Measuring and testing – Simulating operating condition – Marine
Reexamination Certificate
1999-11-01
2002-09-17
Dombroske, George (Department: 2855)
Measuring and testing
Simulating operating condition
Marine
C073S023320, C060S277000
Reexamination Certificate
active
06450018
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a process and a device for monitoring and observation of the aging of a catalytic converter in the exhaust gas of internal combustion engines, for example in motor vehicles, and for registration of the times of the largest emission of hazardous materials of the internal combustion engine.
Catalytic converters in the exhaust gas system of internal combustion engines first begin, after reaching a relatively high operating temperature, to convert the hazardous materials in the exhaust gas, i.e., hydrocarbons, carbon monoxide, and nitrogen oxides, largely into non-hazardous materials. In the first time interval after the internal combustion engine is started, the hazardous materials can pass through the catalytic converter in a practically unhindered manner. Therefore, the newer exhaust gas specifications provide for measurement cycles, which especially include cold and warm start-up phases. It is apparent therein that during these measurement cycles the major part of the hydrocarbon emission arises during the cold start phases. In order to reduce the emission of hazardous materials, a low “light-off temperature” of the catalytic converter, and thus after starting, as short as possible a “light-off time” without exhaust gas cleaning, must be sought in particular. Many proposals have already been made for reducing the light-off time.
In order to check the operation of the catalytic converter by OBD (on board diagnosis), many tests are made using sensors, especially for hydrocarbons (CH
x
) and for nitrogen oxides (NO
x
). Measurements using expensive measurement systems (with flame ionization detectors: FID) show, however, that after commercial, hot, new exhaust gas catalytic converters or ones that have already been used for a longer time, at least the CH
x
-concentrations are exceptionally small. These concentrations cannot be measured in a fully certain manner, even with the FID, and are much less able to be quantitatively determined using sensors for CH
x
or NO
x
thus far known. Therefore, it is also difficult to use these mechanisms to track the aging of the catalytic converter by any gradual increase in the CH
x
concentration in the exhaust gas after the catalytic converter.
In order to assess the aging of the exhaust gas catalytic converters, a series of processes have been proposed, in which the hazardous materials concentrations in the exhaust gas are not measured directly. Frequently, the necessary oscillation between rich and lean in the fuel supply is not only regulated using a lambda sensor, which is an oxygen sensor, before the catalytic converter, but also, its effect is tracked using a second lambda sensor after the catalytic converter (see German patent publications DE 23 04 622, DE 24 44 334, DE 35 00 594, DE 41 39 560, DE 42 11 116, DE 43 37 793). Therein, certain charging programs on the catalytic converter system and different switching operations of the signals are used in order to be able to assess the functioning ability of the catalytic converter. Furthermore, it has been proposed to monitor the catalytic converter activity with one temperature sensor shortly before the catalytic converter and another one within the catalytic converter (DE 26 43 739). These proposals generally refer to the operating condition of the catalytic converter system and produce no direct statement about the light-off of the catalytic converter.
The aging of the exhaust gas catalytic converter can be noticed, however, especially in the increase of its light-off temperature, and thus also of the light-off time. Therefore, it has already been proposed to determine the light-off temperature of the catalytic converter and to assess the functional ability of the catalytic converter in this way. It is assumed therein that the temperature in the exhaust gas catalytic converter increases more quickly as soon as the conversion begins, so that the light-off temperature as well as the time span until the beginning of the conversion can be read directly from the temperature-time curve and can be compared to predetermined threshold values (DE 42 11 092). It should be advantageous if the temperature is determined particularly in the area of the catalytic converter system, which is decisive for the warm-up emission (DE 43 30 997). However, the light-off temperature is not represented clearly at all in the temperature-time curve; it is possibly blurred by endothermic desorption processes during the light-off. With the gradual aging of the catalytic converter, the light-off temperature is less and less recognizable. Therefore, these processes are evidently not adequate. As a gradual process, the aging cannot be followed, using the processes known thus far, up to the point at which the catalytic converter is declared to be functionally inoperative.
On motor test stands the light-off of the catalytic converter can be clearly observed, using expensive stationary FID-devices, by the drastic drop of the CH
x
-concentration in the exhaust gas. On board motor vehicles correspondingly repeatedly reliable observations for checking the aging of exhaust gas catalytic converters and the hazardous materials emission have thus far not been possible using simple mechanisms.
SUMMARY OF THE INVENTION
It is an object of the invention to eliminate the disadvantages of the prior art, in particular to provide a process with the corresponding device by which the aging of exhaust gas catalytic converters can not only be monitored on occasion, but also over its entire gradual progression, and which at the same time leads to a quantity that is characteristic for individual starting phases or for the total of the hazardous materials emitted in the start phases.
This object is achieved according to the present invention by a process wherein, after the start of the internal combustion engine, the light-off temperature of the catalytic converter is detected, using a temperature measuring sensor in the catalytic converter, as the temperature at which a sensor for oxygen, carbon dioxide, water vapor or combustible materials in the exhaust gas after the catalytic converter indicates the light-off of the catalytic converter by a signal change as a result of a sudden change of the concentration of the material or material mixture for which the sensor is sensitive, and wherein the light-off time is measured from the start-up of the internal combustion engine to the sensor-indicated light-off of the catalytic converter. The light-off temperature is measured at the exact point in time at which the change in the concentration of the material or material mixture in the exhaust gas detected by the sensor goes through an extreme value, where this extreme value can be obtained by calculating the differences of the sensor signals directly measured in equivalently short time intervals, or mathematical expressions calculated therefrom, or concentrations calculated thereby.
The sensor-indicated light-off temperature as well as the light-off time are measured externally in workshops or monitoring stations and/or determined in the motor vehicle and displayed on board. Advantageously, the values determined after every start-up will be continuously saved on board and processed into statements about the aging and hazardous material emission. As a sensor, one is used that requires a shorter time for heating to operating temperature than the exhaust gas catalytic converter and can immediately follow the concentration changes very quickly. If such prerequisites are not provided, the heating up of the sensor to its operating temperature is to be provided before start-up.
It is advantageous if, as the sensor for the determination of the light-off of the catalytic converter, an oxygen sensor is used in which the catalytic activity of the measuring sensor is smaller than the conventional lambda sensors. In particular, it is expedient that the oxygen sensor used be brought to a temperature at which its combustion gas sensitivity is smaller than its oxygen sensitivity.
It is further advantageous if th
Akin Gump Strauss Hauer & Feld L.L.P.
Dombroske George
Herneus Electro-Nite International N.V.
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