Selective catalytic reduction system

Abstract

A selective catalytic reduction system includes a urea aqueous solution tank to retain a urea aqueous solution to be injected into an exhaust pipe of an engine, a level sensor to detect a solution level height in the tank, a lowpass filter having a signal response characteristic in which a time constant is small when an engine rpm is low and the time constant is larger when the engine rpm is high, with respect to an output signal of the sensor, a remaining amount indicator to indicate a remaining amount of the solution based on an output signal of the sensor processed by the lowpass filter, and a unit to prohibit the engine from being started when the remaining amount of the solution is less than a lower limit value.

Description

TECHNICAL FIELD[0001]The present invention relates to an SCR system that purifies exhaust gas by injecting a urea aqueous solution to the exhaust gas of a diesel vehicle, and more particularly, to an SCR system that can rapidly cancel engine start prohibition after filling the urea aqueous solution as well as preventing improper indication of deficiency of the urea aqueous solution by variation in solution level in a urea aqueous solution tank and unwanted engine start prohibition.BACKGROUND ART[0002]As an exhaust gas purifying system for purifying NOx in the exhaust gas of a diesel engine, an SCR system using a SCR (selective catalytic reduction) apparatus has been developed.[0003]The SCR system supplies the urea aqueous solution to upstream of the exhaust gas of the SCR apparatus, generates ammonia by heat of the exhaust gas, and reduces and purifies NOx on an SCR catalyst by the ammonia (see, for example, Patent Document 1).PRIOR ART DOCUMENTSPatent Documents[0004]Patent Document...

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Benefits of technology

[0012]The present invention provides excellent effects as follows.

[0013](1) Improper indication of deficiency of the urea aqueous solution by variation in a solution level in a u

Problems solved by technology

Therefore, the indication of the remaining amount on an actual solution level is followed with delay.

Although the urea aqueous solution is filled up, when the deficiency of the urea aqueous solution is indicated or the engine is not started, the driver feels a sense of strangeness.

Further, when the urea aqueous solution is being filled up, if the indication of the remaining amount is

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