Power plants – Internal combustion engine with treatment or handling of... – Having means analyzing composition of exhaust gas
Reexamination Certificate
2002-12-02
2004-03-09
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Having means analyzing composition of exhaust gas
C060S274000, C073S023310
Reexamination Certificate
active
06701706
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to an exhaust system for the cleaning or purification of an exhaust gas, including an exhaust pipe which conducts the exhaust gas from an internal combustion engine downstream into the environment. The exhaust pipe has a sensor for determining the pollutant concentration at a first position. The invention also relates to a method for determining pollutant concentration in the exhaust gas. Exhaust systems and methods of that type are used in particular in automotive engineering.
Monitoring of exhaust systems is becoming increasingly important due to increasingly stringent exhaust guidelines and statutory limitations, which restrict pollutant concentrations in the exhaust gas that is ultimately released to the environment. In many cases, sensors are used for that purpose, for example to monitor the functionality of components for converting the pollutants in the exhaust gas or transmitting recorded measured values in connection therewith directly to an engine management system, which takes into account the measured data received when controlling the operating performance of the internal combustion engine. The concentrations of various pollutants in the exhaust gas are also measured, in addition to the temperature and pressure of the exhaust gas in the exhaust system. Examples of pollutants of that type are various hydrocarbons or nitrogen oxides. Gas sensors, in particular for determining the concentration of hydrocarbons and nitrogen oxides in the exhaust gas, are particularly temperature-sensitive and pressure-sensitive, with the result that the extent to which they can be used in an exhaust system is limited.
It is known to transmit the recorded measured values to a diagnosis unit in order to monitor the operation of the exhaust system and the functionality of the sensors. The received data are, for example, compared with stored information. If the diagnosis unit identifies malfunctions, they are either displayed or a suitable engine management system is used to determine the cause of the malfunction and counteract it by suitable measures.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide an exhaust-gas purification system with delayed recording of measured values and a method for determining pollutant concentration in exhaust gas, which overcome the hereinafore-mentioned disadvantages of the heretofore-known systems and methods of this general type and which ensure monitoring of an exhaust system even with temperature-sensitive or pressure-sensitive sensors, having recorded measured values being transmitted to an engine management system in such a manner that they are correlated to other measured values.
With the foregoing and other objects in view there is provided, in accordance with the invention, an exhaust system for purifying an exhaust gas, comprising an exhaust pipe conducting exhaust gas from an internal combustion engine downstream into the environment. The exhaust pipe has a first position and a second position. A sensor is disposed at the second position for determining a pollutant concentration at the first position. A time function element is connected to the sensor and to a diagnosis unit for taking into account a time difference between a measured value recording at the first and second positions and transmitting the recorded measured value, correlated to other undelayed measured values, to the diagnosis unit.
As has already been explained in the introduction hereto, known sensors cannot be used at any desired position in an exhaust system. This may make it necessary to position the temperature-sensitive and pressure-sensitive sensors at positions in the exhaust system which are at a distance from the desired measurement position. In this way, the service life of the sensors can be extended.
In most cases, the measured values recorded by the sensors are transmitted to a higher-level diagnosis unit. The measured values are also analyzed in this diagnosis unit. In order to achieve a valid result, in many cases a plurality of measured values are set in a relationship with respect to one another. Therefore, it is particularly important for the corresponding measured values to be correlated to one another in terms of time.
Since the sensor at the second position records the pollutant concentration at a different time than the measured values which are set in relationship with the recorded pollutant concentration, the time difference between an imaginary measured value recording at the first position and the measured value recording which actually took place at the second position, is taken into account with the aid of a time function element. The time difference is not constant, since the flow rate of the exhaust gas in the exhaust system varies as a function of the driving operating state. The time function element ensures that the correct, temporally correlated measured values are set in relationship with one another in the diagnosis unit.
In accordance with another feature of the invention, the sensor for determining the pollutant concentration is a gas sensor. These sensors are particularly temperature-sensitive and pressure-sensitive. Therefore, using a gas sensor close to the engine and directly downstream of a catalytic converter, where temperatures of from 900° C. to 1000° C. prevail, causes problems. The combination of a sensor and a time function element ensures the functionality of the sensor over a long period and at the same time allows the measured values to be analyzed in conjunction with other measured values from the exhaust system.
In accordance with a further feature of the invention, the sensor is suitable for recording the nitrogen oxide concentration in the exhaust gas. In this context, the nitrogen oxide concentration is particularly important, since this pollutant can only be converted with difficulty, especially during the cold-start phase, and it may be necessary to adapt the operating performance of the internal combustion engine accordingly.
In accordance with an added feature of the invention, the sensor is suitable for recording hydrocarbon concentration. This makes it possible, for example, to assess the operating performance of the internal combustion engine, since the concentration of unburnt or only partially burnt hydrocarbons is a measure of the quality of the combustion operations.
In accordance with an additional feature of the invention, the exhaust system has at least one component for at least partially converting the pollutants. It is particularly advantageous to construct at least one component as a catalytic converter. For example, the catalytic converter removes from the exhaust gas carbon monoxide and nitrogen oxide, which are present as a result of incomplete combustion of the fuel. The catalytic converter promotes a reaction between nitrogen oxide and carbon monoxide to form molecular nitrogen and carbon dioxide.
In accordance with yet another feature of the invention, the first position (desired position for taking a measured value) is disposed directly downstream of a component for at least partially converting the pollutants, and the sensor is disposed downstream of a muffler. It is necessary to record measured values directly downstream of a catalytic converter, for example, if the functionality of the catalytic converter is to be monitored. In order to improve the light-off performance of catalytic converters of this type immediately after the internal combustion engine has been started, such catalytic converters are disposed as close as possible to the internal combustion engine, in order for the required temperature for catalytic conversion to be reached very quickly. In addition, the catalytic reaction leads to an increase in the exhaust-gas temperature. Accordingly, the exhaust gas immediately downstream of the catalytic converter is often at a temperature in the region of approximately 1000° C. According to the invention, the sensor is disposed downstream of a muffler and the maximum temperatures of the
Brück Rolf
Maus Wolfgang
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