JP2894135B2 - Degradation diagnosis device for HC adsorbent in exhaust gas purification device of internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine, and more particularly to a technique for diagnosing deterioration of an adsorbent in an apparatus provided with an adsorbent for temporarily adsorbing HC in exhaust gas.

[0002]

2. Description of the Related Art In an internal combustion engine for a vehicle, HC (unburned gas) and CO in exhaust gas are oxidized to H ₂ O and CO ₂ in an exhaust passage, while NO _X is converted to N ₂ for purifying exhaust gas. An exhaust purification catalyst called a three-way purification catalyst for reducing and purifying is interposed. By the way, among the harmful components in the exhaust gas, H
The amount of C discharged is particularly susceptible to the exhaust gas temperature. In other words, even when a noble metal catalyst is used, generally 3
Requires a catalyst temperature of 00 ° C or higher. Therefore, in an exhaust gas purifying apparatus provided only with the three-way catalyst, it is difficult to purify HC by the catalyst when the exhaust gas temperature is low, such as immediately after a cold start of the engine.

[0003] Therefore, as an exhaust purification device for vehicles,
As disclosed in JP-A-63-68713, there has been proposed a catalyst in which an adsorbent for adsorbing HC is interposed in an exhaust passage upstream of the exhaust purification catalyst. In this device, the adsorbent adsorbs HC at a low temperature and desorbs the adsorbed HC at a high temperature, and utilizes the adsorbent in a part of an exhaust passage upstream of an exhaust purification catalyst. The interposed bypass passages are connected in parallel to selectively open and close the main passage and the bypass passage. The bypass passage is opened at a low temperature before the exhaust purification catalyst is activated, and HC is added to the adsorbent. After the bypass passage is once closed, the exhaust gas purifying catalyst is activated after the temperature becomes high, and then the bypass passage is opened again so that the adsorbed HC is desorbed and purified by the exhaust gas purifying catalyst. It has become. As the adsorbent, for example, a monolithic carrier coated with zeolite has been proposed because zeolite has excellent adsorbability.

[0004]

However, when such an adsorbent deteriorates due to exposure to exhaust heat, etc.,
The adsorption capacity decreases, and the desorption temperature shifts to a lower temperature side. Therefore, if desorption is started under the same desorption conditions as a new product that has not deteriorated, HC in the adsorbent will flow into the exhaust purification catalyst at a stretch, and the exhaust purification catalyst will not be able to process the exhaust gas, resulting in an increase in HC emission. There was something to do. Even if the exhaust temperature at the start of desorption is lowered, the activation of the exhaust purification catalyst is insufficient this time, so that the HC purification performance also falls.
Therefore, conversely, the desorption start temperature is increased to sufficiently promote the activation of the exhaust gas purification catalyst to enhance the purification performance. If the purification is still not possible, air is introduced into the exhaust gas to promote the oxidation. It is required to use what is done together. Further, if the deterioration has progressed to a point where HC cannot be completely purified, the adsorbent must be replaced.

However, it is necessary to know the degree of deterioration of the adsorbent when performing any fail-safe processing. However, diagnosis of such deterioration of the adsorbent has not been conventionally performed. The present invention has been made in view of such conventional problems, and provides an apparatus for diagnosing deterioration of an HC adsorbent in an exhaust gas purification apparatus of an internal combustion engine, which is capable of highly accurately diagnosing the state of deterioration of the adsorbent. With the goal.

[0006]

Therefore, an apparatus for diagnosing deterioration of an HC adsorbent in an exhaust gas purifying apparatus for an internal combustion engine according to the present invention comprises, as shown in FIG. Exhaust temperature detecting means for detecting the exhaust gas temperature on the inlet and outlet sides of the adsorbent, and the exhaust gas temperature on the adsorbent inlet side and the exhaust flow rate during the dew point period of the exhaust based on the exhaust gas temperature state on the adsorbent outlet side. An actual supply calorie equivalent value computing means for computing a value corresponding to the actual supply calorie supplied from the exhaust gas to the adsorbent, and the total amount of HC adsorbed on the adsorbent under predetermined adsorption conditions based on the engine operating state. Estimated HC
A total adsorption amount estimating means, and a standard for calculating a value corresponding to a standard supply heat amount estimated to be supplied from the exhaust gas to the non-degraded adsorbent during the dew point period of the exhaust gas based on the estimated total HC adsorption amount. The apparatus includes a supply heat amount equivalent value calculating means, and a deterioration degree detection means for detecting the degree of deterioration of the adsorbent based on the calculated standard supply heat amount equivalent value and the actual supply heat amount equivalent value. And

In addition, the actual supply heat amount equivalent value calculation means and the standard heat amount equivalent value calculation means calculate the actual dew point time and the standard dew point time maintained in the dew point state under the same operating condition by the respective supply heat amounts, and The degree detecting means may be configured to detect the degree of deterioration of the adsorbent by shortening the actual dew point time with respect to the standard dew point time.

[0008]

The HC adsorbing total amount estimating means detects the engine operating state such as the load and the rotational speed detected by the engine operating state detecting means when the HC adsorbing is performed under predetermined conditions such as when the engine coolant temperature is constant. The total amount of adsorption of HC is estimated and calculated based on this. The standard supply calorie equivalent value calculation means calculates, for example, a calorie (standard supply calorie) or a value corresponding to the calorie (standard supply calorie) supplied to the adsorbent during the exhaust dew point period due to the moisture adsorbed by the adsorbent with respect to the different total adsorption amounts of HC in advance. The dew point time under standard conditions (standard dew point time) and the like are obtained, and values such as the standard heat supply amount or the dew point time with respect to the estimated HC adsorption amount are calculated.

On the other hand, the actual amount of heat supplied to the adsorbent during the dew point period based on the inlet temperature of the adsorbent and the exhaust flow rate (which can be substituted by the intake air flow rate or load, etc.) or a value corresponding thereto is the same as above. Dew point time under certain conditions
(Actual dew point time) is calculated. The deterioration degree detecting means detects the degree of deterioration of the adsorbent based on the ratio of the actual supply heat amount to the standard supply heat amount or the shortened time of the actual dew point time with respect to the standard dew point time.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 2 showing the configuration of one embodiment of the present invention, an exhaust gas purifying catalyst (three-way catalyst) having a function of purifying pollutants in exhaust gas under a predetermined high temperature condition is provided in an exhaust passage 2 of an internal combustion engine 1. 3) is interposed, and a part of the exhaust passage 2 upstream of the exhaust gas purifying catalyst 3 is connected to the main passage 4 in parallel with the main passage 4 and has a function of adsorbing HC at a predetermined low temperature condition. And a bypass passage 6 having an adsorbent 5 interposed therebetween. At the branch point on the upstream side between the main passage 4 and the bypass passage 6, an electromagnetic control for continuously controlling the degree of opening of the main passage 4 and the bypass passage 6 in conjunction with each other to control the split ratio of exhaust gas. Valve 7 is interposed. The control valve 7 may be provided at a branch point on the downstream side, or may be provided on both the upstream side and the downstream side.

The engine 1 is equipped with an air flow meter 9 for detecting an intake air flow rate Q in an intake passage 8 and an engine cooling water temperature (water temperature) T in a water jacket.
A water temperature sensor 10 for detecting _W is mounted, and a rotational speed sensor for detecting an engine rotational speed N to a distributor or the like.
11 is installed. These sensors constitute operating state detecting means. Further, the temperature sensor 12 as an exhaust temperature detection means for detecting the respective exhaust temperature T _E is mounted on the inlet side and the outlet side of the adsorbent 5, the detection signals from these sensors to the control unit 14 Is entered.

Further, the bypass passage 6 and the exhaust purification catalyst 3
A secondary air supply passage 16 for supplying the secondary air discharged from the electric pump 15 is connected between the second air supply path and the second air supply path. The control unit 14 controls the adsorption and desorption of HC in the exhaust gas based on the detection signals from the various sensors, detects the degree of deterioration of the adsorbent 5, and desorbs the adsorbent 5 in accordance with the degree of deterioration. The start condition and the drive of the electric pump 15 are controlled to adjust the amount of secondary air.

The operation of detecting the degree of deterioration of the adsorbent 5 by the control unit 14 will be described with reference to the flowcharts shown in FIGS. Here, the characteristics of the adsorbent 5 will be described. The adsorbent adsorbs both HC and moisture, and as the adsorbent deteriorates, the amount of adsorbed HC decreases. At this time, the performance of adsorbing moisture also decreases as does the amount of adsorbed HC. For this reason, when observing the exhaust temperature downstream of the adsorbent, the amount of water adsorbed in the adsorbent varies greatly depending on the degree of deterioration, resulting in a difference in the exhaust dew point period downstream of the adsorbent.

In general, when high-temperature exhaust gas passes through a low-temperature adsorbent, the moisture in the exhaust gas, which is initially in a supersaturated state due to a decrease in the exhaust temperature, is condensed on the adsorbent while the exhaust gas rises. Although the temperature is observed, when the temperature rises to the dew point of the moisture in the exhaust gas, the exhaust gas temperature becomes substantially constant. That is, when the temperature rises to the dew point of the moisture adsorbed by the adsorbent, the exhaust temperature becomes substantially constant. That is, the latent heat of vaporization of the moisture adsorbed by the adsorbent and the calorific value of the exhaust gas are balanced, and the exhaust gas temperature does not change. Thereafter, when the adsorbed moisture has been vaporized, the exhaust gas temperature rises again.

Therefore, as a result of the amount of water adsorbed on the adsorbent depending on the degree of deterioration, the temperature rise dead zone time (exhaust dew point period) from the dew point of the exhaust temperature downstream of the adsorbent differs. FIG. 3 shows a routine for estimating the total amount of HC adsorbed on the adsorbent 5 and calculating the standard dew point time based on the estimation.
That is, this routine corresponds to the HC adsorption total amount estimating means and the standard supply heat amount equivalent value calculating means.

Step (S in the figure; hereinafter the same) 1
Now, the detected engine speed N _{and the} basic fuel injection amount T _P
And read the water temperature T _W. In step 2, the water temperature T _W is compared with HC start temperature of 40 ° C. And
If it is determined that T _W = 40 ° C., the process proceeds to step 3, and
The HC adsorption prediction coefficient K _HC in the current operating region (x) determined by the engine speed N and the basic fuel injection amount _TP is determined from the map for 40 ° C. Here, the HC adsorption prediction coefficient K _HC, advance a value corresponding to the ratio for the basic fuel injection quantity T _P of the amount of HC is predicted to adsorb to the adsorbent 5 when remained in the operating region unit time experiments And is stored for each corresponding operating region of the map. Further, such maps are prepared for the water temperature of 40 ° C. and for the temperature of 20 ° C.

In step 2, it is determined that the temperature is lower than 40 ° C.
In this case, the process proceeds to step 4 where the water temperature T _WIs below 20 ° C
Is determined. It is determined that it is higher than 20 ° C in step 4.
If so, proceed to step 5 and use the above for 20 ° C and 40 ° C
Of HC adsorption in the corresponding operating region from two types of maps
Coefficient K _HC, And the detected water temperature T_WH according to
C adsorption prediction coefficient K_HCIs interpolated between the two search values
We ask by doing.

In step 4, the water temperature T _W is 20 ° C.
If it is determined as follows, the process proceeds to step 6, where the HC adsorption prediction coefficient K _HC is searched from the map for 20 ° C. Next, the routine proceeds to step 7, where the integrated value SUM of the HC adsorption prediction coefficient K _HC
Is freely rewritten and stored in the RAM for each operation area, and the integrated value SUM _X of the corresponding operation area (x) is retrieved from the map.

In step 8, the HC determined in step 7
Prediction coefficient K_HCIntegrated value SUM up to the previous time_XI asked this time
HC adsorption prediction coefficient K_HCBy adding the values of
Value SUM_XTo update. This HC adsorption operation is performed.
Water temperature T_WRises, and in step 2, the water temperature T _WIs 40 °
If it is determined to be higher than C, the process proceeds to step 9 where the suction operation is performed.
Immediately after, that is, determine whether or not the suction operation was performed last time.
You.

If it is determined that the adsorption has just been performed, the process proceeds to step 10, where the total sum of the integrated value SUM _X of the HC adsorption prediction coefficient K _HC stored in all the operation regions of the RAM map is calculated. The total sum of the integrated value SUM _X corresponds to the total amount of HC adsorbed from the start of the adsorption of HC to the end thereof. Finally, go to step 11 and step 10
Calorific value Q _st corresponding to the total amount of adsorbed HC obtained in
The standard dew point time T _st and the standard dew point time T _st are retrieved experimentally in advance from a map stored in the ROM. Here, the standard supply heat quantity _Qst is defined as a time period during which the exhaust gas temperature downstream of the adsorbent 5 is at the dew point temperature of HC under a constant load condition when the adsorbent 5 has not deteriorated with respect to the total HC adsorption amount. The amount of heat expected to be supplied from the exhaust gas to the adsorbent 5, and the standard dew point time T
_“st” is a predicted time of a period at the exhaust dew point temperature.

Next, a routine for calculating the amount of heat supplied from the exhaust gas to the adsorbent 5 when desorbing the HC adsorbed by the adsorbent 5 will be described with reference to the flowchart shown in FIG. That is, this routine corresponds to the actual supply heat amount equivalent value calculation means. In step 21, it is determined whether or not the water temperature T _W has reached a temperature at which the desorption of HC starts.

If it is determined that the desorption start temperature has been reached, that is, if desorption has started, the process proceeds to step 22,
It is determined whether or not the exhaust temperature downstream of the adsorbent 5 is equal to or lower than the exhaust dew point temperature due to moisture in the exhaust. If it is determined to be kept below the dew point temperature proceeds to step 23, it reads the inlet temperature t _in and the basic fuel injection quantity T _P of the adsorbent 5 detected by the temperature sensor 12.

[0023] At step 24, accumulating the amount of heat supplied to the adsorbent 5 each time on the basis of said inlet temperature t _in the basic fuel injection quantity T _P. That is, the inlet temperature t _in the temperature of the exhaust gas introduced into the adsorbent 5, since the basic fuel injection quantity T _P is a value corresponding to the amount of exhaust gas introduced into the adsorbent 5 per each time, these The amount of heat supplied each time is determined by the product of the values, and the total amount of the amount of heat supplied from the start of desorption is determined by integrating them. Note that this routine is applied when it is performed in synchronization with engine rotation, it may be used intake air flow rate Q detected by the air flow meter in place of the basic fuel injection quantity T _P when executed every unit time .

Then, as the total amount of heat supplied to the adsorbent 5 increases, the adsorbed HC becomes supersaturated, and
When it is determined that the exhaust gas temperature downstream of the adsorbent 5 exceeds the dew point temperature, the routine proceeds to step 25, where the total heat quantity supplied up to that time, that is, the total heat quantity supplied to the adsorbent 5 during the dew point period is determined. . Specifically, since the latest value obtained in step 24 corresponds to this value, this value may be read.

In step 26, the actual dew point time _Tr is calculated based on the total amount of heat supplied and the inlet temperature of the adsorbent 5 obtained in step 25. This actual dew point time _Tr is obtained as follows. By dividing the time T _in the case of total heat supplied Q _t calculated in step 25 is the dew point temperature or less, determining an actual unit time supplied heat quantity Q _tan. On the other hand, the standard supply heat quantity Q obtained by the flowchart of FIG.
_By dividing _st by the standard dew point time T _st , a standard unit time supply heat quantity Q _sttan is obtained. In that case, considering the amount of heat released from the adsorbent 5, the value obtained by multiplying the supplied heat amount by the supplied heat amount per unit time is a value close to the value that actually contributes to the heating of HC during the dew point period, and The predicted calorific value that is predicted to have contributed to the heating of the adsorbed HC is obtained as k · Q _t · Q _tan. Is obtained as k · Q _st · Q _sttan . Value real dewpoint time T _r divided by comparing heat value the predicted heat value to the standard dew point time T _st to decrease in response to the deterioration of the adsorbent _{5 (Q t · Q tan)} ) / (Q st · _Qsttan ).

Next, a routine for judging the degree of deterioration of the adsorbent 5 based on the calculation results and adjusting the HC desorption start condition based on the judgment results will be described with reference to FIG. That is, this routine includes deterioration degree detecting means.
In step 31, the standard dew point time T of the actual dew point time _Tr is calculated.
calculating a shortened time ΔT (= T _st -T _r) for _st.

In step 32, the degree of deterioration is obtained by searching a ROM map stored in advance by obtaining the relationship between the reduced time ΔT and the degree of deterioration based on the shortened time ΔT. When it is determined that there is almost no deterioration, the same desorption lower limit load at the time of non-deterioration, that is, the load at the time of starting desorption, for example, the lower limit of the intake negative pressure, is maintained, and the secondary air is introduced. Is not performed (step 33).

If there is any deterioration, the desorption lower limit load and the amount of secondary air introduced are set in accordance with the determined degree of deterioration (steps 34 to 38). Specifically, in the case of the deterioration degree 1 having the smallest deterioration degree, the desorption lower limit load is -45.
0 mmHg, the secondary air introduction rate is 20 l / min, and as the degree of deterioration increases, the lower limit of desorption is -400 mmHg at the deterioration degree 2, 25 l / min at the secondary air introduction rate, and Separation lower limit load is -300mmHg, secondary air introduction amount is 35
Liters / min, Degradation level 4-270mmHg
, The secondary air introduction rate is 50 liters / min, the degradation lower limit load is -250mmHg and the secondary air introduction quantity is 50 liters at the deterioration degree 5.
Adjust so as to increase both the lower desorption load and the amount of secondary air introduced, such as / min.

With this configuration, the amount of adsorbed HC is estimated based on the amount of heat supplied to the adsorbent 5 and the exhaust dew point time due to moisture adsorbed on the adsorbent 5 in proportion to HC. 5 can be detected with high accuracy, and the higher the degree of deterioration, the greater the desorption start load, the higher the exhaust gas temperature, and the larger the amount of secondary air introduced to increase the amount of HC in the exhaust gas purifying catalyst 3. Since HC is desorbed in a state where the oxidizing function is high, the amount of HC emission can always be well controlled.

It should be noted that a warning may be issued for the deterioration of the adsorbent, and further different warnings may be issued according to the degree of deterioration. Also,
In this embodiment, the degree of deterioration is detected by a shortened time from the standard dew point time obtained by dividing the predicted calorie value by the comparative calorie value and multiplying the dew point time, but the calorie predicted value is divided by the comparative calorie value. Since the value itself is also an index of the degree of deterioration of the adsorbent 5, a method of detecting the degree of deterioration may be used.

[0031]

As described above, according to the present invention, the degree of deterioration of the adsorbent can be detected with high accuracy, and accordingly, a change in HC desorption conditions or a warning corresponding to the degree of deterioration can be issued. It is possible to emit.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration and functions of the present invention.

FIG. 2 is a diagram showing a system configuration according to an embodiment of the present invention;

FIG. 3 is a flowchart showing a routine for calculating the total amount of adsorbed HC and the standard dew point time in the embodiment.

FIG. 4 is a flowchart showing a routine for calculating an actual dew point time.

FIG. 5 is a flowchart showing a routine for determining the degree of deterioration of the adsorbent.

[Explanation of symbols]

 Reference Signs List 1 internal combustion engine 2 exhaust passage 3 exhaust purification catalyst 4 main passage 5 adsorbent 6 bypass passage 7 control valve 9 air flow meter 10 water temperature sensor 11 rotation speed sensor 12, 13 temperature sensor 14 control unit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ identification code FI F01N 3/24 F01N 3/24 E 3/32 301 3/32 301A (58) Investigated field (Int.Cl. ⁶ , DB name ) F01N 3/08-3/32

Claims (2)

(57) [Claims] An exhaust system of an engine has an adsorbent having a function of adsorbing HC in exhaust gas at a predetermined low temperature condition and a function of purifying pollutants in exhaust gas containing HC at a predetermined high temperature condition. An exhaust gas purifying catalyst, wherein the HC is adsorbed to the adsorbent in a low temperature state before the activation of the exhaust gas purifying catalyst, and the HC adsorbed by the adsorbent in a high temperature state after the exhaust gas purifying catalyst is activated is removed. In an exhaust gas purifying apparatus for an internal combustion engine, wherein the exhaust gas purifying catalyst is separated and separated, an operating state detecting means for detecting an engine operating state, and an exhaust temperature detecting means for detecting an exhaust gas temperature at an inlet and an outlet of an adsorbent, respectively. And the actual amount of heat supplied to the adsorbent from the exhaust gas based on the exhaust gas temperature on the adsorbent inlet side and the exhaust gas flow rate during the dew point period of the exhaust gas detected based on the exhaust gas temperature state on the adsorbent outlet side. Actual supply calorie phase to calculate the value Value calculating means, HC total adsorbing amount estimating means for estimating the total amount of HC adsorbed on the adsorbent under predetermined adsorption conditions based on the engine operating state, and the dew point period of the exhaust gas based on the estimated total HC adsorbing amount. Standard supply calorie equivalent value computing means for computing a value corresponding to the standard supply calorie value estimated to be supplied from the exhaust gas to the non-degraded adsorbent; and the calculated standard supply calorie equivalent value and the actual supply calorie value. A deterioration degree detecting means for detecting the degree of deterioration of the adsorbent based on the equivalent value; and a deterioration diagnosis apparatus for the HC adsorbent in the exhaust gas purifying apparatus for the internal combustion engine, comprising: 2. The actual supply heat amount equivalent value calculating means and the standard heat amount equivalent value operation means calculate an actual dew point time and a standard dew point time maintained in a dew point state under the same operating condition by respective supply heat amounts, and The HC adsorbent deterioration diagnosis apparatus according to claim 1, wherein the degree detecting means detects the degree of deterioration of the adsorbent by shortening the actual dew point time with respect to the standard dew point time.