DE102009060285A1 - Method for determining ammonia-loading condition of storage of ammonia storage system of selective catalytic reduction catalyst system in vehicle, involves detecting state variable that characterizes heating and/or cooling characteristics - Google Patents

Abstract

The invention relates to a system for determining an NH3 loading level of a store (34) of an ammonia storage system (32) of a catalyst system (28) operating on the principle of selective catalytic reduction (SCR), the store (34) containing an NH3 storage material which Depending on the temperature, ammonia (NH3) can bind reversibly and is equipped with a heating device (38). It is provided that at least one state variable of the memory (34) characterizing a heating behavior and / or a cooling behavior of the memory (34) is recorded during a heat input into the memory (34) and / or heat discharge from the memory (34) and the NH3 loading level of the memory (34) is determined as a function of the at least one state variable.

Description

The invention relates to a method for determining an NH ₃ loading level of a storage of an ammonia storage system, in particular of a reducing agent storage, of a catalyst system operating on the principle of selective catalytic reduction (SCR). The invention further relates to an SCR catalyst system configured for carrying out the method and to a corresponding vehicle.

Internal combustion engines that are operated intermittently or predominantly with a lean air-fuel mixture produce nitrogen oxides NO _x (mainly NO ₂ and NO), which require NO _x -reducing measures. A motor measure for reducing the NO _x raw emission in the exhaust gas is the exhaust gas recirculation, in which part of the exhaust gas of the internal combustion engine is recirculated into the combustion air, whereby the combustion temperatures are lowered and thus the NO _x formation is reduced. However, the exhaust gas recirculation is not always sufficient to comply with legal NO _x limits, so in addition an active exhaust aftertreatment is required, which reduces the NO _x -Edemission. A known NO _x exhaust aftertreatment provides for the use of NO _x storage catalysts that store nitrogen oxides in the form of nitrates during lean operation (at λ> 1) and desorb the stored nitrogen oxides at short intervals with a rich exhaust gas atmosphere (λ <1) and reduce to nitrogen N ₂ in the presence of the reducing agent present in the rich exhaust gas.

As another approach to the conversion of nitrogen oxides in exhaust gases mlauflauffähiger internal combustion engines, the use of catalyst systems is known which operate on the principle of selective catalytic reduction (SCR for selective catalytic reduction). These systems comprise at least one SCR catalyst which, in the presence of a reducing agent continuously fed to the exhaust gas, usually ammonia NH ₃ , converts the nitrogen oxides of the exhaust gas into nitrogen and water. In this case, the ammonia can be added from an aqueous ammonia solution to the exhaust gas stream or be obtained from a precursor compound, for example urea, by way of thermolysis and hydrolysis. A promising new approach to ammonia storage in vehicles is NH ₃ storage materials, which reversibly bind ammonia as a function of temperature. In particular, metal-ammonium stores are known in this connection, for example MgCl ₂ , CaCl ₂ and SrCl ₂ , which store ammonia in the form of a complex compound in order then to contain, for example, MgCl ₂ (NH ₃ ) _x , CaCl ₂ (NH ₃ ) _x or SrCl ₂ (NH ₃ ) _{x to be} present. From these compounds, by supplying heat, the ammonia can be released again. The advantage of metal-ammonium storage is that these compounds can store a large amount of ammonia in very small volumes. For example, one mole of SrCl ₂ binds eight moles of NH ₃ . In addition, these compounds allow a good controllable release of ammonia and are very safe.

In order to achieve a faster start-up readiness, it is known to provide, in addition to one or two main memories, a comparatively small-volume sized start memory, which usually has an electrical heating device. The main memory can be heated either with an electric heater or with a supplied with engine cooling water heater. In the warm-up phase, the startup tank, which is heated and ready for use due to its low volume, takes over the NH ₃ supply of the SCR catalytic converter. Its heating takes place until the operating pressure is built up in the main memory. Only when the thermally inert main memory has built up its operating temperature and operating pressure, the entire NH ₃ supply is taken from this. The starting memory is then loaded with NH ₃ from the main memory and thus has at virtually every system start a virtually identical NH ₃ level.

DE 10 2006 061 370 A1 describes a similar system in which the main memory has a NH ₃ storage material with a relatively high NH ₃ vapor pressure, in particular SrCl ₂ , and a small-volume operating memory is provided which contains a NH ₃ storage material with comparatively lower NH ₃ vapor pressure, in particular MgCl ₂ . Due to the different vapor pressures, the mass transfer from the SrCl ₂ storage to the MgCl ₂ storage is supported, so that the filling of the latter is accelerated. In this system, the NH ₃ dosage is made exclusively from the operating memory, which in turn is filled from the main memory.

Out EP 1 977 817 A1 an embodiment corresponding to the system described above is known in which, depending on a current ammonia requirement, a required heating power for heating the main storage is calculated.

Currently, there is no concept to determine an NH ₃ level of ammonia storage for SCR catalyst systems. However, the knowledge of the level is to predict the range of a Vehicle important. There is also an interest in controlling freshly used memory cartridges for their correct level.

The invention is based on the object to provide a method with which a determination of the NH ₃ -Bleadungszustandes (level) of new and operating ammonia storage with good reliability and low overhead is possible. It is also intended to provide an SCR catalyst system suitable for carrying out the method and a corresponding vehicle.

These objects are achieved by a method, an SCR catalyst system and a vehicle having the features of the independent claims.

The method according to the invention relates to the determination of an NH ₃ loading state of a storage tank of an ammonia storage system in a selective catalytic reduction (SCR) catalyst system. The storage tank contains an NH ₃ storage material that can reversibly bind (absorb or adsorb) ammonia NH ₃ depending on the temperature. The memory is equipped with a heater to bring this to its operating temperature or its operating pressure. According to the invention, at least one state variable of the memory, which characterizes a heating behavior and / or a cooling behavior of the memory, is detected from the memory during a heat input (actively effected by the heating device) into the memory and / or during a heat discharge (taking place spontaneously after switching off the heating). Depending on the at least one state variable, the NH ₃ charge state of the memory is determined. The invention makes use of the fact that the heating behavior and the cooling behavior of the memory depends on its heat capacity, which in turn depends on the loading state of the memory or of the storage material contained therein. For example, NH ₃ -enriched metal ammine complexes have a much higher specific heat capacity than their NH ₃ -depleted or their NH ₃ -free form. This is reflected in an altered heating behavior or cooling behavior, which can thus be used as an indicator of the loading condition. It is particularly advantageous that the method allows the determination of the absolute load state and not just a relative load change since system start. In this way, even with a newly inserted memory cartridge their actual NH ₃ -Beladungszustand can be determined with high accuracy. Another advantage of the method is that no constructive measures are required to carry it out.

In a preferred embodiment of the method, the at least one, the cooling behavior and / or the heating behavior of the memory characterizing state variable is observed during an operating phase in which no ammonia is removed from the memory. In this way, the relationships between the NH ₃ loading state and the observed state variable are simplified. In particular, here is a heating phase of the memory at system startup or a cooling phase of the memory after turning off the system into consideration.

In a preferred embodiment of the method, the at least one state variable characterizing the heating behavior or the cooling behavior of the memory is a temperature-related variable and / or a pressure-related variable. Since the usual storage systems often already have appropriate temperature and / or pressure sensors or can be easily retrofitted with these, the detection of these state variables can be carried out without significant design effort. Preferably, a pressure-related variable is detected, since the storage pressure is present with very high homogeneity in the memory, while the storage temperature fluctuates more locally and / or temporally.

In particular, the at least one state variable can be selected from the group comprising a temperature change in the memory; a pressure change in the memory; a period of time and / or cumulative heating power until a predetermined temperature is reached in the memory; a period of time and / or cumulative heating power until a predetermined pressure is reached in the reservoir; a temperature reached in the memory after a predetermined time and / or predetermined cumulative heating power and / or a pressure reached in the memory after a predetermined time and / or predetermined cumulative heating power.

According to a particular embodiment of the method, the heat capacity of the memory is determined as a function of the at least one state variable and determined as a function of the heat capacity of the NH ₃ -Beladungszustand the memory. As already stated, the heat capacity of the memory is a very accurate indicator of its loading condition.

According to an advantageous embodiment of the method, the determination of the NH ₃ loading state of the memory takes place mathematically using stored calculation instructions and / or algorithms. Such computational rules can readily be deduced from the known laws of thermodynamics and represent the relationship between the observed state variable and the NH ₃ loading state of the memory with good accuracy.

In an alternative embodiment, the determination of the loading state of the memory is carried out using stored maps (which in the present case also characteristic curves are understood as a special case). Such maps can be determined empirically in test series in which the state variable of interest is determined as a function of the NH ₃ loading state. If a state variable is then detected within the scope of the method according to the invention, the associated NH ₃ loading state of the memory can be readily read from the corresponding map. The advantage of using empirically determined maps is that no computational approximations have to be applied. Rather, the relationship can be determined exactly for exactly the ammonia storage system used.

In addition, it is conceivable to use combinations of the computational approach using calculation rules and the empirical approach using maps. For example, the heat capacity of the system can be calculated using a suitable calculation rule and the NH ₃ -loading state can be read out of a map representing the load state as a function of the heat capacity.

With great advantage, the determination according to the invention of the NH ₃ charging state of the memory can be carried out to forecast an anticipated range of a vehicle equipped with the SCR catalytic converter system. In this way, a signal can be output to a driver and / or to an onboard diagnostic system (OBD system) requesting the replacement of the memory.

In addition, the method according to the invention can also be carried out for level control of a newly replaced storage, in particular in order to check whether it is filled in accordance with the regulations. In this way, an abusive manipulation can be encountered in which a driver tries to overcome the diagnostic system by using an empty memory. In this context, it may be provided that the level control is performed once after Einwechselung the memory and a re-control can not be triggered before the expiry of a predetermined operating time or predetermined distance covered route.

The invention further relates to an SCR catalyst system comprising at least one SCR catalyst and an ammonia storage system comprising at least one equipped with a heater ammonia storage, which contains a NH ₃ storage material, which is capable of reversibly binding ammonia reversible. The SCR catalyst system has a control device that is set up to carry out the method according to the invention. For this purpose, the control device can in particular comprise a control algorithm for executing the method in computer-readable form as well as suitable computational rules and / or characteristic diagrams which are likewise stored in computer-readable form.

The NH ₃ storage material of the store is preferably selected from the group of NH ₃ -complexing metal salts, in particular the alkali and alkaline earth metal salts and transition metal salts, this group preferably MgCl ₂ (NH ₃ ) _x , CaCl ₂ (NH ₃ ) _x and SrCl ₂ (NH ₃ ) _x . The main advantage of this group, also referred to as metal amines, is their very high ammonia storage capacity with low volume and weight. However, it is also possible to use NH ₃ -adsorbing solids, such as acid-activated activated carbon or zeolites, which, in contrast to the metal amines, do not chemically absorb NH ₃ but physically adsorb it. It is crucial that the NH ₃ bond is reversible.

Finally, the invention relates to a vehicle comprising a corresponding SCR catalytic converter system.

Further advantageous embodiments are the subject of the remaining dependent claims.

The invention will be explained in more detail in embodiments with reference to the accompanying drawings. Show it:

1 a schematic representation of an exhaust system with an inventive SCR catalyst system according to a first embodiment of the invention;

2 a time course of the NH ₃ vapor pressure in an ammonia storage with continuous heating and at different NH ₃ levels;

3 Temperature-pressure equilibrium curves for the first and second decomposition stages of the NH ₃ storage material SrCl ₂ (NH ₃ ) _x ;

4 a schematic representation of an exhaust system with an inventive SCR catalyst system according to a second embodiment of the invention; and

5 a schematic representation of an exhaust system with an inventive SCR catalyst system according to a third embodiment of the invention.

1 shows a total of 10 designated motor vehicle, of which here only an internal combustion engine 12 with a connected exhaust system 14 is shown. In the internal combustion engine 12 it is an at least temporarily or permanently lean running engine, such as a diesel engine. He has in the example shown an injection system 16 that inject fuel directly into cylinders 18 injects the engine. However, the invention is basically also suitable for premix-forming internal combustion engines. The combustion air is the internal combustion engine 12 via a suction channel 20 supplied and is via a throttle device 22 controllable.

An exhaust gas of the internal combustion engine 12 gets into an exhaust duct 24 the exhaust system 14 initiated, where at a near-engine position, a first catalyst 26 may be arranged, for example, an oxidation or 3-way catalyst.

The exhaust system 14 further comprises an SCR catalyst system operating on the selective catalytic reduction principle 28 that is an SCR catalyst 30 Namely, a NO _x reduction catalyst, and an ammonia storage system 32 having. The ammonia storage system 32 includes at least one main memory 34 and a small-volume memory compared to the main memory 36 which can be designed as a starting memory or operating memory. The stores 34 and 36 each include an unillustrated NH ₃ storage material which is capable of reversibly chemically or physically binding or desorbing ammonia NH _{3 as a} function of the temperature. This means that with increasing temperature, the thermodynamic equilibrium shifts from the bound form (the NH ₃ -enriched form) to the desorbed form (the NH ₃ -depleted or -free form), that is, the NH ₃ vapor pressure increases with increasing Temperature.

The relationship between the vapor pressure of ammonia p _NH3 and the temperature T can be described by the thermodynamic equation 1, where ΔH _{r is} the reaction enthalpy of desorption of the used NH ₃ storage material, ΔS _r the reaction entropy of desorption and R _m the universal gas constant (R _m = 8.314 J / mol · K).

To the ammonia storage system 32 to bring to its required operating pressure, are the memories 34 and 36 each with a heater 38 respectively 40 fitted. These can each be electrical heaters, which are known per se in the prior art, and, for example, one in each interior of the memory 34 . 36 may contain arranged heating coil. Alternatively, the main memory 34 Also be equipped with a running with a liquid medium heating device, for example one with a cooling water of the internal combustion engine 12 operated heating device.

In the NH ₃ storage material of the memory 34 . 36 it is preferably an NH ₃ -complexing metal salt, which is also referred to as metal ammine. For example, the compounds MgCl ₂ (NH ₃ ) _x , CaCl ₂ (NH ₃ ) _x and SrCl ₂ (NH ₃ ) _x are suitable here, which release the bound NH ₃ partly in stages. For example, the strontium chloride ammine complex, which can store up to eight moles of NH ₃ per mole of SrCl _2, releases seven moles of NH ₃ upon reaching a temperature of about 60-80 ° C and the eighth mole of NH ₃ at about 150 ° C. Main and start memory 34 . 36 may contain the same NH ₃ storage material or different.

The main memory 34 and the memory 36 each with a gas supply line 42 in conjunction, upstream of the SCR catalyst 30 in the exhaust duct 24 empties. In this case, at a connection point of the conduit system, a switchable valve 44 arranged that either the main memory 34 or the memory 36 with the gas supply line 42 combines. The valve 44 can be configured for example as a 3/2-way valve. In addition, a further valve position may be provided, which the two memory 34 and 36 connects to each other, but from the line 42 separates. Downstream of the valve 44 is a controllable throttle device 46 arranged for variable adjustment of the NH ₃ stream, which may be configured as a throttle valve (mass flow controller) or as a controllable Gasdosierventil about.

In main memory 34 is also a temperature sensor at one or more positions 48 arranged to detect a storage temperature T _memory . There is also a pressure sensor 50 at one or more positions of the main memory 34 provided, which measures the accumulator pressure p _memory . For the execution of the method, it is not absolutely necessary for both sensors to be present; on the contrary, only one temperature sensor or one pressure sensor can be installed. In addition, corresponding sensors can also be used in the piping system 42 and / or in memory 36 be arranged (not shown).

The signals of the sensors 48 and 50 find entrance into a control device 52 for controlling the operation of the ammonia storage system 32 , The control device 52 controls in response to these and other signals, the heating power of the electric heaters 38 and 40 , the position of the switching valve 44 as well as the position of the throttle device 46 ,

The control device 52 is in the example shown in an engine control unit 54 integrated, but can also be installed as a stand-alone device. The engine control unit 54 essentially serves the control of the internal combustion engine 12 and controls, in particular depending on an operating point, the opening of the throttle device 22 as well as the injection system 16 , For this purpose, different signal to the engine control unit 54 For example, an engine speed through a speed sensor, a requested engine load by a pedal encoder, an engine temperature by a cooling water temperature sensor, etc. In addition, various gas and temperature sensors in the exhaust duct 24 be arranged, whose signals are also input to the engine control unit 54 or the controller 52 Find.

This in 1 illustrated ammonia storage system 32 shows - when designing the small-volume memory 36 as boot memory - the following operation. When the system is put into operation after a cold start, the required operating pressure is usually not available in order to ensure sufficient ammonia supply upstream of the SCR catalytic converter 30 to ensure. At the same time, both stores are heated for this purpose 34 and 36 each via their heater 38 respectively 40 , Due to its low volume, the boot memory has 36 after a short heating time reached its required temperature and thus the operating pressure. Once this is the case, the valve becomes 44 switched to a position that only the start memory 36 with the gas supply line 42 combines. In this phase, therefore, the entire ammonia requirement of the SCR catalyst 30 through the boot memory 36 fed, the NH ₃ mass flow through the throttle valve 46 is controlled. The NH ₃ requirement of the SCR catalyst 30 is preferably determined operating point dependent, so that the supply via a suitable control of the valve 46 or Massflow controller takes place as needed.

As soon as the main memory 34 has reached its operating pressure, there is a switchover of the ammonia supply via the valve 44 , so that the main memory 34 with the gas supply line 42 connected is. Now the entire ammonia supply can be removed from the main memory 34 be covered. In addition, a replenishment of the starting memory 36 with ammonia, also from the main storage 34 is covered. It can either the connection between the main and start memory 34 . 36 immediately after the supply change to the main memory 34 or at a later time, for example after the system has been switched off.

In an alternative embodiment, the small-volume memory 36 designed as a working memory, the throughout the operation of the NH ₃ supply of the SCR catalyst 30 takes over and in turn continuously or discontinuously through the main memory 34 is loaded with NH ₃ . In this case, main memory 34 , Operating memory 36 and SCR catalyst 30 also be connected in series.

Hereinafter, the determination of the NH ₃ loading state becomes one of the memories of the SCR catalyst system 28 described. The inventive method can in principle for each of the memory 34 . 36 however, is for main memory 34 Of particular interest, since the start or operating memory 36 anyway is constantly refilled, which is why the following description is only on the main memory 34 refers.

Level monitoring of the NH ₃ storage tank

To a level of main memory 34 To determine, the present invention takes advantage of the fact that the heat capacity of the memory 34 changes with the loading state of the NH ₃ storage material. This is shown in Table 1 using the example of SrCl ₂ (NH ₃ ) _x , from which it can be seen that the saturated salt (NH ₃ -enriched form) has almost ten times the specific heat capacity of the NH ₃ -free form. Table 1: SrCl ₂ (NH ₃ ) ₈ SrCl ₂ NH ₃ spec. Heat capacity [J / mol · K] 707.4 76 35.8 (at 25 ° C) Molecular weight [g / mol] 294.76 158.52 17.03

There is thus a dependence of the heat capacity on the NH ₃ loading state of the storage 34 in front. The heat capacity of the store 34 , which is composed of the heat capacity of the NH ₃ storage material as well as all constructive elements (storage jacket, insulation material, heating device and sensors), has a direct influence on the cooling and heating behavior of the storage tank. According to the invention, therefore, during a heat input into the memory 34 and / or a Wärmeaustrags from the same at least one state variable of the memory detected, which characterizes its heating behavior and / or its cooling behavior. Depending on the state variable, the NH ₃ charge state can then be determined by calculation and / or via maps. In particular, as state variables temperature-related or pressure-related variables come into question, with the temperature sensor 48 or the pressure sensor 50 can be detected.

In particular, a temperature change or a temperature gradient in the memory with the temperature sensor 48 be recorded. The temperature change can be described by Equation 2, in which the first term of the parenthesized expression is the temperature change due to heating by means of the heater 38 taken into account the amount of heat supplied, the second term, the heat exchange with the environment and the third term, the desorption or absorption heat of the NH ₃ storage material. In Equation 2, T _{memory means} the temperature of the memory 34 , C _memory (level) the level-dependent heat capacity of the store, Q _ZU that via the heater 38 supplied heat quantity, α the heat transfer coefficient between a storage _jacket and the environment, A the shell surface of the storage tank, T _jacket the temperature of the storage _jacket , T _ambient the ambient temperature, n _NH3 the NH ₃ substance quantity and ΔH _r the desorption or absorption enthalpy of the NH ₃ - storage material.

The temperature change of the memory during its heating or during its cooling and the change in the free amount of NH ₃ in the gas phase of the available pore and line volume cause a pressure change in the memory 34 , This relationship can be described, for example, by Equation 3, in which ΔS _{r is} the desorption or absorption entropy of the NH ₃ storage material, R _m the universal gas constant and V _free the free gas volume in the store 34 , in particular in the pores of the storage material and in the lines mean.

Since according to equation 3 on the temperature change dT _memory / dt the level-dependent heat capacity according to equation 2 is included in the pressure change, the latter is also suitable as a state variable used in the present invention for monitoring the cooling and heating behavior of the memory and the determination of its loading condition can be.

The equations 2 and 3 show examples of ways to describe the dependencies of the change in temperature or pressure change in the memory 34 during its heating or cooling. By detecting the temperature and / or pressure change thus the heat capacity of the memory _storage C may be calculated and from this the heat capacity of the storage material, ₃ -Beladungszustand can be closed resulting in its NH. These equations may be in computer readable form in the controller 52 be stored and used for the determination of the NH ₃ -Beladungszustandes.

In an advantageous embodiment, this determination is carried out during a heating phase and / or a cooling phase, that is, in operating phases in which no NH ₃ from the memory 34 is removed to this in the exhaust duct 24 to dose. This simplifies the connections.

In an alternative embodiment, the relationships between heat inlet and outlet and the temperature or pressure change in the memory 34 determined empirically at defined NH ₃ Belandungszuständen and stored in maps that in the control device 52 be deposited in computer-readable form.

2 shows an example of the time course of the with the pressure sensor 50 detected NH ₃ vapor pressure in the case of a 60% and 90% NH ₃ level. Here, the continuous heating was stopped as soon as the desired operating pressure (indicated by the horizontal bar) was reached. This is in the case of practically full memory at a heating time 1 the case and the only partially loaded memory only during the heating time 2 , It will thus be seen that the necessary heat-up time to reach the operating pressure (or other predetermined pressure) with decreasing level of the memory 34 rises sharply.

2 illustrates that in the context of the present invention, instead of the temperature or pressure change, a heating time (or a cumulative, by the heater 38 introduced heating power) can be measured, up to which a predetermined pressure is built up in the memory, and depending on the thus detected heating time of the NH ₃ -Beladungszustand the memory can be read from a map or a characteristic. Likewise, a time span and / or cumulative heating power can be detected until reaching a predetermined storage temperature and used for determining the load.

The diagnosis may be during a heating or cooling phase of the memory 34 be performed. The implementation during the cooling phase has the advantage that the memory no heat is supplied. Since the cooling process is a relatively slow process, the temperature and / or pressure change in the memory very well follows the absorption and desorption equilibrium of Equation 1. The diagnostic process during the cooling phase becomes a corresponding tracking strategy in the controller 52 applied. On the other hand, the consideration of the state variables during the heating phase has the advantage that the evaluation can be carried out during vehicle operation.

To improve the diagnosis, further diagnosis times can be defined at predefined time intervals at which the current storage pressure and / or the current storage temperature is queried. These state variables can also be used with suitable, in the control device 52 stored characteristic curves and maps are adjusted and from this the level can be determined.

Evaluation of the transition between two decomposition stages

The release of the NH ₃ amount stored in a metal ammine salt takes place in several decomposition stages. For example, the SrCl ₂ (NH ₃ ) _x system has two decomposition stages, with 7 mol of NH _{3 released} per mole of SrCl ₂ in the first decomposition stage and 1 mol of NH ₃ per mol of SrCl ₂ in the second decomposition stage. In the second decomposition stage, the required operating temperature and desorption enthalpy (heating power) are higher than in the first decomposition stage. For energy reasons, it makes sense, therefore, the memory 34 not completely empty, but only the first decomposition stage for the NH ₃ supply of the catalyst system 30 to use. Thus, in the strontium chloride storage material, the 12.5% of the releasable in the second stage decomposition NH ₃ amount can be kept in reserve as a reserve to ensure system functionality.

In the context of the present invention, therefore, it is possible with advantage to determine that NH ₃ filling level which characterizes the transition from the first to the second decomposition stage of the NH ₃ storage material used.

3 shows the example of the strontium chloride salt temperature-pressure equilibrium curves for the memory material in its first decomposition stage (SrC1 ₂ (NH ₃ ) _x with x = 2 to 8) and for its second decomposition stage (SrCl ₂ (NH ₃ )). In order to determine in which decomposition stage the storage material is present, the two state variables storage temperature and storage pressure can now be measured. By matching with a stored pressure-temperature map, the decomposition level can be determined.

This method becomes even more accurate when two or more "bases" are detected to determine the decomposition level. For example, in a first step before starting the system, it can be checked which pressure is present in the memory at the given temperature. Based on the in the control device 52 deposited equilibrium curves can be differentiated, whether the point lies on the curve for the first or the second decomposition stage. Then, by heating the system, a certain desired pressure is adjusted, which is preferably in the range of 1.5 to 3.5 bar. This operating pressure is in 3 illustrated by the horizontal bar. If the temperature present at the predetermined pressure is now detected, it can again be determined on the basis of the stored characteristic curves which decomposition level corresponds to the point.

Since the cooling process is relatively slow, the system follows very well the equilibrium curve according to equation 1, so that the real measuring system correlates well with the model.

Once the transition to the second stage of decomposition is diagnosed, the controller will 52 a cartridge change signal is output to the driver and / or to an OBD system. Since there is still a reserve of 12.5% of the maximum storable NH ₃ amount at this point in time, it is possible on this basis to determine a route which can presumably still be covered by the vehicle until the next memory change. This information can also be displayed to the driver.

Level control after memory change

The method according to the invention is also suitable for carrying out plausibility checks which can be used to ensure that it is not possible to manipulate a memory change. For example, it must be prevented that, after a driver has been asked to change memory, the empty memory from its holder removed and the same memory is immediately reinstated to simulate an OBD system memory change and re-initialize the system.

In this context, during the first system start, after the onset of a memory, during a heat input into this and / or a heat discharge, this state variable is again detected from this at least one characterizing the heating behavior and / or the cooling behavior of the memory. The detected state variable is then checked as part of a plausibility check with suitable criteria, which ensure that the state variable correlates with a NH ₃ -loading state of the memory, which corresponds to an at least approximately full cartridge. For example, here the time span and / or the cumulative heating power can be detected until a predetermined pressure in the memory, in particular its usual operating pressure, is reached. With reference to 2 Thus, the detected heating time can be adjusted to reach the operating pressure with the heating time 1, which was determined for a memory, the NH ₃ -Beladungszustand is at least 90%. In this case, a tolerance range .DELTA.t can be specified for the heating time. If the detected heating time is within the tolerance range Δt, the system determines a properly filled memory and releases it. On the other hand, if the detected heating time is below the tolerance range, the driver is still requested to change the memory. Falling below a predetermined lower critical value for the heating time or another criterion, even the vehicle operation can be disabled.

As an alternative to the recorded heating duration or cumulative heating power, it is also possible to check whether a pressure gradient and / or the course of the pressure lie within a predetermined tolerance range.

In order to detect the insertion of a new memory in the cartridge holder, in the cartridge holder, a suitable mechanism, such as a push button switch or an optical signal transmitter, be integrated, which is triggered when inserting the cartridge. In order to handle system manipulations even more securely, in the control algorithm of the control unit 52 a counter (timer) integrated which is reset after a memory change and starts to run. If, after a memory change, the above-described plausibility check has been carried out once, a predetermined operating time and / or a predetermined distance traveled must be reached before the level control may be triggered again after a memory change.

However, the prerequisite should be that the initial level control could actually be completed, which can not always be ensured in the case of short-haul operations. If, therefore, the initial fill level control can not be completed after a memory change, for example due to a too short operating time, it may be provided to carry out the plausibility check so often that it can be completed.

In addition, plausibility checks can be carried out with the help of NO _x sensors and / or NH ₃ sensors.

Sealing the memory

To further ensure that only properly filled memory is used, according to an embodiment of the invention, the memory cartridges are sealed at the factory after their re-filling or initial filling. For this purpose, a suitable mechanically actuable device may be present on the storage cartridge and / or on the vehicle-mounted cartridge holder. When inserting the memory in its holder is actuated by the seal on the cartridge, the mechanism on the cartridge holder. This procedure should only be possible once to prevent a cartridge that is not filled properly from changing cartridges.

The sealing mechanism on the storage cartridge may be, for example, a spring-loaded bolt that exerts a defined force on the triggering mechanism on the vehicle-mounted cartridge holder when the cartridge is inserted. Once this pin has been pressed, in particular pushed in, it is locked. This lock should only be able to be handled by special tools by the companies responsible for refilling.

Memory chip on the memory cartridge

As a further measure to ensure that the empty cartridge is replaced by a full cartridge during a memory change, a memory chip is attached to a further embodiment of the cartridge, the control device 52 reports that a new full memory cartridge has been inserted. In a further advantageous embodiment, additional data can be stored on the chip, for example the amount of NH ₃ stored, a quantity of NH ₃ which can be withdrawn while maintaining a reserve, and / or other data. Further details can include, for example, information on the storage material, in particular a pressure-temperature characteristic curve, characteristic curves for level detection, information on desorption enthalpy and / or entropy, etc.

Once the memory cartridge is empty or has reached a lower level limit, this is registered on the memory chip. The memory chip is then reset by default after refilling.

leak test

A further aspect of the invention relates to a method and a device for checking the tightness of the ammonia storage system 32 of the SCR catalyst system 28 , in particular the line system 42 in particular all lines between the different memories 34 . 36 and the exhaust duct 24 includes.

A first version is in 4 in which an SCR catalyst system 28 corresponding 1 is shown, wherein like components are designated by the same reference numerals. Some elements, such as the controller 52 , for the sake of clarity in the 4 and 5 not shown. In addition to the throttle valve 46 includes the gas supply pipe system 42 according to 4 further shut-off devices 56 . 58 , in particular valves or solenoid valves, through which the memory 34 . 36 from the pipe system 42 can be separated. With 60 is also called a check valve. In order to check now if the line system 42 has a sufficient tightness, is a predetermined overpressure in the conduit system 42 with closed shut-off devices 46 . 56 . 58 built up. The separation the memory 34 and 36 from the pipe system 42 is necessary so that no pressure change can take place through a possible NH ₃ desorption or adsorption process. Then by means of a gas supply line system 42 installed pressure sensor 62 checks whether the pressure can be maintained for a predetermined period of time. If this is the case, then by means of the control device 52 the system marked as in order. On the other hand, if a pressure drop exceeding a predetermined tolerance is observed, a leak is detected and reported and the system deactivated. In addition, safety valves can be integrated into the system, which are closed in the event of a leak to prevent ammonia leakage into the environment. Then by the control device 52 a signal is issued to the driver requesting that he visit a workshop.

In an alternative embodiment of a system for leak testing the gas supply pipe system 42 , what a 5 are shown, are the sections of the line system to be checked 42 with a double outer wall 64 designed.

In one embodiment, a gas, for example air, is present between the two conduit walls at a predetermined pressure which is connected to the pressure sensor 62 is detected. The gap between the two walls should be hermetically sealed from the environment, especially not with the exhaust duct 24 and the stores 34 . 36 communicate. If, within a predetermined time interval, a pressure change which exceeds a predetermined limit value is detected, the presence of a leak by the control device is detected 52 detected. So that a hole in the outer jacket of the double-walled pipe 64 can be detected, a pressure deviating from the ambient pressure, ie a negative pressure or an overpressure is applied in the intermediate space.

In case of double-walled piping according to 5 For example, further variants for leak testing can be provided which are based on the direct or indirect detection of penetrating ammonia into the intermediate space. In particular, a strongly NH ₃ -adsorbierendes material can be arranged in the gap, which adsorbs NH ₃ -endothermally, but especially exothermic. A temperature change with a temperature sensor 66 is detected in the gap and does not correlate with a change in ambient temperature leads to the detection of leakage.

Alternatively, also a strong NH ₃ adsorbing material in the space of the double-walled conduit system 64 be arranged, which leads to a pH change due to the adsorption. This pH change can be monitored by means of a pH sensor (in 5 not shown).

In a further alternative embodiment, an NH ₃ sensor 68 in the intermediate space of the double-walled pipe system 64 be arranged, which makes a direct measurement of the NH ₃ concentration in the intermediate space.

Function check of the dosing device

To the example designed as a throttle valve metering 46 Functionally check is proposed, in a first step with closed dosing 46 to perform a pressure build-up in the pipe system. As soon as a suitable pressure build-up is registered after a system start, this indicates that gaseous NH _{3 is present} for the metering in the system and that a tightness of the valve 46 is present. In addition, it can be checked during system operation whether a predetermined pressure in the piping system 42 is present.

In addition, the system function can be monitored by means of a flow measurement of the metering device designed as massflow regulator. Additionally or alternatively, the NO _x conversion at the SCR catalyst 30 monitored via NO _x sensors in the exhaust duct 24 upstream and / or downstream of the catalyst 30 are installed.

Alternatively, via the detection of NH ₃ upstream of the SCR catalyst 30 by means of a NH ₃ sensor installed there or by means of an NH ₃ cross sensitivity of the NO _x sensor, the correct metering function of the metering device 46 be monitored.

LIST OF REFERENCE NUMBERS

10

vehicle

12

internal combustion engine

14

exhaust system

16

injection

18

cylinder

20

intake port

22

throttling device

24

exhaust duct

26

first catalyst

28

SCR-catalyst system

30

SCR catalyst

32

Ammonia storage system

34

main memory

36

Memory (start memory / operating memory)

38

heater

40

heater

42

Gas supply line

44

Valve

46

Dosing device (throttle valve / massflow controller)

48

temperature sensor

50

pressure sensor

52

control device

54

Engine control unit

56

Valve

58

Valve

60

check valve

62

pressure sensor

64

Double outer wall

66

temperature sensor

68

NH ₃ sensor

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 102006061370 A1 [0005]
• EP 1977817 A1 [0006]

Claims (13)

Method for determining an NH ₃ charge level of a memory ( 34 ) of an ammonia storage system ( 32 ) of a catalytic system operating on the principle of selective catalytic reduction (SCR) ( 28 ), whereby the memory ( 34 ) contains an NH ₃ storage material which is capable of reversibly binding ammonia (NH ₃ ) as a function of temperature, and with a heating device ( 38 ), characterized in that during a heat input into the memory ( 34 ) and / or heat discharges from the memory ( 34 ) at least one, a heating behavior and / or a cooling behavior of the memory ( 34 ) characterizing state quantity of the memory ( 34 ) and the NH ₃ level of the store ( 34 ) is determined as a function of the at least one state variable. A method according to claim 1, characterized in that the at least one, the cooling behavior and / or the heating behavior of the memory ( 34 ) characterizing state variable is observed during an operating phase in which the memory ( 34 ) no ammonia is removed, in particular during heating of the memory ( 36 ) at system start or when the memory cools down ( 34 ) after switching off the system. Method according to claim 1 or 2, characterized in that the at least one state variable is a temperature-related and / or pressure-related variable, in particular a pressure-related variable. A method according to claim 3, characterized in that the at least one state variable a temperature change in the memory ( 34 ); a pressure change in the memory ( 34 ); a time period and / or cumulative heating power until a predetermined temperature in the memory has been reached ( 34 ); a period of time and / or cumulative heating power until a predetermined pressure is reached in the memory ( 34 ); a temperature reached after a predetermined time and / or predetermined cumulative heating power in the memory ( 34 ) and / or a pressure reached after a predetermined time and / or predetermined cumulative heating power in the memory ( 34 ). Method according to one of the preceding claims, characterized in that depending on the at least one state variable, a heat capacity of the memory ( 34 ) and depending on the heat capacity of the memory ( 34 ) the NH ₃ charge level of the memory ( 34 ) is determined. Method according to one of claims 1 to 5, characterized in that the determination of the NH ₃ -loading level of the memory ( 34 ) is done arithmetically using stored computational rules. Method according to one of claims 1 to 5, characterized in that the determination of the NH ₃ -loading level of the memory ( 34 ) using stored maps. Method according to one of the preceding claims, characterized in that the determination of the NH ₃ loading level for predicting a range of a with the SCR catalyst system ( 28 ) equipped vehicle ( 10 ) is carried out. Method according to one of the preceding claims, characterized in that the determination of the NH ₃ -loading level for level control of a newly loaded memory ( 34 ) is carried out. A method according to claim 9, characterized in that the level control once after Einwechselung the memory ( 34 ) is carried out and a renewed check is not triggered before expiry of a predetermined operating time or a predetermined distance traveled. Method according to one of the preceding claims, characterized in that the NH ₃ storage material of the memory ( 34 ) from the group of NH ₃ -complexing metal salts, in particular the alkali and alkaline earth metal salts, preferably comprising MgCl ₂ (NH ₃ ) _x , CaCl ₂ (NH ₃ ) _x and SrCl ₂ (NH ₃ ) _x ; and NH ₃ adsorbing solids, especially activated carbon and zeolites. SCR catalyst system ( 28 ) with at least one SCR catalyst ( 30 ) and an ammonia storage system ( 32 ) the at least one with a heating device ( 38 ) equipped memory ( 34 ) which contains an NH ₃ storage material which is capable of reversibly binding ammonia (NH ₃ ) as a function of temperature, characterized by a control device ( 52 ) configured to carry out a method according to any one of claims 1 to 11. Vehicle ( 10 ) with an SCR catalyst system ( 28 ) according to claim 12.

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