JP2011127535A - Nox detecting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an NOx detecting device capable of relatively accurately detecting an NOx quantity passing through an exhaust gas passage per unit time even if the NOx concentration is relatively low. <P>SOLUTION: This NOx detecting device includes a holding part 42 for discharging and reducing holding NOx by a reducing substance when reducing the oxygen concentration in exhaust gas, a temperature sensor 41 for measuring the temperature of the holding part and an oxygen concentration reducing means 44 for reducing the oxygen concentration around the holding part, and starts reduction in the oxygen concentration around the holding part by the oxygen concentration reducing means after a first preset time from when holding no NOx in the holding part when the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio, and detects a temperature rise value of the holding part after a second preset time after starting the reduction in the oxygen concentration around the holding part by the oxygen concentration reducing means, and detects the NOx quantity in the exhaust gas passed through the exhaust gas passage for the first preset time based on the temperature rise value when the second preset time is a shorter time than the first preset time. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a NO _x detection device.

It has been proposed to arrange an NO _x concentration sensor for detecting the NO _x concentration in the exhaust gas in the engine exhaust system (see Patent Document 1). A general NO _x concentration sensor detects an instantaneous NO _x concentration in exhaust gas.

JP2005-140002 JP 2000-054824 A

The NO _X concentration sensor for detecting the concentration of NO _X such instant, the low concentration of NO _X in the exhaust gas, it is difficult to detect an accurate NO _X concentration.

Accordingly, an object of the present invention is to provide a NO _x detection device capable of detecting the amount of NO _x passing through the exhaust gas passage per unit time relatively accurately even if the NO _x concentration is relatively low. .

The NO _x detection device according to claim 1 of the present invention holds NO _x in the exhaust gas passing through the exhaust gas passage when the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio, and oxygen in the exhaust gas A holding unit that releases the reduced NO _x when the concentration is reduced and reduces it by a reducing substance; a temperature sensor that measures the temperature of the holding unit; and an oxygen concentration reducing unit that reduces the oxygen concentration around the holding unit; After the first set time from when the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio and NO _x is not held in the holding portion, oxygen around the holding portion is obtained by the oxygen concentration reducing means The temperature sensor detects a temperature rise value of the holding unit after a second set time after the oxygen concentration reducing unit starts to reduce the oxygen concentration around the holding unit. Second setting And wherein is a short time compared to the first set time, detecting _the amount of NO _X in the exhaust gas passing through the exhaust gas passage between the temperature rise value based on the first set time To do.

According to a second aspect of the present invention, there is provided the NO _x detection device according to the first aspect, wherein the NO _x detection device according to the first aspect is disposed downstream of the holding portion of the exhaust gas passage based on the detected amount of NO _x. air-fuel ratio of the exhaust gas Te is characterized by estimating the amount of NO _X held in the NO _X catalyst device for holding the NO _X in the exhaust gas when it is leaner than the stoichiometric air-fuel ratio.

NO _X detection device according to claim 3 of the present invention, in NO _X detection device according to claim 1 or 2, wherein the holding unit, the exhaust gas when the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio also it holds SO _X in the exhaust gas passing through the passage, only reduced the oxygen concentration in the exhaust gas without releasing SO _X held, NO _X held as stored SO _X amount increases in the holding portion possible amount by utilizing the reducing, the stored SO _X amount of the holding portion is estimated by detecting the amount of NO _X held in the maximum to the holding portion, the exhaust gas during a period of time The present invention is characterized in that an integrated amount of SO _X passing through the passage or a value based on the integrated amount is detected.

According to the NO _x detection device of the first aspect of the present invention, when the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio, the NO _x in the exhaust gas passing through the exhaust gas passage is held, and the exhaust gas A holding unit that releases the reduced NO _x when the oxygen concentration of the holding unit is reduced and is reduced by a reducing substance, a temperature sensor that measures the temperature of the holding unit, and an oxygen concentration reducing unit that reduces the oxygen concentration around the holding unit, After the first set time from when the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio and NO _x is not held in the holding portion, the oxygen concentration around the holding portion is reduced by the oxygen concentration reducing means was initiated, it is reduced by a reducing agent present around the holder by releasing the NO _X held in the holding unit. Thereby, the temperature of the holding part rises due to the reduction of the released NO _x , and after the second set time after the oxygen concentration reduction means starts to reduce the oxygen concentration around the holding part, the first set time While all the NO _x held during this period is released and reduced, the second set time is shorter than the first set time, so the NO _x existing around the holding part is held The temperature rise value of the holding unit after the second set time detected by the temperature sensor corresponds to the amount of NO _x held during the first set time. Since a known ratio of NO _x in the exhaust gas that has passed through the exhaust gas passage during the first set time is held in the holding unit, the temperature rise value is maintained even if the NO _x concentration in the exhaust gas is relatively low. Based on this, it is possible to detect the amount of NO _x in the exhaust gas that has passed through the exhaust gas passage during the first set time relatively accurately.

According to the NO _X detection device according to claim 2 according to the present invention, the NO _X detection device according to claim 1, based on the detected amount of NO _X, is disposed downstream of the holding portion of the exhaust gas passage air-fuel ratio of the exhaust gas is estimated amount of NO _X held in the NO _X catalyst device for holding the NO _X in the exhaust gas when it is leaner than the stoichiometric air-fuel ratio. Thereby, as compared with the case of integrating the amount retention of the NO _X per unit time in the NO _X catalyst device which is set for each engine operating state, a relatively amount of NO _X held in the NO _X catalyst device It can be estimated accurately.

According to the NO _X detection device according to claim 3 of the present invention, the exhaust when the NO _X detection device according to claim 1 or 2, holding part, the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio It also holds SO _x in the exhaust gas that passes through the gas passage, and does not release the held SO _x just by reducing the oxygen concentration in the exhaust gas, but keeps NO _x as the SO _x holding amount increases in the holding section. By utilizing the decrease in the possible amount, it is possible to estimate the amount of SO _x retained in the retaining unit by detecting the maximum amount of NO _x retained in the retaining unit. Since a known ratio of SO _X in the exhaust gas that has passed through the exhaust gas passage during a certain period is held in the holding unit, the NO _X detection device performs a certain period of time based on the estimated SO _X holding amount. It is possible to detect the integrated amount of SO _X that has passed through the exhaust gas passage or a value based on the integrated amount.

The engine exhaust system NO _X detecting device is arranged according to the present invention is a schematic diagram showing. The embodiments of the NO _X sensor according to the present invention is a schematic sectional view showing. 4 is a flowchart for detecting the amount of NO _x passing through the exhaust gas passage per unit time by the NO _x detection device according to the present invention.

FIG. 1 is a schematic view showing an engine exhaust system in which a NO _x detecting device according to the present invention is arranged. In FIG. 1, 1 is an exhaust passage of an internal combustion engine. The internal combustion engine is an internal combustion engine that performs lean combustion, such as a diesel engine or a direct injection spark ignition internal combustion engine. The exhaust gas of such an internal combustion engine, in order to contain a relatively large amount of NO _X, in the exhaust passage 1, NO _X catalyst device 2 for purifying NO _X is arranged.

The NO _X catalyst device 2 carries a NO _X holding material and a noble metal catalyst such as platinum Pt. The NO _x holding material is at least selected from alkali metals such as potassium K, sodium Na, lithium Li and cesium Cs, alkaline earth metals such as barium Ba and calcium Ca, and rare earths such as lanthanum La and yttrium Y. One.

When the exhaust gas has a lean air-fuel ratio, that is, when the oxygen concentration in the exhaust gas is high, the NO _x catalyst device 2 holds NO _x in the exhaust gas well, that is, absorbs it well as nitrate. , NO ₂ adsorbs well. However, it is impossible to hold indefinitely NO _X, before _the NO _X holding amount becomes impossible to retain the more NO _X reached the NO _X holdable amount, as the reproduction process, the air-fuel ratio of the exhaust gas The stoichiometric air-fuel ratio or rich air-fuel ratio is set, that is, the oxygen concentration in the exhaust gas is reduced. As a result, the retained NO _x is desorbed, that is, the absorbed NO _x is released, and the adsorbed NO ₂ is desorbed, and these desorbed NO _x is reduced and purified to N ₂ by the reducing substance in the exhaust gas.

When such NO _X catalyst device 2 occludes SO _X in the exhaust gas as sulfate, since sulfate is a stable substance compared to nitrate, it cannot be released in the regeneration process. The amount of NO _{X that} can be stored decreases (S poisoning). As a result, the S trap device 3 for storing SO _X in the exhaust gas is disposed upstream of the NO _X catalyst device 2 in the exhaust passage 1 to suppress S poisoning of the NO _X catalyst device 2.

Regeneration process of the NO _X catalyst device 2 worsens fuel consumption in order to make the air-fuel ratio of the exhaust gas the stoichiometric air-fuel ratio or a rich air-fuel ratio. Accordingly, the regeneration process is preferably performed to the minimum necessary. For that purpose, it is necessary to accurately estimate the amount of NO _x held in the NO _x catalyst device 2. In general, the amount of NO _x held in the NO _x catalyst device 2 per unit time for each operating state is determined in advance, and the NO _x amount is held in the NO _x catalyst device 2 by integrating the amount of NO _x . Although _the amount of NO _X is estimated, _the amount of NO _X held to advance per defined unit time NO _X catalyst device 2 for each operating condition may differ from actual, such a presumption NO _X catalyst device 2 It is difficult to accurately estimate the amount of NO _x held in the tank.

NO _X detection apparatus 4 of the present embodiment, for example, is disposed between the S trap device 3 and NO _X catalyst device 2, NO passing through per exhaust passage 1 unit time at the position of the NO _X detector 4 _X the amount, i.e., can be detected amount of NO _X flowing into the unit time per NO _X catalyst device 2, thereby the amount of NO _X held in the unit time per NO _X catalyst device 2 is calculated accurately, it becomes possible to accurately estimate the amount of NO _X held in the NO _X catalyst device 2.

FIG. 2 is a schematic cross-sectional view showing an embodiment of the NO _x detection device 4 according to the present invention. In the figure, reference numeral 10 denotes an outer wall of the exhaust passage 1. Reference numeral 41 denotes a temperature sensor such as a thermocouple that constitutes the NO _x detector 4. Reference numeral 42 denotes a NO _x holding part arranged so as to cover the temperature sensing part of the temperature sensor 41. A cylindrical case 43 surrounds the NO _X holding portion 42 and penetrates the outer wall 10 of the exhaust passage 1.

A plurality of opening holes 43 a are formed in the case 43, and exhaust gas that passes through the exhaust passage 1 flows into the case 43 through the opening holes 43 a. 44 is an oxygen pump that reduces the oxygen concentration around the NO _X holding part 42 in the case 43, and is located around the temperature sensor 41 and the space around the NO _X holding part 42 in the case 43 and the low oxygen chamber 45. Isolate. The oxygen pump 44 is made of zirconia or the like, and moves oxygen from the inside of the case 43 to the low oxygen chamber 45 by applying a voltage in the opposite direction to the zirconia oxygen concentration sensor. Thereby, the oxygen concentration around the NO _x holding part 42 in the case 43 can be reduced.

_The NO _X holding section 42 is for holding the NO _X in the exhaust gas, for example, by applying a noble metal catalyst such as _the NO _X holding material and platinum Pt as described above the temperature sensing portion of the temperature sensor 41 Can be formed.

The NO _X detection device 4 configured as described above operates the oxygen pump 44 by an electronic control device (not shown) according to the flowchart shown in FIG. 3 and also detects the temperature of the NO _X holding unit 42 detected by the temperature sensor 41. Is input to the electronic control unit to detect the amount of NO _x passing through the exhaust passage at the position of the NO _x detecting device 4 per unit time.

First, in step 101, it is determined whether or not it is time to detect the amount of NO _x passing through the exhaust passage per unit time by the NO _x detector 4. When this determination is denied, that is, when it is not required to detect the NO _x amount by the NO _x detecting device 4, the process is ended as it is. On the other hand, when the determination in step 101 is affirmed, it is determined in step 102 whether or not all NO _x is released from the NO _x holding unit 42 of the NO _x detecting device 4. The time at all NO _X in _the NO _X holding portion 42 is not held, the process proceeds to step 104 determination is affirmative in step 102. However, when the result of step 102 is negative, the processing to complete release of NO _X from _the NO _X holding unit 42 after performing the step 103, the process proceeds to step 104.

In step 104, whether _the NO _X holding unit 42 the time t elapsed after all of the NO _X is released in becomes the first set time t1 (e.g. 10 seconds) is determined. This determination is repeated until affirmed. When the determination in step 104 is affirmative, that is, when the elapsed time t from the release of all NO _x in the NO _x holding unit 42 becomes the first set time t1, in step 105, the NO _x detecting device. 4, the temperature T1 of the NO _X holding unit 42 is measured. At this time, the holding portion 42 becomes that occludes NO _X only exhaust gas during a first set time t1. The first set time t1 must only choose not to retain _the amount of NO _X below _the NO _X holding possible amount of the current of the NO _X holding portion 42.

Next, at step 106, as the oxygen concentration reduction process, the oxygen concentration around the NO _X holding unit 43 in the case 43 is reduced by the oxygen pump 44. Next, in step 107, it is determined whether or not the elapsed time t from the start of the oxygen concentration lowering process has become a second set time t2 (for example, 0.5 seconds), and the oxygen concentration is determined until this determination is affirmed. A reduction process is performed. If the determination in step 107 is affirmed, in step 108, the temperature sensor 41 measures the temperature T2 of the NO _x holding unit 42. At this time, NO _X held in _the NO _X holding unit in the first set time t1 is, NO _X when all the reduction of the oxygen concentration of the holding portion 42 around discharge simultaneously _the NO _X holding portion HC of the exhaust gas around And reduced using a reducing substance such as CO.
Ba (NO ₃ ) ₂ + CO → BaCO ₃ + N ₂ + 2O ₂ + heat generation

Thereby, _the NO _X holding portion 42 becomes a possible rise in temperature by reducing the heat of reaction corresponding to _the amount of NO _X held in the first set time t1, in step 109, the temperature rise value of the NO _X holding portion 42, i.e., a temperature T2 which is measured in step 108, based on the difference (T2-T1) between the temperature T1 measured in step 105, NO _X amount held in _the NO _X holding unit in the first set time t1 is calculated, This NO _x amount is a value obtained by multiplying the NO _x amount that has passed through the exhaust passage 1 at the position of the NO _x detecting device during the first set time t1 as a unit time, for example, by a NO _x holding ratio that can be set experimentally. to become, NO _X amount passing through the exhaust passage 1 at a position of the NO _X detection device during a first set time t1, i.e., the NO _X catalyst device 2 during a first set time t1 It is possible to estimate the amount of NO _X to enter relatively accurately. Thus, it is possible to relatively accurately calculate the amount of NO _X held in the unit time per NO _X catalyst device 2, relatively accurately estimate the amount of NO _X held in the NO _X catalyst device 2.

Very wherein the second set time t2 (for example, 0.5 seconds) for implementing the oxygen concentration reduction process, as compared to the first set time t1 (e.g. 10 seconds) to hold the NO _X to _the NO _X holding portion 42 for short, it is not almost reduced in the NO _X is _the NO _X holding portion 42 of such a short time the exhaust gas of _the NO _X holding section 42 around also even been reduced, the first set It is negligible in comparison to the amount of nO _X held in the time t1, little effect on the temperature rise of the nO _X holding unit 42 used in step 109.

In the second set time t2, has been to utilize a reducing substance in the exhaust gas to reduce NO _X that was released from _the NO _X holding unit 42, in order to improve the reduction, NO _X in the case 43 You may make it supply reducing agents, such as HC (fuel), to the holding | maintenance part 42 vicinity.

By the way, the timing for detecting the amount of NO _x passing through the exhaust passage per unit time by the NO _x detecting device 4 may be, for example, when the temperature T2 of the NO _x holding portion 42 is measured in step 108. That is, when was all releases NO _X which is held in the NO _X holding portion 42 in the second set time t2, the next NO _X detection device 4 detects the amount of NO _X passing through the exhaust passage per unit time as time, the first set time t1 by _the NO _X holding unit 42 so as to hold the NO _X, thus, may be the first set time t1 and the second set time t2 are continuously repeated . Thereby, the amount of NO _x flowing into the NO _x catalyst device 2 is continuously estimated, and the amount of NO _x retained in the NO _x catalyst device 2 can be estimated fairly accurately. In addition, the time when the NO _X amount that passes through the exhaust passage per unit time is detected by the NO _X detection device 4 is always the time when the second set time t2 has elapsed, and NO _X is completely discharged from the NO _X holding unit 42. Therefore, it is not necessary to perform the NO _X complete release process of Step 103.

The timing for detecting the amount of NO _x passing through the exhaust passage per unit time by the NO _x detector 4 may be when the engine operating state (at least one of the engine speed and the engine load) has changed. At a steady time when the engine operating state does not change, the amount of NO _x flowing into the NO _x catalyst device per unit time can also be made constant. However, if the engine operating state changes, the amount of NO _x flowing into the NO _x catalyst device per unit time also changes, so that a new amount of NO _x flowing into the NO _x catalyst device per unit time is estimated. Moreover, it is preferable to detect the amount of NO _x passing through the exhaust passage per unit time by the NO _x detection device 4.

In this case, the NO _X holding portion 42 by the time elapsed from the time lapse of the second set time t2 of the last to NO _X in the exhaust gas is occluded, the determination in step 102 is negative, the first to retain only nO to _X holder 42 nO _X at set time t1, must be completely releasing nO _X from the nO _X holding portion 42 in front of it. At this time, for example by the oxygen pump 42 longer than the second set time t2 to reduce the oxygen concentration of the NO _X holding section 42 around the NO _X held in _the NO _X holding unit 42 it is sufficient to completely released.

The timing for detecting the amount of NO _x passing through the exhaust passage per unit time by the NO _x detector 4 may be set every set time. Even in this case, the NO _X complete release process of Step 103 is performed as necessary.

By the way, since the NO _X holding part 42 of the NO _X detecting device 4 of the present embodiment is formed by the NO _X holding material and the noble metal catalyst carried on the NO _X catalyst device 2, as described above, the exhaust gas is exhausted. SO _X in the gas is also retained as sulfate. Sulfate is a stable substance compared to nitrate, and is not released from the NO _x holding part only by reducing the oxygen concentration. Thereby, NO SO _X amount of retained _X holding portion 42 is in one of increasing, holding possible amount of the NO _X or SO _X in _the NO _X holding unit 42 for constant is, _the NO _X holding portion 42 in the SO _X When the holding amount increases, the NO _X holdable amount decreases.

Maximum By utilizing this, that by holding the NO _X to maximize the NO _X holding unit 42 in the current, and to release all of the NO _X from _the NO _X holding portion 42 held in _the NO _X holding portion 42 If a limited amount of NO _x is detected, the amount of SO _x retained in the NO _x retaining unit can be calculated. The stored SO _X amount is SO _X amount held in _the NO _X holding unit in a predetermined period up to the present from the start of the internal combustion engine to the first exhaust at the position of the NO _X detection device during the predetermined period This corresponds to a value obtained by multiplying the SO _X amount passing through the passage 1 by, for example, an experimentally set SO _X retention ratio. Thus, the amount of SO _x flowing into the NO _x catalyst device 2 during this fixed period can be detected. Further, it is possible to average the SO _X amount flowing into NO _X catalyst device 2 between the SO _X average concentration or a certain period of the exhaust gas flowing into the NO _X catalyst device 2 and the like are also detected during the predetermined period. For example, when the amount of SO _x flowing into the NO _x catalyst device 2 exceeds the set amount, the S trap device 3 may be replaced.

In this way, when detecting the amount of SO _X held in the NO _X holding unit 42 of the NO _X detecting device 4, it is necessary to cause the NO _X holding unit 42 to hold NO _X to the maximum extent, that is, NO _X holding. the section 42, to hold the NO _X in the exhaust gas during the longer than the first set time t1, the _the NO _X holding portion 42, of the NO _X current of the NO _X holdable amount to be held There must be.

Maximum amount of NO _X in _the NO _X holding section, when the release all NO _X held in the maximum is reduced simultaneously, increasing the temperature of the NO _X holding portion by the reduction reaction heat, _the NO _X holding portion 42 It is detected based on the temperature rise value. To the _the NO _X holding unit 42 to release NO _X is the oxygen pump 44 it is sufficient to decrease around the oxygen concentration of the NO _X holding portion 42. Further, at the time of reproduction processing of the NO _X catalyst device 2 is the stoichiometric air-fuel ratio or a rich air-fuel ratio of the exhaust gas as described above, at this time, it is all also NO _X held in _the NO _X holding unit 42 release Therefore, it is reduced by the reducing substance in the exhaust gas. Thus, prior to starting the regeneration process of the NO _X catalyst device 2, if maximally hold the NO _X in _the NO _X holding portion 42 of the NO _X detection device 2, the temperature of the NO _X holding portion reproduction processing o'clock rise value is a value corresponding to the amount of NO _X held in the maximum current of the NO _X holding part, can be as described above, it detects the stored sO _X amount of current of the NO _X holding portion .

Of course, the air-fuel ratio of the exhaust gas may be the stoichiometric air-fuel ratio or the rich air-fuel ratio irrespective of the regeneration process of the NO _X catalyst device 2 in order to detect the current SO _X holding amount of the NO _X holding unit. In order to set the air-fuel ratio of the exhaust gas to the stoichiometric air-fuel ratio or rich air-fuel ratio, the combustion air-fuel ratio is set to the stoichiometric air-fuel ratio or rich air-fuel ratio, additional fuel is supplied into the cylinder in the expansion stroke or exhaust stroke, or What is necessary is just to supply a fuel to an exhaust passage.

1 exhaust passage 2 NO _X catalyst device 4 NO _X detection device 41 temperature sensor 42 NO _X holding unit 43 casing 44 oxygen pump

Claims (3)

Reducing substance air-fuel ratio of the exhaust gas holds the NO _X in the exhaust gas passing through the exhaust gas passage when it is leaner than the stoichiometric air-fuel ratio, and releases the NO _X held to decrease the oxygen concentration in the exhaust gas And a temperature sensor for measuring the temperature of the holding unit, and oxygen concentration reducing means for reducing the oxygen concentration around the holding unit, wherein the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio. Then, after the first set time from when NO _X is not held in the holding part, the oxygen concentration reducing means starts to reduce the oxygen concentration around the holding part, and the oxygen concentration reducing means holds the holding The temperature increase value of the holding part after the second set time after the start of the decrease in oxygen concentration around the part is detected by the temperature sensor, and the second set time is shorter than the first set time. And before NO _X detection device and detecting the amount of NO _X in the exhaust gas passing through the exhaust gas passage between the basis of the temperature rise value the first set time. Based on the detected amount of NO _X, NO _X catalyst air-fuel ratio of the exhaust gas is disposed downstream of the holding portion of the exhaust gas passage to retain the NO _X in the exhaust gas when it is leaner than the stoichiometric air-fuel ratio The NO _x detection device according to claim 1, wherein the amount of NO _x held in the device is estimated. The holding unit also holds SO _x in the exhaust gas that passes through the exhaust gas passage when the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio, and the SO that is held only by reducing the oxygen concentration in the exhaust gas. without releasing _X, by utilizing the fact that the more _the NO _X holding amount capable stored SO _X amount increases is reduced in the holding unit, by detecting the amount of NO _X held in the maximum to the holding portion 3. The SO _x holding amount of the holding unit is estimated, and an integrated amount of SO _X that has passed through the exhaust gas passage during a predetermined period or a value based on the integrated amount is detected. NO _X detection device according to.

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