WO2012072666A1

WO2012072666A1 - Method for determining a current fill quantity of a liquid in a container, in particular for a motor vehicle

Info

Publication number: WO2012072666A1
Application number: PCT/EP2011/071354
Authority: WO
Inventors: Paul Rodatz; Michael Nienhoff; Ingo Koops; Tino Arlt
Original assignee: Continental Automotive Gmbh
Priority date: 2010-12-01
Filing date: 2011-11-30
Publication date: 2012-06-07
Also published as: DE102010062302A1

Abstract

The invention relates to a method for determining a current fill quantity (V_t) of a liquid (100) in a container (10), in particular the current residual fill quantity (V_t) of a reducing agent (100) in a reducing agent container (10) of an SCR dosing device of a motor vehicle, wherein a presence of liquid (100) at a measurement site (112) on/in the container (10) is determined by means of a discontinuously or discretely operating fill level sensors, wherein the current fill quantity (V_t) of the liquid (100) in the container (10) is concluded on the basis of a temporal characteristic (Char; f, pw) of a signal (S₁₁₀) of the fill level sensor (110) resulting from sloshing of the liquid (100) in the container (10).

Description

description

Method for determining a current filling quantity of a liquid in a container, in particular for a motor vehicle

The invention relates to a method for determining a current filling quantity of a liquid in a container, in particular the current residual filling quantity of a reducing agent in a reducing agent container of an SCR metering device of a motor vehicle.

In an operation of an internal combustion engine, for. As that of a motor vehicle, exhaust gas is produced, which contains pollutants such as hydrocarbon (HC), carbon monoxide (CO), nitrogen oxides (NO _x ) and particles. For various pollutants exist statutory regulations that limit pollutant emissions during operation of the internal combustion engine. In order to comply with these legal regulations, it is usually necessary to purify the exhaust gas produced. For this purpose, an exhaust gas purification system is usually used, which contains one or a plurality of catalysts, different gas sensors ^¬ off, and in the case of a diesel engine usually a particulate filter. In the case of lean-burn engines (diesel engines or gasoline lean-burn engines) special, nitrogen oxide reducing processes based on nitrogen oxide storage catalysts or

SCR catalysts used.

SCR (Selective Catalytic Reduction) refers to the technique of selective catalytic reduction of nitrogen oxides in exhaust gases. The chemical reaction of the reduction is selective, ie not all exhaust gas components are reduced, only the nitrogen oxides. SCR catalysts require a reducing agent, usually ammonia (NH ₃ ), for nitrogen oxide reduction. The ammonia is usually by injection or injection of a urea-water solution and its hydrolysis in Exhaust tract of the engine generates and then fed to the SCR catalyst. A metering of the reducing agent is effected by a timing of a metering valve, wherein the reducing agent is provided by a pump and a pressure regulator with a defined pressure from the metering valve. The metered addition of the reducing agent must be continuously monitored as an overdose causes emissions of ammonia and underdosing may lead to excessive nitrogen oxide emissions.

To ensure the continuous availability of ammonia in such an SCR emission control system reliable monitoring of a level of the reducing agent in the reducing agent tank is necessary. If the level drops below a predetermined value, then the driver of the motor vehicle should be made visually and / or acoustically aware of the container, z. As part of the next refueling, to fill again. Furthermore, it should be possible to conclude from a change in the level of a consumption of the reducing agent, thereby improving the control of the

SCR procedure or a diagnosis of an associated one

To allow metering device.

Conventional equipment with a level sensor with float and potentiometer, as is commonly used for

Fuel tanks are used for application in aqueous urea solution because of the conductivity of the reducing agent, a corrosivity and crystallization during drying out problematic. In existing systems, the level is determined by comparatively short and repeated measurements of the electrical resistance between two well-conductive electrodes (stainless steel rods). The electrical resistance results from the limited conductivity of the reducing agent solution between the electrodes. Thus, the electrical resistance is in principle indirectly proportional to the immersion depth of the electrodes.

DE 10047 594 A1 discloses a method and a device for determining a level of a liquid in a container, in particular a reducing agent in a Re ^¬ duktionsmittelbehälter. A discreet working

Fill level sensor comprises three electrodes, wherein a bare, functioning as a ground electrode reference electrode, an electrically insulated level electrode and an electrically insulated reference electrode are provided. By means of the level sensor, the level of the liquid in the container can be determined in three places, for which the

Level electrode is freed at both and the reference electrode only at its free Längsendendabschnitt of their respective insulating material.

It is an object of the invention to provide an improved method by which a level or a fill volume or volume of a liquid in a container can be determined in a simple manner. This should be as simple as possible built-up level sensor are used, wherein, for. B. on the basis of a single or multiple measuring points, over a wide level range across the level of the liquid in the container should be determined. Here, the method should not be limited only to applications in the automotive sector.

The object of the invention is a reduction ^¬ achieved by a method for determining a current capacity of a liquid in a container, in particular the current residual capacity means in a reducing agent tank of an SCR dosing device of a motor vehicle, according to Claim. 1 Advantageous developments of the invention will become apparent from the dependent claims.

In the method according to the invention, a presence of liquid at a measuring point on / in the container is sensed or detected by a discontinuously and / or a discretely operating filling level sensor. Here, a single or a plurality of measuring points can be used, with a measuring point on a container inner wall is preferred. According to The invention is based on a temporal characteristic of a signal of the level sensor, due to a sloshing or a back and forth of the liquid in the container, closed on the current capacity of the liquid in the container or determines the current capacity of the liquid in the container.

According to the invention it is z. B. possible to determine based on a measured frequency and / or a pulse width of the measuring signal, the filling amount or the level of the liquid in the container with only a single measuring point within the container for a wide range around the measuring point around. This z. B. a simply constructed level sensor are used. In addition to the frequency and / or the pulse width, an additional parameter can be used. Furthermore, instead of the frequency and / or the pulse width of the signal of

Level sensor another or a plurality of other parameters are used.

Preferably, the temporal characteristic of the signal of the level sensor is a digital signal, wherein by a

Evaluation of the information present in the digital signal, the current amount of liquid in the container can be determined. But also an analogue signal can be used. In embodiments of the invention, for. B. from the temporal characteristics of the digital signal, a frequency and / or a pulse width of the signal or portions of the signal, so an analogue to the behavior of the liquid in the container with respect to the measuring point, are determined. On the basis of the frequency and / or the pulse width of the signal or portions of the signal then the current amount of liquid in the container is determined. Furthermore, for the determination of the actual filling quantity of the liquid in the container, an acceleration of the liquid, of the container or in the field of motor vehicle technology can be used for that of the motor vehicle. According to the invention, for determining a current level characteristic of the liquid in the container, within a function over a certain period or over certain periods, the frequency and / or the pulse width of the signal or portions of the signal are determined, further wherein the acceleration of the container or the

Motor vehicle can be used with.

In embodiments of the invention, one or a plurality of parameters can be used for determining the current filling level characteristic of the liquid in the container, within the function. These are in addition to the above-mentioned patent, in particular a rametern, optionally temperature-dependent visco sity ^¬ the liquid, a geometric factor of the container and / or a predetermined filling amount of the liquid in the container.

In preferred embodiments of the invention, a multiplicity of fill-level characteristics of the characteristics can be determined in a characteristic diagram

Liquid in the container be stored in advance in time, the corresponding level characteristics is preferably determined in driving tests with the motor vehicle. Furthermore, it is preferred that a current filling level of the liquid in the container is determined on the basis of the current filling level characteristic using the characteristic field. In this case, the current fill level of the liquid in the container can then be determined based on the current fill level of the liquid in the container, preferably by means of a characteristic curve.

In embodiments of the invention, the at least one measuring point of the discontinuously and / or discretely operating level sensor, with the exception of a reserve of the container, in an upper third with respect to a fully filled container, approximately at half height, in a lower third, in a lower Quarter, and / or as far as possible in / on the container arranged below. According to the invention, the at least one discontinuously and / or discretely operating level sensor can be provided on / in the container, the level sensor preferably having at least one electrode immersed in the liquid in the container. The invention will be explained in more detail below with reference to exemplary embodiments with reference to the accompanying drawings. In the schematic drawing: FIG. 1 shows a block diagram of an internal combustion engine

associated emission control system, in which the inventive method is applicable; and

2 shows a flow chart of the method according to the invention. The invention will be described below with reference to a method for

Determining a filling amount of a liquid reducing agent in a reducing agent container for an SCR metering device in a motor vehicle explained in more detail. However, the invention is not limited to such embodiments, but rather can be applied to all liquids or containers as long as the container or the liquid does not rest therein too much. Ie. the liquid and possibly also the container must be subjected to certain accelerations in at least one direction.

1 shows, in simplified form, an internal combustion engine 3 which can be operated with excess air and has an associated exhaust gas aftertreatment system which has a metering device 1, in particular an SCR metering device 1. Only those parts are shown, which are necessary for the understanding of the invention. The internal combustion engine 3 is preferably a lean-burn engine, such as. B. a diesel or an Ot-to-lean engine, wherein as entrained liquid reducing agent 100 for the aftertreatment of an exhaust gas 50 z. As urea, a urea-water solution, AdBlue®, Denoxium®, Aminex® o. A. is applicable, which releases 50 in the aftertreatment of the exhaust gas preferably ammonia.

The internal combustion engine 3 is supplied via an intake tract 32 a fresh air necessary for combustion. An injection system, such as a common rail with fuel injectors (not shown), can inject the fuel directly into the cylinders of the internal combustion engine 3. The exhaust 50 of the Internal combustion engine 3 flows into an exhaust tract 34 for Ab ^¬ gas aftertreatment system and from this via a silencer, not shown, into the open. For controlling and / or regulating the internal combustion engine 3, a known control unit 2 is provided, which is designed in particular as an ECU (Engine Control Unit). The control unit 2 is electrically or electronically connected to the internal combustion engine 3 via a data and / or control line indicated only in FIG. About this data and / or

Signals from sensors (eg, temperature sensors for intake air, charge air, coolant, load sensor, speed sensor, etc.) and signals for actuators (eg, injection valves, actuators, etc.) between the internal combustion engine 3 and the control unit 2 are transmitted to the control line ,

The exhaust aftertreatment system has a catalyst 20 designed in particular as an SCR catalytic converter 20, which preferably contains a plurality of catalyst units connected in series and unspecified. Upstream (reference numeral 40) and / or downstream (not shown) of the

SCR catalyst 20 may additionally be arranged in each case one preferably designed as an oxidation catalyst catalyst. Further, a metering control device 16 is provided which a reducing agent container 10 with an electric

controllable pump 12 is assigned for conveying the reducing agent 100. In contrast to the representation of FIG. 1, the pump 12 can also be arranged inside the reducing agent tank 10.

As a reducing agent 100 is used in this embodiment AdBlue®, which is stored in the reducing agent tank 10. The reducing agent container 10 preferably has an electrical heating device and sensors which detect the temperature of the reducing agent 100 in the reducing agent container 10. Signals of a temperature sensor arranged upstream of the SCR catalytic converter 20 and of a downstream of the SCR catalytic converter 8 are also sent to the dosing control device 16 arranged Abgasmessaufnehmers, such. B. a NO _x sensor passed (not shown).

The Dosiersteuereinrichtung 16 controls a metering valve 14 preferably elec- romagnetisches, which is supplied as required through a supply AdBlue by the pump 12 from the reductive ^¬ tion agent container 10th In the feed line, a pressure sensor is preferably inserted, which detects a fluid pressure in the metering device 1 and emits a corresponding signal to the metering control device 16. The injection of AdBlue® by means of the metering valve 14 takes place in the exhaust gas tract 34 upstream of the SCR catalytic converter 20 in or in the opposite flow direction of the exhaust gas 50. Further, in an operation of the internal combustion engine 3, the fresh air flows in the direction of the arrow shown in FIG. 2 into the internal combustion engine 3 into it and the exhaust gas 50 also in the arrow indicated there through the exhaust tract 34 therethrough.

The metering control device 16 is preferably connected to the control unit 2 for mutual data transfer via an electrical or electronic bus system, which is indicated by the arrows shown in FIG. 1. However, it may be realized in other embodiments such that the

Dosing control device 16 is realized in the control unit 2. The bus system is used to calculate the quantity of Vioo to be dispensed to AdBlue®, such as operating parameters. B. a speed, a fresh air mass, a fuel quantity, a control path of an injection pump, an exhaust gas mass flow, an operating temperature, a charge air temperature, an injection start, etc. passed to the dosing control 16.

Based on these parameters and the measured values for the exhaust gas temperature and a NO _x content calculates the

Dosing control device 16 an amount to be injected Vioo to AdBlue® and via an electrical or electronic Ver ^{¬ connection line from} a corresponding electrical / electronic signal to the metering valve 14 from. By injection into the exhaust tract 34, urea is hydrolyzed in AdBlue® and mixed with the Exhaust gas 50 mixed. In the catalyst units of

SCR catalyst 20 is the catalytic reduction of NO _x in the exhaust gas 50 to N ₂ and H ₂ 0. The metering valve 14 for introducing AdBlue® in the exhaust tract 34 may largely correspond to a conventional low-pressure gasoline injection valve.

To keep an SCR system operational, a level of reductant in the reductant tank must be monitored. So far, the level has only been at the discreet when using discontinuously operating level sensors

Measuring point determined. As a result, the filling level can not be sensed in a wide area around the measuring point. This has the disadvantage that refilling a small amount of AdBlue® is difficult to detect. However, this is of particular importance in SCR systems, since from the legal side in some cases considerable restrictions are required when reaching a low level, eg. B. from a speed / torque limit of the engine to prohibiting their start.

In order to determine a filling level h - see Fig. 2 - in the reducing agent container 10 is according to the invention a

Level sensor 110 used, which may be formed differently ^¬ . In particular, it is cost-effective to use a single, discontinuous and / or discrete working one

Level sensor 110 is used, which at least at a single measuring point 112 in or inside the reducing agent container 10 can sense, detect or measure whether a level of the reducing agent 100 is above or below a measuring point 112 of the level sensor 110. Of course, one or more level sensors 110 are also applicable, which can possibly also sense at several measuring points 122 whether reducing agent 100 is located at / in the measuring point 122. If the reducing agent tank 10 or the motor vehicle is moved or accelerated, then the reducing agent 100 sloshes in the reducing agent tank 10 - see the left in FIG. 2. According to the invention, an evaluation function F, KF of the or the filling level sensors 110 no longer determine the filling level h or a current filling quantity V _t or volume V _t , ie a current residual filling quantity V _t or volume V _t , of the sloshing reducing agent 100 only at a specific level in the reducing agent container 10, but in a wide area around the measuring point 112 around. In a completely filled reducing agent ^¬ container 10 is correspondingly an output fill quantity V ₀ or volume V ₀ . The sloshing of the reducing agent 100 during driving, which is disadvantageous in the prior art, is now recognized as an advantage and correspondingly utilized in that the measuring range of the fill level sensor 110 is widened. Ie. In contrast to the state of the art, it is possible to determine reliable information about the current filling quantity V _t while driving.

In order to be able to describe the filling level h of the reducing agent 100 also in a wide range around the discrete measuring point 112, the discrete measuring signal Sno of the filling level sensor 110 is evaluated, which in the case of a sloshing of the reducing agent 100 within the reducing agent container 10 between the values "0" and " 1 "changes. Furthermore, it is preferred if an acceleration a of the reducing agent 100 or of the reducing agent tank 10 or of the motor vehicle is used. For example, the acceleration a is directly present as an input signal, e.g. B. from an ESP control unit, or can by means of a speed of the motor vehicle, for. B. from an ABS control unit, are calculated. The acceleration a can be an acceleration a in / against a forward direction of travel of the motor vehicle or else a transverse acceleration a.

Within a function F, a characteristic Char of the signal Sno is evaluated at a specific time period / point t and / or over a longer period t, with preferably a frequency f and / or a pulse width pw in the signal Sno or in a region or section of the signal Sno. With the aid of this information, a filling level characteristic of the sloshing reduction stored in a characteristic field KF can be determined. tion means 100 in the reducing agent tank 10, the filling height h or the current (residual) filling amount V _{t of} the reducing agent 100 in the reducing agent container 10 are calculated. The level characteristic stored in the characteristic field KF should be identified beforehand by driving tests with the motor vehicle or by other suitable methods. This can z. As computer simulations ^¬ or Schwappversuche with the reducing agent container 10 at different frequencies, fill levels, etc. be. Through the map KF a quasi-stationary level h of the reducing agent 100 in the reducing agent tank 10 is determined. In this case, the level characteristic recorded in the map KF is a behavior of the reducing agent 100 sloshing at the time t or in the period t in the reducing agent tank 10, from previously determined frequencies f, pulse widths pw and / or accelerations a with respect to the measuring point 112. From the filling level h of the reducing agent 100 in the reducing agent container 10, the current volume V _t and the current (residual) filling quantity V _t of reducing agent 100 in the reducing agent container 10 can be determined via a characteristic curve KL. The characteristic curve KL of the reducing agent container 10 takes into account its geometry with respect to the filling height h of the reducing agent 100.

Claims

claims

1. Method for determining a current filling quantity (V _t ) of a liquid (100) in a container (10), in particular the current residual filling quantity (V _t ) of a reducing agent (100) in a reducing agent container (10) of an SCR metering device (1) a motor vehicle, wherein

by a discontinuously or discretely operating level sensor (110) a presence of liquid (100) at a measuring point (112) on / in the container (10) is determined, characterized in that

based on a temporal characteristic (Char, f, pw) of a signal (Sno) of the filling level sensor (110) due to a sloshing of the liquid (100) in the container (10), to the actual filling quantity (V _t ) of the liquid (100) in the container (10) is closed.

2. The method according to claim 1, characterized in that the temporal characteristic (Char; f, pw) of the signal (Sno) of the

Level sensor (110) is a digital signal (Sno), wherein by an evaluation of the information present in the digital signal (Sno) the current filling quantity (V _t ) of the liquid (100) in the container (10) is determined, and / or

from the temporal characteristic (Char; f, pw) of the signal

(Sno) of the level sensor (110) a frequency (f) and / or a pulse width (pw) of the signal (Sno) or portions of the signal (Sno) is or will be determined.

3. The method according to any one of the preceding claims, characterized in that based on the frequency (f) and / or the pulse width (pw) of the signal (Sno) or portions of the signal (Sno), the current filling quantity (V _t ) of the liquid ( 100) in the container (10) is determined.

4. The method according to any one of the preceding claims, characterized in that further for the determination of the current filling quantity (V _t ) of the liquid (100) in the container (10) has a Acceleration (a) of the container (10) or the motor vehicle is used.

5. The method according to any one of the preceding claims, characterized in that for determining a current level characteristic of the liquid (100) in the container (10), within a function (F) over a certain period (t) or over certain periods (t) , the frequency (f) and / or the pulse width (pw) of the signal (Sno) or of sections of the signal (Sno) are determined.

6. The method according to any one of the preceding claims, characterized in that for determining the current level characteristic of the liquid (100) in the container (10), within the function (F) further parameters, in particular:

• the acceleration (a) of the container (10) or the

Motor vehicle;

• a, possibly temperature-dependent, viscosity of the liquid (100);

A geometric factor of the container (10); and or

A predetermined filling quantity (V _t ) of the liquid (100) in the container (10)

is additionally used or become.

7. The method according to any one of the preceding claims, characterized in that in a characteristic field (KF) a plurality of level characteristics of the liquid (100) in the container (10) are stored in advance in time, the corresponding level characteristic preferably determined in a driving test with the motor vehicle becomes.

8. The method according to any one of the preceding claims, characterized in that based on the current level characteristic using the map (KF) a current level (h) of the liquid (100) in the container (10) is determined, wherein based on the current level (h) the liquid (100) in the container (10) preferably by means of a characteristic (KL) the actual filling quantity (V _t ) of the liquid (100) in the container (10) is determined.

9. The method according to any one of the preceding claims, characterized in that the at least measuring point (112) of discontinuously or discretely operating level sensor (110), with the exception of a reserve of the container (10) with respect to a completely filled container (10) in an upper third, approximately halfway up, in a lower third, in a lower quarter, and / or as far as possible at the bottom of / in the container.

10. The method according to any one of the preceding claims, characterized in that at least one discontinuously or discretely operating level sensor (110) on / in the container (10) is provided which preferably at least one in the liquid (100) in the container (10) immersed electrode having.