JP2005351734A - Concentration detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive concentration detector capable of precisely detecting the concentration of a predetermined component in exhaust gas over a wide range of concentration. <P>SOLUTION: The concentration detector is equipped with a detection part 58 for detecting the concentration of NO<SB>X</SB>in a target atmosphere, and the output of the detection part to the concentration of NO<SB>X</SB>becomes different with the temperature of the detection part. The concentration detector is further equipped with a temperature control means for controlling the temperature of the detection part to a target temperature and a concentration range estimating means for estimating the concentration range capable of being taken up by NO<SB>X</SB>, on the basis of a parameter separate from the output of the detection part. The temperature control means alters the target temperature so that the output of the detection part, corresponding to the concentration range estimated by the concentration range estimating means, is held to a predetermined output range. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a concentration detection apparatus.

For the purpose of precise air-fuel ratio control of an internal combustion engine or detection of catalyst deterioration, various in-vehicle sensors (hereinafter referred to as “exhaust gas sensors”) for detecting predetermined components in exhaust gas such as NO _x , CO, and HC, respectively. Has been proposed. Examples of such an exhaust gas sensor include a sensor (hereinafter referred to as “electromotive force type sensor”) that uses a change in electromotive force due to a concentration difference such as NO _x between the reference electrode and the detection electrode, and an electric resistance of a metal oxide semiconductor. Is a sensor (hereinafter referred to as a “semiconductor sensor”) that utilizes the fact that the concentration of NOx varies depending on the concentration of NO _x or the like.

Patent Document 1 discloses an electromotive force sensor. This sensor is provided and the reference electrode does not respond to the detection electrode and the NO _X responsive to the NO _X on the surface of the ion-conductive solid electrolyte, the electrodes are both exposed to the same measurement object atmosphere. In such a configured sensor, electromotive force corresponding to the NO _X concentration with the reference electrode that does not respond to the detection electrode and the NO _X in response to the NO _X is produced. It is NO _X concentration by measuring the electromotive force is detected.

Further, in the above electromotive force type sensor and semiconductor sensor, not concentration change of the NO _X only, the output by the element temperature change of the sensor changes, the output change with respect to the element temperature change of the sensors is large. For this reason, when using these sensors, the output change by the element temperature change is suppressed by maintaining the temperature constant using a heater or the like.

JP-A-7-63724 JP 2003-194759 A JP 2003-50227 A JP 2001-74693 A

By the way, the NO _x sensor is often required to detect the NO _x concentration in a wide concentration range from a low concentration to a high concentration. However, when concentration detection is performed while keeping the element temperature of the NO _x sensor constant, the output at a low concentration is small. Therefore, in order to obtain a high output even at a low concentration, a method of amplifying the output via an amplifier circuit when the NO _x concentration is low is employed.

That is, the two detection circuits and the low concentration detection circuit and the high-concentration detecting circuit is provided as a detection circuit of the NO _X sensor, if NO _X concentration is low and output through a low-concentration detecting circuit, NO _X concentration is high In this case, the signal is output through a high concentration detection circuit. The amplification factor of the low concentration detection circuit is higher than the amplification factor of the high concentration detection circuit. In this way, NO _X concentration is low, therefore even small generated electromotive force, it is possible to obtain a high output.

However, when using such a technique, problems and such causes an increase in manufacturing cost for the entire detection circuit is complicated, the value obtained by amplifying the output detected when NO _X concentration is low amplification The problem is that the error is large due to the high rate.

  Accordingly, an object of the present invention is to provide an inexpensive concentration detection device that can accurately detect the concentration of a predetermined component in exhaust gas in a wide concentration range.

In order to solve the above-described problem, the first invention includes a detection unit that detects a concentration of a predetermined component in a target atmosphere, and an output of the detection unit with respect to the concentration of the predetermined component depends on a temperature of the detection unit. In different concentration detection devices, a temperature control unit that controls the temperature of the detection unit to be a target temperature and a concentration range that the predetermined component can take are estimated based on parameters different from the output of the detection unit. Concentration range estimation means, and the temperature control means sets the target temperature so that the output of the detection unit corresponding to the concentration range estimated by the concentration range estimation means is maintained within a predetermined output range. change.
According to the first invention, since the output of the detection unit is maintained within a predetermined output range, it is not necessary to provide two detection circuits, a low concentration detection circuit and a high concentration detection circuit, and the manufacturing cost can be reduced. . Even when the concentration of the predetermined component is low, the output of the detection unit is maintained within the predetermined output range by adjusting the temperature of the detection unit, so that the concentration of the predetermined component can be detected with high accuracy. Can do.
In the following embodiment, “target atmosphere” means exhaust gas of an internal combustion engine, and “predetermined component” means components in the exhaust gas, particularly nitrogen oxide (NO _x ), carbon monoxide (CO) or Means hydrocarbon (HC). In addition, the “detection unit” means, for example, an electrode structure including two electrodes and a solid electrolyte in the case of an electromotive force type sensor, and a metal oxide semiconductor in the case of a semiconductor type sensor.

In a second invention, in the first invention, the temperature control means adjusts the target temperature so that the output of the detection unit is maintained within a certain output range or a certain value or more.
In the second invention, since the output of the detection unit is maintained at a certain output range or a certain value or more, an output range lower than the certain output range or an output less than the certain value does not occur. Therefore, there is no need to provide an amplifier circuit for use when the output of the detection unit is a low output range or an output less than a certain value.

According to a third invention, in the first or second invention, the target atmosphere is exhaust gas of an internal combustion engine, and the output of the detection unit decreases as the temperature of the detection unit increases. When it is estimated that the concentration range of the predetermined component is increased by executing high-concentration control in which the concentration of the predetermined component is higher than that during normal operation of the engine in the internal combustion engine, before the start of execution of the high-concentration control. Increase the target temperature.
If the execution of the high concentration control and the temperature rise of the detection unit are started at the same time, the concentration of the predetermined component may increase before the temperature of the detection unit increases. In this case, the output of the detection unit becomes too large. According to the third aspect of the invention, since the temperature of the detection unit is raised before the execution of the high concentration control is started, a situation in which the output of the detection unit becomes too large in this way is prevented.
The high concentration and control, for example, _the NO _X storage reduction catalyst NO _X leaving control to disengage the NO _X occluded in the, and _the NO _X storage reduction catalyst sulfur regeneration control disengaging the SO _X which is stored in such It is.

According to a fourth invention, in any one of the first to third inventions, the target atmosphere is an exhaust gas of an internal combustion engine, and the concentration range estimation means is configured such that the predetermined component is based on an operating state of the internal combustion engine. Estimating whether the concentration range that can be taken is a low concentration range or a high concentration range that is higher than the low concentration range, and the temperature control means determines the concentration range that the predetermined component can take by the concentration range estimation means. When it is estimated that the concentration range is a low concentration range, a predetermined temperature is set as a target temperature, and when the concentration range that can be taken by the predetermined component is estimated to be a high concentration range by the concentration range estimation means, A predetermined temperature different from the predetermined temperature is set as the target temperature.
According to the fourth aspect of the invention, the control performed by the concentration detection device performs the target temperature when the operating state of the internal combustion engine satisfies a certain condition (for example, when the concentration range that the predetermined component can take is the low concentration range). Is set to a predetermined temperature, and if the operating state of the internal combustion engine does not satisfy the certain condition, the target temperature is only set to a predetermined temperature different from the certain temperature. The control circuit of the detection device is very simple, so that the manufacturing cost of the control circuit can be kept low.
Note that “based on the operating state of the internal combustion engine” means, for example, based on whether or not the high concentration control described above is being executed. In addition, the case where the concentration range estimation unit estimates that the concentration range is a high concentration range means, for example, the case where NO _X separation control is being executed.

In order to solve the above problems, in the fifth aspect of the invention, a detection unit that detects the concentration of the predetermined component in the target atmosphere is provided, and the output of the detection unit with respect to the concentration of the predetermined component depends on the temperature of the detection unit. In the different concentration detection devices, temperature control means for controlling the temperature of the detection unit to be a target temperature is further provided, and the temperature control means has a concentration of the predetermined component detected by the detection unit equal to or higher than a predetermined value. The target temperature is changed depending on whether the value is less than a certain value.
According to the fifth aspect, the target temperature of the detection unit is changed according to the detected NO _x concentration. Therefore, for example, when the concentration of the predetermined component is high, the target temperature is set so that the output of the detection unit with respect to the concentration of the predetermined component becomes small, and when the concentration of the predetermined component is low, the output of the detection unit with respect to the concentration of the predetermined component becomes large. With the target temperature, the concentration of the predetermined component can be detected with high accuracy regardless of the level of the concentration of the predetermined component. Also, it is not necessary to provide two detection circuits, a low concentration detection circuit and a high concentration detection circuit, and the manufacturing cost can be reduced.

  According to the concentration detection apparatus of the first to fourth inventions, it is not necessary to provide two detection circuits, and the concentration of the predetermined component can be detected with high accuracy even if the concentration of the predetermined component is low. For this reason, an inexpensive concentration detection device that can accurately detect the concentration of a predetermined component in exhaust gas in a wide concentration range is provided.

  According to the concentration detection apparatus of the fifth aspect of the present invention, it is not necessary to provide two detection circuits, and the concentration of the predetermined component can be detected with high accuracy regardless of the concentration level of the predetermined component. For this reason, an inexpensive concentration detection device that can accurately detect the concentration of a predetermined component in exhaust gas in a wide concentration range is provided.

  FIG. 1 shows an in-cylinder spark ignition internal combustion engine in which the concentration detection device of the present invention is used. In the following, the present invention will be described by taking this in-cylinder spark ignition internal combustion engine as an example, but the present invention can also be applied to a compression ignition internal combustion engine.

  Referring to FIG. 1, 1 is an engine body, 2 is a cylinder block, 3 is a piston, 4 is a cylinder head, 5 is a combustion chamber, 6 is an intake valve, 7 is an intake port, 8 is an exhaust valve, 9 is an exhaust port, Reference numeral 10 denotes a spark plug, 11 denotes a fuel injection valve, and 12 denotes a cavity. The fuel injection valve 11 is attached to the cylinder head 4 so as to inject fuel directly into the combustion chamber 5.

The intake port 7 of each cylinder is connected to a surge tank 14 via a corresponding intake branch pipe 13, and the surge tank 14 is connected to an air cleaner (not shown) via an intake duct 15 and an air flow meter 16. . A throttle valve 18 driven by a step motor 17 is disposed in the intake duct 15. On the other hand, the exhaust port 9 of each cylinder is connected to an exhaust manifold 19, and the exhaust manifold 19 passes the NO _x storage reduction catalyst 23 through a catalytic converter 21 containing an oxidation catalyst or a three-way catalyst 20 and an exhaust pipe 22. It is connected to a built-in casing 24. The exhaust manifold 19 and the surge tank 14 are connected to each other via a recirculated exhaust gas (hereinafter referred to as EGR gas) conduit 26, and an EGR gas control valve 27 is disposed in the EGR gas conduit 26.

The electronic control unit 31 is composed of a digital computer and includes a RAM (random access memory) 33, a ROM (read only memory) 34, a CPU (microprocessor) 35, an input port 36 and An output port 37 is provided. The air flow meter 16 generates an output voltage proportional to the amount of intake air, and this output voltage is input to the input port 36 via the corresponding AD converter 38. An air-fuel ratio sensor 28 for detecting the air-fuel ratio is attached to the exhaust manifold 19, and an output signal of the air-fuel ratio sensor 28 is input to the input port 36 via the corresponding AD converter 38. Further, NO _X in the storage reduction catalyst 23 connected to an exhaust pipe 25 to the outlet of the casing 24 with a built-in, the NO _X sensor 29 NO _X concentration capable of detecting in the exhaust gas is arranged, of the NO _X sensor 29 The output signal is input to the input port 36 via the corresponding AD converter 38.

  A load sensor 41 that generates an output voltage proportional to the amount of depression of the accelerator pedal 40 is connected to the accelerator pedal 40. The output voltage of the load sensor 41 is input to the input port 36 via the corresponding AD converter 38. For example, the crank angle sensor 42 generates an output pulse every time the crankshaft rotates 30 degrees, and the output pulse is input to the input port 36. The CPU 35 calculates the engine speed from the output pulse of the crank angle sensor 42. On the other hand, the output port 37 is connected to the spark plug 10, the fuel injection valve 11, the step motor 17, and the EGR control valve 27 via a corresponding drive circuit 39.

Next, the structure of the NO _X sensor 29 shown in FIG. 1 will be described with reference to FIG. The sensor 29 is a so-called electromotive force type NO _x sensor, and includes an ion conductive solid electrolyte element 51, and a reference electrode 52 and a detection electrode 53 provided on one surface of the solid electrolyte element 51. The solid electrolyte element 51 is formed of, for example, zirconia that is completely stabilized or partially stabilized with yttria, calcia, ceria, or magnesia. The reference electrode 52 is configured as an electrode that does not react with NO _x (that is, a component whose concentration is to be detected among components in the exhaust gas) in the exhaust gas flowing through the exhaust pipe 25. Specifically, the reference electrode 52 is made of, for example, a noble metal such as platinum, gold, palladium, or an alloy thereof, and is baked or vapor-deposited on the surface of the solid electrolyte element 51. The detection electrode 53 includes a metal nitrate layer 53a provided on the surface of the solid electrolyte element 51 and a noble metal, an alloy thereof, or a conductive ceramic layer provided on the metal nitrate layer 53a (hereinafter referred to as “noble metal layer”). 53b. As the metal nitrate layer 53a, sodium nitrate, barium nitrate or a composite salt thereof is used, and is provided by applying a molten salt on the solid electrolyte element 51, for example. The noble metal layer 53b is baked, vapor-deposited or the like on the metal nitrate layer 53a.

The reference electrode 52 and the detection electrode 53 are connected to the electromotive force measurement circuit 54. The electromotive force measurement circuit 54 outputs a voltage proportional to the electromotive force generated between the reference electrode 52 and the detection electrode 53 to the output unit 55. In the NO _X sensor 29 configured as described above, the unipolar potential of the detection electrode 53 changes according to the NO _X concentration in the exhaust gas to which the NO _X sensor 29 is exposed, whereas the reference electrode 52 Produces a constant unipolar potential regardless of the NO _x concentration. Therefore, an electromotive force is generated between the reference electrode 52 and the detection electrode 53 in accordance with the NO _X concentration in the exhaust gas to which the NO _X sensor 29 is exposed, and the electromotive force measurement circuit 54 causes the electromotive force measurement circuit 54 to connect the electrodes 52 and 53. By measuring the generated electromotive force (hereinafter referred to as “interelectrode electromotive force”), an output voltage corresponding to the NO _x concentration of the exhaust gas can be obtained. In general, the electromotive force proportional to the logarithm of the NO _X concentration between the reference electrode 52 and the detection electrode 53 is caused, thus the output voltage proportional to the logarithm of the NO _X density.

Furthermore, the NO _X sensor 29 of the present embodiment has a heater 57 provided via an insulating layer 56 on the surface of the solid electrolyte element 51 opposite to the surface on which the electrodes 52 and 53 are disposed. The heater 57 heats and raises the temperature of an electrode structure (detection unit) 58 including the solid electrolyte element 51, the reference electrode 52, and the detection electrode 53. Such a heater 57 is conventionally used in an electromotive force type sensor, for the following reason.

That is, the inter-electrode electromotive force varies depending not only on the NO _x concentration in the exhaust gas but also on the temperature of the electrode structure. This is shown in FIG. FIG. 3 is a diagram showing the relationship between the temperature of the electrode structure and the electromotive force for different NO _x concentrations. As can be seen from FIG. 3, the inter-electrode electromotive force decreases as the temperature of the electrode structure increases, and conversely, the inter-electrode electromotive force increases as the temperature of the electrode structure decreases. Therefore, unless the temperature of the electrode structure is kept constant, it is difficult to obtain an output corresponding to the NO _x concentration in the exhaust gas by the sensor, and the detection accuracy of the NO _x concentration is low. For this reason, the detection accuracy of the NO _x concentration is kept high by heating the electrode structure so that the temperature of the electrode structure is kept substantially constant by the heater.

By the way, when detecting the NO _x concentration in the exhaust gas by the NO _x sensor, even if the NO _x concentration is in a relatively low concentration range (hereinafter referred to as “low concentration range”), a relatively high concentration is obtained. Even in the range (hereinafter referred to as “high concentration range”), it is necessary to be able to detect the NO _x concentration with high accuracy.

For example, when determining the deterioration of the exhaust gas purifying catalyst such as _the NO _X storage reduction catalyst 23 provided in the exhaust pipe 25 of an internal combustion engine, _the NO _X storage reduction catalyst without being purified by the deterioration of the NO _X occluding and reducing catalyst 23 Therefore, it is necessary to detect a minute amount (for example, several tens of ppm or less) of NO _x that has flowed out downstream of the gas flow. That is, in this case, it is necessary to be able to detect the NO _x concentration in the low concentration range with high accuracy.

Air On the other hand, _the NO _X storage reduction catalyst 23, the _the NO _X storage reduction air-fuel ratio of the exhaust gas flowing into the catalyst 23 _(the NO _X storage and reduction catalyst 23 upstream of the exhaust passage 25, is supplied to the combustion chamber 5 and the intake passage the ratio of the fuel) is substantially the stoichiometric air-fuel ratio or rich when _the NO _X storage reduction catalyst 23 a NO _X that is occluded disengaging and reduced to thereby occlude NO _X in the exhaust gas when a lean. Then, in _the NO _X storage reduction catalyst 23, in order to maintain the _the NO _X storage ability, it is necessary to periodically disengage the NO _X which is stored in _the NO _X storage reduction catalyst 23, _the NO _X storage reduction catalyst for the It is necessary to perform control to make the air-fuel ratio of the exhaust gas flowing into the engine 23 approximately the stoichiometric air-fuel ratio or rich (hereinafter referred to as “NO _X separation control”). When performing this NO _X withdrawal control, when the withdrawal amount of the NO _X from _the NO _X storage reduction catalyst 23 is large, NO _X flows out downstream of the NO _X occluding and reducing catalyst 23 without being reduced. To adjust of the NO _X withdrawal control based on the leaked amount of NO _X, it is necessary to detect the amount of the NO _X which was to flow out to the downstream of the NO _X occluding and reducing catalyst 23. In this case, NO _x may flow out at a higher concentration (for example, about 1000 ppm) compared to the case where the deterioration of the NO _x storage reduction catalyst 23 described above is detected. In particular, the detection of the NO _x concentration in such a case is possible. Therefore, it is necessary to detect the NO _x concentration in the high concentration range with high accuracy.

Thus, conventionally, the requirement for detecting the NO _x concentration with high accuracy in both the low concentration range and the high concentration range has been dealt with by providing a double detection circuit. That is, the high concentration detection circuit is used when the NO _x concentration in the high concentration range is to be detected, and the low concentration detection circuit is used when the NO _x concentration in the low concentration range is to be detected. Since the inter-electrode electromotive force than when it is high when the NO _X concentration is low is small, the amplification factor in the low concentration detection circuit is set to be higher than the amplification factor of the high density detection circuit.

However, when the double detection circuit is provided in this way, the detection circuit becomes complicated, and the cost required for its manufacture becomes high. Further, when the low concentration detection circuit is used, a small inter-electrode electromotive force is amplified with a high amplification factor to be output from the NO _X sensor. Therefore, when the NO _X concentration in the exhaust gas is low, an error in the sensor output occurs. It gets bigger.

Here, in the electromotive force type NO _x sensor 29 as described above, the inter-electrode electromotive force changes according to the temperature of the electrode structure 58, and the output voltage of the NO _x sensor 29 also changes accordingly. Even the concentration of NO _X exhaust gas as shown in FIG. 3 the same, the output voltage of the temperature of the electrode structure 58 is lowered electromotive force and NO _X sensor 29 is increased.

FIG. 4 shows the relationship between the NO _x concentration in the exhaust gas and the output voltage of the NO _x sensor 29 for each case where the temperature of the electrode structure 58 is different. The x axis represents the logarithm of the NO _x concentration in the exhaust gas, and the y axis represents the output voltage of the sensor. The two graphs in the figure show the NO _x concentration and the output of the NO _x sensor 29 when the temperature of the electrode structure 58 is high (650 ° C.) and when the temperature of the electrode structure 58 is low (600 ° C.), respectively. Show the relationship. 4 that the output voltage of the NO _x sensor 29 is proportional to the logarithm of the NO _x concentration in the exhaust gas.

Moreover, as it can be seen from Figure 4, when the temperature of the electrode structures 58 is lower than that when the temperature of the electrode structure 58 is high, the output voltage at all NO _X density region is larger and the total NO _X concentration range The proportional coefficient of the output voltage with respect to the logarithm of the NO _x concentration is large. Therefore, when the temperature of the electrode structure 58 is high, the output voltage of the NO _x sensor 29 does not become too high even if the NO _x concentration in the exhaust gas is high. However, in this case, a small change in the output voltage of the NO _X sensor 29 for concentration of NO _X in the exhaust gas is low NO _X concentration change. For this reason, when the temperature of the electrode structure 58 is high, it is suitable for detecting the NO _x concentration when the NO _x concentration in the exhaust gas is high.

On the other hand, if the temperature of the electrode structure 58 is low, resulting a great change in the output voltage of the NO _X sensor 29 against a slight NO _X concentration change even at low concentration of NO _X in the exhaust gas. However, in this case, the output voltage of the high concentration of NO _X in the exhaust gas NO _X sensor 29 becomes too large. For this reason, when the temperature of the electrode structure 58 is low, it is suitable for detecting the NO _x concentration when the NO _x concentration in the exhaust gas is low.

Therefore, the present invention uses such a property to estimate the concentration range (hereinafter referred to as “expected concentration range”) that NO _X in the exhaust gas can take based on parameters other than the output of the NO _X sensor 29. The temperature of the electrode structure 58 is adjusted so that the output of the NO _X sensor 29 corresponding to the expected concentration range is maintained within the predetermined output range. That is, when the expected concentration range is low and therefore a small amount of NO _{x is} to be detected, the temperature of the electrode structure 58 is set to a relatively low temperature (for example, 600 ° C., hereinafter referred to as “low set temperature”). The output voltage of the NO _X sensor 29 with respect to the NO _X concentration is assumed to be high. On the other hand, when the expected concentration range is high and therefore a large amount of NO _{x is} to be detected, the temperature of the electrode structure 58 is set to a relatively high temperature (for example, 650 ° C., hereinafter referred to as “high set temperature”). The output of the NO _X sensor 29 with respect to the NO _X concentration is assumed to be low.

Thus, the expected concentration range increases the output voltage of the NO _X sensor 29 for NO _X concentration when low, by reducing the output voltage of the NO _X sensor 29 for NO _X concentration when expected concentration range is high, resulting , it is possible to maintain the output range of the NO _X sensor 29 for NO _X concentration definitive when NO _X concentration is in each of the predicted temperature range within a predetermined output range. That is, according to the concentration detection device of the present invention, the temperature of the electrode structure 58 is changed according to the expected concentration range, so that the output voltage of the NO _X sensor 29 when the NO _X concentration is in the expected concentration range is predetermined. Is maintained within the output range. Therefore, in the concentration detection apparatus of the present invention, the NO _x concentration in each expected concentration range is provided without providing a double detection circuit of a detection circuit used when the expected concentration range is low and a detection circuit used when the expected concentration range is high. Can be detected with high accuracy.

In the present embodiment, the NO _X sensor 29 is provided in the exhaust pipe 25 downstream of the NO _X storage reduction catalyst 23. As the parameters other than the output of the NO _X sensor 29 used for estimating the above-described expected concentration range, for example, a parameter indicating the operating state of the internal combustion engine (hereinafter referred to as “operating parameter”) is used. .

For example, when the internal combustion engine is operating normally, NO _x in the exhaust gas discharged from the engine body 1 is purified by the NO _x storage reduction catalyst 23, and therefore, in the exhaust gas reaching the NO _x sensor 29, nO _X is almost non-existent. Therefore, when it is determined that the internal combustion engine is operating normally based on various operating parameters, the NO _X concentration in the exhaust gas flowing downstream of the NO _X storage reduction catalyst 23 is low, and as described above, the NO _X storage catalyst 23 It is suitable for determining deterioration, and the expected density range is set to the low density range.

On the other hand, NO _{when X} withdrawal control is performed, _the NO _X storage reduction NO _X and NO _X leaving a large amount of a catalyst 23 as described above flows out downstream of the NO _X occluding and reducing catalyst 23, NO _X concentration of NO _X exhaust gas reaching the sensor 29 becomes high. Therefore, when it is determined that the internal combustion engine is performing NO _X detachment control based on various operating parameters, the exhaust gas flowing downstream of the NO _X storage reduction catalyst 23 may have a high NO _X concentration in the gas, and the expected concentration range. Is the high concentration range. Note that during the NO _x release control, the NO _x concentration may actually be low, but even in such a case, the expected concentration range is set to the high concentration range.

In addition to NO _X separation control, sulfur poisoning regeneration control or the like is performed as control (high concentration control) in which the expected concentration range of NO _{X in} the exhaust gas flowing downstream of the NO _X storage reduction catalyst 23 is set to a high concentration range. Can be mentioned. Here, the sulfur and the poisoning regeneration control refers to control performed for disengaging the _the NO _X storage and reduction catalyst 23 are inserted in the SO _X, in order to disengage the NO _X occluded in the NO _X occluding and reducing catalyst 23 This control is different from the NO _X separation control to be performed. That, NO _X occluding and reducing catalyst 23 occludes also SO _X not only NO _X in the exhaust gas, since the occluded SO _X is not detached by NO _X withdrawal control, apart from the NO _X withdrawal control, storage sulfur poisoning regeneration control is performed in order to disengage the been SO _X. When the sulfur NO _X disengaged control as well as _the NO _X storage occluded NO _X in reducing catalyst 23 is made to leave in poisoning regeneration control, leaving the amount of the NO _X from _the NO _X storage reduction catalyst 23 is large, NO _X Flows out downstream of the NO _x storage reduction catalyst 23 without being reduced. Therefore, even when sulfur poisoning regeneration control is performed, the expected concentration range of NO _{x in} the exhaust gas is set to the high concentration range.

As described above, in order to change the output of the NO _X sensor 29 with respect to the NO _X concentration, it is necessary to adjust the temperature of the electrode structure 58, and the temperature of the electrode structure 58 is adjusted by the heater 57. . That is, the operating temperature of the electrode structure 58 is the exhaust gas flowing through the exhaust pipe 25 in which the electrode structure 58 is disposed, regardless of whether the temperature is set to a low set temperature or a high set temperature. Therefore, it is necessary to raise the temperature of the electrode structure 58 by the heater 57 in any case. Therefore, the temperature of the electrode structure 58 is adjusted by changing the amount of heat applied from the heater 57 to the electrode structure 58 depending on whether the operating temperature of the electrode structure 58 is a high set temperature or a low set temperature. Is called.

Specifically, the electrode structure 58 is adjusted to the target temperature by any one of the following controls. As the first control, there is feedback control for controlling the temperature of the heater 57 so that the resistance value of the heater 57 becomes a predetermined value that changes according to the target temperature. This utilizes the fact that the resistance value of the heater 57 changes according to the temperature of the heater 57. As the second control, the temperature of the electrode structure 58 is actually detected by a temperature sensor (for example, a thermocouple) that detects the temperature of the electrode structure 58, and the temperature detected by this temperature sensor is the above target temperature. The feedback control which controls the temperature of the heater 57 is mentioned. The third control includes feedback control that controls the temperature of the heater 57 so that the impedance of the NO _X sensor 29 becomes a predetermined value that changes according to the target temperature. This utilizes the fact that the impedance of the NO _x sensor 29 changes according to the temperature of the electrode structure 58.

The execution of NO when trying to start the _X withdrawal control, and begins execution before the NO _X withdrawal control higher the target temperature of the electrode structure 58, NO _X withdrawal control when the internal combustion engine is performing a normal operation Is started, the temperature of the electrode structure 58 is set to a high set temperature. That, NO _X concentration is by starting execution of the NO _X withdrawal control if the expected concentration range expected concentration range that is high is estimated by starting with a and NO _X leaving control when in the low concentration range Before the temperature actually increases, the target temperature of the electrode structure 58 is set to a high temperature in advance.

That is, since it takes some time to change the temperature of the electrode structure 58 from the low set temperature to the high set temperature, when the execution start of the NO _x detachment control and the change of the target temperature of the electrode structure 58 are performed simultaneously, There are cases where the actual NO _x concentration becomes high before the temperature of the electrode structure 58 reaches a high set temperature. For this reason, there is a possibility that the output of the NO _X sensor 29 becomes too large. On the other hand, in the present embodiment, the temperature of the electrode structure 58 is raised in advance so that the electrode structure 58 is at a high set temperature when the actual NO _x concentration reaches the high concentration range. This prevents the situation where the output of the NO _X sensor 29 becomes too large.

FIG. 5 is a flowchart showing a control routine for temperature control of the electrode structure 58. First, in step 101, it is determined whether or not NO _X detachment control is being executed. Whether NO _X withdrawal control is executed, it is determined by whether, for example, by ECU31 for controlling the operating parameters of the fuel injection amount and an internal combustion engine such as the throttle opening NO _X withdrawal control is executed. If it is determined in step 101 that NO _X separation control is not being executed, the routine proceeds to step 102. In step 102, it is determined whether or not a NO _X separation control start condition is satisfied. NO _X withdrawal control start condition is satisfied for example, such as _the NO _X storage amount by the NO _X occluding and reducing catalyst 23 exceeds a predetermined amount, when it is necessary to detach the NO _X from _the NO _X storage reduction catalyst 23.

If it is determined in step 102 that the NO _X separation control start condition is not satisfied, the routine proceeds to step 103. In step 103, the target temperature Ttr of the electrode structure 58 is set to a low set temperature (600 ° C. in the present embodiment). Therefore, feedback control is performed by the heater 57 so that the temperature of the electrode structure 58 becomes a low set temperature. Next, at step 104, the high temperature flag XT is set to the set release state (XT = 0). The high temperature flag XT is a flag that is set when the temperature of the electrode structure 58 is high, and is released when the temperature is not high.

On the other hand, if it is determined in step 102 that the NO _X separation control start condition is satisfied, the routine proceeds to step 105. In step 105, the target temperature Ttr of the electrode structure 58 is set to a high set temperature (650 ° C. in this embodiment). Therefore, feedback control is performed by the heater 57 so that the temperature of the electrode structure 58 becomes high. Next, in step 106, delay control is performed. This delay control is a control that delays the start of the NO _X release control for a certain period of time from the satisfaction of the condition, even though the NO _X release control start condition is satisfied. This fixed time is expected to take until the temperature of the electrode structure 58 actually reaches the high set temperature by the heater 9 after the target temperature Ttr of the electrode structure 58 is changed from the low set temperature to the high set temperature. It is time and is predetermined in this embodiment. Then, the NO _X separation control is started with the end of the delay control. Next, at step 107, the high temperature flag XT is set (XT = 1).

When NO _X separation control is started, the routine proceeds from step 101 to step 108 in the next routine. In step 108, the target temperature Ttr of the electrode structure 58 is continuously set to the high set temperature, and in the subsequent step 109, the high temperature flag XT is maintained in the set state (XT = 1).

FIG. 6 is a flowchart showing a control routine for concentration calculation control by the NO _X sensor 29. First, at step 151, the output voltage Vs of the NO _X sensor 29 is detected. Next, at step 152, it is determined whether or not the high temperature flag XT used in the temperature control is set. If it is determined in step 152 that the high temperature flag XT is not set (XT = 0), that is, if the temperature of the electrode structure 58 is a low set temperature, the process proceeds to step 153. In step 153, the NO _x concentration is calculated from the output voltage Vs detected in step 151 and the low temperature map. On the other hand, if it is determined in step 152 that the high temperature flag XT is set (XT = 1), that is, if the temperature of the electrode structure 58 is the high set temperature, the process proceeds to step 154. In step 154, the NO _x concentration is calculated from the output voltage Vs detected in step 151 and the high temperature map.

The low temperature map and the high temperature map are two-dimensional maps showing the relationship between the output voltage Vs of the NO _X sensor 29 and the NO _X concentration, such as the map shown in FIG. In particular, the low temperature map is a map corresponding to the 600 ° C. straight line in FIG. 4, and the high temperature map is a map corresponding to the 650 ° C. straight line in FIG. These maps are stored in the ROM34 of the ECU 31, the relationship between the output voltage Vs and the NO _X concentration in these maps is determined by by experiment or calculation.

In the above embodiment, the case where the temperature of the electrode structure is adjusted to either the low set temperature or the high set temperature corresponding to the two concentration ranges of the low concentration range and the high concentration range has been described. In this way, the temperature may be adjusted to three or more temperatures corresponding to three or more concentration ranges, respectively. In this case, the ECU 31 stores a map indicating the relationship between the temperature of the electrode structure and the NO _x concentration for each set temperature. As described above, by increasing the set temperature, the output range of the NO _X sensor 29 corresponding to each concentration range can be limited to a narrower range.

  Next, the concentration detection apparatus according to the second embodiment of the present invention will be described. The configuration of the concentration detection device of the second embodiment is basically the same as the configuration of the concentration detection device of the first embodiment.

However, a concentration detection apparatus of the second embodiment is different from the concentration detecting device of the first embodiment, the case NO _X concentration detected by the sensor is equal to or greater than a predetermined value, the target temperature in the case of less than the predetermined value I am trying to change it. That is, when the NO _x concentration is equal to or higher than a certain value, the target temperature is increased, and when the NO _x concentration is less than the certain value, the target temperature is decreased. Thus, the sensor output becomes small with respect to NO _X concentration when NO _X concentration is high, the sensor output increases with respect to NO _X concentration when NO _X concentration is low.

Specifically, when the temperature of the electrode structure is a low set temperature, when the output of the sensor is equal to or higher than the output corresponding to the above-mentioned constant value, that is, when the NO _x concentration is above the above-mentioned constant value The target temperature of the electrode structure is changed to a high set temperature. On the contrary, when the temperature of the electrode structure is a high set temperature, when the output of the sensor becomes less than the output corresponding to the above-mentioned fixed value, that is, when the concentration of NO _x becomes less than the above-mentioned fixed value. Changes the target temperature of the electrode structure to a low set temperature.

In each of the above embodiments, the case where an electromotive force type sensor in which the output voltage of the NO _x sensor 29 is reduced with respect to the NO _x concentration when the temperature of the electrode structure 58 is increased is described. Depending on the configuration of the type sensor, there is an electromotive force type sensor in which the output voltage of the NO _X sensor 29 with respect to the NO _X concentration increases as the temperature of the electrode structure 58 rises. Such an electromotive force sensor can also be used in the same manner as in the above embodiment. In this case, when the expected concentration range is a low concentration range, for example, the temperature of the electrode structure is increased during normal operation of the internal combustion engine, while when the detection target temperature is set high, for example, NO _x detachment control is performed. At the time of execution, the temperature of the electrode structure is lowered.

Further, in each of the above embodiments, the case where an electromotive force type sensor that detects NO _x by exposing both the detection electrode and the reference electrode to the exhaust gas is described. For example, only the detection electrode is connected to the exhaust gas. Other types of electromotive force sensors may be used, such as an electromotive force sensor in a form in which the reference electrode is exposed to the atmosphere without being exposed to exhaust gas. Moreover, although the said embodiment demonstrated the case where an electromotive force type sensor was used, you may use for another type of sensor. However, as the sensor of electromotive force type sensor and other types of other types, the output value is not only the concentration of such NO _X in a subject atmosphere, is a sensor that varies with the temperature of the detecting portion of the sensor It is necessary.

Other types of sensors include semiconductor sensors. A semiconductor sensor utilizes the fact that the electrical resistance of a metal oxide semiconductor changes depending on the concentration of NO _x or the like in the target atmosphere, and the metal oxide semiconductor is placed in the target atmosphere and is fixed to the metal oxide semiconductor. This is a sensor that detects the concentration of NO _x or the like in the target atmosphere by measuring the flowing current by applying the above voltage. Since the electric resistance of the metal oxide semiconductor also changes depending on the temperature of the metal oxide semiconductor itself as well as the concentration of NO _x or the like, it can be used in the same manner as in the above embodiment.

Furthermore, the above-described embodiments have described the case of a concentration detecting device for detecting the concentration of NO _X in exhaust gas of an internal combustion engine, but the subject an atmosphere of concentration detecting device is limited to an exhaust gas of an internal combustion engine It is not a thing. Further, even if the target atmosphere at a concentration detecting device is an exhaust gas of an internal combustion engine, the concentration detection target component is not limited to NO _X, it may be other components such as CO and HC.

It is a figure which shows the internal combustion engine by which the sensor of this invention is utilized. The structure of the sensor of this invention is shown. Shows the relationship between the temperature and the electromotive force of the electrode structure at different NO _X concentrations. The relationship between the NO _x concentration and the output voltage of the sensor is shown for each case where the temperature of the electrode structure is different. It is a flowchart which shows the control routine of the temperature control of an electrode structure. It is a flowchart which shows the control routine of density | concentration calculation control by a sensor.

Explanation of symbols

1 ... engine body 23 ... NO _X occluding and reducing catalyst 25 ... exhaust pipe 29 ... NO _X sensor 31 ... ECU
51 ... Solid electrolyte element 52 ... Reference electrode 53 ... Detection electrode 54 ... Electromotive force measuring circuit 56 ... Insulator 57 ... Heater 58 ... Electrode structure

Claims (5)

In a concentration detection apparatus comprising a detection unit for detecting a concentration of a predetermined component in a target atmosphere, wherein the output of the detection unit with respect to the concentration of the predetermined component differs depending on the temperature of the detection unit,
Temperature control means for controlling the temperature of the detection unit to be a target temperature, and concentration range estimation means for estimating a concentration range that the predetermined component can take based on a parameter different from the output of the detection unit. And a temperature detecting unit configured to change the target temperature so that an output of the detection unit corresponding to the concentration range estimated by the concentration range estimating unit is maintained within a predetermined output range.   The concentration detection apparatus according to claim 1, wherein the temperature control unit adjusts the target temperature so that an output of the detection unit is maintained within a certain output range or a certain value or more.   The target atmosphere is the exhaust gas of the internal combustion engine and the output of the detection unit decreases as the temperature of the detection unit increases. The temperature control means has a higher concentration of the predetermined component than during normal operation of the internal combustion engine. The target temperature is increased before starting the execution of the high concentration control when it is estimated that the concentration range of the predetermined component is increased when the high concentration control is executed in the internal combustion engine. Concentration detector.   The target atmosphere is exhaust gas of an internal combustion engine, and the concentration range estimation means has a concentration range that the predetermined component can take based on the operating state of the internal combustion engine is a low concentration range or higher than the low concentration range The temperature control unit estimates whether the concentration range is a high concentration range, and the temperature control unit targets a predetermined temperature when the concentration range estimation unit estimates that the concentration range that the predetermined component can take is a low concentration range. When the concentration range estimation means estimates that the concentration range that the predetermined component can take is a high concentration range, a predetermined temperature different from the predetermined temperature is set as a target temperature. Item 4. The concentration detection apparatus according to any one of Items 1 to 3. In a concentration detection apparatus comprising a detection unit for detecting a concentration of a predetermined component in a target atmosphere, wherein the output of the detection unit with respect to the concentration of the predetermined component differs depending on the temperature of the detection unit,
The apparatus further comprises temperature control means for controlling the temperature of the detection unit so as to become a target temperature, and the temperature control means has a case where the concentration of the predetermined component detected by the detection unit is greater than or equal to a certain value and less than a certain value. A concentration detector that changes the target temperature depending on the case.

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