] In this case, the oxygen concentration detection unit can derive a modified zero point corresponding to a zero point after the deviation of the zero point of the first correspondence relationship, based on the zero point of the first correspondence relationship and the extent of the deviation from the zero point. It can derive a straight line passing through the measurement point A1 and the modified zero point as a corrected first correspondence relationship and can detect the oxygen concentration in the sample gas based on the measured value p and the corrected first correspondence relationship. In this way, not only is the zero point correction performed, but the change in the slope of the first correspondence relationship can also be corrected using the corrected first correspondence relationship.Accordingly, not only is the accuracy of measuring the oxygen concentration improved when the oxygen concentration in the gas being measured is zero, but also the accuracy of measuring the oxygen concentration when the oxygen concentration is not zero.

[0015] In the gas sensor according to the present invention, the measurement time can be a time at which the gas surrounding the sensor body is considered to be the atmosphere. If the gas surrounding the sensor is the atmosphere, the oxygen concentration is considered to be the known value, and the measured value b1 can be obtained in a suitable manner by considering this time as the measurement time.

[0016] In this case, the gas being measured is exhaust gas from an internal combustion engine. The unit includes a unit for obtaining information that receives information regarding the execution of a fuel interruption, indicating that a fuel interruption is taking place in the internal combustion engine. The unit for obtaining a measurement can determine the measurement time based on the information received regarding the execution of a fuel interruption. The exhaust gas from the internal combustion engine during the fuel interruption is considered to be the atmosphere or air, and the unit for obtaining a measurement can therefore appropriately determine the measurement time in such a way that the measurement time is determined based on information regarding the execution of a fuel interruption.

[0017] A gas sensor, which can be assumed to differ from the gas sensor described above according to the present invention, comprises an element body having an oxygen-ion-conducting solid electrolyte layer and containing a sample gas flow section into which a sample gas is introduced for flow, a main pump cell that sets an oxygen concentration in a first interior space formed in the sample gas flow section, an auxiliary pump cell that sets the oxygen concentration in a second interior space of the sample gas flow section located downstream of the first interior space, a measuring electrode arranged in a measuring chamber of the sample gas flow section located downstream of the second interior space, and a reference electrode arranged in the element body that comes into contact with a reference gas.which serves as a reference for measuring the concentration of a specific gas in the gas of the object being measured, a measuring voltage detection unit that detects a measuring voltage between the reference electrode and the measuring electrode, a unit for detecting the concentration of a specific gas that performs an auxiliary pump control operation of controlling the auxiliary pump cell such that the oxygen concentration in the second interior space becomes a target concentration, and a main pump control operation of controlling the main pump cell such that an auxiliary pump current that flows when the auxiliary pump cell sets the oxygen concentration in the second interior space becomes a target value, and which obtains a detection value dependent on the oxygen that is generated in the measuring chamber and that originates from a specific gas, based on the measuring voltage during the execution of the auxiliary pump control operation and the main pump control operation,and which detects the concentration of a specific gas in the gas of the object being measured based on the detection value, a storage unit which stores a correspondence relationship of the concentration of a specific gas, which is a correspondence relationship between the concentration of a specific gas in the gas of the object being measured and the detection value, and a unit for obtaining a measured value, which performs the auxiliary pump control process and the main pump control process and which obtains a measured value b1 at a measuring point B1, where a known value of the oxygen concentration and the main pump flow are relevant to each other, by measuring the main pump flow, which flows during the execution of the auxiliary pump control process and the main pump control process, at a measurement time when the oxygen concentration in the gas of the object being measured around the element body is detected,as the known value. The unit for measuring the concentration of a specific gas measures the concentration of a specific gas based on the measurement value and the correspondence relationship of the concentration of a specific gas stored in the storage unit, and the unit for measuring the concentration of a specific gas corrects the measurement value or the correspondence relationship of the concentration of a specific gas based on the measured value b1 at the measuring point B1.

[0018] The more foreign matter, such as soot, accumulates in the sample gas flow section during the use of the gas sensor, the greater the diffusion resistance near the sample gas flow section's inlet becomes, and consequently, the smaller the amount of sample gas flowing into the sample gas flow section as described above. Even if the oxygen concentration in the sample gas remains constant, the main pump flow rate decreases. Therefore, the more foreign matter accumulates, the lower the slope of the relationship between the oxygen concentration in the sample gas and the main pump flow rate during both the main pump control and the auxiliary pump control processes.Accordingly, the more foreign substance accumulates, the lower the measured value becomes, even if the concentration of a specific gas in the gas used for measurement remains the same. Therefore, the slope of the relationship between the concentration of a specific gas in the gas used for measurement and the measured value decreases as the amount of foreign substance accumulates during both the main pump control and auxiliary pump control processes. The rate of change of the slope of the relationship between the oxygen concentration in the gas used for measurement and the main pump flow rate is equal to the rate of change of the slope of the relationship between the concentration of a specific gas in the gas used for measurement and the measured value.For this reason, the measured value b1 at measuring point B1, which is measured during the auxiliary pump control process and the main pump control process, correlates not only with the degree of change in the slope of the relationship between the oxygen concentration and the main pump flow, but also with the degree of change in the slope of the relationship between the concentration of a specific gas and the measured value. Accordingly, in this other gas sensor, the unit for measuring the concentration of a specific gas corrects the measured value or the relationship between the concentration of a specific gas based on the measured value b1 at measuring point B1.In this way, the change in the slope of the correspondence relationship between the concentration of a specific gas and the detection value can be corrected, and a reduction in the accuracy of the detection of the concentration of a specific gas during the use of the gas sensor can consequently be prevented. Brief description of the drawings Fig. Figure 1 is a schematic sectional view of a gas sensor 100. Fig. Figure 2 is a block diagram showing the electrical connection relationships between a control device 90 and cells. Fig. Figure 3 is a graph showing a relationship between an oxygen concentration C and a pump current Ip0 during a first control process. Fig. Figure 4 is a graph showing a relationship between the oxygen concentration C and the pump current Ip0 during a second control process. Fig. Figure 5 is a flowchart of an example of a control routine. Fig. Figure 6 is a graph showing a relationship between a NOx concentration D and a pump current Ip2 during the first control process. Fig. Figure 7 is a schematic sectional view of a sensor element 201 according to a modification. Description of embodiments

[0019] One embodiment of the present invention is described below with reference to the drawings. Fig. Figure 1 is a schematic sectional view of an example of the structure of a gas sensor 100 according to an embodiment of the present invention. Fig. Figure 2 is a block diagram showing the relationships of an electrical connection between a control device 90 and cells. The gas sensor 100 is mounted in a pipe, such as the exhaust pipe of an internal combustion engine, for example, a gasoline or diesel engine. The gas sensor 100 uses the exhaust gas of the internal combustion engine as the sample gas to detect the concentration of a specific gas, such as ammonia or NOx, in the sample gas. According to the present embodiment, the gas sensor 100 measures a NOx concentration as the concentration of a specific gas. The gas sensor 100 comprises a sensor element 101, which has an elongated rectangular cuboid shape, cells 15, 21, 41, 50, and 80 to 83, which contain parts of the sensor element 101, and the control device 90, which controls the entire gas sensor 100.

[0020] The sensor element 101 has a multilayer body consisting of six layers: a first substrate layer 1, a second substrate layer 2, a third substrate layer 3, a first solid electrolyte layer 4, a spacer layer 5, and a second solid electrolyte layer 6. These layers are composed of oxygen-ion-conducting solid electrolyte layers, such as zirconium oxide (ZrO2) layers, and are stacked in this order from bottom to top in the figure. The solid electrolyte used to construct the six layers is high-density and airtight. The sensor element 101 is manufactured, for example, by performing a predefined process and circuit structure printing on ceramic green layers corresponding to the respective layers. The layers are then stacked and fired to form an integrated component.

[0021] At a position near an end section (near a left end section in the Fig. 1) of the sensor element 101, a gas inlet 10, a first diffusion control section 11, a buffer chamber 12, a second diffusion control section 13, a first interior space 20, a third diffusion control section 30, a second interior space 40, a fourth diffusion control section 60 and a third interior space 61 are formed between a lower surface of the second solid electrolyte layer 6 and an upper surface of the first solid electrolyte layer 4 such that they adjoin each other in this order and are connected to each other.

[0022] The gas inlet 10, the buffer chamber 12, the first interior 20, the second interior 40 and the third interior 61 are spaces in the sensor element 101, each of which is formed by hollowing out the spacer layer 5 such that an upper part is defined by the lower surface of the second solid electrolyte layer 6, a lower part is defined by the upper surface of the first solid electrolyte layer 4 and a side part is defined by a side surface of the spacer layer 5.

[0023] Each of the first diffusion control section 11, the second diffusion control section 13, and the third diffusion control section 30 is configured as two slots extending from side to side (the longitudinal direction of openings is perpendicular to the figure). The fourth diffusion control section 60 is configured as a slot forming a gap adjacent to the lower surface of the second solid electrolyte layer 6, also extending from side to side (the longitudinal direction of openings is perpendicular to the figure). A section extending from the gas inlet 10 to the third interior space 61 is also referred to as the sample gas flow section.

[0024] A reference gas introduction chamber 43 is located at a position further from the end than the sample gas flow section and at a position where a side part is defined by a side surface of the first solid electrolyte layer 4 between the upper surface of the third substrate layer 3 and the lower surface of the spacer layer 5. For example, when the NOx concentration is measured, air is introduced into the reference gas introduction chamber 43 as the reference gas.

[0025] An air introduction layer 48 is a layer composed of a porous ceramic, and the reference gas is introduced into the air introduction layer 48 via the reference gas introduction chamber 43. The air introduction layer 48 is configured to cover a reference electrode 42.

[0026] The reference electrode 42 is an electrode configured such that it is positioned between the upper surface of the third substrate layer 3 and the first solid electrolyte layer 4, and the air introduction layer 48, which communicates with the reference gas introduction chamber 43, is arranged around it, as described above. The use of the reference electrode 42 enables the measurement of an oxygen concentration (an oxygen partial pressure) in the first chamber 20, the second chamber 40, and the third chamber 61, as described below. The reference electrode 42 is configured as a porous cermet electrode (for example, a cermet electrode composed of Pt and ZrO2).

[0027] In the sample gas flow section, the gas inlet 10 is a region open to the outside, and the sample gas is introduced from the outside into the interior of the sensor element 101 via the gas inlet 10. The first diffusion control section 11 exerts a predetermined diffusion resistance on the sample gas introduced via the gas inlet 10. The buffer chamber 12 is configured such that the sample gas introduced via the first diffusion control section 11 is directed to the second diffusion control section 13. The buffer chamber 12 also serves as a space (pre-chamber) for pumping oxygen into the sample gas introduced via the first diffusion control section 11. The oxygen is pumped into the buffer chamber 12 by the operation of the pre-pump cell 15.The second diffusion control section 13 exerts a predetermined diffusion resistance on the gas sample introduced from the buffer chamber 12 into the first interior chamber 20. When the gas sample is introduced into the first interior chamber 20 from a location outside the sensor element 101, the gas sample, which is rapidly drawn into the interior of the sensor element 101 via the gas inlet 10 as a result of a pressure variation in the external chamber (in the case where the gas sample is exhaust gas from a motor vehicle, the pulsation of exhaust pressure), is not drawn directly into the first interior chamber 20. Instead, after the pressure variation of the gas sample is eliminated, it is drawn into the first interior chamber 20 via the first diffusion control section 11, the buffer chamber 12, and the second diffusion control section 13.Consequently, the variation in the pressure of the gas introduced into the first chamber 20 is almost negligible. The first chamber 20 is designed to adjust the oxygen partial pressure in the gas introduced via the second diffusion adjustment section 13. The oxygen partial pressure is adjusted by the operation of the main pump cell 21.

[0028] The pre-pump cell 15 is an electrochemical pump cell comprising a pre-pump electrode 16, which is arranged substantially over the entire lower surface of the second solid electrolyte layer 6 facing the buffer chamber 12, an outer pump electrode 23, which is arranged on a portion of the outer surface of the sensor element 101 that is to be exposed to the sample gas, and the second solid electrolyte layer 6, which is arranged between the electrodes. The pre-pump electrode 16 is located at the most upstream position relative to the electrodes in the sample gas flow section. A variable power supply 17, arranged between the pre-pump electrode 16 and the outer pump electrode 23, applies a pump voltage Vp0s, causing a pump current Ip0s to flow between the pre-pump electrode 16 and the outer pump electrode 23, and consequently the pre-pump cell 15 can pump oxygen in the outer space into the buffer space 12.

[0029] The main pump cell 21 is an electrochemical pump cell comprising an inner pump electrode 22, which includes an upper electrode section 22a, which is arranged on substantially the entire lower surface of the second solid electrolyte layer 6, which is directed towards the first interior space 20, the outer pump electrode 23, which is arranged in a region of the upper surface of the second solid electrolyte layer 6 opposite to the upper electrode section 22a such that the outer pump electrode 23 is exposed to the exterior space, and the second solid electrolyte layer 6, which is arranged between the electrodes.

[0030] The inner pump electrode 22 is designed to extend over the upper and lower solid electrolyte layers (the second solid electrolyte layer 6 and the first solid electrolyte layer 4), which define the first interior 20 and the spacer layer 5, which define the side walls.In particular, the upper electrode section 22a is formed on the lower surface of the second solid electrolyte layer 6, which defines the upper surface of the first interior space 20; a lower electrode section 22b is formed on the upper surface of the first solid electrolyte layer 4, which defines its lower surface; side electrode sections (not shown) are formed on side wall surfaces (inner surfaces) of the spacer layer 5, which define both side wall sections of the first interior space 20, such that the upper electrode section 22a and the lower electrode section 22b are connected to each other; and the side electrode sections are connected such that a tunnel-shaped structure is formed at the positions where the side electrode sections are arranged.

[0031] The inner pump electrode 22 and the outer pump electrode 23 are designed as porous cermet electrodes (for example, cermet electrodes composed of Pt containing 1% Au and ZrO2). The inner pump electrode 22, which comes into contact with the gas of the sample, is made of a material that has a reduced capacity to reduce NOx components in the gas of the sample.

[0032] In the main pump cell 21, a desired pump voltage Vp0 is applied between the inner pump electrode 22 and the outer pump electrode 23, causing a pump current Ip0 to flow in a positive direction or in a negative direction between the inner pump electrode 22 and the outer pump electrode 23, and consequently the oxygen in the first interior space 20 can be pumped out to the outer space or the oxygen in the outer space can consequently be pumped into the first interior space 20.

[0033] To detect the oxygen concentration (oxygen partial pressure) in the atmosphere in the first interior space 20, an electrochemical sensor cell is included, i.e., the oxygen partial pressure detection sensor cell for main pump control 80, the inner pump electrode 22, the second solid electrolyte layer 6, the spacer layer 5, the first solid electrolyte layer 4, the third substrate layer 3 and the reference electrode 42.

[0034] An electromotive force V0 in the oxygen partial pressure sensing sensor cell for the main pump control 80 is measured, and the oxygen concentration (the oxygen partial pressure) in the first chamber 20 is consequently known. A control of the pump voltage Vp0 of a variable power supply 24 is implemented such that the electromotive force V0 reaches a target value, and the pump current Ip0 is consequently controlled or adjusted. This allows the oxygen concentration in the first chamber 20 to be maintained at a predetermined constant value.

[0035] The third diffusion control section 30 exerts a predetermined diffusion resistance on the gas of the object being measured, whose oxygen concentration (oxygen partial pressure) has been controlled or set by the operation of the main pump cell 21 in the first interior space 20, and directs the gas of the object being measured in the direction of the second interior space 40.

[0036] The second interior chamber 40 is designed as a space in which the auxiliary pump cell 50 sets the oxygen partial pressure of the gas being measured, which is introduced via the third diffusion adjustment section 30 after the oxygen concentration (the oxygen partial pressure) in the first interior chamber 20 has been preset. This allows the oxygen concentration in the second interior chamber 40 to be kept constant with high accuracy, and the gas sensor 100 can consequently measure the NOx concentration with high accuracy.

[0037] The auxiliary pump cell 50 is an electrochemical auxiliary pump cell comprising an auxiliary pump electrode 51, which includes an upper electrode section 51a, which is arranged on substantially the entire lower surface of the second solid electrolyte layer 6, which is directed towards the second interior space 40, the outer pump electrode 23 (which is not limited to the outer pump electrode 23, and a suitable electrode outside the sensor element 101 is sufficient) and the second solid electrolyte layer 6.

[0038] The auxiliary pump electrode 51 is arranged in the second interior space 40 on a tunnel-shaped structure similar to that of the inner pump electrode 22, which is located in the first interior space 20 described above. That is, the upper electrode section 51a is formed on the second solid electrolyte layer 6, which forms the upper surface of the second interior space 40, a lower electrode section 51b is formed on the first solid electrolyte layer 4, which forms the lower surface of the second interior space 40, and the tunnel-shaped structure is present in which side electrode sections (not shown), connecting the upper electrode section 51a and the lower electrode section 51b, are formed on both wall surfaces of the spacer layer 5, defining the side walls of the second interior space 40.The auxiliary pump electrode 51 is composed of a material that has a reduced ability to reduce the NOx components in the gas of the object being measured, as is the case with the inner pump electrode 22.

[0039] In the auxiliary pump cell 50, a desired voltage Vp1 is applied between the auxiliary pump electrode 51 and the outer pump electrode 23, and oxygen in the atmosphere in the second interior space 40 can consequently be pumped out to the outside space or the oxygen in the outside space can consequently be pumped into the second interior space 40.

[0040] For controlling or adjusting the oxygen partial pressure in the atmosphere in the second interior space 40, an electrochemical sensor cell is included, i.e., the oxygen partial pressure detection sensor cell for auxiliary pump control 81, the auxiliary pump electrode 51, the reference electrode 42, the second solid electrolyte layer 6, the spacer layer 5, the first solid electrolyte layer 4 and the third substrate layer 3.

[0041] The auxiliary pump cell 50 is operated using a variable power supply 52, the voltage of which is controlled or adjusted based on an electromotive force V1 detected by the oxygen partial pressure sensing sensor cell for auxiliary pump control 81. Consequently, the oxygen partial pressure in the atmosphere in the second interior space 40 is controlled or adjusted to a low partial pressure that does not substantially affect the NOx measurement.

[0042] In addition, a pump current Ip1 is used to control the electromotive force of the oxygen partial pressure sensing sensor cell for the main pump control 80. Specifically, the pump current Ip1 is fed into the oxygen partial pressure sensing sensor cell for the main pump control 80 as a control signal, and the target value of the electromotive force V0 described above is set. Consequently, the gradient of the oxygen partial pressure in the gas of the sample, which is introduced into the second chamber 40 via the third diffusion control section 30, is controlled or set so that it remains constant. In the case of a NOx sensor, the oxygen concentration in the second chamber 40 is maintained at a constant value of approximately 0.001 ppm by the operation of the main pump cell 21 and the auxiliary pump cell 50.

[0043] The fourth diffusion control section 60 exerts a predetermined diffusion resistance on the gas of the sample, whose oxygen concentration (oxygen partial pressure) has been controlled or set by the operation of the auxiliary pump cell 50 in the second chamber 40, and directs the gas of the sample towards the third chamber 61. The fourth diffusion control section 60 has a function of limiting the amount of NOx that flows into the third chamber 61.

[0044] The third chamber 61 is designed as a chamber in which the concentration of nitrogen oxide (NOx) in the gas sample, introduced via the fourth diffusion control section 60, is measured after the oxygen concentration (oxygen partial pressure) has been preset in the second chamber 40. The NOx concentration is primarily measured by the operation of the measuring pump cell 41 in the third chamber 61.

[0045] The measuring pump cell 41 measures the NOx concentration in the sample gas in the third chamber 61. The measuring pump cell 41 is an electrochemical pump cell comprising a measuring electrode 44, which is arranged on the upper surface of the first solid electrolyte layer 4 and faces the third chamber 61, the outer pump electrode 23, the second solid electrolyte layer 6, the spacer layer 5, and the first solid electrolyte layer 4. The measuring electrode 44 is a porous cermet electrode composed of a material that exhibits a higher level of NOx reduction capacity in the sample gas than that of the inner pump electrode 22. The measuring electrode 44 also acts as an NOx reduction catalyst for reducing NOx present in the atmosphere within the third chamber 61.

[0046] In the measuring pump cell 41, oxygen, which is formed by the decomposition of nitrogen oxide in the atmosphere around the measuring electrode 44, is pumped out and its quantity can be recorded as pump current Ip2.

[0047] To detect the oxygen partial pressure around the measuring electrode 44, an electrochemical sensor cell, i.e., the oxygen partial pressure detection sensor cell for measuring pump control 82, comprises the first solid electrolyte layer 4, the third substrate layer 3, the measuring electrode 44, and the reference electrode 42. A variable power supply 46 is controlled on the basis of an electromotive force V2, which is detected by the oxygen partial pressure detection sensor cell for measuring pump control 82.

[0048] The sample gas, which is directed into the second chamber 40, reaches the measuring electrode 44 in the third chamber 61 via the fourth diffusion control section 60, where the oxygen partial pressure is set. The nitrogen oxide in the sample gas around the measuring electrode 44 is reduced (2 NO → N2 + O2) and oxygen is generated. The generated oxygen is pumped through the measuring pump cell 41. A voltage Vp2 of the variable power supply 46 is controlled or set such that the electromotive force V2, which is detected by the oxygen partial pressure sensing sensor cell for the measuring pump control 82, remains constant (target value). The amount of oxygen generated around the measuring electrode 44 is proportional to the concentration of nitrogen oxide in the sample gas, and the nitrogen oxide concentration in the sample gas is calculated using the pump current Ip2 in the measuring pump cell 41.

[0049] The electrochemical sensor cell 83 comprises the second solid electrolyte layer 6, the spacer layer 5, the first solid electrolyte layer 4, the third substrate layer 3, the outer pump electrode 23, and the reference electrode 42. The oxygen partial pressure in the gas of the sample outside the sensor can be detected using an electromotive force (a voltage Vref) obtained by the sensor cell 83.

[0050] In the gas sensor 100 with this structure, the sample gas, whose oxygen partial pressure is always kept at a constant low value (a value that does not significantly affect the NOx measurement), is supplied to the measuring pump cell 41 by the operation of the main pump cell 21 and the auxiliary pump cell 50. Accordingly, the NOx concentration in the sample gas can be determined based on the pump flow Ip2, which results in oxygen, generated by a reduction of NOx essentially proportional to the NOx concentration in the sample gas, being pumped out through the measuring pump cell 41.

[0051] The sensor element 101 also includes a heating element section 70, which has a temperature control function for heating the sensor element 101 and maintaining its temperature to improve the oxygen ion conductivity of the solid electrolyte. The heating element section 70 includes a heating element connection electrode 71, a heating element 72, a through-hole 73, a heating element insulating layer 74, and a pressure relief hole 75.

[0052] The heating element electrode 71 is configured to be in contact with the lower surface of the first substrate layer 1. Connecting the heating element electrode 71 to an external power supply allows electricity to be supplied from outside to the heating element section 70.

[0053] The heating element 72 is an electrical resistor configured such that it is positioned vertically between the second substrate layer 2 and the third substrate layer 3. The heating element 72 is connected to the heating element connection electrode 71 via the through-hole 73 and generates heat. This heat allows external electricity to be supplied via the heating element connection electrode 71 to heat the solid electrolyte from which the sensor element 101 is formed and to maintain its temperature.

[0054] The heating device 72 is embedded in the entire area with a length from the first interior 20 to the third interior 61 and can set the temperature of the entire sensor element 101 to a temperature at which the solid electrolyte is activated.

[0055] The heating element insulating layer 74 is composed of an insulator, such as aluminum oxide, on the upper and lower surfaces of the heating element 72. The heating element insulating layer 74 is configured to provide electrical insulation between the second substrate layer 2 and the heating element 72, and electrical insulation between the third substrate layer 3 and the heating element 72.

[0056] The pressure relief hole 75 is designed to extend through the third substrate layer 3 and the air introduction layer 48, and is designed to communicate with the reference gas introduction chamber 43, and is designed to reduce an increase in internal pressure due to an increase in the temperature of the interior of the heating device insulating layer 74.

[0057] As it is in the Fig. As shown in Figure 2, the control device 90 comprises the variable power supplies 17, 24, 46 and 52 described above and a control unit 91.

[0058] The control unit 91 is a microprocessor comprising a CPU 92 and a memory unit 94. The control unit 91 receives the electromotive force V0, detected by the oxygen partial pressure sensing sensor cell for the main pump control 80; the electromotive force V1, detected by the oxygen partial pressure sensing sensor cell for the auxiliary pump control 81; the electromotive force V2, detected by the oxygen partial pressure sensing sensor cell for the measuring pump control 82; the voltage Vref, detected by the sensor cell 83; the pump current Ip0s, detected by the pre-pump cell 15; the pump current Ip0, detected by the main pump cell 21; the pump current Ip1, detected by the auxiliary pump cell 50; and the pump current Ip2, detected by the measuring pump cell 41.The control unit 91 controls the voltages Vp0s, Vp0, Vp1, and Vp2, which are output by the variable power supplies 17, 24, 46, and 52, to control the pre-pump cell 15, the main pump cell 21, the measuring pump cell 41, and the auxiliary pump cell 50. The memory unit 94 stores, for example, target values ​​Ip0s*, V0*, V1*, and V2*, which will be described later. The CPU 92 of the control unit 91 refers to the target values ​​Ip0s*, V0*, V1*, and V2* and controls cells 15, 21, 41, and 50.

[0059] The control unit 91 performs a pre-pump control operation of the pre-pump cell 15 such that the constant pump current Ip0s flows. In particular, the control unit 91 implements a control of the voltage Vp0s of the variable power supply 17 so that the pump current Ip0s of the pre-pump cell 15 reaches the constant target value Ip0s* for controlling the pre-pump cell 15. The control unit 91 controls the voltage Vp0s such that oxygen is pumped into the buffer chamber 12 during the pre-pump control operation, but does not control the voltage Vp0s such that oxygen is pumped out of the buffer chamber 12. Since the target value Ip0s* is to be a constant value, the control device 90 controls the pre-pump cell 15 such that oxygen is pumped into the buffer chamber 12 at a constant flow rate.Even if the sample gas outside the sensor element 101 is a low-oxygen atmosphere (for example, an atmosphere with an oxygen concentration of 0.1% by volume or less, less than 0.2% by volume, or less than 1% by volume), the target value Ip0s* is determined such that the sample gas (i.e., the sample gas introduced into the first interior space 20) does not become a low-oxygen atmosphere after oxygen has been pumped in through the pre-pump cell 15. In the case where the air-fuel ratio of the sample gas is less than a theoretical air-fuel ratio, i.e., in the case of a rich atmosphere, the sample gas contains hydrocarbons (HC) or carbon monoxide as an unburned component, and the oxygen concentration can be obtained from the amount of oxygen just sufficient to combust the unburned component.Accordingly, the oxygen concentration of the rich atmosphere is represented by a negative value. For this reason, the target value Ip0s* is determined, for example, in the manner described below. The minimum value of the exhaust gas oxygen concentration in various operating states of the combustion engine utilizing gas sensor 100 (the case where the minimum value decreases to a negative value is included) is investigated beforehand. The target value Ip0s* is determined based on the amount of oxygen required to increase the minimum oxygen concentration of the gas being measured to an oxygen concentration higher than that of the low-oxygen atmosphere (for example, the oxygen concentration is more than 0.1% by volume, 0.2% by volume or more, or 1% by volume or more).The target value Ip0s* can be determined in a suitable manner based on an experiment as described above, or, for example, it can be no less than 0.5 mA and no more than 3 mA. The control unit 91 does not need to regulate the voltage Vp0s of the variable power supply 17 such that the pump current Ip0s becomes the constant target value Ip0s* in the pre-pump control process, but can control the pre-pump cell 15 such that the pump current Ip0s becomes a constant value (the target value Ip0s*) by controlling the voltage Vp0s of the variable power supply 17 such that the voltage becomes constant. When the sample gas, which is the low-oxygen atmosphere, is introduced into the first chamber 20, it is assumed that the inner pump electrode 22 acts as a catalyst and that NOx is reduced in the first chamber 20 before it reaches the third chamber 61.In the case where the gas used for measurement is the rich atmosphere containing the unburned component, it is assumed that NOx reacts with the unburned component and is reduced before reaching the third chamber 61. However, the gas used for measurement, which is the low-oxygen atmosphere, can be prevented from entering the first chamber 20, and the unburned component in the gas used for measurement can react with oxygen in such a way that the pre-pump cell 15 pumps the oxygen into the buffer chamber 12. Accordingly, the reduction of NOx before it reaches the third chamber 61 is prevented, and the accuracy of the NOx concentration measurement is improved.In many cases, such as with a gasoline engine, the air-fuel ratio shifts within proportions close to the theoretical air-fuel ratio, and the gas used for measurement is sometimes always the atmosphere with a low oxygen content, or in other cases frequently the rich atmosphere. Even in these cases, the NOx concentration can be accurately measured by pumping oxygen into the pre-pump cell 15.

[0060] The control unit 91 performs an auxiliary pump control process by controlling the auxiliary pump cell 50 such that the oxygen concentration in the second chamber 40 reaches a target concentration. Specifically, the control unit 91 controls the auxiliary pump cell 50 by implementing a regulation of the voltage Vp1 of the variable power supply 52 such that the electromotive force V1 reaches a constant value (referred to as the target value V1*). The target value V1* is set such that the oxygen concentration in the second chamber 40 reaches a predetermined low concentration, which does not significantly affect the NOx measurement.

[0061] The control unit 91 performs a main pump control operation of the main pump cell 21 such that the pump current Ip1, which flows when the auxiliary pump cell 50 sets the oxygen concentration in the second chamber 40, reaches a target value (referred to as target value Ip1*). In particular, the control unit 91 sets (regulates) a target value (referred to as target value V0*) of the electromotive force V0 based on the pump current Ip1 such that the pump current Ip1, which flows at voltage Vp1, reaches the constant target value Ip1*. The control unit 91 implements a control of the pump voltage Vp0 of the variable power supply 24 such that the electromotive force V0 reaches the target value V0* (i.e., such that the oxygen concentration in the first chamber 20 reaches the target concentration).The gradient of the oxygen partial pressure in the sample gas, which is to be introduced into the second chamber 40 via the third diffusion control section 30, is kept constant by the main pump control process. The pump current Ip0, which flows in the main pump control process, changes depending on the oxygen concentration in the sample gas and the flow rate of oxygen pumped in through the pre-pump cell 15. For this reason, the control unit 91 can determine the oxygen concentration in the sample gas based on the pump current Ip0.

[0062] The control unit 91 performs a measuring pump control process of controlling the measuring pump cell 41 based on the electromotive force V2 such that oxygen, which is generated in the third chamber 61 and which originates from the specific gas (here NOx), is pumped out of the third chamber 61 and the oxygen concentration in the third chamber 61 reaches a predetermined low concentration. In particular, the control unit 91 controls the measuring pump cell 41 by implementing a regulation of the voltage Vp2 of the variable power supply 46 such that the electromotive force V2 reaches a constant value (referred to as the target value V2*) (i.e., the oxygen concentration in the third chamber 61 reaches a predetermined low concentration).Consequently, the oxygen is pumped out of the third chamber 61 in such a way that the amount of oxygen produced by reducing NOx in the gas of the sample in the third chamber 61 becomes essentially zero. The control unit 91 receives the pump flow rate Ip2 as a detection value, dependent on the oxygen produced in the third chamber 61 and originating from the specific gas (here NOx), while the pre-pump control process, the auxiliary pump control process, the main pump control process, and the measuring pump control process described above are carried out, and calculates the NOx concentration in the gas of the sample based on the pump flow rate Ip2. The pre-pump control process, the auxiliary pump control process, and the main pump control process are collectively referred to as the first control process.

[0063] The storage unit 94 stores, for example, a relational expression (such as a linear function) or a characteristic curve as a correspondence relationship (referred to as the correspondence relationship of the concentration of a specific gas) between the measured value (here the pump current Ip2) and the concentration of a specific gas (here the NOx concentration). The relational expression or the characteristic curve can be obtained beforehand through an experiment.

[0064] The present inventors investigated the relationship between the oxygen concentration in the test gas and the pump flow rate Ip0. This relationship was investigated during the first control procedure described above. A model gas was used as the test gas. Nitrogen was used as the base gas, ethylene gas was used to simulate the unburned component, the temperature was set to 260 °C, the flow rate was set to 50 L / min, the amount of added water was set to 3% by volume, the NO concentration was set to 0 ppm, and the oxygen concentration was set to -10, -5, 0, 5, 10, 18, or 21% by volume. The diameter of the conduit used to deliver the model gas was 20 mm.The relationship between the oxygen concentration in the gas sample and the pump current Ip0 was then investigated during a pre-pump stop operation (stopping the operation of the pre-pump cell 15, as the variable power supply 17 stopped applying the voltage Vp0s, so that the pump current Ip0s did not flow), an auxiliary pump control operation, and a main pump control operation. The pre-pump stop operation, the auxiliary pump control operation, and the main pump control operation are collectively referred to as the second control operation. A ceramic paste was applied to the gas inlet 10 of the sensor element 101 to simulate a condition in which a foreign substance had accumulated on the gas inlet 10 (and the first diffusion control section 11).Regarding sensor element 101 in this state, the relationship between the oxygen concentration in the gas used for measurement and the pump current Ip0 during the execution of the first control operation as described above, and the relationship between the oxygen concentration in the gas used for measurement and the pump current Ip0 during the execution of the second control operation, were investigated. Both relationships were investigated not only during the execution of the first control operation or the second control operation, but also during the execution of the measuring pump control operation.

[0065] The Fig. Figure 3 is a graph showing a relationship between an oxygen concentration C and the pump current Ip0 during the first control operation. Fig. Figure 4 is a graph showing the relationship between the oxygen concentration C and the pump current Ip0 during the second control process. Circles that are in the Fig. The values ​​shown in point 3 represent the result of a measurement during the first control process without simulated accumulation of the foreign substance. A straight line R0, represented by a thick line, is an approximate straight line derived from the plotted result. Similarly, triangles and a straight line R1, represented by a dotted line in the Fig. Figure 3 shows the result of a measurement during the first control process with simulated accumulation of the foreign substance and an approximate straight line based on this. Circles and a straight line S0, which is defined by a thick line in the Fig. Figure 4 shows the result of a measurement during the second control process without simulated accumulation of the foreign substance and an approximate straight line based on this. Triangles and a straight line S1, which is defined by a dashed line in the Fig. Figure 4 shows the result of a measurement during the second control process with simulated accumulation of the foreign substance and an approximate straight line based on this. In the Fig. 3 are the straight lines S0 and S1 in the Fig. Figure 4 is also shown for comparison with the straight lines R0 and R1. Regarding the pump current Ip0 in the Fig. 3 and the Fig. 4. The current flowing when oxygen is pumped out of the first interior space 20 has a positive value, and the current flowing when oxygen is pumped into the first interior space 20 has a negative value.

[0066] As can be seen from the circles and the straight line R0 in the Fig. As can be seen in Figure 3, the oxygen concentration C in the gas being measured and the pump current Ip0 exhibit a linear relationship during the execution of the first control operation. That is, the relationship between the oxygen concentration C and the pump current Ip0 during the first control operation is approximately a linear function (the straight line R0). For this reason, using the relationship of the straight line R0 allows the oxygen concentration C to be derived based on the pump current Ip0. According to the present embodiment, the storage unit 94 stores the relationship of expression (1), which represents the straight line R0 described below, in advance as the first relationship. A slope K0 and an intersection point L0 in expression (1) described below are constants. The intersection point L0 is the value of the pump current Ip0 when the oxygen concentration C is zero, and a point where (C, Ip0) = (0, L0) in the Fig. The point where condition 3 is satisfied is called the origin of the line R0. As can be seen from the circles and the line S0 in the Fig. As can be seen in Figure 4, the oxygen concentration C in the gas sample and the pump current Ip0 exhibit a linear relationship during the second control operation. That is, the relationship between the oxygen concentration C and the pump current Ip0 during the second control operation is approximately a linear function (the straight line S0). One difference between the first control operation and the second control operation is whether oxygen is pumped in through the pre-pump cell 15. The value of the pump current Ip0s is controlled so that it is constant (so that the amount of oxygen pumped in through the pre-pump cell 15 is constant), as described above, and the main pump cell 21 pumps out oxygen in an amount that corresponds to the amount of oxygen pumped in and the amount of oxygen originally contained in the gas sample in the first chamber 20.Accordingly, the line R0 is a straight line in the case where the pump current Ip0 increases by a value corresponding to the amount of oxygen pumped through the pre-pump cell 15, compared to the line S0. That is, the line R0 and the line S0 have the same slope but different zero points (intersection points). During the second control operation, i.e., in a state where no oxygen is pumped through the pre-pump cell 15 and the oxygen concentration in the gas of the sample is zero, the oxygen concentration in the second chamber 40 is low even if the main pump cell 21 hardly pumps any oxygen in and out, and the line S0 passes almost through the origin. For this reason, as expressed in the later-described expression (2), the line S0 has the same slope K0 as the line R0 and an intersection point of 0.According to the present embodiment, the storage unit 94 stores the relationship of expression (2), which represents the line S0 described below, in advance as a second correspondence relationship. While the second control operation is being carried out and the oxygen concentration C is zero, the main pump cell 21 is controlled such that the pump current Ip1 reaches the constant target value Ip1*, i.e., a certain amount of oxygen is always pumped out of the second interior space 40, and the main pump cell 21 is controlled such that oxygen is pumped in advance into the first interior space 20 in an amount corresponding to the target value Ip1*. Consequently, the pump current Ip0 (i.e., the intersection of the line S0) has a slightly negative value in a strict sense while the second control operation is being carried out and the oxygen concentration C is zero.According to the present embodiment, the target value Ip1* is set to a very small value (for example, several µA). However, the pump current Ip0 in the investigation described above is a relatively large current and is measured in mA. An actual measured value of the pump current Ip0 when the oxygen concentration C in the . Fig. 4. Zero was 0 mA. In view of this, according to the present embodiment, the straight line S0 is defined such that it is an approximate straight line that lies on the circles in the Fig. 4 is based and runs through the origin. Ip0=K0*C+L0 Ip0=K0*C

[0067] As can be seen from the triangles and the line R1 in the Fig. As can be seen in Figure 3, for the sensor element 101 with simulated accumulation of the foreign substance, the oxygen concentration C and the pump current Ip0 exhibit a linear relationship. However, the slope and the intersection point (zero point) are modified with respect to those of the line R0, which corresponds to the relationship without accumulated foreign substance. In particular, the line R1 is given as expression (3) described later. The slope K1 of the line R1 is smaller than the slope K0 of the line R0, and the intersection point L1 of the line R1 changes with respect to the intersection point L0 of the line R0 and increases. For this reason, it was found that when a foreign substance, such as soot, accumulates in the sample gas flow section during the use of the gas sensor 100, the actual relationship (the line R1) deviates from the first relationship (the line R0) described above.The following reason can be assumed. The diffusion resistance (for example, the diffusion resistance of the gas inlet 10 and the first diffusion control section 11) near the inlet of the sample gas flow section increases when the foreign substance accumulates near the gas inlet 10, and the amount of sample gas flowing into the sample gas flow section decreases. Consequently, even if the oxygen concentration C is the same, the amount of oxygen flowing into the sample gas flow section from outside decreases, and the pumping current Ip0 decreases.For this reason, it is assumed that the more foreign substance accumulates near the inlet of the measured object gas flow section, the smaller the slope of the actual correspondence relationship between the oxygen concentration C and the pump current Ip0 during the execution of the first control operation, compared to the slope of the first correspondence relationship (straight line R0) before the accumulation. Oxygen pumped into the buffer chamber 12 by the pre-pump cell 15 during the first control operation does not flow entirely downstream towards the first interior space 20, but a portion of it moves upstream and flows outwards from the sensor element 101 via the gas inlet 10.The ratio between the oxygen flowing upstream from the buffer chamber 12 and the oxygen flowing downstream is determined, for example, by a ratio between the diffusion resistance of the gas inlet 10 and the first diffusion control section 11 and the diffusion resistance of the second diffusion control section 13. Of the oxygen pumped in through the pre-pump cell 15, the proportion of oxygen flowing downstream changes when the foreign substance accumulates near the inlet of the sample gas flow section. In particular, as more foreign substance accumulates near the inlet, the proportion of oxygen flowing downstream increases, accompanied by an increase in the diffusion resistance of the gas inlet 10 and the first diffusion adjustment section 11, and the value of the pump current Ip0 increases overall due to the increase.Consequently, it is assumed that the more foreign substance accumulates near the inlet of the measuring object gas flow section, the stronger the actual correspondence relationship between the oxygen concentration C and the pump current Ip0 becomes during the execution of the first control process in the . Fig. 3 shifts upwards (a direction in which the pump current Ip0 increases), compared to the first correspondence relationship (the straight line R0) before the accumulation. For this reason, it is assumed that the more foreign substance accumulates, the more the zero point of the actual correspondence relationship between the oxygen concentration C and the pump current Ip0 deviates during the execution of the first control process in the direction in which the pump current Ip0 increases, compared to the zero point of the first correspondence relationship (the straight line R0) before the accumulation (in the Fig. 3. It changes from the intersection point L0 to the intersection point L1, which is larger than the other one). Ip0=K1*C+L1(where K1<K0 und L1> L0)

[0068] As can be seen from the triangles and the line S1 in the Fig. As can be seen in Figure 4, even with sensor element 101 and simulated accumulation of the foreign substance, only the slope changes from that of the straight line S0, which corresponds to the relationship without accumulated foreign substance, and the intersection point (zero point) does not change during the execution of the second control process. As can be seen from the Fig. 3 and the Fig. As can be seen in Figure 4, the slope of line S1 is equal to the slope K1 of line R1. That is, line S1 is given by the expression (4) described later. The reason for this is presumably that no oxygen is pumped through the pre-pump cell 15 in the second control process, and consequently, the zero point does not change due to the accumulation of the foreign substance described above. Since the second control process includes the main pump control process and the auxiliary pump control process, as in the first control process, it is assumed that the same change in slope occurs regardless of whether the first or second control process is taking place, and that the slope of line S1 and the slope of line R1 are equal to the slope K1. Ip0=K1*C

[0069] If the foreign substance accumulates near the inlet of the gas flow section of the gas sensor 100 during its use, the relationship between the oxygen concentration C and the pump current Ip0 changes during the first control operation such that the slope and the zero point change, as described above. Specifically, when the oxygen concentration C is zero, the zero point and the value of the pump current Ip0 consequently deviate (in the Fig. 3. It deviates from the intersection point L0 to the intersection point L1). For this reason, the use of the first correspondence relation (the straight line R0), which is pre-stored in the memory unit 94, leads to a decrease in the accuracy of the measurement of the oxygen concentration C in the case where the oxygen concentration C is zero. In the case where the oxygen concentration C is zero, the air-fuel ratio (A / F) of the gas being measured is the theoretical air-fuel ratio (stoichiometry), and it is important to accurately measure that the air-fuel ratio is the theoretical air-fuel ratio. With this in mind, the present inventors have observed, as in the Fig. Figure 4 shows that the slope of the correspondence relationship between the oxygen concentration C and the pump current Ip0 deviates during the second control operation similarly to the first control operation, but that the zero point does not deviate. It was assumed that this could be used to correct the deviation of the zero point of the correspondence relationship between the oxygen concentration C and the pump current Ip0 during the first control operation. An example of this is described below.

[0070] The Fig. Figure 5 is a flowchart showing an example of a control routine executed by control unit 91. The routine is stored, for example, in storage unit 94 within control unit 91. Control unit 91 begins the control routine, for example, when the temperature of heating device 72 reaches a target temperature (e.g., 800 °C) by controlling the power supplied to heating device 72 beforehand by a heating device power supply (not shown).

[0071] When the control routine begins, the CPU 92 of the control unit 91 first executes the first control operation and the measuring pump control operation described above (steps S100 and S110). The CPU 92 then determines whether the measurement time has arrived at which the pump current Ip0 is measured (step S120). The measurement time is a point in time at which the oxygen concentration in the gas surrounding the sensor element 101 is considered to be a known value. According to the present embodiment, the measurement time is a point in time at which the gas surrounding the sensor element 101 is considered to be the atmosphere or air. That is, the known value is the value (21% by volume) of the oxygen concentration in the atmosphere or air.According to the present embodiment, the measurement time is a time at which the gas around the sensor element 101 is considered exhaust gas during a fuel interruption of the internal combustion engine. For example, the CPU 92 determines whether the control device 90 receives information regarding the execution of a fuel interruption, which represents a fuel interruption of the internal combustion engine performed by an engine ECU (engine control unit) not shown, for example, at predetermined intervals, and determines that the fuel interruption is performed when the information regarding the execution of a fuel interruption is received.When a predetermined delay time has elapsed since the information regarding the execution of a fuel interruption was received, the CPU 92 determines that the sample gas around the sensor element 101 is exposed to the exhaust gas during the fuel interruption; that is, it determines that this is the measurement time. The delay time is determined in advance based on the time required for the sample gas to flow from the combustion engine to the sensor element 101 and is stored in the memory unit 94.

[0072] When step S120 determines that the measurement time has arrived, CPU 92 begins executing the second control process described above (step S130). The pump current Ip0 during the execution of the second control process is measured (injected) and the measured value is recorded as measured value b1 (see the Fig. 4) stored at a measuring point B1 in the storage unit 94 (step S140). Measuring point B1 is a point at which the previously described known value of the oxygen concentration (here 21 volume%) is relevant for the pump current Ip0 (= the measured value b1) during the second control operation. If the foreign substance accumulates near the inlet of the sample gas flow section of the sensor element 101 during the use of the gas sensor 100, the correspondence relationship between the oxygen concentration C and the pump current Ip0 changes during the second control operation, starting from the straight line S0, which corresponds to the initial (before accumulation) correspondence relationship as described above. For this reason, the measured value b1 at measuring point B1, obtained in step S140, is equal to a value (a reference value b0 at a reference point B0 in the Fig. 4) on the straight line S0, when the oxygen concentration C is 21 volume%, if no foreign substance accumulates, but is smaller than the reference value b0 when the foreign substance accumulates. Here, the measured value b1 is measured at measuring point B1, which is in the Fig. Figure 4 shows that the foreign substance accumulates.

[0073] The CPU 92 then begins executing the first control operation described above (step S150). The pump current Ip0 during the execution of the first control operation is measured (injected) and the measured value is recorded as measured value a1 (see the Fig. 3) stored at a measuring point A1 in the storage unit 94 (step S160). Measuring point A1 is a point at which the known value of the oxygen concentration described above (here 21 volume %) is relevant for the pump current Ip0 (= the measured value a1) during the first control operation. If the foreign substance accumulates near the inlet of the sample gas flow section of the sensor element 101 during the use of the gas sensor 100, the correspondence relationship between the oxygen concentration C and the pump current Ip0 changes during the first control operation, moving away from the straight line R0, which corresponds to the initial (before accumulation) correspondence relationship. For this reason, the measured value a1 at measuring point A1, obtained in step S160, is equal to a value (a reference value a0 at a reference point A0 in the Fig. 3) on the straight line R0, when the oxygen concentration C is 21 volume%, when no foreign substance accumulates, but differs from the reference value a0 when the foreign substance accumulates. Here, the measured value a1 at measuring point A1, which is in the Fig. 3 is shown, measured, as the foreign substance accumulates.

[0074] The CPU 92 then derives the slope K1, which is a value that has changed from the slope K0 of the line S0, representing the second correspondence relation, based on a difference between the second correspondence relation stored in memory unit 94 and the measurement point B1, and causes memory unit 94 to store the slope K1 (step S170). For example, the CPU 92 derives the value of the slope K1 using the relation of expression (5) described later. In expression (5), “D1 / b0” corresponds to the “difference between the second correspondence relation and the measurement point B1”.As the foreign substance accumulates, the relationship between the oxygen concentration C and the pump current Ip0 changes during the second control process, starting from the second relationship (the straight line S0), so that the slope changes, but the zero point does not change, as described above. It can be assumed that the changed relationship is a straight line (here, the line S1) that has the same zero point as the line S0 and passes through the measuring point B1. The degree of difference (for example, a ratio or a difference between the reference value b0 and the measured value b1) between the measuring point B1 and the second relationship (the straight line S0) in the... Fig. 4 is proportional to the degree of change in the slope from line S0 to line S1. Accordingly, the slope K1 of line S1 can be derived based on the difference between the second correspondence relation and the measurement point B1. For example, CPU 92 calculates the slope K0 and the reference value b0 based on the second correspondence relation (for example, expression (2)), which is stored in memory unit 94, and derives the slope K1 from expression (5) described later, based on a read value and the measurement b1. Since line S0 passes through the origin, CPU 92 can derive the slope K0, given as K0 = b0 / 21, if the coordinates of the reference point B0, i.e., (C, Ip0) = (21, b0), can be identified. For this reason, memory unit 94 can only store information about the reference point B0 as the second correspondence relation, such as...Information representing the coordinates of the reference point B0 (C, Ip0) = (21, b0). The CPU 92 can derive the reference value b0, which corresponds to the known oxygen concentration (here 21 volume %), if the slope K0 is stored as the second correspondence relationship in memory unit 94. The second correspondence relationship stored in memory unit 94 can contain information that enables the determination of the second correspondence relationship (the line S0), in particular information required to derive the value of the slope K1. K1=K0*(b1 / b0)

[0075] After deriving the slope K1, the CPU 92 derives a modified zero point (the intersection point L1), which corresponds to a zero point after the zero point (the intersection point L0) of the first correspondence relationship (the straight line R0) has deviated, based on a straight line passing through the measuring point A1 and having the slope K1, and causes the memory unit 94 to store the modified zero point (step S180). As the foreign substance accumulates, the correspondence relationship between the oxygen concentration C and the pump current Ip0 changes during the first control operation, starting from the first correspondence relationship (the straight line R0), so that the slope and the zero point change as described above, and the modified slope is equal to the slope of the correspondence relationship between the oxygen concentration C and the pump current Ip0 during the second control operation.For this reason, it can be assumed that the slope of the correspondence relationship that changes from the first correspondence relationship (the line R0) is equal to the slope K1 derived at step S170. Accordingly, it can be assumed that the correspondence relationship that changes from the first correspondence relationship is the line (here, the line R1) that passes through the measurement point A1 and has the slope K1, and the zero point (the intersection point L1) of the line can be derived. For example, the CPU 92 can derive the changed zero point (the intersection point L1) using expression (3) described above to determine that the pump current Ip0 is equal to the measured value a1 and that C is equal to 21 volume% (the known oxygen concentration), and by using the value derived at step S170 as the slope K1.

[0076] Based on the derived modified zero point (intersection L1) and the zero point (intersection L0) of the first correspondence relation stored in memory unit 94, CPU 92 derives a magnitude of deviation from zero point Ld corresponding to a deviation between them and causes memory unit 94 to store the magnitude of deviation from zero point Ld (step S190). CPU 92 derives the magnitude of deviation from zero point Ld, for example, by expression (6) described below. Ld=L1−L0

[0077] After steps S130 to S190, or if the measurement point at step S120 is not present, CPU 92 determines whether a concentration derivation point exists at which the NOx and oxygen concentrations are derived (step S200). CPU 92 determines that the concentration derivation point exists, for example, whenever a predetermined time has elapsed or when an instruction for a concentration derivation is fed in by the engine ECU. Since the second control operation begins at step S130 and the first control operation subsequently begins at step S150, the first control operation is carried out when CPU 92 performs an operation at step S200, even after steps S130 to S190 or even if the measurement point at step S120 is not present.

[0078] If it is determined that the concentration derivation time is present at step S200, the CPU 92 measures (and injects) the pump current Ip0 while the first control operation is performed and obtains a measured value p, which is the measured value (step S210). Subsequently, in the case where the extent of the deviation from the zero point Ld is derived at step S190, the CPU 92 performs a zero-point correction to correct the obtained measured value p (step S220). The zero-point correction is a process of correcting the deviation of the zero point from the first correspondence relationship, wherein, according to the present embodiment, a corrected measured value p' is derived by expression (7) described below, based on the measured value p and the extent of the deviation from the zero point Ld. p'=p−Ld

[0079] CPU 92 derives the oxygen concentration C based on the measured value p (or the corrected measured value p') and the first correspondence relationship stored in memory unit 94 (step S230). For example, if the corrected measured value p' has not been derived, CPU 92 derives the value of the oxygen concentration C using expression (1) for the first correspondence relationship when the pump current Ip0 equals the measured value p. If the corrected measured value p' has been derived, CPU 92 derives the value of the oxygen concentration C using expression (1) for the first correspondence relationship when the pump current Ip0 equals the measured value p'. CPU 92 outputs the derived value of the oxygen concentration C to the engine ECU or causes memory unit 94 to store the derived value.In the case where the gas being measured is the exhaust gas of the combustion engine, the CPU 92 can derive the air-fuel ratio as the oxygen concentration of the gas being measured at step S230. Since the air-fuel ratio of the exhaust gas and the oxygen concentration can be converted into each other, the air-fuel ratio can also be considered a type of oxygen concentration. A conversion formula for the oxygen concentration and the air-fuel ratio (A / F) is known (see, for example, Johannes Brettschneider, "Calculation of the air-fuel ratio λ of air-fuel mixtures and the influence of measurement errors on λ", Bosch Technical Reports, Volume 6, Issue 4, pages 177-186, Stuttgart, 1979).

[0080] The corrected measurement p' is obtained by correcting the measurement p in such a way that a deviation (a deviation from the intersection point L0 to the intersection point L1) from the zero point (the intersection point L0) of the first correspondence relation (the line R0) is eliminated. Therefore, using the corrected measurement p' allows at least the correction of the zero point deviation from the first correspondence relation during the use of the gas sensor 100, and prevents a decrease in the accuracy of the oxygen concentration C measurement when the oxygen concentration C is zero. That is, it can at least be accurately determined that the value of the oxygen concentration C is 0.For example, if the zero point of the first correspondence relationship deviates (from the intersection point L0 to the intersection point L1), the measured value p, when the actual oxygen concentration C in the gas being measured is 0, also deviates from L0 to L1. In this case, the corrected measured value p' satisfies L0 (= p - Ld = L1 - Ld), and the value of the oxygen concentration C is correctly derived as a value of 0 based on the corrected measured value p' and the first correspondence relationship. The oxygen concentration C is derived as a positive value if the corrected measured value p' is greater than L0, and the oxygen concentration C is derived as a negative value if the corrected measured value p' is less than L0. Both positive and negative values ​​of the oxygen concentration are derived correctly.According to the present embodiment, the oxygen concentration C is derived using the first correspondence relationship at step S230, even if the first correspondence relationship (the straight line R0) changes, for example, to the straight line R1. For this reason, a change from the slope K0 to the slope K1 is not corrected, and if the actual oxygen concentration C in the sample gas is not 0, the greater the difference between the derived value of the oxygen concentration C and the actual value, the greater the difference. In the case where the engine ECU controls the internal combustion engine, for example, such that the value of the oxygen concentration C becomes 0 (i.e.,While the air-fuel ratio reaches its theoretical value, it is more important to know whether the oxygen concentration C is zero (whether the air-fuel ratio is the theoretical air-fuel ratio) and whether the oxygen concentration C is positive or negative (whether the gas being measured is in a rich or lean atmosphere). Therefore, it is important to correct for zero-point deviation, and the difference described above is unlikely to be a problem other than zero-point deviation.

[0081] The CPU 92 measures the pump current Ip2 (and supplies it) while the first control operation and the measuring pump control operation are performed, and derives the NOx concentration in the sample gas based on the measured value and the corresponding concentration relationship of a specific gas stored in the memory unit 94 (step S240). The CPU 92 outputs the derived value of the oxygen concentration C to the engine ECU or causes the memory unit 94 to store the derived value.

[0082] After step S240, or in the case where step S200 is not the concentration derivation time point, the CPU 92 performs operations after step S120. The CPU 92 derives the magnitude of the deviation from zero point Ld whenever step S120 is determined to be the measurement time point, and performs the zero-point correction using the magnitude of the deviation from zero point Ld that was last derived at step S220, i.e., the most recent magnitude of the deviation from zero point Ld.

[0083] The correspondence relationships between components according to the present embodiment and components according to the present invention are explained below. The multilayer body consisting of layers 1 to 6, stacked in this order according to the present embodiment, corresponds to an element body according to the present invention; the buffer chamber 12 corresponds to a pre-chamber; the pre-pump cell 15 corresponds to a pre-pump cell; the first interior space 20 corresponds to a first interior space; the main pump cell 21 corresponds to a main pump cell; the second interior space 40 corresponds to a second interior space; the auxiliary pump cell 50 corresponds to an auxiliary pump cell; the third interior space 61 corresponds to a measuring chamber; the measuring electrode 44 corresponds to a measuring electrode; the reference electrode 42 corresponds to a reference electrode; and the electromotive force V2 corresponds to a measuring voltage.The oxygen partial pressure sensing sensor cell for measuring pump control 82 corresponds to a measuring voltage sensing unit, the pump current Ip0s corresponds to a pre-pump current, the pump current Ip1 corresponds to an auxiliary pump current, the pump current Ip2 corresponds to a sensing value, the storage unit 94 corresponds to a storage unit, the pump current Ip0 corresponds to a main pump current, the CPU 92 of the control unit 91 corresponds to a unit for sensing the concentration of a specific gas, an oxygen concentration sensing unit and a unit for obtaining a measured value. The CPU 92 corresponds to a unit for obtaining information.

[0084] In the gas sensor 100 described above, according to the present embodiment, the CPU 92 performs the second control operation at the measurement time when the oxygen concentration in the gas sample around the sensor element 101 is considered to be the known value and measures the pump current Ip0 flowing during the second control operation, so that the measured value b1 is obtained at the measurement point B1 where the known value of the oxygen concentration and the main pump current are relevant to each other. The CPU 92 detects the oxygen concentration in the gas sample based on the measured value p of the pump current Ip0 flowing during the first control operation and the information (here, information about the first correspondence relationship) regarding the zero point, which is stored in the memory unit.The CPU 92 causes the zero-point correction to correct the measured value p so that the deviation (the deviation from the intersection point L0 to the intersection point L1 in the . Fig. 3) the zero point is corrected from the first correspondence relationship based on the measured value b1 at the measurement point B1. In particular, the CPU 92 performs the zero point correction based on the difference between the second correspondence relationship, which is stored in the memory unit 94, and the measurement point B1. The difference between the measurement point B1 and the second correspondence relationship correlates with the degree of change in the slope of the line that represents the correspondence relationship between the oxygen concentration and the pump current Ip0, as described above. The degree of change in the slope correlates with the degree of foreign substance accumulation near the inlet of the sample gas flow section, i.e., the degree of increase in diffusion resistance near the inlet, and thus correlates with the extent of the deviation of the zero point from the first correspondence relationship.For this reason, the difference between measurement point B1 and the second correspondence relationship also correlates with the extent of the zero point's deviation from the first correspondence relationship. Therefore, the zero point's deviation from the first correspondence relationship due to foreign substance accumulation can be corrected based on the difference between measurement point B1 and the second correspondence relationship. Consequently, a decrease in the accuracy of the oxygen concentration measurement when the oxygen concentration in the gas being measured is zero can be prevented during the use of the gas sensor.

[0085] The CPU 92 measures the pump current Ip0 flowing during the first control operation at the measurement time, so that the measured value a1 is obtained at measurement point A1, where the known value of the oxygen concentration and the pump current Ip0 are relevant to each other. The CPU 92 performs the zero-point correction based on the measured value b1 at measurement point B1 and the measured value a1 at measurement point A1. In particular, the CPU 92 performs the zero-point correction based on the difference between the second correspondence relationship and measurement point B1 and the measured value a1. The degree of difference between the second correspondence relationship and measurement point B1 correlates with the degree of change (the change from the slope K0 to the slope K1 in the Fig. 3 and the Fig. 4) the slope starting from the slope of the first correspondence relationship and the slope of the second correspondence relationship due to the accumulation of the foreign substance, as described above. The measured value a1 is a value during the first control process and is influenced by both the change in the slope and the change in the zero point, as described above. For this reason, the deviation (the deviation from the intersection point L0 to the intersection point L1 in the Fig. 3) the zero point of the first correspondence relationship due to the accumulation of the foreign substance on the basis of the difference between the second correspondence relationship and the measuring point B1 and the measured value a1, and the zero point correction can consequently be carried out in a suitable manner.

[0086] The CPU 92 derives the slope K1, which is a value that has changed from the slope K0 of the line representing the first correspondence relationship (and the second correspondence relationship), based on the measurement point B1. Specifically, the slope K1 is derived based on the difference between the second correspondence relationship and the measurement point B1. The CPU 92 derives the changed zero point (the intersection point L1 in the Fig. 3), which corresponds to the zero point after the zero point deviates from the first correspondence relation, on the basis of the line (the line R1 in the Fig. 3), which passes through measuring point A1 and has a slope of K1, and performs the zero-point correction based on the changed zero point. In this way, the zero-point correction can be carried out appropriately by differentiating the changed zero point.

[0087] The measurement time point is the point in time at which the gas surrounding the sensor element 101 is considered to be the atmosphere. If the gas surrounding the sensor element is the atmosphere, the oxygen concentration is considered to be the known value, and the measured value b1 can be obtained in a suitable manner by considering this point in time as the measurement time point.

[0088] The gas being measured is the exhaust gas from the internal combustion engine, and the CPU 92 receives information regarding the execution of a fuel cut-off, which represents the fuel interruption taking place in the internal combustion engine. The CPU 92 determines the measurement time based on this information. The exhaust gas from the internal combustion engine during the fuel cut-off is considered to be the atmosphere, and the CPU 92 can therefore appropriately determine the measurement time based on this information.

[0089] It is self-evident that the present invention is not limited to the embodiment described above and can be carried out in various aspects within the technical scope of the present invention.

[0090] For example, according to the embodiment described above, the CPU 92 performs the zero-point correction by correcting the measured value p at step S220, but alternatively, it can perform the zero-point correction by correcting the first correspondence relationship stored in the memory unit 94. For example, the CPU 92 can determine the corrected first correspondence relationship such that it is a straight line R0' (Ip0 = K0 * C + L0 + Ld) obtained by shifting the straight line R0, which represents the first correspondence relationship, so that the pump current Ip0 increases overall by the amount of the deviation from zero Ld at step S220, and can derive the oxygen concentration C based on the measured value p and the corrected first correspondence relationship at step S230.Furthermore, in this case, the deviation of the slope of the first correspondence relationship is not corrected; however, the deviation of the zero point is corrected (the information regarding the zero point of the first correspondence relationship is corrected), as is the case in the embodiment described above. Consequently, the reduction in the accuracy of the oxygen concentration measurement when the oxygen concentration in the gas being measured is zero during the use of the gas sensor can be prevented. It can be assumed that the line R0' is a straight line (Ip0 = K0 * C + L1) which has the same slope as the line R0 and the modified zero point (the intersection point L1). For this reason, the intersection point L1 can be derived at step S180 even if step S190 is omitted, and the line R0', i.e., the corrected first correspondence relationship, can be derived.CPU 92 can cause memory unit 94 to store the corrected first correspondence relationship and can use the corrected first correspondence relationship at step S230 until the next measurement time. In this way, CPU 92 does not need to derive the corrected first correspondence relationship every time.

[0091] According to the embodiment described above, the CPU 92 corrects the deviation of the zero point of the first correspondence relationship during the use of the gas sensor 100 by deriving the corrected measured value p' at step S220, but can additionally correct the change in the slope of the first correspondence relationship. For example, the CPU 92 can determine that the corrected first correspondence relationship is a straight line (the straight line R1 in the Fig. 3) is obtained by using the value of the modified slope K1, derived at step S170, and the value of the modified intersection point L1, derived at step S180, for expression (3), and can derive the oxygen concentration C based on the measured value p and the corrected first correspondence relationship at step S230. In this way, not only is the zero-point correction performed, but the change in the slope of the first correspondence relationship can also be corrected, and this improves the accuracy of the measurement of the oxygen concentration C not only when the oxygen concentration C in the sample gas is zero, but also when the oxygen concentration is not zero.

[0092] According to the embodiment described above, the CPU 92 derives the modified slope K1 and derives the modified zero point (the intersection point L1) and the magnitude of the deviation from the zero point Ld using the same method. However, a different derivation method can be used, provided that at least the modified zero point or the magnitude of the deviation from the zero point Ld is derived. For example, the CPU 92 can derive the magnitude of the deviation from the zero point Ld based on the difference between the magnitude of the deviation between the measured value b1 and the reference value b0, which is the value of the pump current Ip0 relevant for the known value of the oxygen concentration in the second correspondence relationship, and the magnitude of the deviation between the measured value a1 and the reference value a0, which is the value of the pump current Ip0 relevant for the known value of the oxygen concentration in the first correspondence relationship.The magnitude of the deviation (for example, a difference or a ratio) between the reference value b0 and the measured value b1 correlates with the change in the slope from the first and second correspondence relationships described above, and the magnitude of the deviation (for example, a difference or a ratio) between the reference value a0 and the measured value a1 correlates with the change in the slope and the change in the zero point from the first correspondence relationship described above. Therefore, a difference (for example, a difference or a ratio) between the magnitudes of the deviation correlates with the change in the zero point from the first correspondence relationship.Accordingly, the magnitude of the deviation from zero Ld can be derived based on the difference between these magnitudes of deviation, and the zero-point correction can be performed appropriately using the magnitude of the deviation from zero Ld. For example, the CPU 92 can derive the magnitude of the deviation from zero Ld based on expression (8) described later. The reference value a0 in expression (8) can be derived based on the first correspondence relationship previously stored in memory unit 94, and the reference value b0 can be derived based on the second correspondence relationship previously stored in memory unit 94. In expression (8), the units of reference value a0, measurement a1, reference value b0, measurement b1, and the magnitude of the deviation from zero Ld are the same unit of current (for example, mA). Ld=(b0−b1)−(a0−a1)

[0093] Furthermore, in the case where the expression (8) described above is used, the CPU 92 can correct the measured value p or derive the corrected first correspondence relationship. In addition, the CPU 92 can derive the correspondence relationship that is corrected such that the change in slope from the first correspondence relationship is corrected. For example, the CPU 92 first derives the modified zero point (the intersection point L1) from the relationship of the expression (6) described above, based on the zero point (the intersection point L0) of the first correspondence relationship and the magnitude of the deviation from the zero point Ld, which is derived using expression (8).The CPU 92 can then derive the corrected first correspondence relationship as a straight line that passes through the measurement point A1, measured at step S160, and the modified zero point (the intersection point L1). Furthermore, the CPU 92 can thus derive the corrected first correspondence relationship (the straight line R1 in the...). Fig. 3) derive. For example, the CPU 92 can derive the straight line passing through the measurement point A1 and the modified zero point, i.e., the corrected first correspondence relation, using the coordinates of measurement point A1, i.e., (C, Ip0) = (21, a1), and the intersection point L1 for expression (3) described above to derive the slope K1. In this way, not only is the zero-point correction performed, but the change in the slope of the first correspondence relation can also be corrected. Accordingly, not only is the accuracy of the measurement of the oxygen concentration C improved when the oxygen concentration C in the sample gas is zero, but also the accuracy of the measurement of the oxygen concentration C when the oxygen concentration is not zero.

[0094] According to the embodiment described above, the CPU 92 derives and outputs the oxygen concentration C based on the corrected measured value p' and the first correspondence relationship. However, it is not limited to the case where the value of the oxygen concentration C is derived, and it can detect the oxygen concentration in another way. For example, the CPU 92 can detect the air-fuel ratio as the oxygen concentration in the gas being measured. The CPU 92 can determine whether the oxygen concentration is zero (whether the air-fuel ratio is the theoretical air-fuel ratio) or whether the oxygen concentration is within a predetermined range that can be considered zero (whether the air-fuel ratio is considered the theoretical air-fuel ratio) in order to detect the oxygen concentration.The CPU 92 can determine whether the oxygen concentration is positive (whether the gas being measured is lean) or negative (whether the gas being measured is rich) in order to measure the oxygen concentration. The CPU 92 can perform one or more measurements and output the result(s) of the oxygen concentration measurement to the engine ECU. When these measurements are performed, the deviation in the slope of the first correlation relationship has a less significant impact on the accuracy of the measurement.Accordingly, in this case it is not necessary for the memory unit 94 to store the first correspondence relationship, provided that at least the information (for example, (0, L0), which represent the coordinates of the zero point) with respect to the zero point (the intersection point L0) is stored in the first correspondence relationship. Furthermore, in this case, the determinations described above can be made by comparing the measured value p and the information (for example, the value of the intersection point L0) with respect to the zero point. Furthermore, in this case, the CPU 92 can perform operations at steps S170 to S190 and S220 in the... Fig. 5. The corrected measured value p' can be derived as described above. A comparison between the corrected measured value p' and the information (for example, the value of the intersection point L0) regarding the zero point can prevent a decrease in the accuracy of the oxygen concentration measurement when the oxygen concentration in the gas being measured is zero during the use of the gas sensor. That is, it can prevent the accuracy of the determinations described above from decreasing.For example, if the corrected measurement p' is within a given range where there is virtually no difference from the intersection point L0, it can be determined that the air-fuel ratio is the theoretical air-fuel ratio; if the corrected measurement p' exceeds the given range and is greater than the intersection point L0, it can be determined that the gas being measured is the lean atmosphere; and if the corrected measurement p' exceeds the given range and is less than the intersection point L0, it can be determined that the gas being measured is the rich atmosphere.Alternatively, the CPU 92 can correct the information regarding the zero point (for example, the intersection point L0 is corrected to the intersection point L1), compare the measured value p and the corrected zero point, and perform the same determinations.

[0095] According to the embodiment described above, the memory unit 94 stores the second correspondence relationship in advance, and the CPU 92 derives the slope K1 based on the difference between the second correspondence relationship and the measurement point B1 at step S170, but is not limited to this. For example, at step S170, the CPU 92 can derive the slope K1 as the slope of a straight line that is in the Fig. 4 passes through measuring point B1 and the origin (the point where the oxygen concentration and the pump current Ip0 are zero). For example, the CPU 92 can derive the slope K1 based on the relationship of expression (9) described later instead of expression (5) described above. Since there is a tendency for more foreign substance to accumulate in the sample gas flow section as measuring point B1 changes, causing the measured value b1 to decrease in the manner described above, and since measuring point B1 is not affected by the change in the zero point described above, the measured value b1 at measuring point B1 correlates with the degree of change in the slope described above.For this reason, the CPU 92 can derive the changed slope K1 based on the measured value b1 at the measuring point B1, for example, using the relationship of expression (9) described later, instead of using the second correspondence relationship that was previously stored in memory unit 94. In this case, memory unit 94 does not need to store the second correspondence relationship. Furthermore, if the slope K1 is derived using the relationship of expression (9) described later, the CPU 92 can also perform the zero-point correction by carrying out the operations after step S180 described above, as described in the embodiment described above. The CPU 92 can also correct the change in the slope of the first correspondence relationship in addition to the zero-point correction, as in a modification described above. K1=(b1 / 21)

[0096] According to the embodiment described above, the CPU 92 performs the zero-point correction based on the difference between the second correspondence relationship and measurement point B1 and the measured value a1 at measurement point A1, but it can perform the zero-point correction in another way. For example, a correspondence relationship between the difference (e.g., the difference between the reference value b0 and the measured value b1) between the second correspondence relationship and measurement point B1 and the extent of the deviation from zero point Ld or the altered zero point (e.g., the value of the intersection point L1) can be investigated by an experiment, and the memory unit 94 can store a relationship expression or a characteristic map that defines the correspondence relationship.The CPU 92 can derive the extent of the deviation from zero point Ld or the altered zero point, or both, based on the difference between the second correspondence relationship and measurement point B1 and the correspondence relationship stored in memory unit 94 after step S140. Zero point correction can be performed based on the derived value. Since the difference between measurement point B1 and the second correspondence relationship also correlates with the extent of the zero point's deviation from the first correspondence relationship, as described above, examining the correspondence relationship described above and pre-storing it in memory unit 94 allows the derivation of the extent of the deviation from zero point Ld or the altered zero point, or both, without measuring the measured value a1 at measurement point A1.A correspondence between the measured value b1 at measuring point B1 and the extent of the deviation from the zero point Ld or the modified zero point (for example, the value of the intersection point L1) can be investigated experimentally, and a relationship expression or a characteristic map defining the correspondence can be stored in memory unit 94. Furthermore, the CPU 92 can thus derive the extent of the deviation from the zero point Ld or the modified zero point, or both, based on the measured value b1 at measuring point B1, obtained in step S140, and the correspondence stored in memory unit 94. In this case, memory unit 94 does not need to store the second correspondence.

[0097] According to the embodiment described above, the CPU 92 corrects the change in the correspondence relationship between the oxygen concentration in the gas being measured and the pump current Ip0 due to the accumulation of the foreign substance based on the measured value b1 at measuring point B1, but can also correct the change in the correspondence relationship between the concentration of a specific gas (for example, the NOx concentration) in the gas being measured and the measured value (for example, the pump current Ip2) depending on the oxygen that is generated in the third interior space 61 and originates from the specific gas, based on the measured value b1. Fig. Figure 6 is a graph showing the relationship between the NOx concentration 0 [ppm] and the pump current Ip2 [µA] during the first control operation. The pump current Ip2 in the Fig. 6 represents a current that flows when oxygen is pumped out of the third interior space 61 using a positive value. A straight line T0 in the Fig. Figure 6 represents the relationship between the NOx concentration D in the sample gas and the pump current Ip2 during the execution of the first control operation without any foreign substance accumulated in the sample gas flow section. The line T0 is an example of the relationship between the concentration of a specific gas according to the embodiment described above. In the case where the relationship (for example, the relationship of expression (10) described below) of the line T0 has been pre-stored in the memory unit 94, the CPU 92 derives the NOx concentration D based on the measured pump current Ip2 and the relationship between the concentration of a specific gas, i.e., the line T0, at the step S240 described above. For example, in the case where the measured pump current Ip2 has a value e0, the CPU 92 derives a value f (= e0 / K2) as the NOx concentration D (see Figure 6). Fig. 6) The slope K2 is a constant. The more foreign substance, such as soot, accumulates in the sample gas flow section during the use of the Gas Sensor 100, the greater the diffusion resistance near the inlet of the sample gas flow section and the smaller the amount of sample gas flowing into the sample gas flow section, as described above. Therefore, the more foreign substance accumulates, the smaller the pumping current Ip2 will be, even if the NOx concentration in the sample gas remains the same. Accordingly, the more foreign substance accumulates, the smaller the slope of the relationship between the NOx concentration in the sample gas and the pumping current Ip2 during the first control operation. For example, if the foreign substance accumulates as described above, the pumping current Ip2 will be significantly lower. Fig. As shown in Figure 6, the slope changes from that of line T0, which corresponds to the relationship without accumulated foreign substance, and the relationship changes to a line T1 (expression (11) described later), which has a slope K3 (< K2). That is, when the foreign substance accumulates, the actual relationship (line T1) deviates in some cases from the relationship of the concentration of a specific gas (line T0) that was previously stored in storage unit 94. The rate of change of the slope from line S0 to line S1 in the Fig. 4. Due to the accumulation of the foreign substance, the rate of change of the slope from line T0 to line T1 is caused by the same increase in diffusion resistance and has the same value. For this reason, the measured value b1 at the measurement point B1 described above correlates not only with the degree of change in the slope of the correspondence relationship between the oxygen concentration C and the pump current Ip0, but also correlates with the degree of change in the slope of the correspondence relationship between the NOx concentration D and the pump current Ip2. Therefore, the pump current Ip2 or the correspondence relationship of the concentration of a specific gas can be corrected so that the change in slope from line T0 to line T1 is corrected based on the measured value b1 at measurement point B1. For example, the CPU 92 derives the rate ΔK of change in slope from line S0 to line S1 in the Fig. 3 is based on the difference between the second correspondence relationship stored in memory unit 94 and the measurement point B1 obtained at step S140. The rate of change of the slope can be derived, for example, according to ΔK = K0 / K1, using K1, derived at step S170, and K0, stored in memory unit 94, or it can be derived according to ΔK = b0 / b1 using the measured value b1, measured at step S140, and the reference value b0, stored in memory unit 94. The rate ΔK of change of the slope is essentially equal to the rate of change (= K2 / K3) of the slope from line T0 to line T1 in the Fig. 6, and the rate ΔK of change of the slope can be used to correct the pump current Ip2 or the correspondence relationship of the concentration of a specific gas. For example, CPU 92 derives a corrected pump current Ip2' according to Ip2' = Ip2 / ΔK by correcting the pump current Ip2 obtained at step S240 using the rate ΔK of change of the derived slope. The NOx concentration D is derived based on the corrected pump current Ip2' and the correspondence relationship of the concentration of a specific gas (the straight line T0) stored in memory unit 94. For example, in the case where the correspondence relationship is derived from the straight line T0 in the Fig. 6 to the straight line T1 changes due to the accumulation of the foreign substance and the actual NOx concentration changes the value f in the Fig. 6, the pump current Ip2 obtained at step S240 has a value e1. The corrected pump current Ip2' is given as Ip2' = e1 / ΔK = e1 / (K2 / K3) = e0, and the value f can be derived as the correct NOx concentration based on the corrected pump current Ip2' and the correspondence relationship of the concentration of a specific gas (the straight line T0) stored in storage unit 94. Consequently, the accuracy of the detection of the concentration of a specific gas can be prevented from decreasing during the use of gas sensor 100.In the case where the pump current Ip2 is not corrected, but rather the concentration-correlation relationship of a specific gas stored in memory unit 94 is corrected, the CPU 92 derives the slope K3 according to K3 = K2 * ΔK based on the slope K2 of the concentration-correlation relationship of a specific gas (the line T0) and the rate ΔK of change of the slope. The CPU 92 then determines the line T1 (Ip2 = K3 * D) of slope K3 as the corrected concentration-correlation relationship of a specific gas. The CPU 92 causes memory unit 94 to store the corrected concentration-correlation relationship of a specific gas and derives the NOx concentration D based on the pump current Ip2 obtained at step S240 and the corrected concentration-correlation relationship of a specific gas (the line T1).Even in the case where the correspondence relationship of the concentration of a specific gas is corrected in this way, it is possible to prevent the accuracy of the detection of the concentration of a specific gas from decreasing during the use of the gas sensor 100. Ip2=K2*D Ip2=K3*D

[0098] In an example described above, CPU 92 derives the rate ΔK of change of slope based on the difference between the second correspondence relationship stored in memory unit 94 and the measurement point B1 obtained at step S140, although there is no restriction in this regard. It is sufficient that the rate ΔK of change of slope, or the changed slope K3, can be derived based on the measurement b1 at measurement point B1. For example, even if memory unit 94 does not store the second correspondence relationship, the rate ΔK of change can still be derived based on the measurement b1 at measurement point B1.For example, memory unit 94 can store in advance a ratio Kr (= K2 / K0) of the slope K2 of line T0 to the slope K0 of line S0, and CPU 92 can derive the changed slope K3 according to K3 = K1 * Kr based on the slope K1, the measured value b1, and the ratio Kr. Alternatively, since there is a correlation between the measured value b1 and the rate ΔK of change of the slope, and between the measured value b1 and the slope K3 of line T1, a correspondence relationship between the measured value b1 and the rate ΔK of change or the slope K3 can be investigated in advance and stored in memory unit 94, and CPU 92 can derive the rate ΔK of change or the slope K3 based on the correspondence relationship and the measured value b1.

[0099] According to the embodiment described above, the gas sensor 100 includes the pre-pump cell 15; however, the detection value or the correspondence relationship of the concentration of a specific gas based on the measurement point B1 described above can be corrected even if the pre-pump cell 15 is not included. In the case where the pre-pump cell 15 is not included, the first control operation and the second control operation are the same operation. The CPU 92 can omit steps S130 and S150 to S190, can obtain the measured value b1 at measurement point B1 by performing an operation at step S140 during the execution of the first control operation (the main pump control operation and the auxiliary pump control operation), and can detect the detection value or the correspondence relationship of the concentration of a specific gas based on the measured value b1 at the measurement point B1 described above.

[0100] According to the embodiment described above, the CPU 92 performs operations at steps S130 to S190 when it is determined that the measurement time is at step S120, but can perform the operations at steps S170 to S190 at any time other than the measurement time. For example, the CPU 92 can perform the operations at steps S170 to S190 immediately before step S220.

[0101] According to the embodiment described above, the CPU 92 derives the oxygen concentration C and the NOx concentration when it is determined that the concentration derivation time is at step S200, but there is no restriction in this regard. For example, the time at which the oxygen concentration C is derived and the time at which the NOx concentration is derived may be different from each other.

[0102] According to the embodiment described above, the second diffusion control section 13 is located between the buffer chamber 12 and the first interior space 20, but is not limited to this. For example, the second diffusion control section 13 can be omitted, and the buffer chamber 12 and the first interior space 20 can be a single space. According to the embodiment described above, as shown in the Fig. As shown in Figure 1, the gas inlet 10 is located at the front end of the first diffusion control section 11, but is not limited to this location, and the first diffusion control section 11 can, for example, be located downstream of the gas inlet 10 in the direction of flow of the gas in the sample. That is, the first diffusion control section 11 can be located, with respect to its position in the Fig. 1 further back. The first diffusion control section 11, the second diffusion control section 13, the third diffusion control section 30 and the fourth diffusion control section 60 are designed as slots. One or more diffusion control sections may, however, be porous, for example, so that a diffusion resistance can be exerted on the gas being measured.

[0103] According to the embodiment described above, the CPU 92 performs the measuring pump control process by implementing a control of the voltage Vp2 of the variable power supply 46 such that the electromotive force V2 reaches the target value V2*, and thereby detects the NOx concentration in the gas sample based on the detection value (the pump current Ip2), but is not limited to this. For example, the CPU 92 can perform the measuring pump control process by controlling the measuring pump cell 41 (for example, by controlling the voltage Vp2) such that the pump current Ip2 reaches the constant target value Ip2*, and can detect the NOx concentration using the detection value (the electromotive force V2). Since the measuring pump cell 41 is controlled so that the pump current Ip2 reaches the target value Ip2*, oxygen is pumped out of the third interior space 61 at a substantially constant flow rate.For this reason, the oxygen concentration in the third chamber 61 changes depending on the amount of oxygen produced, resulting in a reduction of NOx in the gas sample in the third chamber 61 and consequently a change in the electromotive force V2. Accordingly, the electromotive force V2 has a value that depends on the NOx concentration in the gas sample. Therefore, the NOx concentration can be calculated based on the electromotive force V2. For example, the storage unit 94 pre-stores a correspondence relationship between the electromotive force V2 and the NOx concentration.

[0104] According to the embodiment described above, the gas sensor 100 detects the NOx concentration as the concentration of a specific gas, but is not limited to this and can detect an oxide concentration different from the concentration of a specific gas. In the case where the specific gas is an oxide, oxygen is produced when the specific gas itself is reduced in the third chamber 61, as is the case in the embodiment described above, and the CPU 92 can consequently detect the concentration of a specific gas by obtaining the detection value dependent on the oxygen. The specific gas can be a non-oxide, such as ammonia. In the case where the specific gas is a non-oxide, the specific gas is converted into an oxide (for example, ammonia is converted into NO), and consequently, oxygen is produced when the converted gas is reduced in the third chamber 61.Accordingly, the CPU 92 can detect the concentration of a specific gas by obtaining a detection value dependent on the oxygen. For example, if the pre-pump electrode 16 contains a metal with a catalyst function that facilitates the oxidation of ammonia, the catalyst function of the pre-pump electrode 16 enables the conversion of the specific gas into an oxide in the buffer chamber 12. The same can be true for the inner pump electrode 22. Since ammonia is converted into NO as an oxide, the ammonia concentration is measured essentially according to the same principle as the NOx concentration.

[0105] According to the embodiment described above, the sensor element 101 of the gas sensor 100 has, but is not limited to, the first interior space 20, the second interior space 40, and the third interior space 61. For example, the third interior space 61 need not be configured as in the sensor element 201 in the Fig. 7 is the case. In the sensor element 201 according to a modification that is in the Fig. As shown in Figure 7, the gas inlet 10, the first diffusion control section 11, the buffer chamber 12, the second diffusion control section 13, the first interior chamber 20, the third diffusion control section 30, and the second interior chamber 40 are configured to adjoin one another and are connected in this order between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4. The measuring electrode 44 is located on the upper surface of the first solid electrolyte layer 4 in the second interior chamber 40. The measuring electrode 44 is covered by a fourth diffusion control section 45. The fourth diffusion control section 45 is a film composed of a porous ceramic material, such as aluminum oxide (Al₂O₃).The fourth diffusion control section 45 has a function of limiting the amount of NOx flowing into the measuring electrode 44, as is the case in the fourth diffusion control section 60 according to the embodiment described above. The fourth diffusion control section 45 also acts as a protective film for the measuring electrode 44. The upper electrode section 51a of the auxiliary pump electrode 51 extends to a position immediately above the measuring electrode 44. Furthermore, with this structure, the sensor element 201 can detect the NOx concentration, for example, based on the pump current Ip2, as is the case in the embodiment described above. In this case, the circumference of the measuring electrode 44 acts as a measuring chamber.

[0106] According to the embodiment described above, the sensor element body 101 is, but is not limited to, the multilayer body of the solid electrolyte layers (layers 1 to 6). It is sufficient that the sensor element body 101 comprises at least one oxygen-ion-conducting solid electrolyte layer and contains the gas flow section of the object being measured. For example, layers 1 to 5, excluding the second solid electrolyte layer 6, can be in the Fig. 1. A structural layer (for example, an aluminum oxide layer) composed of a material other than a solid electrolyte. In this case, the electrodes incorporated into the sensor element 101 are arranged in the second solid electrolyte layer 6. For example, the measuring electrode 44 is located in the Fig.1 is arranged on the lower surface of the second solid electrolyte layer 6. The reference gas introduction chamber 43 is formed in the spacer layer 5 instead of the first solid electrolyte layer 4, the air introduction layer 48 is arranged between the second solid electrolyte layer 6 and the spacer layer 5 instead of between the first solid electrolyte layer 4 and the third substrate layer 3, and the reference electrode 42 is arranged at a position further back than the third interior space 61 and on the lower surface of the second solid electrolyte layer 6.

[0107] According to the embodiment described above, in the main pump control process, the control unit 91 sets (regulates) the target value V0* of the electromotive force V0 based on the pump current Ip1 such that the pump current Ip1 reaches the target value Ip1* and implements a control of the pump voltage Vp0 such that the electromotive force V0 reaches the target value V0*, but can also perform a different operation. For example, in the main pump control process, the control unit 91 can implement a control of the pump voltage Vp0 based on the pump current Ip1 such that the pump current Ip1 reaches the target value Ip1*. That is, the control unit 91 can omit obtaining the electromotive force V0 from the oxygen partial pressure sensing sensor cell to the main pump control 80 and setting the target value V0* and directly control the pump voltage Vp0 based on the pump current Ip1 (and thus control the pump current Ip0).

[0108] According to the embodiment described above, the outer pump electrode 23 serves as an outer pre-pump electrode, which is arranged on a part of the pre-pump cell 15 that is to be exposed to the gas of the object being measured outside the sensor element 101, an outer main pump electrode, which is arranged on a part of the main pump cell 21 that is to be exposed to the gas of the object being measured outside the sensor element 101, an outer auxiliary pump electrode, which is arranged on a part of the auxiliary pump cell 50 that is to be exposed to the gas of the object being measured outside the sensor element 101, and an outer measuring electrode, which is arranged on a part of the measuring pump cell 41 that is to be exposed to the gas of the object being measured outside the sensor element 101, but is not limited to this.The outer pre-pump electrode, the outer main pump electrode, the outer auxiliary pump electrode or the outer measuring electrode or some of the electrodes may be arranged outside the sensor element 101 separately from the outer pump electrode 23. Commercial applicability

[0109] The present invention can be used for a gas sensor that detects the concentration of a specific gas, such as NOx, in a measuring gas, such as the exhaust gas of a motor vehicle.

Claims

[1] Gas sensor (100), comprising: an element body (1, 2, 3, 4, 5, 6) which has an oxygen ion-conducting solid electrolyte layer and which contains a sample gas flow section into which a sample gas is introduced for flow around; a pre-pump cell (15) that pumps oxygen into a pre-chamber (12) of the measuring object gas flow section; a main pump cell (21) that sets an oxygen concentration in a first interior space (20) of the sample gas flow section located downstream of the prechamber (12); an auxiliary pump cell (50) which adjusts the oxygen concentration in a second interior space (40) of the sample gas flow section, which is located downstream of the first interior space (20); a measuring electrode (44) which is arranged in a measuring chamber (61) of the object gas flow section which is located downstream of the second interior space (40); a reference electrode (42) which is arranged in the element body (1, 2, 3, 4, 5, 6) and which comes into contact with a reference gas which serves as a reference for detecting a concentration of a specific gas in the gas of the object being measured; a measuring voltage acquisition unit (82) that acquires a measuring voltage (V2) between the reference electrode (42) and the measuring electrode (44); a unit for measuring the concentration of a specific gas (92) which performs a first control process which determines a measurement value depending on oxygen, which is generated in the measuring chamber (61) and originates from the specific gas, is based on the measuring voltage (V2) while the first control process is carried out, and which detects the concentration of a specific gas in the gas of the object being measured based on the detection value, wherein the first control process is a pre-pump control process of controlling the pre-pump cell (15) such that a constant pre-pump current (Ip0s) flows through the pre-pump cell (15), an auxiliary pump control process of controlling the auxiliary pump cell (50) such that the oxygen concentration in the second interior space (40) becomes a target concentration, and a main pump control process of controlling the main pump cell (21) such that an auxiliary pump current (Ip1) which flows when the auxiliary pump cell (50) sets the oxygen concentration in the second interior space (40) becomes a target value; a storage unit (94) which stores information regarding a zero point at which an oxygen concentration of zero and a main pumping current (Ip0) are relevant to each other in a first correspondence relationship, wherein the first correspondence relationship is a linear correspondence relationship between the oxygen concentration in the gas of measurement and the main pumping current (Ip0) flowing through the main pumping cell (21) while the first control operation is carried out; an oxygen concentration detection unit (92) which detects the oxygen concentration in the gas being measured based on a measured value p of the main pump flow (Ip0) flowing during the execution of the first control operation and the zero-point information stored in the storage unit (94); and a unit for obtaining a measured value (92) which performs a second control operation and which obtains a measured value b1 at a measuring point B1, where a known value of the oxygen concentration and the main pump flow (Ip0) are relevant to each other, by measuring the main pump flow (Ip0) flowing during the execution of the second control operation, at a measurement time where the oxygen concentration in the gas of the object being measured around the element body (1, 2, 3, 4, 5, 6) is considered to be the known value, wherein the second control operation comprises a pre-pump stop operation of stopping the operation of the pre-pump cell (15), the auxiliary pump control operation and the main pump control operation, wherein the oxygen concentration detection unit (92) performs a zero-point correction to correct the measured value p or the information relating to the zero point such that any deviation of the zero point from the first correspondence relation based on the measured value b1 at the measuring point B1 is corrected. [2] Gas sensor (100) according to claim 1, wherein the unit for obtaining a measured value (92) obtains a measured value a1 at a measuring point A1, where the known value of the oxygen concentration and the main pumping current (Ip0) are relevant to each other, by measuring the main pumping current (Ip0) flowing while the first control operation is being carried out at the time of measurement, and wherein the oxygen concentration detection unit (92) performs the zero point correction on the basis of the measured value b1 and the measured value a1. [3] Gas sensor (100) according to claim 2, wherein the oxygen concentration detection unit (92) derives a slope K1, which is a value that has changed from a slope of a straight line representing the first correspondence relationship, on the basis of the measuring point B1, derives a modified zero point, which corresponds to a zero point after the zero point of the first correspondence relationship has deviated, on the basis of a straight line passing through the measuring point A1 and having a slope equal to the slope K1, and performs the zero point correction on the basis of the modified zero point. [4] Gas sensor (100) according to claim 2 or claim 3, wherein the storage unit (94) stores the first correspondence relationship and wherein the oxygen concentration detection unit (92) derives a slope K1, which is a value that has changed starting from a slope of a straight line representing the first correspondence relationship, on the basis of the measuring point B1, derives a straight line passing through the measuring point A1 and having a slope equal to the slope K1 as a corrected first correspondence relationship, and detects the oxygen concentration in the gas of the object being measured on the basis of the measured value p and the corrected first correspondence relationship. [5] Gas sensor (100) according to claim 2, wherein the storage unit (94) stores a second correspondence relationship which represents a linear correspondence relationship between the oxygen concentration in the gas of the object being measured and the main pump flow (Ip0) flowing while the second control operation is carried out, and wherein the oxygen concentration detection unit (92) derives an extent of deviation from zero corresponding to an extent of deviation of zero from the first correspondence relation on the basis of a difference between an extent of deviation between a reference value b0, which is a value of the main pump flow (Ip0) relevant for the known value of the oxygen concentration in the second correspondence relation, and the measured value b1, and an extent of deviation between a reference value a0, which is a value of the main pump flow (Ip0) relevant for the known value of the oxygen concentration in the first correspondence relation, and the measured value a1, and performs the zero-point correction on the basis of the extent of deviation from zero. [6] Gas sensor (100) according to claim 5, wherein the oxygen concentration detection unit (92) derives a modified zero point corresponding to a zero point after the deviation of the zero point of the first correspondence relationship on the basis of the zero point of the first correspondence relationship and the extent of the deviation from the zero point, derives a straight line passing through the measuring point A1 and the modified zero point as a corrected first correspondence relationship, and detects the oxygen concentration in the gas of the object being measured on the basis of the measured value p and the corrected first correspondence relationship. [7] Gas sensor (100) according to any one of claims 1 to 6, wherein the measurement time is a time when the gas of the object being measured is considered as an atmosphere around the element body (1, 2, 3, 4, 5, 6). [8] Gas sensor (100) according to claim 7, wherein the gas to be measured is an exhaust gas from an internal combustion engine, further comprising a unit for obtaining information (92) which receives information regarding the execution of a fuel interruption, indicating that a fuel interruption is being carried out in the internal combustion engine, and wherein the unit for obtaining a measured value (92) detects the measurement time on the basis of the information obtained regarding the execution of a fuel interruption.

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