DE102010062302A1 - Method for determining a current filling quantity of a liquid in a container, in particular for a motor vehicle - Google Patents

Abstract

The invention relates to a 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 Motor vehicle, wherein by a discontinuous or discrete working level sensor, a presence of liquid (100) at a measuring point (112) on / in the container (10) is determined, based on a temporal characteristic (Char; f, pw) of a signal (S ₁₁₀ ) of the level sensor (110) due to a sloshing of the liquid (100) in the container (10), the current amount (V _t ) of the liquid (100) in the container (10) is closed.

Description

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. To meet these legal requirements, a purification of the exhaust gas is usually necessary. For this purpose, an exhaust gas purification system is usually used, which contains one or a plurality of catalysts, different exhaust gas sensors, 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 are increasingly being 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 generated by injecting or injecting a urea-water solution and its hydrolysis in the exhaust tract of the internal combustion engine 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 falls below a predetermined value, 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 enabling an improved control of the SCR method or a diagnosis of an associated metering device.

Conventional devices with float and potentiometer fill level sensors commonly used for fuel tanks are problematic for use in aqueous urea solution because of the conductivity of the reducing agent, corrosivity and crystallization upon drying. 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.

The DE 100 47 594 A1 discloses a method and apparatus for determining a level of a liquid in a container, in particular a reducing agent in a reducing agent container. A discretely operating fill level sensor in this case 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 at three points, 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 achieved by 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. 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, 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 amount of liquid in the container or determines the current amount of 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 the level sensor, another or a plurality of other parameters may be used.

The temporal characteristic of the signal of the filling level sensor is preferably a digital signal, wherein the current filling quantity of the liquid in the container can be determined by an evaluation of the information present in the digital signal. 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 of time or over certain periods of time, the frequency and / or the pulse width of the signal or portions of the signal can be determined; 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 fill level characteristic of the liquid in the container within the function. In addition to the parameters mentioned above, these are in particular one, possibly temperature-dependent, viscosity of the liquid, a geometry factor of the container and / or a previously determined filling quantity of the liquid in the container.

In preferred embodiments of the invention, a plurality of fill-level characteristics of the liquid in the container can be stored in advance in a map, wherein the corresponding fill-level characteristics are 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 fill level sensor can be provided on / in the container, the fill 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 embodiments with reference to the accompanying drawings. In the schematic drawing show:

1 a block diagram of an internal combustion engine with associated emission control system, in which the inventive method is applicable; and

2 a flow diagram of the method according to the invention.

The invention will be explained in more detail below with reference to a method for determining a filling amount of a liquid reducing agent in a reducing agent tank for an SCR metering device in a motor vehicle. 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.

The 1 shows simplified an operable with excess air internal combustion engine 3 with an associated exhaust aftertreatment system, which is a metering device 1 , in particular an SCR metering device 1 having. 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. As a diesel or Otto lean engine, as entrained liquid reducing agent 100 for after-treatment of an exhaust gas 50 z. As urea, a urea-water solution, AdBlue ^® , Denoxium ^® , Aminex ^® oa is applicable, which in the aftertreatment of the exhaust gas 50 preferably liberates ammonia.

The internal combustion engine 3 is via an intake system 32 supplied to a fresh air necessary for combustion. An injection system, such as a common rail with fuel injectors (not shown), can direct the fuel into the cylinders of the internal combustion engine 3 inject. The exhaust 50 the internal combustion engine 3 flows into an exhaust tract 34 to the exhaust aftertreatment system and from this via a silencer, not shown, into the open.

For controlling and / or regulating the internal combustion engine 3 is a known control unit 2 provided, which is designed in particular as an ECU (Engine Control Unit). The control unit 2 is about one in the 1 only indicated as arrows data and / or control line with the internal combustion engine 3 electrically or electronically connected. 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 are transmitted via this data and / or control line 3 and the control unit 2 transfer.

The exhaust aftertreatment system has one in particular as an SCR catalyst 20 trained catalyst 20 on, which preferably includes a plurality of series-connected, unspecified catalyst units. 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. Furthermore, a metering control device 16 provided, which is a reducing agent tank 10 with an electrically controllable pump 12 for conveying the reducing agent 100 assigned. The pump 12 can in contrast to the representation of the 1 also within the reducing agent tank 10 be arranged.

As a reducing agent 100 serves in this embodiment AdBlue ^® , in the reducing agent tank 10 is stored. The reducing agent tank 10 preferably has an electrical heater and sensors, which the temperature of the reducing agent 100 in the reducing agent tank 10 to capture. To the dosing control device 16 In addition, signals from upstream of the SCR catalytic converter are detected 20 arranged temperature sensor and one downstream of the SCR catalyst 8th arranged Abgasmessaufnehmers, such. B. a NO _x sensor passed (not shown).

The dosing control device 16 controls a preferred electromagnetic metering valve 14 On demand, via a supply line AdBlue ^® with the help of the pump 12 from the reducing agent tank 10 is supplied. In the supply line, a pressure sensor is preferably inserted, the fluid pressure in the metering device 1 detected and a corresponding signal to the dosing control device 16 emits. The injection of AdBlue ^® by means of the metering valve 14 takes place in the exhaust tract 34 upstream of the SCR catalyst 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 in the in 2 Plotted arrow direction in the internal combustion engine 3 into it and the exhaust 50 also in the arrow indicated there by the exhaust gas tract 34 therethrough.

The dosing control device 16 is for mutual data transfer via an electrical or electronic bus system preferably with the control unit 2 connected, what by in 1 indicated arrows is indicated. However, it may be realized in other embodiments such that the dosing control device 16 in the control unit 2 is realized. The bus system is used to calculate the quantity V ₁₀₀ to be metered on ^AdBlue® relevant operating parameters, such as, for example, As a speed, a fresh air mass, an amount of fuel, a control path of an injection pump, an exhaust gas mass flow, an operating temperature, a charge air temperature, an injection start, etc. to the dosing control 16 to hand over.

On the basis of these parameters and the measured values for the exhaust gas temperature and a NO _x content, the dosing control device calculates 16 an amount of V ₁₀₀ to be injected to AdBlue ^® and sends an appropriate electrical / electronic signal to the dosing valve via an electrical or electronic connecting line 14 from. By injection into the exhaust tract 34 urea is hydrolyzed in the AdBlue ^® and with the exhaust gas 50 mixed. In the catalyst units of the SCR catalyst 20 the catalytic reduction of NO _x takes place in the exhaust gas 50 to N ₂ and H ₂ O. The metering valve 14 for introducing AdBlue ^® into the exhaust tract 34 can largely correspond to a conventional low-pressure gasoline injector.

To keep an SCR system operational, a level of reductant in the reductant tank must be monitored. So far, the level has been determined when using discontinuously operating level sensors only at the discrete measuring point. 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 particularly important in SCR systems, as required by law sometimes significant restrictions in achieving a low level, z. B. from a speed / torque limit of the engine to prohibiting their start.

To a filling height h - see 2 - in the reducing agent tank 10 to be able to determine according to the invention, a level sensor 110 used, which can be designed differently. In particular, a single, discontinuously and / or discretely operating fill level sensor is cost-effective 110 used, which at least at a single measuring point 112 in or on the reducing agent tank 10 can sense, detect or measure whether there is a level of the reducing agent 100 above or below a measuring point 112 of the level sensor 110 located. Of course, there are also one or more level sensors 110 applicable, the or the possibly also at several measuring points 122 can sense whether at / in the measuring point 122 reducing agent 100 located.

Will the reducing agent tank 10 or the motor vehicle moves or accelerates, the reducing agent spills 100 in the reducing agent tank 10 - see left in the 2 , According to the invention, an evaluation functionality F, KF of the level sensor (s) 110 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 not only at a certain level in the reducing agent tank 10 determined, but in a wide range around the measuring point 112 around. In a completely filled reducing agent tank 10 is output according to a filling quantity V ₀ and volume V _0th The disadvantageous in the prior art sloshing of the reducing agent 100 when driving is now recognized as an advantage and used accordingly by the fact that the measuring range of the level sensor 110 is extended. 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.

To the filling height h of the reducing agent 100 also in a wide range around the discrete measuring point 112 to be able to describe, is the discrete measurement signal S _{110 of} the level sensor 110 evaluated, the sloshing of the reducing agent 100 within the reducing agent tank 10 between the values "0" and "1". Furthermore, it is preferable if an acceleration a of the reducing agent 100 or the reducing agent tank 10 or 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 may be an acceleration a in / against a forward direction of travel of the motor vehicle or a lateral acceleration a.

Within a function F, a characteristic Char of the signal S _{110 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 S ₁₁₀ or in a range or portion of signal S ₁₁₀ . With the aid of this information, a fill level characteristic of the sloshing reducing agent stored in a characteristic field KF can be used 100 in the reducing agent tank 10 , the filling height h or the current (residual) filling quantity V _{t of} the reducing agent 100 in the reducing agent tank 10 be calculated. The level characteristic stored in the map KF should be identified beforehand by driving tests with the motor vehicle or by other suitable methods. This can z. B. computer simulations or Schwappversuche with the reducing agent tank 10 be at different frequencies, fill levels, etc.

Through the map KF is a quasi-stationary level h of the reducing agent 100 in the reducing agent tank 10 certainly. Here, the recorded in the map KF level characteristic is a behavior of the time t or in the period t in the reducing agent tank 10 sloshing reducing agent 100 , 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 tank 10 can via a characteristic curve KL, the current volume V _t and the current (remaining) filling amount V _t of reducing agent 100 in the reducing agent tank 10 be determined. The characteristic curve KL of the reducing agent tank 10 takes into account its geometry with respect to the filling level h of the reducing agent 100 ,

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10047594 A1 [0006]

Claims (10)

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 tank ( 10 ) of an SCR metering device ( 1 ) of a motor vehicle, wherein by a discontinuous or discrete working level sensor ( 110 ) a presence of liquid ( 100 ) at a measuring point ( 112 ) on / in the container ( 10 ), characterized in that based on a temporal characteristic (Char; f, pw) of a signal (S ₁₁₀ ) 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. A method according to claim 1, characterized in that the temporal characteristic (Char; f, pw) of the signal (S ₁₁₀ ) of the level sensor ( 110 ) is a digital signal (S ₁₁₀ ), wherein by an evaluation of the information present in the digital signal (S ₁₁₀ ), the current filling quantity (V _t ) of the liquid ( 100 ) in the container ( 10 ), and / or from the temporal characteristic (Char; f, pw) of the signal (S ₁₁₀ ) of the filling level sensor ( 110 ) a frequency (f) and / or a pulse width (pw) of the signal (S ₁₁₀ ) or portions of the signal (S ₁₁₀ ) is or will be determined. Method according to one of the preceding claims, characterized in that based on the frequency (f) and / or the pulse width (pw) of the signal (S ₁₁₀ ) or portions of the signal (S ₁₁₀ ), the current filling quantity (V _t ) of the liquid ( 100 ) in the container ( 10 ) is determined. Method according to one of the preceding claims, characterized in that, furthermore, for the determination of the actual filling quantity (V _t ) of the liquid ( 100 ) in the container ( 10 ) an acceleration (a) of the container ( 10 ) or the motor vehicle is used. Method according to one of the preceding claims, characterized in that for determining a current filling 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 (S ₁₁₀ ) or portions of the signal (S ₁₁₀ ) is determined. Method according to one of the preceding claims, characterized in that for determining the current filling 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 geometry factor of the container ( 10 ); and / or • a previously determined filling quantity (V _t ) of the liquid ( 100 ) in the container ( 10 ) is additionally used. Method according to one of the preceding claims, characterized in that in a characteristic field (KF) a multiplicity of fill-level characteristics of the liquid ( 100 ) in the container ( 10 ) are stored in advance in advance, wherein the corresponding level characteristic is preferably determined in a driving test with the motor vehicle. Method according to one of the preceding claims, characterized in that based on the current filling level characteristic using the characteristic map (KF), a current level (h) of the liquid ( 100 ) in the container ( 10 ), whereby based on the current level (h) of the liquid ( 100 ) in the container ( 10 ) preferably by means of a characteristic curve (KL) the current filling quantity (V _t ) of the liquid ( 100 ) in the container ( 10 ) is determined. Method according to one of the preceding claims, characterized in that the at least measuring point ( 112 ) of the discontinuous or discrete filling level sensor ( 110 ), except for 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. Method according to one of the preceding claims, characterized in that at least one discontinuously or discretely operating level sensor ( 110 ) on / in the container ( 10 ), which preferably at least one into the liquid ( 100 ) in the container ( 10 ) has a dipping electrode.

Images