DE102006033027A1 - Method for operating SCR-catalytic converter's dosing device e.g. for combustion engine, involves determining amount of reagent material in engine duct system - Google Patents

Abstract

A SCR- catalytic converter operating method utilizes a dosing device (110) via a duct system (141) for dosing a reagent material into the exhaust stream. For determining the amount of the reagent material present in the duct system , the filling- and/or emptying-rate for the duct system is determined from the operating variables of the dosing device (110).

Description

State of the art

The The invention is based on a method for operating a metering device an SCR catalyst according to the preamble of the independent claim 1.

Around especially future ones legal requirements regarding To meet the nitrogen oxide emissions of motor vehicles, exhaust gases need an exhaust treatment be subjected. To reduce nitrogen oxide emissions of Internal combustion engines, in particular of diesel engines, but also of Petrol engines, among other things, the so-called Slective Catalytic Reduction (SCR) method used. Here, the exhaust system is a defined amount of Reducing agent urea or a urea-water solution (HWL) was added. For the stoichiometric Sales of ammonia generated from urea in the exhaust system with the existing in the exhaust nitrogen oxides, the HWL is the exhaust system the internal combustion engine metered. In this case, in a first reaction stage, especially in the exhaust line of urea contained in the HWL hydrolyzed with water to ammonia and carbon dioxide. In a second Reaction stage reduces the ammonia contained in the exhaust line Nitrogen oxides to nitrogen, wherein as a byproduct water is generated.

The In this case, reagent is conveyed by a conveyor, also referred to as a conveyor module, controlled by a control device, in particular for the control unit of the internal combustion engine, via a Pressure line arranged in the exhaust line of the internal combustion engine Metering valve supplied and in a finely atomized Spray jet injected in the area of an SCR catalyst. The pipe system includes in motor vehicles line lengths of several meters, for example at a middle class vehicle 4 to 5 in.

Of the Freezing point of the reagent is about -11 ° C. When falling below this Temperature must therefore be ensured that the piping system between the pump, which is part of the conveyor, and the Dosing valve is emptied so far that no reducing agent after to shut down the system in the hydraulic components can damage that way on the conveyor module, avoid the lines and / or the metering valve.

From the prior art, for example from the DE 101 39 122 A1 Now, an exhaust gas treatment unit has become known in which the level in the tank is detected by means of a level sensor. However, this does not allow any conclusions about the present in the line system reagent.

Disclosure of the invention

Advantages of the invention

The inventive method with the characteristics of the independent Claim 1 has the opposite the advantage of being a precise one Detection of the amount of the reagent contained in the conduit system by determining the filling and / or Discharge rate of the line system from operating variables of the metering allows.

By those in the dependent Claims listed measures are advantageous developments and improvements of the independent claim specified method possible.

So is the filling and / or emptying rate preferably from the drive signal of a metering valve the metering device and the drive signal of a feed pump the metering determined. It goes without saying that more Sizes, which the volume of a reagent delivery device and the conduit system characterizing operating variables and at least one of the reagent itself characterizing size in the Provision taken into account become. These sizes are but not changeable, but immutable, the Conveyor and the conduit system and the reagent characterizing Sizes. The im Line system existing reagent is thus made exclusively the variable drive signal of the metering valve and the variable Control signal of the feed pump certainly. That way you can Flow sensors or other means for detecting the flow account in the management system. Since the drive signal of the feed pump and the metering valve of the metering device in each case the power Characterize the pump and the metering valve allows the method according to the invention, in a particularly advantageous manner in case of failure or power fluctuation the pump and / or the metering valve to respond immediately and the Fill / empty rate very accurately.

A advantageous embodiment provides that dependency the filling / emptying rate from the drive signal of the feed pump and the drive signal of the metering valve of the metering device in a map are stored.

The The amount of reagent present in the conduit system is preferred determined by an integrator, which determines the time integral of the feed / discharge rate forms.

This integrator is according to an advantage Embodiment when entering the state filling / emptying initialized. In this way, the amount of reagent added or removed from the line system is detected at each filling / emptying operation.

Brief description of the drawings

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

It demonstrate:

1 schematically a metering device, in which the inventive method is used;

2 a flowchart of a first embodiment of the method and

3 a flowchart of another embodiment of the method according to the invention.

Embodiments of the invention

A metering device, shown in 1 , Has a conveyor also called conveyor module 110 on top of that by a control unit 120 is controllable. The conveyor 110 promotes from a tank 130 a reagent, such as HWL (urea-water solution) via a suction line 132 , The reagent is passed through a metering valve 112 , For example, a 4/2-way valve of a feed pump 114 supplied and under a predetermined pressure by a pressure regulator 116 is adjustable, a pressure line 141 supplied to them in a conventional manner by a metering valve 140 into the (not shown) exhaust tract of an internal combustion engine in the region of an SCR catalyst inject. The injection takes place by spraying in the finest droplets (spray). Excess reagent is passed through the pressure regulator 116 via a return line 138 again your tank 130 fed. As 1 it can be seen by the control unit 120 both the metering valve 112 through an input signal 221 and the delivery pump 114 through an input signal 222 depending on a the pressure in the pressure line 141 characterizing signal 142 , which by a pressure sensor 117 captured and the control unit 120 is supplied, controllable.

In the suction line 132 is also a filter 111 intended. The injection into the exhaust tract of an internal combustion engine takes place as in the DE 101 39 142 A1 , in particular paragraphs [0038] to [0056], to which reference is made in full in the present case.

To determine the in the line system, in particular in the pressure line 141 existing reagent now the fill rate and / or the discharge rate can be detected in the manner described below.

In 2a the flow of the method for determining the filling rate is described schematically. An arithmetic unit 210 of the control unit 120 becomes the input signal 221 of the metering valve 112 as well as the input signal 222 the feed pump 114 fed. These input signals are, for example, preferably pulse-width-modulated signals. The arithmetic unit 210 then determines the fill rate 212 , that is the filling quantity per time. This will - as in 2 B shown schematically - in a level of the reagent in the line system, in particular in the pressure line 141 converted. For this purpose, the computing device 210 next to the input signal 221 of the metering valve 112 as well as the input signal 222 the feed pump 114 also the density of the reagent 231 , the pipe diameter 232 , the line length 233 as well as the entire volume 234 the conveyor 110 supplied and this in corresponding steps 251 to 254 in the filling rate 212 converted.

Leg entry into the state Filling this is an integrator 260 initialized with the last valid fill status. The integrator forms a time integral over a predefinable period of time. The integrator value corresponds to the current level after filling the pressure line 141 , In this way, the current filling status in the pressure line is determined.

If emptying the pressure line 141 takes place, becomes an emptying factor 235 additionally considered as it is schematic in 3 is shown. In this case, there are more calculation steps 255 . 256 required, leading to a signal 213 , which characterizes the emptying rate, lead. This emptying rate is again in the integrator 260 after initial initialization of the integrator 260 integrated over time and in this way the outflow of the reagent from the pressure line 141 certainly.

It should be mentioned at this point that the input signal of the metering valve 221 by means of a map 223 or converted by appropriate arithmetic operations in an opening cross section or the like. In a corresponding manner, a delivery curve becomes 224 and from the input signal 222 the feed pump 114 determined a flow rate per time. This flow rate is corrected in a known per se by the density of the medium. From the length and the inner diameter of the pressure line their volume is determined. The flow rate is determined by the volume of the pressure line and the entire delivery unit 110 divided, multiplied by the factor 100 and with a correction factor resulting from the so-called dutycycle of the metering valve 112 and the characteristic of the metering valve 223 calculated, multiplied.

The determined level in the pressure line 141 gets into a in the control unit 120 provided EEPROM written and is so for example in an emergency stop as a stored value at a restart available.

Claims (5)

Method for operating a metering device ( 110 ) of an SCR catalyst for the reduction of nitrogen oxides in an exhaust gas flow, in particular of an internal combustion engine, wherein by means of the metering device ( 110 ) via a pipeline system ( 141 ) a reagent is metered into the exhaust stream, characterized in that for determining the in the line system ( 141 ) amount of the reagent present the filling and / or emptying rate of the line system from operating variables of the metering device ( 110 ) is determined. A method according to claim 1, characterized in that the filling and / or emptying rate from the drive signal ( 221 ) of a metering valve ( 112 ) of the metering device ( 110 ) as well as from the drive signal ( 222 ) a feed pump ( 114 ) of the metering device ( 110 ) is determined. A method according to claim 2, characterized in that the dependence of the filling / emptying rate of the drive signal ( 221 ) of the metering valve ( 112 ) of the metering device ( 110 ) as well as from the drive signal ( 222 ) of the feed pump ( 114 ) of the metering device ( 110 ) in at least one characteristic diagram ( 223 ) is stored. Method according to one of the preceding claims, characterized in that in an integrator ( 260 ) the time integral of the delivery / discharge rate is formed and from this to the amount of in the line system ( 141 ) existing reagent is closed. Method according to Claim 4, characterized in that the integrator ( 260 ) is initialized by the current fill level when entering the Fill / Empty state.