DE102006055235A1 - Urea water solution's quality detecting method for exhaust gas treatment unit, involves concluding urea water solution to be of inferior quality, in case of deviation of signal from reference value at predetermined threshold value - Google Patents

Abstract

The method involves comparing a signal of an exhaust gas sensor (120) with a predetermined reference value, during a predetermined time period after filling a urea water solution tank (106). The sensor is arranged downstream of a selective catalytic reduction catalyst (103), for determining nitrogen oxide and ammonia concentration. A urea water solution (105) is concluded to be of inferior quality, in case of deviation of the signal from the reference value at a predetermined threshold value.

Description

The The invention relates to a method for detecting the quality of a Urea-water solution.

State of the art

to Reduction of nitrogen oxide emissions from motor vehicles are out Known in the prior art exhaust treatment units, in which a Urea-water solution (HWL), which in a storage device, for example in a Tank, stored in the exhaust line of a combustion unit, For example, an internal combustion engine, is supplied. To reduce The nitrogen oxide emission is the so-called Selective Catalytic Reduction (SCR) method used. Since the HWL by injecting into the exhaust system of the internal combustion engine is consumed in the area of an SCR catalyst over a longer term, it has to be refilled from time to time.

The Reduction of nitrogen oxides is only possible if the urea-water solution is sufficiently high quality having. When filling the HWL tank with a lower quality urea-water solution is against it a reduction of nitrogen oxides in the exhaust gas of the combustion unit not ensured.

by virtue of statutory regulations must vehicles Today's design, an on-board diagnostic unit have all emission-related systems of the vehicle monitored (OBD II). When filling the Urea-water solution tank with a urea-water solution less quality becomes a common error by an on-board diagnostic unit the exhaust treatment unit detected, for example, the error "too low Nitrogen oxide conversion rate. " However, this error can have several causes, for example It can occur if a component in the dosing system is defective SCR catalyst aged, if there is a nitric oxide sensor drift or if just a wrong or a reducing agent of poor quality was refilled. The requirement prescribed in the laws of various states after a precise specification of the error (pin-pointing) can with such a general error statement not be met.

Disclosure of the invention

Advantages of the invention

The inventive method with the features of claim 1 has the advantage that the quality of the urea-water solution recognized can be. This happens because a filling of the Urea aqueous solution reservoir or tanks is detected and, following such filling, a measurement of the exhaust gas composition downstream an SCR catalyst is made. Due to the signal of the Exhaust gas sensor can affect the quality the urea-water solution be closed by the fact that the signal with comparative values is compared and if this taking into account definable thresholds differs from the comparative values, it is concluded that the liquid in the urea water solution tank either no urea-water solution or such a minor quality is.

The filling of the urea water solution tank can by means of a level sensor due to the level be determined by the fact that the level after a restart the combustion unit detected and with a stored value is compared, the immediately before the shutdown of the internal combustion engine is stored. When the level after restarting the combustion unit is greater than the stored Value, must be a filling process have taken place.

In In this case, after the expiry of the aforementioned time interval a Emission measurement downstream made of the SCR catalyst.

Of the level For example, in an internal combustion engine in a memory a control device, in particular a control device of the internal combustion engine get saved.

Brief description of the drawings

embodiments The invention is illustrated in the drawings and in the following Description closer explained.

It demonstrate:

1 an embodiment of an exhaust gas treatment unit, in which the inventive method is used and

2 schematically a flowchart of the method according to the invention.

Embodiments of the invention

In 1 is an embodiment of an exhaust gas treatment unit for nitrogen oxide reduction of Rohabgasstroms 101 a combustion device, not shown, such as a diesel or gasoline engine shown. In 1 is only an example and without limiting the generality of an internal combustion engine with an exhaust treatment illustrated unit for nitrogen oxide reduction with air support, as it can be used for example in trucks. The invention is not limited to those in 1 shown exhaust gas treatment unit limited, but can also be used in conjunction with an exhaust gas treatment unit for nitrogen oxide reduction without air support for trucks and in conjunction with an exhaust gas treatment unit for nitrogen oxide reduction without air support for passenger cars, which are not shown below.

The raw gas flow 101 is optional in an oxidation catalyst 102 pretreated. Preferably in the flow direction behind the oxidation catalyst 102 is by means of a nozzle 104 a urea-water solution (HWL) 105 in the range of an SCR catalyst 103 (Selective-Catalytic-Reduction) largely evenly diluted.

In a manner not shown is in the SCR catalyst 103 in a first reaction stage in the HWL 105 contained urea with water to ammonia and carbon dioxide reacted or hydrolyzed. In a second reaction stage, ammonia and in particular nitrogen monoxide and nitrogen dioxide are converted into nitrogen and water.

According to 1 can both the hydrolysis and the reduction in a structural unit 103 respectively. Alternatively, however, may be provided in a manner not shown, both for the hydrolysis and for the reduction of a separate, preferably catalytically active unit.

In general, in a manner not shown, other components such as (diesel soot) particulate filter or the like for the exhaust gas treatment of the crude gas stream 101 be provided.

For the stoichiometric conversion of the HWL 105 with the nitrogen oxide emissions of the internal combustion engine is in a tank 106 stored HWL 105 by means of a pump 107 and a control valve 108 , a metering valve 109 under pressure, which may for example be between 20 to 25 bar fed. For the injection of the HWL 105 In addition, preferably, an atmospheric air flow 110 by means of a pump 111 and a pressure accumulator 112 and a control valve 113 the metering valve 109 fed. The HWL Lufteindüsung in the exhaust stream 101 is realized in such a way that a largely uniform flow of the SCR catalyst 103 is reached. Optionally, this advantageous flow elements such as baffles or the like in the SCR catalyst 103 be provided.

In the tank 106 is a level sensor 117 arranged, the level of the HWL 105 detected. Next to the level sensor 117 can be more sensors, such as a pressure sensor 114 and / or a temperature sensor 116 be provided, which can also be used to determine the level. The signals from these sensors become a control device 115 , For example, a control unit 115 fed, in which the level is determined. The Tank 106 is by means of a fuel filler neck 118 largely gas-tight.

Since now the HWL 105 in the tank 106 To produce the above-described reactions for the reduction of nitrogen oxides in the exhaust gas is consumed over a certain period of time, it must be refilled within certain intervals. The refilling takes place by opening the closure 118 and filling the tank 106 ,

If now a HWL 105 inferior quality or no HWL 105 in the tank 106 is filled, the reduction of nitrogen oxides in the exhaust gas is not possible. To the quality of the tank 106 filled HWL 105 to recognize, the following is used in conjunction with in 2 explained procedure.

First, it checks if there is a filling of the tank 106 was carried out. This is done by measuring the level by means of the level sensor 117 in one step 202 and comparing this level with a stored value stored immediately before the engine is shut down in one step 205 , When in step 205 it is determined that the detected value is equal to or less than the stored value, there is no filling of the tank 106 in front. If the opposite is the case, a filling of the tank is closed and signaled. It then takes place after a predetermined time interval has elapsed, which is detected by recording the time in one step 210 and queries in one step 220 Whether the time has exceeded a predetermined period of time is determined, a measurement of the composition of the exhaust gas flow 109 by means of the sensors 120 . 121 in one step 230 ,

In step 240 be through the sensors 120 . 121 detected values compared with comparison values stored in a memory device (not shown) of the controller 115 are stored. It is understood that intervals around the comparison values are taken into account by setting appropriate threshold values and it is examined whether the measured values lie within these intervals. Comparison values may be operating point-dependent variables as well as signals which characterize the efficiency of the SCR catalytic converter, signals which characterize the maximum control limit of the metering valve or else the sticko xid concentration in the exhaust. If this is the case, in step 260 concluded that the HWL 105 has a sufficiently high quality and there is no error entry in a fault memory. However, if this is not the case, that is, if exhaust limits are not met, those with a suitable HWL 105 sufficiently high quality would have to be achieved in step 270 concluded that the HWL 105 has a lower quality and there is an error entry in a fault memory in step 280 before the procedure is terminated. By the method described above is a recognition of the quality of the HWL 105 possible without having to use expensive and therefore expensive HWL quality sensors for this purpose.

Claims (4)

Method for detecting the quality of a urea-water solution (HWL) ( 105 ) an exhaust gas treatment unit for the implementation, in particular for the reduction of nitrogen oxide compounds, an exhaust gas stream ( 101 ) a combustion device, in particular a diesel internal combustion engine, wherein during a predefinable period of time after filling a HWL tank ( 106 ) the signal of at least one downstream of an SCR catalyst ( 103 ) arranged exhaust gas sensor ( 120 . 121 ) is compared with predeterminable comparison values for determining the nitrogen oxide or ammonia concentration, and in the event of a deviation of the signal from the comparison values by predefinable threshold values to a HWL (FIG. 105 ) inferior quality is closed. A method according to claim 1, characterized in that as comparison values one or more of the following variables is used: - operating point-dependent variables, - signals which the efficiency of the SCR Katlysators ( 103 ), signals indicating the maximum control limit of a metering valve ( 109 ) for the addition of the HWL ( 105 ), - the nitrogen oxide concentration in the exhaust gas. A method according to claim 1 or 2, characterized in that the filling of the HWL tank ( 106 ) by detecting the level by means of at least one sensor ( 116 . 114 ), in particular a fill level sensor ( 117 ) is compared by comparing the measured level with a level value stored before the combustion device is switched off, and it is then concluded that it has been filled when the detected level value is greater than the value stored before the combustion device was switched off. A method according to claim 3, characterized in that the level of the HWL tank in a memory of a control device ( 115 ) of the combustion device, in particular in a control unit of an internal combustion engine is stored.