Device for reducing nitrogen oxide content in exhaust gases of internal combustion engines
Es wird eine in sich abgeschlossene Vorrichtung zur Reduzierung des NOx-Gehaltes im Abgas einer mit Luftüberschuß betriebenen Brennkraftmaschine, die nach dem SCR-Prinzip arbeitende Reduktions-Katalysatoren (11, 12) vorsieht, beschrieben, wobei das Reduktionsmittel-Steuergerät (1) keinen Rückgriff a...
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Sprache: | eng ; fre ; ger |
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Zusammenfassung: | Es wird eine in sich abgeschlossene Vorrichtung zur Reduzierung des NOx-Gehaltes im Abgas einer mit Luftüberschuß betriebenen Brennkraftmaschine, die nach dem SCR-Prinzip arbeitende Reduktions-Katalysatoren (11, 12) vorsieht, beschrieben, wobei das Reduktionsmittel-Steuergerät (1) keinen Rückgriff auf im Steuergerät vorhandene Daten in der Brennkraftmaschine nehmen muß und der Einbau in ein Fahrzeug stark vereinfacht wird, inbesondere die Nachrüstung bereits im Verkehr befindlicher Fahrzeuge möglich ist.
Temperature and volumetric flow rate sensors (5, 4) are directly connected to the reduction control unit (1). These and the NOx sensor (6) are used to determine the quantity of reductant to be injected. There is no recourse to data stored in the engine management system. Dosing of reductant is controlled as a function of the catalyst operational parameters and the exhaust gas composition. Preferred Features: The reductant is urea, supplied from a tank (2) by a pump (3) to the reductant injection valve (7). The reductant controller (1) is built-onto the supply tank (2). As reductant, fuel may be injected (7), the dosing system being connected to the fuel system. A volumetric flow rate sensor is located in the exhaust gas system. Alternatively, a pressure sensor ahead of the reduction catalyst (11, 12) measures exhaust gas pressure, the value being a measure of volumetric flow rate. Differential pressure is alternatively measured across the reduction catalyst, for the same purpose. The reductant controller is directly connected to another exhaust sensor, sensitive to a further component, e.g. NH3 or HC. The NOx sensor (6) has operational temperature-dependent sensitivity to NH3 and/or HC. The controller is also connected to an engine tachometer, used in conjunction with the monitored volumetric flow rate. The tachometer is inductive, relaying information wirelessly to the controller. Its pickup is inductive, self-powered by induction, and floats with respect to vehicle earth. The sensor sensitive to NH3 is located in the reduction catalyst unit. The controller doses sufficient urea to achieve predetermined maximum NH3 and/or predetermined minimal NOx, as indicated by the NOx sensor. The reduction catalyst comprises two or more units in series, the NOx sensor being upstream of the last. The predetermined NH3 or NOx content is a function of the conversion capacity of the catalyst unit following the sensor. Using urea as reductant, the reductant injection valve |
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