JP2008121428A - Catalyst deterioration detection device for internal combustion engine - Google Patents

Abstract

The present invention relates to a catalyst deterioration detection device for an internal combustion engine, and an object thereof is to detect a decrease in the purification ability of the catalyst with high accuracy.
It is determined whether or not the catalyst temperature is stable within a detected temperature range (step 102). If it is determined that the catalyst temperature is not stable within the detected temperature range, it is next determined whether or not the catalyst temperature is lower than the detected temperature range (step 104). If it is determined that the catalyst temperature is lower than the detected temperature range, then energization to the heater that heats the catalyst is turned on (step 106). When the heater is turned on and the catalyst temperature is stabilized within the detected temperature range, a predetermined amount of fuel is added to the exhaust gas (step 108), and the catalyst deterioration detection process is started (step 110). When the amount of increase in the catalyst temperature before and after the fuel addition is equal to or greater than the determination value, it is determined that the catalyst is normal. On the other hand, when the temperature increase amount is less than the determination value, it is determined that the catalyst has deteriorated.
[Selection] Figure 4

Description

  The present invention relates to a catalyst deterioration detection device for an internal combustion engine.

  2. Description of the Related Art There is known an exhaust purification system that reduces HC, CO, etc. in exhaust gas by disposing an oxidation catalyst in an exhaust passage of an internal combustion engine. When this oxidation catalyst deteriorates, the ability (oxidation ability) to cause oxidization reaction of the inflowed HC, CO and the like decreases. For this reason, the calorific value by an oxidation reaction decreases. The exhaust gas purification system disclosed in Japanese Patent Laid-Open No. 2005-90324 utilizes this fact to detect deterioration of the oxidation catalyst. That is, in this system, when fuel (HC) is added to the exhaust gas upstream of the oxidation catalyst, if the temperature of the exhaust gas that has passed through the oxidation catalyst is below a predetermined temperature, the oxidation catalyst deteriorates. It is determined that

JP 2005-90324 A Japanese Patent Laid-Open No. 10-184344

  The oxidation capacity (purification capacity) of the catalyst increases with the temperature of the catalyst. For this reason, even if it is a deteriorated catalyst, when the temperature of the catalyst is high, sufficient oxidizing ability is exhibited. On the other hand, when the temperature of the catalyst is low, even a normal catalyst cannot exhibit its oxidizing ability sufficiently. In the conventional exhaust purification system, since this is not sufficiently considered, it is difficult to detect the deterioration of the catalyst with high accuracy, and there is still room for improvement.

  In the future, it is expected that OBD (On-Board Diagnostic) regulations that require automatic diagnosis of failures and deterioration of exhaust purification systems on vehicles will be further strengthened. In order to overcome this stricter regulation, it is necessary to detect the deterioration of the catalyst with higher accuracy.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a catalyst deterioration detection device for an internal combustion engine that can detect a reduction in the purification ability of the catalyst with high accuracy.

In order to achieve the above object, a first invention is a catalyst deterioration detection device for an internal combustion engine,
An exhaust purification catalyst disposed in the exhaust passage of the internal combustion engine;
Catalyst temperature acquisition means for detecting or estimating the temperature of the catalyst;
Catalyst deterioration detection means for executing catalyst deterioration detection processing for detecting deterioration of the catalyst;
Prior to the start of the catalyst deterioration detection process, catalyst temperature control means for controlling the temperature of the catalyst so that the temperature of the catalyst falls within a predetermined detection temperature range;
It is characterized by providing.

The second invention is the first invention, wherein
The catalyst deterioration detecting means includes
Fuel supply means for supplying fuel so that the exhaust gas flowing into the catalyst contains unburned fuel;
Determination means for determining a decrease in the purification capacity of the catalyst based on the temperature increase amount of the catalyst when fuel is supplied by the fuel supply means;
It is characterized by including.

The third invention is the first or second invention, wherein
The catalyst temperature control means includes a heating means for heating the catalyst by a method not involving a chemical reaction with the catalyst.

According to a fourth invention, in any one of the first to third inventions,
The catalyst deterioration detection process is a process for detecting a decrease in the oxidation ability of the catalyst,
The lower limit of the detection temperature range is a temperature equal to or higher than the activation start temperature of the oxidation ability of the catalyst,
The upper limit value of the detection temperature range is a temperature sufficiently lower than a temperature at which the oxidation ability of the catalyst is saturated.

  According to the first aspect of the invention, prior to the start of the catalyst deterioration detection process for detecting deterioration of the exhaust purification catalyst disposed in the exhaust passage of the internal combustion engine, the temperature of the catalyst falls within a predetermined detection temperature range. The temperature of the catalyst can be controlled. This predetermined detection temperature range is set to a temperature range in which a difference in purification ability is likely to be large compared to a normal catalyst even when the degree of deterioration of the catalyst is small. According to the first invention, since the catalyst deterioration detection process can be performed after the catalyst temperature is controlled to fall within such a temperature range, even if the degree of deterioration of the catalyst is small, the deterioration is suppressed. It can be detected with high accuracy.

  According to the second invention, the purification capacity of the catalyst is reduced based on the amount of increase in the temperature of the catalyst when the fuel is supplied so that the exhaust gas flowing into the catalyst contains unburned fuel. Can be determined. Thereby, the purification ability of the catalyst, in particular, the oxidation ability of the catalyst can be accurately determined.

  According to the third aspect of the invention, when the catalyst temperature is controlled within the detection temperature range, the catalyst can be heated by a method that does not involve a chemical reaction in the catalyst. Thereby, since the heating amount does not change depending on the degree of deterioration of the catalyst, the catalyst temperature can be accurately controlled.

  According to the fourth aspect of the invention, when detecting a decrease in the oxidation ability of the catalyst, the lower limit value of the detection temperature range is set to a temperature equal to or higher than the activation start temperature of the oxidation ability of the catalyst, and the upper limit value of the detection temperature range is The temperature can be made sufficiently lower than the temperature at which the oxidation ability of saturates. In such a detected temperature range, even when the degree of deterioration of the catalyst is small, a difference in oxidation ability is likely to be large compared to a normal catalyst. For this reason, even when the degree of decrease in the oxidation ability of the catalyst is small, the decrease can be detected with high accuracy.

Embodiment 1 FIG.
[Description of system configuration]
FIG. 1 is a diagram for explaining a system configuration according to the first embodiment of the present invention. The system shown in FIG. 1 includes a diesel engine 10. In the middle of the exhaust passage 12 of the diesel engine 10, a first catalyst (a catalyst with a heater) 14 and a second catalyst 16 are arranged. Both the first catalyst 14 and the second catalyst 16 have a function as an oxidation catalyst for oxidizing and purifying HC and CO. The second catalyst 16 is a catalyst having a larger capacity than the first catalyst 14. The second catalyst 16 is disposed close to (adjacent to) the downstream side of the first catalyst 14.

  The first catalyst 14 is integrally provided with a heater (electric heater) 18. As a method for installing the heater 18, for example, the catalyst support of the first catalyst 14 is made of metal, and the catalyst support can be used as the heater 18. By energizing the heater 18, the first catalyst 14 can be directly heated. Further, when the first catalyst 14 is heated, the heat is transmitted to the exhaust gas passing through the first catalyst 14. Then, the heated exhaust gas flows into the second catalyst 16 so that the second catalyst 16 is heated. That is, the second catalyst 16 can also be indirectly heated by energizing the heater 18.

  A fuel addition valve 20 for adding fuel to the exhaust gas is installed in the exhaust passage 12 upstream of the first catalyst 14. A temperature sensor 22 that detects the exhaust gas temperature and an air-fuel ratio sensor 24 that detects the exhaust air-fuel ratio are installed near the outlet of the second catalyst 16.

  The system further includes an ECU (Electronic Control Unit) 30. The ECU 30 is electrically connected to the above-described heater 18 and each sensor, and is also electrically connected to various actuators and sensors included in the diesel engine 10.

[Features of Embodiment 1]
In the present system, HC, CO and the like in the exhaust gas discharged from the diesel engine 10 can be purified by oxidizing them with the first catalyst 14 and the second catalyst 16. However, as the first catalyst 14 and the second catalyst 16 deteriorate, their oxidation ability (purification ability) gradually decreases. Therefore, the present system executes a catalyst deterioration detection process as described below in order to detect the deterioration (decrease in oxidation ability) of the first catalyst 14 and the second catalyst 16.

  In the catalyst deterioration detection process, first, a predetermined amount of fuel is added to the exhaust gas by injecting fuel from the fuel addition valve 20. The added fuel undergoes an oxidation reaction (combustion) with oxygen in the exhaust gas in the first catalyst 14 and the second catalyst 16 to generate reaction heat. For this reason, when fuel is added to the exhaust gas, the temperatures of the first catalyst 14 and the second catalyst 16 rise. The temperatures of the first catalyst 14 and the second catalyst 16 are correlated with the exhaust gas temperature detected by the temperature sensor 22. Therefore, the temperature rise amount of the first catalyst 14 and the second catalyst 16 can be obtained from the exhaust gas temperature detected by the temperature sensor 22.

  When the oxidation ability of the first catalyst 14 and the second catalyst 16 is reduced, the ratio of the fuel added to the exhaust gas that is oxidized by the first catalyst 14 and the second catalyst 16 is reduced. That is, the proportion of fuel that passes through the first catalyst 14 and the second catalyst 16 without being oxidized increases. For this reason, even when the same amount of fuel is added to the exhaust gas, if the oxidizing ability of the first catalyst 14 and the second catalyst 16 is reduced, the temperature of the first catalyst 14 and the second catalyst 16 is reduced. The amount of increase will be smaller. Therefore, when the temperature increase amount of the first catalyst 14 and the second catalyst 16 is smaller than that in the normal case, it can be determined that the oxidation ability is reduced.

  FIG. 2 is a diagram illustrating an example of the relationship between the oxidizing ability of the first catalyst 14 and the second catalyst 16 and the temperature of the first catalyst 14 and the second catalyst 16. In FIG. 2, the solid line is a graph when the first catalyst 14 and the second catalyst 16 are normal, and the broken line is a graph when the first catalyst 14 and the second catalyst 16 are slightly deteriorated.

  In general, the oxidation ability of a catalyst has the property that even when the catalyst is deteriorated, it is sufficiently exerted to the same extent as a normal catalyst when the catalyst temperature is increased. In other words, in a situation where the temperature of the catalyst is high, it is difficult for a normal catalyst and a deteriorated catalyst to show a difference in oxidation ability. In particular, as in the example shown in FIG. 2, when the degree of deterioration of the first catalyst 14 and the second catalyst 16 is slight, in a relatively high temperature region (for example, about 300 ° C. or more), a normal catalyst is obtained. In comparison, the oxidation ability is hardly lowered. For this reason, it becomes difficult to detect deterioration of the catalyst.

  On the other hand, in a relatively low temperature region (for example, a region around 250 ° C.) such as the “detected temperature region” in FIG. 2, even if the degree of deterioration is slight, it is smaller than that of a normal catalyst. A relatively large reduction in oxidation ability is observed. Therefore, if the catalyst deterioration detection process is executed when the temperatures of the first catalyst 14 and the second catalyst 16 are within the detected temperature range, the deterioration can be accurately detected even if the degree of deterioration is slight. It becomes. As shown in FIG. 2, the lower limit value of the detected temperature range is preferably set to a temperature equal to or higher than the activation start temperature of the first catalyst 14 and the second catalyst 16 (200 ° C. in the example shown in FIG. 2). The upper limit value of the detection temperature range is preferably set to a temperature sufficiently lower than the temperature at which the oxidizing ability of the first catalyst 14 and the second catalyst 16 is saturated (in the example shown in FIG. 2, about 350 ° C.).

  FIG. 3 is a diagram illustrating an example of temperature changes of the first catalyst 14 and the second catalyst 16 during travel of the vehicle on which the diesel engine 10 is mounted. The solid lines in FIG. 3 indicate the temperature changes of the first catalyst 14 and the second catalyst 16 when the temperatures of the first catalyst 14 and the second catalyst 16 are not controlled, that is, when the heater 18 is always OFF. Since the above-mentioned detection temperature range suitable for detecting catalyst deterioration (decrease in oxidation ability) is narrow, as shown in FIG. 3, the temperatures of the first catalyst 14 and the second catalyst 16 are usually within the detection temperature range. It is rare that a stable state appears. For this reason, there exists a problem that there are few opportunities to perform the above highly accurate catalyst deterioration detection processing.

  In particular, since the exhaust temperature of the diesel engine 10 generally tends to be low, the temperatures of the first catalyst 14 and the second catalyst 16 are often lower than the lower limit value of the detection temperature range as shown in FIG. And as the displacement of the diesel engine 10 is larger, the engine load at the time of traveling becomes relatively smaller, and this tendency becomes more remarkable.

  Therefore, in the present embodiment, when the catalyst deterioration detection process is executed, the first catalyst 14 and the second catalyst 16 are heated by the heater 18 so that the temperatures of the first catalyst 14 and the second catalyst 16 fall within the detection temperature range. Was heated. That is, normally, when the temperature of the first catalyst 14 and the second catalyst 16 is lower than the lower limit value of the detection temperature range, the first catalyst 14 and the second catalyst 16 are heated by the heater 18. The temperature of the first catalyst 14 and the second catalyst 16 is controlled to be stable within the detected temperature range.

When the temperature of the first catalyst 14 and the second catalyst 16 is raised to the detection temperature range, the energy Erg to be added to the exhaust gas from the heater 18 can be calculated by the following equation.
Erg = Ga × κ × (target temperature−inflow gas temperature) (1)

  However, in the above equation (1), Ga is the exhaust gas flow rate. This Ga can be calculated based on an air flow meter signal provided in the diesel engine 10 or the like. κ is the specific heat of the exhaust gas, and is a known value. The “target temperature” is a predetermined temperature within the detected temperature range. The “inflow gas temperature” is the temperature of the exhaust gas flowing into the first catalyst 14. Since the inflow gas temperature correlates with the engine load and the engine speed, it can be calculated based on a map stored in the ECU 30 in advance. Alternatively, the inflow gas temperature may be obtained directly by a temperature sensor provided upstream of the first catalyst 14.

On the other hand, the electric power Ent to be energized to the heater 18 can be calculated by the following formula using the Erg.
Ent = k × Erg (2)

  However, in said Formula (2), k is a constant larger than 1, and is a value regarding the efficiency at the time of electric power being converted into calorie | heat amount.

  The broken lines in FIG. 3 indicate the first catalyst 14 and the second catalyst 14 when the catalyst temperature control is performed in which the electric power Ent calculated by the above equation (2) is supplied to the heater 18 when the inflow gas temperature is lower than the target temperature. 3 is a diagram illustrating an example of a temperature change of a catalyst 16. FIG. When such catalyst temperature control is executed, as shown in FIG. 3, the first catalyst 14 and the second catalyst 16 are used when the exhaust gas temperature is low, for example, when warming up immediately after startup or when the load is low. The temperature can be increased and stabilized within the detected temperature range. Therefore, an opportunity to execute highly accurate catalyst deterioration detection processing can be created.

[Specific Processing in Embodiment 1]
FIG. 4 is a flowchart of a routine executed by the ECU 30 in the present embodiment in order to realize the above function. This routine is repeatedly executed every predetermined time. According to the routine shown in FIG. 4, it is first determined whether or not the detection end flag is ON (step 100). If the detection end flag is ON, it can be determined that the catalyst deterioration detection process has already ended. In this case, since it is not necessary to execute the catalyst deterioration detection process, the current process cycle is ended as it is.

  On the other hand, if the detection end flag is OFF, it is next determined whether or not the temperatures of the first catalyst 14 and the second catalyst 16 are stable within the detected temperature range (step 102). The temperatures of the first catalyst 14 and the second catalyst 16 can be estimated from the exhaust gas temperature detected by the temperature sensor 22. Alternatively, a temperature sensor may be installed on the first catalyst 14 or the second catalyst 16 to directly detect the catalyst temperature.

  If it is determined in step 102 that the temperatures of the first catalyst 14 and the second catalyst 16 are not stable within the detected temperature range, the temperatures of the first catalyst 14 and the second catalyst 16 are then detected. It is determined whether or not it is lower than the range (step 104). As a result, when it is determined that the temperatures of the first catalyst 14 and the second catalyst 16 are not lower than the detected temperature range, the processing from step 102 onward is executed again. On the other hand, when it is determined that the temperatures of the first catalyst 14 and the second catalyst 16 are lower than the detected temperature range, energization to the heater 18 is then turned on (step 106). In this case, the power supply amount to the heater 18 is calculated by the above equations (1) and (2).

  Subsequent to the process of step 106, the process of step 102 and subsequent steps is executed again. When the heater 18 is turned on, the temperatures of the first catalyst 14 and the second catalyst 16 are easily stabilized within the detected temperature range. When the temperatures of the first catalyst 14 and the second catalyst 16 are stabilized within the detected temperature range, the determination in step 102 is affirmed. If the determination in step 102 is affirmative, a predetermined amount of fuel is subsequently added to the exhaust gas from the fuel addition valve 20 (step 108), and the catalyst deterioration detection process is started (step 110). .

  In the catalyst deterioration detection process, first, the temperature rise amounts of the first catalyst 14 and the second catalyst 16 before and after the fuel addition to the exhaust gas are detected. Next, the temperature increase amount is compared with a predetermined determination value. When the temperature rise amount is equal to or greater than the determination value, it is determined that the first catalyst 14 and the second catalyst 16 are normal. On the other hand, when the temperature increase amount is less than the determination value, it is determined that the first catalyst 14 and the second catalyst 16 are deteriorated.

  Following the processing in step 110, it is determined whether or not the catalyst deterioration detection processing has been completed (completed) (step 112). When the catalyst deterioration detection process is completed, the detection end flag is turned ON (step 114). On the other hand, if the catalyst deterioration detection process is incomplete due to some reason (for example, when the catalyst temperature is out of the detection temperature range in the middle), the detection end flag is turned OFF (step 116).

  As described above, according to the present embodiment, the catalyst deterioration detection process can be performed in a state where the temperatures of the first catalyst 14 and the second catalyst 16 are within the detection temperature range. As described above, in the detected temperature range, even if the degree of deterioration is small, a difference in oxidation ability tends to occur. Therefore, even when the degree of deterioration of the first catalyst 14 and the second catalyst 16 is small, the deterioration can be accurately detected. For this reason, it is advantageous in complying with strict OBD regulations.

  Moreover, according to this embodiment, the temperature of the 1st catalyst 14 and the 2nd catalyst 16 is controlled by the heater 18, and the opportunity which the 1st catalyst 14 and the 2nd catalyst 16 exist in a detection temperature range is produced actively. be able to. For this reason, the opportunity to perform the catalyst deterioration detection process can be surely reached, and after the operation of the diesel engine 10 is started, the catalyst deterioration detection can be ended early.

  In the present embodiment, the temperature of the first catalyst 14 and the second catalyst 16 is controlled using an electric heater (heater 18), but a method that does not involve chemical reaction (combustion or the like) in the catalyst, The temperature of the first catalyst 14 and the second catalyst 16 may be controlled by another type of heater as long as the calorific value does not change depending on the degree of catalyst deterioration.

  Further, in the present embodiment, the first catalyst 14 is directly heated by the heater 18 and the second catalyst 16 is indirectly heated. However, the first catalyst 14 and the second catalyst 16 are not heated. The whole catalyst may be directly heated by a heater without distinction. Alternatively, the entire catalyst may be indirectly heated by heating the exhaust gas upstream of the catalyst without directly heating the catalyst with a heater.

  Further, when the temperature of the first catalyst 14 and the second catalyst 16 is higher than the detection temperature range, the temperature of the first catalyst 14 and the second catalyst 16 is detected by cooling the first catalyst 14 and the second catalyst 16. It is good also as controlling so that it may enter in a temperature range. Examples of the mechanism for cooling the first catalyst 14 and the second catalyst 16 include a mechanism for providing a bypass passage that can be cooled by circulating the exhaust gas on the upstream side of the first catalyst 14 and the second catalyst 16. . In this case, the temperature of the first catalyst 14 and the second catalyst 16 can be lowered by flowing the exhaust gas through the bypass passage to cool the exhaust gas.

  In the present embodiment, the first catalyst 14 and the second catalyst 16 are not limited to oxidation catalysts, but may be catalysts such as NOx storage reduction catalysts and three-way catalysts. That is, the NOx occlusion reduction type catalyst and the three-way catalyst also have an oxidizing ability, but the present embodiment can also be applied when detecting a reduction in their oxidizing ability.

  Further, the present invention is not limited to the catalyst deterioration detection device of the diesel engine 10 but can be applied to a catalyst deterioration detection device of a spark ignition internal combustion engine such as a gasoline engine.

  Further, the method of adding exhaust fuel is not limited to the method of using the fuel addition valve 20, but a method of injecting fuel into the cylinder in the exhaust stroke (post injection), or a mixture of a lean combustion cylinder and a rich combustion cylinder. A method or the like may be used.

  In the first embodiment described above, the first catalyst 14 and the second catalyst 16 are the “catalyst” in the first invention, and the fuel addition valve 20 is the “fuel supply means” in the second invention. The heaters 18 correspond to the “heating means” in the third invention. Further, the ECU 30 estimates the temperatures of the first catalyst 14 and the second catalyst 16 based on the output of the temperature sensor 22, so that the “catalyst temperature acquisition means” in the first invention performs the processing of steps 108 and 110. When the “catalyst deterioration detecting means” in the first invention is executed, the “catalyst temperature control means” in the first invention is executed by adding the exhaust fuel. The “determination means” according to the second aspect of the present invention is realized by determining a decrease in the catalytic oxidation capacity based on the amount of increase in the catalyst temperature before and after the above.

It is a figure for demonstrating the system configuration | structure of Embodiment 1 of this invention. It is a figure which shows an example of the relationship between the oxidation ability of a catalyst, and catalyst temperature. It is a figure which shows an example of the temperature change of the catalyst during driving | running | working of a vehicle. It is a flowchart of the routine performed in Embodiment 1 of the present invention.

Explanation of symbols

10 diesel engine 12 exhaust passage 14 first catalyst 16 second catalyst 18 heater 20 fuel addition valve 22 temperature sensor 24 air-fuel ratio sensor 30 ECU

Claims (4)

An exhaust purification catalyst disposed in the exhaust passage of the internal combustion engine;
Catalyst temperature acquisition means for detecting or estimating the temperature of the catalyst;
Catalyst deterioration detection means for executing catalyst deterioration detection processing for detecting deterioration of the catalyst;
Prior to the start of the catalyst deterioration detection process, catalyst temperature control means for controlling the temperature of the catalyst so that the temperature of the catalyst falls within a predetermined detection temperature range;
A catalyst deterioration detection device for an internal combustion engine, comprising: The catalyst deterioration detecting means includes
Fuel supply means for supplying fuel so that the exhaust gas flowing into the catalyst contains unburned fuel;
Determination means for determining a decrease in the purification capacity of the catalyst based on the temperature increase amount of the catalyst when fuel is supplied by the fuel supply means;
The catalyst deterioration detecting device for an internal combustion engine according to claim 1, comprising:   3. The catalyst deterioration detecting device for an internal combustion engine according to claim 1, wherein the catalyst temperature control means includes a heating means for heating the catalyst by a method not involving a chemical reaction in the catalyst. The catalyst deterioration detection process is a process for detecting a decrease in the oxidation ability of the catalyst,
The lower limit of the detection temperature range is a temperature equal to or higher than the activation start temperature of the oxidation ability of the catalyst,
The catalyst deterioration detection device for an internal combustion engine according to any one of claims 1 to 3, wherein the upper limit value of the detection temperature range is a temperature sufficiently lower than a temperature at which the oxidation ability of the catalyst is saturated.

Images