JP2010256127A - Gas concentration detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas concentration detector for detecting the concentration of the specific gas component in measuring target gas with high precision even while the amount of exhaust gas is lowered. <P>SOLUTION: In the gas concentration detector 10 calculating the target pumping-out amount of oxygen in the measuring target gas and driving a pump cell according to the target pumping-out amount of oxygen, the amount of the exhaust gas in the measuring target gas introduced into an NOx sensor 1 is obtained on the basis of the data related to the operation state of an internal combustion engine and the concentration of oxygen in the measuring target gas (step 106). The target pumping-out amount of oxygen is increased in the case where amount of the exhaust gas becomes lower than a standard amount (steps 108-110). Preferably, the increase amount of pumped-out oxygen is set according to a change in the amount of air sucked into the internal combustion engine. Further, the increase amount of pumped-out oxygen is set according to the data related to oxygen adsorbed on the electrode of a detection cell 5. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a gas concentration detection device, and more particularly to a gas concentration detection device that detects the concentration of a specific gas in exhaust gas discharged from an engine.

  Conventionally, as disclosed in, for example, Japanese Patent Laid-Open No. 2002-310985, a NOx sensor that measures the NOx concentration in a gas to be measured is known. More specifically, the NOx sensor has a first internal space through which the gas to be measured is introduced, a second internal space through which the atmosphere is further introduced, and an oxygen partial pressure in the first internal space. A gas to be measured on the basis of a pump current flowing by the operation of the second pump means, comprising: a first oxygen pump means to be controlled; and a second oxygen pump means for pumping out oxygen in the second internal space. NOx concentration is determined.

JP 2002-310985 A Japanese Patent Laid-Open No. 10-38845 Japanese Patent Laid-Open No. 10-71325

  As in the prior art, in the NOx sensor, a detection cell for detecting the NOx concentration is arranged at the innermost part in the chamber of the sensor. For this reason, when the amount of exhaust gas flowing around the sensor is decreased, the gas exchangeability of the exhaust gas (measurement target gas) in the chamber may be decreased. In this case, a response delay occurs in the output of the detection cell, and the NOx concentration may not be accurately detected.

  The present invention has been made to solve the above-described problems, and can detect the concentration of a specific gas component in a measurement target gas with high accuracy even when the amount of exhaust gas is decreasing. An object of the present invention is to provide a gas concentration detection device capable of performing the above.

In order to achieve the above object, the first invention is a pump cell that pumps out oxygen in a measurement target gas, and a detection that detects the concentration of a specific gas component contained in the measurement target gas from which oxygen has been pumped out by the pump cell. A gas concentration detection device including a gas sensor having a cell in an exhaust path of an internal combustion engine,
A target pumping amount calculating means for calculating a target pumping amount of oxygen in the measurement target gas;
Pump cell driving means for driving the pump cell according to the target pumping amount;
An exhaust gas amount acquisition means for acquiring an exhaust gas amount in the measurement target gas introduced into the gas sensor based on information on the operating state of the internal combustion engine and the concentration of oxygen in the measurement target gas;
A target pumping amount raising means for raising the target pumping amount when the exhaust gas amount is lower than a reference amount;
It is characterized by providing.

According to a second invention, in the first invention,
The target value raising means sets the raising amount according to a change in the amount of air taken into the internal combustion engine.

According to a third invention, in the first or second invention,
The target value raising means sets the raising amount according to information on oxygen adsorbed on the electrode of the detection cell.

A fourth invention is any one of the first to third inventions,
The apparatus further comprises limiting means for restricting execution of the target value raising means when the concentration of the specific gas component detected from the output of the detection cell follows the actual concentration of the specific gas component in the measurement target gas. Features.

According to a fifth aspect of the present invention, in order to achieve the above object, a pump cell that pumps out oxygen in the measurement target gas, and detection that detects a concentration of a specific gas component contained in the measurement target gas from which oxygen has been pumped out by the pump cell A gas concentration detection device including a gas sensor having a cell in an exhaust path of an internal combustion engine,
An exhaust gas amount acquisition means for acquiring an exhaust gas amount in the measurement target gas introduced into the gas sensor based on information on the operating state of the internal combustion engine and the concentration of oxygen in the measurement target gas;
Correction means for correcting the output value of the detection cell when the exhaust gas amount falls below a reference amount;
It is characterized by providing.

According to a sixth invention, in the fifth invention,
The correction means corrects the output value of the detection cell in accordance with an output change of the detection cell.

A seventh invention is the fifth or sixth invention, wherein
The correction means corrects the output value of the detection cell according to information on the concentration of oxygen in the measurement target gas.

According to an eighth invention, in any one of the fifth to seventh inventions,
The apparatus further comprises a limiting unit that limits execution of the target value raising unit when the concentration of the specific gas component detected by the concentration detection unit follows the actual concentration of the specific gas component in the measurement target gas. And

  According to the first aspect of the invention, the amount of exhaust gas (burned gas) in the measurement target gas introduced into the gas sensor is acquired based on the information regarding the operating state of the internal combustion engine and the concentration of oxygen in the measurement target gas. The When the exhaust gas amount falls below the reference amount, the target pumping amount of the pump cell is increased. For this reason, according to the present invention, when the exhaust gas amount is reduced and the responsiveness of the gas sensor is reduced, the ability to remove residual oxygen in the vicinity of the detection cell is enhanced, thereby eliminating the influence of the responsiveness reduction. Thus, the gas concentration of the specific gas component can be detected with high accuracy.

  According to the second invention, the target pumping amount is set in accordance with the change in the amount of air taken into the internal combustion engine. The response delay of the gas sensor greatly depends on the change in the air amount. For this reason, according to this invention, the optimal raising amount according to the responsiveness of a gas sensor can be set based on the change of air quantity.

  According to the third invention, the raising amount of the target pumping amount is set according to the information on the oxygen adsorbed on the electrode of the detection cell. The response delay of the gas sensor greatly depends on the amount of adsorbed oxygen. For this reason, according to this invention, the optimal raising amount according to the responsiveness of a gas sensor can be set based on the information regarding the said adsorption | suction oxygen.

  According to the fourth invention, when the concentration of the specific gas component of the measurement target gas follows the actual concentration, the increase in the target oxygen pumping amount is limited. For this reason, according to this invention, the situation where unnecessary raising is performed can be avoided effectively.

  According to the fifth aspect, the amount of exhaust gas in the measurement target gas is acquired based on the information related to the operating state of the internal combustion engine and the concentration of oxygen in the measurement target gas. Then, when the exhaust gas amount falls below the reference amount, the output value of the detection cell is corrected. For this reason, according to the present invention, when the exhaust gas amount is reduced and the responsiveness of the gas sensor is reduced, it is possible to directly correct the output value and eliminate the influence of the reduced responsiveness. The gas concentration of the component can be detected with high accuracy.

  According to the sixth aspect, the correction amount of the output value of the detection cell is set in accordance with the change in the output of the detection cell. The output change of the detection cell greatly depends on the air amount change. For this reason, according to this invention, the optimal correction amount according to the responsiveness of a gas sensor can be set based on the output change of a detection cell.

  According to the seventh aspect, the correction amount of the output value of the detection cell is set according to the information regarding the concentration of oxygen in the measurement target gas. The output change due to the response delay of the gas sensor greatly depends on the oxygen concentration. For this reason, according to the present invention, it is possible to set an optimal correction amount according to the responsiveness of the gas sensor based on the information on the oxygen concentration.

  According to the eighth aspect, when the detected concentration of the specific gas component follows the actual concentration, the correction of the output value of the detection cell is limited. For this reason, according to the present invention, it is possible to effectively avoid a situation in which unnecessary output correction is performed.

It is a figure for demonstrating the structure of the gas concentration detection apparatus of Embodiment 1 of this invention. It is a figure for demonstrating the relationship of the response time of NOx output with respect to NOx density | concentration of measurement object gas. It is the figure which compared the NOx output change when the NOx concentration is changed from the high concentration to the low concentration and the actual NOx change. It is a flowchart of the routine performed in Embodiment 1 of the present invention. It is a figure which shows NOx output change and actual NOx change when NOx concentration changes from high concentration to low concentration. It is a flowchart of the routine performed in Embodiment 2 of this invention.

  Several embodiments of the present invention will be described below with reference to the drawings. In addition, the same code | symbol is attached | subjected to the element which is common in each figure, and the overlapping description is abbreviate | omitted. The present invention is not limited to the following embodiments.

Embodiment 1 FIG.
[Configuration of Embodiment 1]
FIG. 1 is a diagram for explaining a configuration of a gas concentration detection apparatus 10 according to Embodiment 1 of the present invention. The gas concentration detection device 10 of the present embodiment is a device that detects the concentration of NOx (nitrogen oxide) in the exhaust gas of an internal combustion engine (hereinafter simply referred to as “engine”). The gas concentration detection device 10 has a NOx sensor 1.

  The NOx sensor 1 is formed by sequentially laminating a spacer 4, a detection cell (sensor cell) 5, a spacer 6, and a heater 7 below the main pump cell 2 and the auxiliary pump cell 3.

  A first chamber 41 and a second chamber 42 are formed in the spacer 4. As a constituent material of the spacer 4, for example, alumina or the like can be used. The first chamber 41 and the second chamber 42 communicate with each other through the communication hole 43. The first chamber 41, the second chamber 42 and the communication hole 43 can be formed by providing a hole in the spacer 4.

The main pump cell 2 has a function of pumping out and removing excess oxygen in the measurement target gas flowing into the first chamber 41. The main pump cell 2 includes a solid electrolyte 21 and a pair of pump electrodes 22 and 23. The solid electrolyte 21, which is an element, has oxygen ion conductivity, and is composed of, for example, ZrO ₂ , HfO ₂ , ThO ₂ , BiO ₃ or the like formed into a sheet shape. The pump electrodes 22 and 23 sandwiching the solid electrolyte 21 from above and below can be formed by a method such as screen printing, for example.

  The first pump electrode 22 formed on the surface of the solid electrolyte 21 faces the space where the exhaust gas that is the measurement target gas exists, that is, the exhaust passage of the engine. As the first pump electrode 22, for example, a porous cermet electrode containing a noble metal such as Pt can be used.

  On the other hand, the second pump electrode 23 provided on the opposite side of the first pump electrode 22 across the solid electrolyte 21 faces the first chamber 41. As the second pump electrode 23, an electrode inert to NOx, for example, a porous cermet electrode containing a Pt—Au alloy and ceramics such as zirconia and alumina can be used.

  The main pump cell 2 is formed with a pinhole 24 as an introduction hole penetrating the solid electrolyte 21 and the pump electrodes 22 and 23. Exhaust gas, which is a measurement object gas, permeates through a porous protective layer 8 described later, flows into the first chamber 41 through the pinhole 24. The hole diameter of the pinhole 24 is designed so that the diffusion speed of the exhaust gas introduced into the first chamber 41 becomes a predetermined speed.

The auxiliary pump cell 3 has a function of detecting the oxygen concentration in the measurement target gas flowing into the second chamber 42 from the first chamber 41 and further pumping out and removing excess oxygen in the gas. The auxiliary pump cell 3 includes a solid electrolyte 31 and a pair of pump electrodes 32 and 33. The solid electrolyte 31 as an element has oxygen ion conductivity, and is composed of, for example, ZrO ₂ , HfO ₂ , ThO ₂ , BiO ₃ or the like formed into a sheet shape. The pump electrodes 32 and 33 sandwiching the solid electrolyte 31 from above and below can be formed by a method such as screen printing, for example.

  The first pump electrode 32 formed on the surface of the solid electrolyte 31 faces the exhaust passage of the internal combustion engine. As this 1st pump electrode 32, the porous cermet electrode containing noble metals, such as Pt, can be used, for example.

  On the other hand, the second pump electrode 33 provided on the opposite side of the first pump electrode 32 across the solid electrolyte 31 faces the second chamber 42. As the second pump electrode 33, an electrode inert to NOx, for example, a porous cermet electrode containing a Pt—Au alloy and ceramics such as zirconia and alumina can be used.

  The first pump electrodes 22 and 32 of the main pump cell 2 and the auxiliary pump cell 3 are covered with the porous protective layer 8. The porous protective layer 8 is made of, for example, porous alumina. The porous protective layer 8 can prevent poisoning of the first pump electrodes 22 and 32 and can prevent the pinhole 24 from being clogged with soot contained in the exhaust gas.

  The detection cell 5 has a function of detecting the NOx concentration from the amount of oxygen generated by NO reductive decomposition. The detection cell 5 includes a solid electrolyte 51 and a pair of detection electrodes 52 and 53 that sandwich the solid electrolyte 51 from above and below. These detection electrodes 52 and 53 can be formed by a method such as screen printing, for example.

  The first detection electrode 52 formed on the surface of the solid electrolyte 51 faces the second chamber 42. As the first detection electrode 52, for example, a porous cermet electrode containing a Pt—Rh alloy and ceramics such as zirconia and alumina can be used.

  On the other hand, the second detection electrode 53 provided on the opposite side of the first detection electrode 52 across the solid electrolyte 51 faces the atmospheric duct 61 formed in the spacer 6. Air is introduced into the air duct 61. As the second detection electrode 53, for example, a porous cermet electrode containing a noble metal such as Pt can be used. The air duct 61 can be formed by providing a cutout in the spacer 6.

  The heater 7 includes sheet-like insulating layers 72 and 73 and a heater electrode 71 provided between the insulating layers 72 and 73. The insulating layers 72 and 73 are made of ceramics such as alumina, for example. The heater electrode 71 is composed of, for example, a cermet of Pt and ceramics such as alumina.

  The gas concentration detection device 10 of the present embodiment includes an ECU (Electronic Control Unit) 9 as a control device. The ECU 9 includes main pump cell control means 91, auxiliary pump cell control means 92, detection cell control means 93, and heater control means 94. The ECU 9 may be configured separately from the engine ECU, or may be configured as a part of the engine ECU.

  The main pump cell control means 91 is connected to the first pump electrode 22 and the second pump electrode 23 of the main pump cell 2. The main pump cell control means 91 is capable of applying a voltage to the first pump electrode 22 and the second pump electrode 23 and detecting a current value flowing through the main pump cell 2.

  The auxiliary pump cell control means 92 is connected to the first pump electrode 32 and the second pump electrode 33 of the auxiliary pump cell 3. The auxiliary pump cell control unit 92 applies a voltage to the first pump electrode 32 and the second pump electrode 33 of the auxiliary pump cell 3 and can detect a current value flowing through the auxiliary pump cell 3.

  The detection cell control means 93 is connected to the first detection electrode 52 and the second detection electrode 53 of the detection cell 5. The detection cell control means 93 can apply a voltage to the first detection electrode 52 and the second detection electrode 53 and can detect the value of the current flowing through the detection cell 5.

  The heater control means 94 is connected to the heater electrode 71. The heater control means 94 supplies power to the heater electrode 71.

  In the NOx sensor 1 as described above, in order for the main pump cell 2, the auxiliary pump cell 3, and the detection cell 5 to exhibit normal characteristics, the temperatures of the solid electrolytes 21, 31, 51 are higher than the activation temperature. It is necessary to be. However, when the engine is stopped or when the fuel is cut for a long time, the temperature of each cell decreases. For this reason, when starting the engine or returning from the fuel cut for a long time, the temperature of each cell is quickly raised to the activation temperature or higher so that the heater 7 is energized to control the NOx sensor 1 to warm up. Executed.

[Operation of Embodiment 1]
(Basic operation of the gas concentration detector 10)
First, the operation of the gas concentration detection device 10 after the completion of warming up of the NOx sensor 1 will be described. Exhaust gas as the measurement target gas is introduced into the first chamber 41 through the porous protective layer 8 and the pinhole 24. The amount of the measurement target gas introduced into the first chamber 41 is determined according to the diffusion resistance of the porous protective layer 8 and the pinhole 24.

When a voltage is applied to the main pump cell 2 by the main pump cell control means 91, oxygen in the first chamber 41 is reduced to oxygen ions O ²⁻ on the second pump electrode 23. The oxygen ions O ²⁻ pass through the solid electrolyte 21 and are discharged to the first pump electrode 22 side. The operation of the main pump cell 2 is controlled so that the residual oxygen concentration of the measurement target gas becomes a predetermined target concentration.

The measurement target gas whose oxygen concentration is sufficiently reduced in the first chamber 41 flows into the second chamber 42. When a predetermined voltage is applied to the auxiliary pump cell 3 by the auxiliary pump cell control means 92, the residual oxygen in the second chamber 42 is reduced to oxygen ions O ²⁻ on the second pump electrode 33. The oxygen ions O ²⁻ pass through the solid electrolyte 31 and are discharged to the first pump electrode 32 side. At this time, a current corresponding to the residual oxygen concentration in the second chamber 42 flows through the auxiliary pump cell 3. Therefore, according to the output of the auxiliary pump cell 3 (hereinafter referred to as “auxiliary pump output”), the residual oxygen concentration in the measurement target gas can be detected.

  The pump capacity (oxygen pumping capacity) of the main pump cell 2 is determined according to the voltage applied to the main pump cell 2. The ECU 9 can feed back and control the auxiliary pump output to the applied voltage of the main pump cell 2 so that the residual oxygen concentration detected by the auxiliary pump cell 3 becomes the target concentration. Thereby, the oxygen concentration of the measurement target gas flowing into the second chamber 42 can be accurately maintained at the target concentration.

  In the above control, when the residual oxygen concentration detected by the auxiliary pump cell 3 is not lowered to the target concentration, by increasing the applied voltage of the main pump cell 2 and increasing the oxygen discharge amount by the main pump cell 2, Control is performed to reduce the oxygen concentration to the target concentration. Instead of such control, the ECU 9 increases the applied voltage of the auxiliary pump cell 3 when the residual oxygen concentration detected by the auxiliary pump cell 3 has not decreased to the target concentration, and the amount of oxygen discharged by the auxiliary pump cell 3. By increasing the value, control may be performed to reduce the oxygen concentration to the target concentration.

As described above, when oxygen is removed by the main pump cell 2 and the auxiliary pump cell 3 and the oxygen concentration in the measurement target gas is sufficiently reduced, a reaction of 2NO ₂ → 2NO + O ₂ occurs, and NOx is converted into NO as a single gas. Is done. When a predetermined voltage is applied to the detection cell 5 by the detection cell control means 93, NO in the second chamber 42 is decomposed on the first detection electrode 52, and oxygen ions O ²⁻ are generated. This oxygen ion O ²⁻ passes through the solid electrolyte 51 and is discharged from the second detection electrode 53 to the atmospheric duct 61. At this time, a current corresponding to the NO concentration in the second chamber 42 flows through the detection cell 5. Thus, according to the output of the detection cell 5 (hereinafter referred to as “NOx output”), the NOx concentration in the exhaust gas can be detected.

(Characteristic operation of the first embodiment)
Next, the characteristic operation of the first embodiment will be described with reference to FIGS. As shown in FIG. 1, in the gas concentration detection device 10 of the present embodiment, a part of the exhaust gas flowing around the NOx sensor 1 is taken into the sensor as a measurement target gas and the NOx concentration is detected. More specifically, the measurement target gas passes through the pinhole 24 and is introduced into the first chamber 41. In the first chamber 41, the oxygen component is removed by the main pump cell 2. The measurement target gas from which the oxygen component has been removed is then introduced into the second chamber 42, and the NOx output is detected by the detection cell 5.

  As described above, the measurement target gas passes through the diffusion path that continues from the pinhole 24 → the first chamber 41 → the communication hole 43 → the second chamber 42 before reaching the vicinity of the detection cell 5. For this reason, in the operation state where the amount of exhaust gas is small, the gas exchangeability of the measurement target gas in the sensor is lowered, and there is a possibility that a response delay occurs in the NOx output.

  FIG. 2 is a diagram for explaining the relationship of the response time of the NOx output to the NOx concentration of the measurement target gas. At the time of deceleration when the NOx concentration in the measurement target gas changes from a high concentration to a low concentration, the amount of exhaust gas becomes smaller than at the time of acceleration when the NOx concentration changes from a low concentration to a high concentration. For this reason, as shown in this figure, there is a large difference in the response time of the NOx output between the deceleration and acceleration of the internal combustion engine.

  FIG. 3 is a diagram comparing the NOx output change and the actual NOx change when the NOx concentration changes from a high concentration to a low concentration. As shown in this figure, when the NOx concentration changes from a high concentration to a low concentration, a response delay occurs in the NOx output, and as a result, the NOx output outputs a value larger than the actual NOx value.

  Therefore, in this embodiment, when it is determined that a response delay has occurred in the NOx output, the target pumping amount of oxygen is increased. More specifically, a response delay occurs in the NOx output when the amount of exhaust gas is small. Therefore, the exhaust gas amount is estimated based on the operating state of the internal combustion engine and the oxygen concentration, and when the exhaust gas amount becomes a predetermined amount or less, the target pumping amount of oxygen is increased. As a result, surplus oxygen in the vicinity of the detection cell can be removed, so that a response delay in NOx output can be effectively reduced.

[Specific Processing in Embodiment 1]
Next, specific processing of the first embodiment will be described with reference to FIG. FIG. 4 is a flowchart of a routine executed by the ECU 9 in the first embodiment. According to the routine shown in FIG. 4, it is first determined whether or not the NOx output of the NOx sensor 1 is normal (step 100). Here, specifically, warm-up determination and OBD determination of the NOx sensor 1 are performed. As a result, when it is determined that the NOx output is not normal, this routine is immediately terminated.

  On the other hand, when it is determined in step 100 that the NOx output is normal, the process proceeds to the next step, and the operation information of the internal combustion engine is acquired (step 102). Here, specifically, factor information (for example, intake air amount, etc.) related to the exhaust gas amount in particular is acquired from the operation information for the required work for the internal combustion engine.

  Next, oxygen concentration information is acquired (step 104). Here, specifically, as the oxygen concentration information from the NOx sensor 1, for example, the first detection electrode estimated from the oxygen concentration in the measurement target gas detected based on the output of the auxiliary pump or the oxygen concentration history The amount of oxygen adsorbed on 52 is acquired. Further, as the oxygen concentration information from the internal combustion engine, for example, the air-fuel ratio of exhaust gas, the presence or absence of execution of fuel cut, and the like are acquired.

  Next, it is determined whether or not the exhaust gas amount is in a lowered state (step 106). Here, specifically, the amount of exhaust gas (burned gas) introduced into the NOx sensor 1 is based on the operation information acquired in step 102 and the oxygen concentration information acquired in step 104. Presumed. Then, it is determined whether or not the exhaust gas amount exceeds a reference amount. As the reference amount, a preset value is used as an exhaust gas amount that causes a response delay in the NOx sensor output. As a result, when it is determined that the exhaust gas amount is not in a reduced state, the process returns to step 102 and the processes of steps 102 to 106 are executed again.

  On the other hand, if it is determined in step 106 that the exhaust gas amount is in a reduced state, it is determined that a response delay occurs in the NOx output, the process proceeds to the next step, and the first chamber 41 and the second chamber are moved. A target value for raising the oxygen concentration in 42 is calculated (step 108). Specifically, the raising target value is calculated by adding the target value based on the air amount change and the target value based on the oxygen adsorption amount to the basic target value of the oxygen concentration. The target value based on the air amount change is specified based on the map using the intake air amount acquired in step 102 as a parameter. Specifically, the target value is specified as a larger value as the intake air amount decreases. Further, the target value based on the oxygen adsorption amount is specified based on a map obtained by using the oxygen adsorption amount to the first detection electrode 52 acquired in step 102 as a parameter. Specifically, the target value is specified as a larger value as the oxygen adsorption amount is larger.

  Next, pump correction is performed (step 110). Here, specifically, an applied voltage for realizing the raising target value calculated in step 108 is applied to the main pump cell 2 and the auxiliary pump cell 3.

  Next, correction end determination is performed (step 112). Specifically, it is determined whether or not the NOx concentration based on the NOx output follows the actual concentration, that is, whether or not the response delay has been eliminated. The response delay cancellation can be determined, for example, when the internal combustion engine deviates from the low NOx condition, when the output of the internal combustion engine increases, when the NOx output changes to about 0 ppm, or the like.

  As described above, according to the present embodiment, the target value of the oxygen concentration is raised when it is determined that the exhaust gas flow rate is reduced, so that the NOx output response delay can be effectively eliminated. it can. Thereby, even if the amount of exhaust gas is small, the NOx concentration can be accurately grasped.

  In the first embodiment described above, the oxygen concentration in the NOx sensor 1 is controlled to the target concentration using the main pump cell 2 and the auxiliary pump cell 3, but the oxygen concentration control method is not limited to this. I can't. That is, in the NOx sensor having only the main pump cell, the oxygen concentration in the NOx sensor 1 may be controlled to the target concentration using the main pump cell.

  In the first embodiment described above, the main pump cell 2 and the auxiliary pump cell 3 correspond to the “pump cell” in the first invention. Further, when the ECU 9 executes the process of step 106, the “exhaust gas amount acquisition means” in the first invention executes the process of step 108, whereby the “target pumping amount in the first invention”. Each “lifting means” is realized.

  In the first embodiment described above, the “restricting means” in the fourth aspect of the present invention is realized by the ECU 9 executing the process of step 112.

Embodiment 2. FIG.
[Features of Embodiment 2]
Next, a second embodiment of the present invention will be described with reference to FIG. 5 and FIG. The system of the present embodiment can be realized by causing the ECU 9 to execute a routine shown in FIG. 6 to be described later using the hardware configuration shown in FIG.

  The present second embodiment is characterized in that the detected NOx output is directly corrected when a decrease state of the exhaust gas flow rate is determined. That is, as described above in the first embodiment, when the NOx concentration changes from a high concentration to a low concentration due to deceleration of the internal combustion engine, a response delay occurs in the NOx output. The NOx output corresponding to the response delay can be estimated based on the change in the intake air amount and the oxygen concentration information. Therefore, in the second embodiment, the NOx output is corrected based on the following equation (1) to eliminate the response delay. The NOx output correction method will be described in detail below.

FIG. 5 is a diagram showing a change in NOx output and a change in actual NOx when the NOx concentration changes from a high concentration to a low concentration. In this figure, the NOx output I (t) at time t is assumed and a response delay occurs from time t. As shown in this figure, there is a response delay in the NOx output at (t + Δt) after Δt from time t. The output change amount ΔI due to the response delay can be expressed by the following equation, where i (t) is a time differential value of I (t).
Output change amount ΔI = i (t) × K (1)

  According to the above equation (1), the greater the NOx output decrease rate, the greater the output change amount ΔI in the minus direction. The change in the NOx output greatly depends on the change in the intake air amount. For this reason, by using the above equation (1), the change in the intake air amount can be reflected in the output change amount ΔI.

Further, the correction value K in the above equation (1) is a correction value reflecting the oxygen concentration change in the measurement target gas, and can be represented by the following equation.
K = k × O (t) (2)

  In the above equation (2), O (t) is a time differential value of the oxygen concentration at time t, and k is a coefficient. According to the above equation (2), the correction value K becomes larger as the increase rate of the oxygen concentration is higher. Therefore, the output change amount ΔI in the above equation (1) becomes a larger value in the minus direction as the increase rate of the oxygen concentration is higher.

Thus, according to the above equations (1) and (2), the output change amount ΔI of the NOx output reflecting the change in the intake air amount and the oxygen concentration can be calculated. Therefore, as shown in the following equation (3), the accurate NOx output I (t + Δt) after Δt is calculated by eliminating the output change amount ΔI after Δt from the NOx output I (t) at time t. Can do.
I (t + Δt) = I (t) + ΔI (3)

[Specific Processing in Second Embodiment]
Next, specific processing of the second embodiment will be described with reference to FIG. FIG. 6 is a flowchart of a routine executed by the ECU 9 in the second embodiment. According to the routine shown in FIG. 6, it is first determined whether or not the NOx output of the NOx sensor 1 is normal (step 200). Here, specifically, the same processing as in step 100 is executed. As a result, when it is determined that the NOx output is not normal, this routine is immediately terminated.

  On the other hand, if it is determined in step 200 that the NOx output is normal, the process proceeds to the next step, and the operation information of the internal combustion engine is acquired (step 202). Next, oxygen concentration information is acquired (step 204). Next, it is determined whether or not the exhaust gas amount is in a lowered state (step 206). Here, specifically, the same processing as in steps 102 to 106 is executed. As a result, when it is determined that the exhaust gas amount is not in a reduced state, the process returns to step 202 and the processes of steps 202 to 206 are executed again.

  On the other hand, if it is determined in step 206 that the exhaust gas amount is in a reduced state, it is determined that a response delay occurs in the NOx output, the process proceeds to the next step, and the output change amount ΔI is calculated. . Here, specifically, first, the correction value K is calculated by calculating the above equation (2) using the oxygen concentration information acquired in step 204. Next, the output change amount ΔI is calculated by calculating the above equation (1) using the operation information such as the intake air amount acquired in step 202 and the correction value K.

  Next, density correction is performed (step 210). Specifically, the NOx output after concentration correction is calculated by substituting the output change amount ΔI calculated in step 208 into the above equation (3).

  Next, correction end determination is performed (step 212). Specifically, it is determined whether or not the NOx concentration based on the NOx output follows the actual concentration, that is, whether or not the response delay has been eliminated. In addition to the determination in step 112, for example, the time delay value of I (t) can be determined at the time when i (t) becomes equal to or less than a predetermined value.

  As described above, according to the present embodiment, since the NOx output is corrected when it is determined that the exhaust gas flow rate is reduced, it is possible to effectively eliminate the response delay of the NOx output. Thereby, even if the amount of exhaust gas is small, the NOx concentration can be accurately grasped.

  In the second embodiment described above, the oxygen concentration in the NOx sensor 1 is controlled to the target concentration by using the main pump cell 2 and the auxiliary pump cell 3, but the oxygen concentration control method is limited to this. I can't. That is, in the NOx sensor having only the main pump cell, the oxygen concentration in the NOx sensor 1 may be controlled to the target concentration using the main pump cell.

  In the second embodiment described above, when calculating the output change amount ΔI, the influence of the change in the oxygen concentration of the measurement target gas is reflected, but instead of the oxygen concentration or the oxygen concentration. In addition, the influence of the change in the oxygen adsorption amount of the first detection electrode 52 may be reflected.

  In the second embodiment described above, the main pump cell 2 and the auxiliary pump cell 3 correspond to the “pump cell” in the first invention. Further, when the ECU 9 executes the process of step 206, the “exhaust gas amount acquiring means” in the fifth invention executes the process of step 208, and the “correcting means” in the fifth invention. Are realized.

  In the second embodiment described above, the “restricting means” according to the eighth aspect of the present invention is realized by the ECU 9 executing the process of step 212 described above.

DESCRIPTION OF SYMBOLS 1 NOx sensor 2 Main pump cell 21 Solid electrolyte 22 1st pump electrode 23 2nd pump electrode 3 Auxiliary pump cell 31 Solid electrolyte 32 1st pump electrode 33 2nd pump electrode 4 Spacer 41 1st chamber 42 2nd chamber 43 Communication hole 5 Detection Cell 51 Solid electrolyte 52 First detection electrode 53 Second detection electrode 6 Spacer 61 Air duct 7 Heater 71 Heater electrodes 72 and 73 Insulating layer 8 Porous protective layer 10 Gas concentration detection device

Claims (8)

A gas sensor having a pump cell that pumps out oxygen in the measurement target gas and a detection cell that detects a concentration of a specific gas component contained in the measurement target gas from which oxygen has been pumped out by the pump cell is provided in an exhaust path of the internal combustion engine. Gas concentration detection device,
A target pumping amount calculating means for calculating a target pumping amount of oxygen in the measurement target gas;
Pump cell driving means for driving the pump cell according to the target pumping amount;
An exhaust gas amount acquisition means for acquiring an exhaust gas amount in the measurement target gas introduced into the gas sensor based on information on the operating state of the internal combustion engine and the concentration of oxygen in the measurement target gas;
A target pumping amount raising means for raising the target pumping amount when the exhaust gas amount is lower than a reference amount;
A gas concentration detection device comprising:   2. The gas concentration detection device according to claim 1, wherein the target value raising means sets the raising amount according to a change in the amount of air taken into the internal combustion engine.   3. The gas concentration detection device according to claim 1, wherein the target value raising means sets the raising amount according to information on oxygen adsorbed on the electrode of the detection cell.   The apparatus further comprises limiting means for restricting execution of the target value raising means when the concentration of the specific gas component detected from the output of the detection cell follows the actual concentration of the specific gas component in the measurement target gas. The gas concentration detection device according to claim 1, wherein the gas concentration detection device is a gas concentration detection device. A gas sensor having a pump cell that pumps out oxygen in the measurement target gas and a detection cell that detects a concentration of a specific gas component contained in the measurement target gas from which oxygen has been pumped out by the pump cell is provided in an exhaust path of the internal combustion engine. Gas concentration detection device,
An exhaust gas amount acquisition means for acquiring an exhaust gas amount in the measurement target gas introduced into the gas sensor based on information on the operating state of the internal combustion engine and the concentration of oxygen in the measurement target gas;
Correction means for correcting the output value of the detection cell when the exhaust gas amount falls below a reference amount;
A gas concentration detection device comprising:   6. The gas concentration detection apparatus according to claim 5, wherein the correction unit corrects the output value of the detection cell in accordance with a change in the output of the detection cell.   7. The gas concentration detection apparatus according to claim 5, wherein the correction unit corrects the output value of the detection cell according to information on the concentration of oxygen in the measurement target gas.   The apparatus further comprises a limiting unit that limits execution of the target value raising unit when the concentration of the specific gas component detected by the concentration detection unit follows the actual concentration of the specific gas component in the measurement target gas. The gas concentration detection device according to any one of claims 5 to 7.

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