Patent Grant
6901742
This is a U.S. national stage of application No. PCT/EP00/05821, filed on Jun. 23, 2000. Priority is claimed on that application and on the following application:
Country: Germany, Application No.: 199 32 715.7, filed Jul. 16, 1999.
The invention pertains to a process for detecting the state of a catalyst system in an exhaust gas channel of an internal combustion engine of a motor vehicle.
It is known that catalysts, especially so-called 3-way catalysts, can be placed in the exhaust gas channel to purify the exhaust gas of the internal combustion engine. When an air-fuel mixture undergoes combustion, pollutants such as soot particles, nitrogen oxides (NOx), carbon monoxide (CO), and incompletely burned hydrocarbons (HCs) are formed in varying proportions. Reducing agents, i.e., CO, HCs, and H2, are oxidized on the catalysts with oxygen and/or nitrogen oxides to form water and carbon dioxide. Oxidizing agents such as NOx, however, are reduced on the catalysts with the help of reducing agents to form nitrogen.
It is also known that sensors can be assigned to a catalyst system of this type to detect, for example, the percentage of a certain gas component in the exhaust gas (lambda probes, NOx sensors) or to measure a temperature (temperature sensors). The way in which such sensors function and their location in the catalyst system are known.
During the dynamic operation of an internal combustion engine, the conversion rate for the pollutants deteriorates over the course of time as a result of reversible and irreversible damage to the catalysts. It is therefore known that sensors can be used to detect the degree of damage to the catalyst system, in that, for example, an NOx emission downstream of the catalyst system is compared with an NOx emission upstream of the catalyst system. To correct reversible damage, appropriate countermeasures are then usually initiated such as the regeneration of the catalyst in a reductive atmosphere. When the irreversible damage exceeds a predetermined threshold, it will be necessary under certain conditions to perform expensive maintenance work.
The disadvantage of the known processes is that, during the dynamic operation of the internal combustion engine, especially during acceleration phases, the variables on which the detection of the state of the catalyst system is based fluctuate widely. Thus, during periods of high engine power demand, the NOx emissions also increase. Thereafter, it is possible for the threshold values for the degree of damage to the catalyst system to be exceeded briefly, even though such severe damage is not actually present. As a result of this incorrect diagnosis, it is possible under certain conditions for unnecessary regeneration or maintenance procedures to be initiated.
The task of the present invention is to provide a way of detecting the state of the catalyst system independently of the dynamic operation of the engine (driving cycle).
This task is accomplished according to the invention by the process for detecting the state of the catalyst system in that:
To compensate for statistical outliers, it is advantageous to form an average characteristic value from a predetermined number of characteristic values. As a function of the characteristic value or the average characteristic value, a maintenance signal can then be generated when, for example, a predetermined threshold value is exceeded.
The total energy output of the internal combustion engine can be detected in a manner known in and of itself by the use of suitable sensors and made available by an engine control unit as a measurement signal. To the same end, however, it is also possible to detect variables which are equivalent to the power output such as in particular a cumulative quantity of air. It has been found that a change in the total energy output is associated with a proportional change in selected operating parameters of the catalyst system.
The operating parameters of the catalyst system which are especially suitable include the catalyst temperature and the amount of HCs, CO, O2, or NOx in the exhaust gas. These operating parameters can be detected as HCs, CO, O2, or NOx concentrations by known means with the use of sensors (lambda probes, NOx sensors) installed in the catalyst system and obtained on the basis of calculated or measured volume flow rates. In the process according to the invention, it is sufficient, for example, to determine the amount of NOx by means of an NOx sensor installed downstream of the catalyst.
In a preferred embodiment of the process, the state of the catalyst system is detected within an acceleration phase of the motor vehicle. In addition, the detection of the state can also be made to depend on whether or not the operating mode of the internal combustion engine is within a predetermined lambda region or on whether the catalyst temperature is in a predetermined temperature range.
The invention is explained in greater detail below on the basis of the associated drawings:
During the combustion process of an air-fuel mixture in the internal combustion engine 16, pollutants are formed in varying proportions, which are converted in the catalyst 18 in the course of a conversion reaction. Thus, for example, NOx is reduced, and CO and HCs are oxidized. The extent to which the conversion reaction takes places in the catalyst 18 can be derived from a conversion rate. This can be determined, for example, by a comparison of a NOx value upstream with an NOx value downstream of the catalyst 18 (by the use of the NOx sensors 22, 23). The upstream and downstream lambda values of the exhaust gas detected by the lambda probes 20, 21 can be used in a similar manner. The process according to the invention, however, also makes it possible to diagnose the catalyst 18 with the use of only one NOx sensor 23 installed downstream of the catalyst 18.
If the conversion rate of the catalyst 18 is low, then reversible or irreversible damage to the catalyst can be present. Reversible damage includes, for example, sulfur poisoning, a coating of soot, or the oxidation of the catalyst components. Suitable regeneration measures may be able to repair reversible damage of this kind.
In contrast, irreversible damage, such as that caused by corrosive processes, leads to a permanent decrease in the conversion rate, and when they exceed a certain level must therefore be corrected by maintenance measures.
In the process according to the invention, the operating parameters of the catalyst system 12 are detected by means of the sensors and/or calculated on the basis of suitable models in the known manner. In addition, selected operating parameters of the internal combustion engine 16 are also determined by known means. Thus, a total energy output of the internal combustion engine 16 is acquired over a predetermined period of time. Because the ratio of the at least one operating parameter of the catalyst system 12 to the total energy output behaves in a proportional manner, it is possible to detect the state of the catalyst 18 independently of the engine power by calculating a characteristic value k which reflects this ratio.
If the vehicle is in an acceleration phase, it is then determined in step S3 whether or not the catalyst temperature is in a predetermined temperature range. In addition, a lambda value of the exhaust gas must also be within a predetermined lambda range (step S4). If these two conditions are satisfied, the time period of the detection of state is fixed in step S5, and the number n of detection of state procedures is possibly defined also.
As previously explained, the operating parameter of the catalyst system 12 is detected in step S6 with the help of the existing sensors. For this purpose, especially the catalyst temperature and the mass of HCs, CO, CO2, or NOx in the exhaust gas are suitable. In addition, the total energy output of the internal combustion engine 16 is also measured over the predetermined time period, either directly or alternatively on the basis of a power-equivalent variable such as a cumulative air quantity.
A ratio of the at least one operating parameter of the catalyst system 12 to the total energy output is used in step S7 to calculate a characteristic value k.
In the exemplary embodiment being discussed here, the determination of the characteristic value is repeated n times to compensate for statistical outliers (step S8), and in step S9, an average characteristic value km is formed as the average value of the n characteristic values k. Then, in step S10, the average characteristic value km is compared with a predetermined threshold value. If the average characteristic value km exceeds the threshold value, it is then possible for a maintenance signal to be generated in step S11, which can be used, for example, for an on-board diagnosis procedure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 199 32 715 | Jul 1999 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP00/05821 | 6/23/2000 | WO | 00 | 2/12/2002 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO01/06223 | 1/25/2001 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5088281 | Izutani et al. | Feb 1992 | A |
| 5341642 | Kurihara et al. | Aug 1994 | A |
| 5400592 | Mukaihira et al. | Mar 1995 | A |
| 5526643 | Mukaihira et al. | Jun 1996 | A |
| 5595061 | Toyoda | Jan 1997 | A |
| 5722236 | Cullen et al. | Mar 1998 | A |
| 5724809 | Mitsutani et al. | Mar 1998 | A |
| 5746049 | Cullen et al. | May 1998 | A |
| 5842341 | Kibe | Dec 1998 | A |
| 5845489 | Dohta et al. | Dec 1998 | A |
| 5884476 | Hirota et al. | Mar 1999 | A |
| 5916130 | Nakae et al. | Jun 1999 | A |
| 5966930 | Hatano et al. | Oct 1999 | A |
| 6082101 | Manaka et al. | Jul 2000 | A |
| 6199374 | Hirota et al. | Mar 2001 | B1 |
| 6513322 | Ohuchi et al. | Feb 2003 | B2 |
| Number | Date | Country |
|---|---|---|
| 42 43 339 | Jun 1993 | DE |
| 195 27 774 | Feb 1996 | DE |
| 196 46 008 | May 1997 | DE |
| 197 32 167 | Jan 1998 | DE |
