Device for Determining the State of a Soot Particle Filter

Abstract

A device determined the state of a soot particle filter of an internal combustion engine. An electrical measuring arrangement is embodied as a soot sensor for measuring a soot deposit and comprises an electrical component with a conductor structure for exciting an electrical or magnetic field which can be influenced by the soot deposit and characterizes an electrical or magnetic characteristic variable of the component. A measuring arrangement measures the electrical or magnetic characteristic variable of the component as a measure of the soot deposit. The conductor structure is arranged so that a partial volume region of the soot particle filter is penetrated by the electrical field, and the partial volume region forms part of the component.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a soot particle filter with a separate soot sensor which is arranged downstream thereof in the flow direction,

FIG. 2 is a perspective view of the soot filter body of a corresponding soot particle filter with pairs of electrodes arranged on the longitudinal sides,

FIG. 3 is a schematic illustration explaining the measuring process,

FIG. 4 shows a further arrangement of a pair of electrodes which are arranged on two adjacent longitudinal sides of the soot filter body,

FIG. 5 shows a pair of electrodes which are arranged in the interior of the soot filter body,

FIG. 6 shows a further arrangement of a pair of electrodes which are arranged in the interior of the soot filter body,

FIG. 7 is a characteristic curve explaining the changing electrical resistance,

FIG. 8 is a characteristic curve explaining the changing capacitance,

FIG. 9 is two characteristic curves explaining the changing alternating current resistance at different frequencies,

FIG. 10 is a first schematic cross-sectional view of a soot particle filter with an associated arrangement of electrodes for determining a filter charge,

FIG. 11 is a second schematic cross-sectional view of a soot particle filter with associated arrangement of electrodes for determining a filter charge,

FIG. 12 is a schematic view of an electrode arrangement, developed onto a plane, for determining a filter charge,

FIG. 13 is a schematic perspective view of a soot particle filter component and an associated measuring arrangement for determining the filter charge,

FIG. 14 is a schematic cross-sectional view of the soot particle filter component as seen in FIG. 13 as well as an associated measuring arrangement for determining the filter charge,

FIG. 15 is a first schematic view of a soot particle filter with associated coil-shaped conductor structure for determining the filter charge,

FIG. 16 is a second schematic view of a soot particle filter with associated coil-shaped conductor structure for determining the filter charge, and

FIG. 17 is a diagram showing the relationship between the filter charge and an electrical characteristic variable which correlates thereto and is measured with measuring equipment.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a soot particle filter for motor vehicles, in particular for diesel vehicles. The filter has a housing 10 with an exhaust gas inlet 11 and an exhaust gas outlet 12. The housing 10 contains a soot filter body 13 composed of a ceramic filter material which has a multiplicity of blind ducts 14 which open on the inlet side and a multiplicity of blind ducts 15 which open on the outlet side. The exhaust gas enters the inlet-end blind ducts 14 and passes through the walls into the outlet-end blind ducts 15. In the process, the soot particles are filtered out through these walls.

A soot sensor 16 is arranged in the exhaust gas outlet 12 downstream of the soot filter body 13 in the flow direction A. The sensor could in principle also be arranged closer to the soot filter body 13 or on its rear side. This soot sensor 16 is composed essentially of a ceramic substrate 17 in the form of a small plate, on which at least two measuring electrodes 18, 19 are provided. They can be provided, for example, using thick film technology, by painting on or spraying on or in the form of an interdigital electrode structure. Soot particles are deposited on the surface of the ceramic substrate 17 and thus change the electrical impedance between the measuring electrodes 18, 19. The changing impedance is a measure of the quantity of the deposited soot particles. This is explained in even more detail in conjunction with FIGS. 4 and 7 to 9. Not only the quality of the exhaust gas but also the state of the soot filter body 13, for example even a passage through this soot filter body, can be determined for this soot sensor 16.

In the embodiment illustrated in FIG. 2, two pairs of electrodes which are composed of measuring electrodes 20 to 23 are arranged on opposite longitudinal side faces of the soot filter body 13. These measuring electrodes 20 to 23 can be provided on the ceramic soot filter body 13 in the form, for example, of wires, small plates, applied surfaces or using thick film technology. In this exemplary embodiment, the soot filter body 13 itself serves as a sensor and the dependence of the electrical impedance between the measuring electrodes 20, 21 and 22, 23 on the charge of the soot filter body with soot particles is utilized. The measured impedance is in each case a measure of the soot charge of the particle filter and thus a measure of the state of the particle filter.

An impedance measuring device 24 (e.g., FIG. 13), which can also be embodied as a simple resistance measuring device, for example also as the DC resistance measuring device, is used to measure the impedance between the measuring electrodes 20, 21 and 22, 23. FIG. 7 shows that the resistance between the measuring electrodes decreases as the operating time t increases because soot particles which are still conductive collect between the measuring electrodes in the soot filter body 13. Correspondingly, FIG. 8 shows the capacitance between the measuring electrodes which changes as the soot charge grows, for the case in which the impedance measuring device 24 is embodied as a capacitance measuring device. Finally, FIG. 9 also shows the changing alternating current resistance for an increasing soot charge g/l (grams per liter volume) for two different measuring frequencies. The resistance measuring scale represented on the left-hand side applies for the measurement frequency 1 MHz, and the resistance measuring scale illustrated on the right-hand side applies for a measurement frequency of 4 MHz.

In addition to the absolute value of the electrical impedance, the phase of the electrical impedance can also be used as a measure of the soot-charged state of the soot particle filter.

The described measuring methods can of course also be used correspondingly for the soot sensor 16 and its measuring electrodes 18, 19.

In the embodiment illustrated in FIG. 2, the two pairs of electrodes with the measuring electrodes 20, 21 and 22, 23 are arranged one behind the other in the flow direction A. As a result, the soot particle charge can also be measured with spatial differentiation. The number of measuring electrodes used for this purpose can of course also be larger. In this context, these pairs of electrodes can also be arranged with an offset with respect to one another in the axial direction and in the radial direction, and can be arranged, for example, in a spiral shape. An alternative or additional arrangement on the end faces of the soot filter body 13 is also contemplated. In the simplest embodiment, it is, of course, also possible to provide just a single pair of electrodes.

Further possibilities for the provision of the measuring electrodes are illustrated in FIGS. 4 to 6. For example, FIG. 4 shows that two measuring electrodes 25, 26 can be arranged on two adjacent longitudinal sides of the soot filter body 13. FIG. 5 shows that two measuring electrodes 27, 28 can be arranged on different blind ducts 14, and FIG. 6 shows that two measuring electrodes 29, 30 can be arranged opposite one another on one of the blind ducts 14. In these illustrated embodiments, a plurality of pairs of electrodes can also be arranged one behind the other in the flow direction A, in which case combinations of the illustrated arrangements are also possible.

The measurement signal for the soot particle charge of the soot filter body 13 or of the ceramic substrate 17 is temperature-dependent. For this reason, for the purpose of compensation the temperature has to be measured by at least one temperature sensor, in which case the temperature measurement signal is then used to compensate the characteristic curves and measurement results illustrated in FIGS. 7 to 9. Such a temperature sensor can be arranged, for example, at any desired location in the soot filter body 13, but it can also be integrated, for example, in or on one of the measuring electrodes, for example in the form of a printed-on thick-film metal resistor. It is also contemplated in this context for the sensor to be a printed-on electrical conductor structure, or a measuring electrode or a plurality of measuring electrodes can be in the shape of an electrical conductor track whose resistance value depends on the temperature. The resistances of the measuring electrodes themselves are then a measure of the temperature, and the impedances between the measuring electrodes are a measure of the filter state or the charge of the filter with soot. Another possibility is for the temperature sensor to be arranged under a measuring electrode, separated by an insulation layer. In the case of the soot sensor 16, the temperature sensor can also be arranged on the rear side of the ceramic substrate 17 or also be arranged under the measuring electrodes 18, 19, separated by a dielectric.

The obtained measured values or the measurement curves shown in FIG. 7 to 9 can also be used for automatic regeneration of the soot particle filter. For this purpose, limiting values can be formed for the resistance or the capacitance or impedance, the regeneration of the filter being triggered automatically after the limiting values are reached. This is usually carried out by changing the engine operating state so that relatively hot exhaust gases are formed and burn off the soot particles which are deposited in the soot particle filter. This regeneration process changes the resistance values or capacitance values and/or impedance values in the rear direction and new limiting values at which the regeneration process is ended can be set.

FIG. 10 illustrates a soot particle filter 13 in a cross section of the gas inlet side. Here, components which correspond to those in FIG. 1 are provided with the same reference symbols. The soot particle filter 13 is installed in the housing (not illustrated here) and is secured mechanically in the housing by a mounting mat 33 which surrounds the soot particle filter 13.

According to the invention, a measuring arrangement for the soot particle filter 13 is provided with a first measuring electrode 31 and a second electrode 32 with which the charge of the soot particle filter 13 can be determined. Here, the measuring electrodes 31, 32 are preferably of planar configuration and are arranged opposite one another. In this context, the measuring electrodes 31, 32, or one of them, can be arranged in the interior of the soot particle filter 13. Details are given below on advantageous arrangements in which the measuring electrodes 31, 32 are arranged on the outer surface of the soot particle filter 13 or at a short distance from the outer surface of the soot particle filter 13.

FIG. 10 illustrates an embodiment in which the electrodes 5, 6 are arranged diametrically opposite one another resting directly on the outer surface of the soot particle filter 13. The measuring electrodes 31, 32 form in this way the plates of a plate capacitor whose dielectric is formed by the material which is located between the measuring electrodes 31, 32. There is provision for the impedance measuring device 24 to be used both for supplying the voltage and current and for evaluating the measurement signal.

The electrical impedance which is effective in the partial volume region of the soot particle filter 13 between the measuring electrodes 31, 32 is dependent, on one hand, on the area of the measuring electrodes 31, 32 and on the distance between them, i.e., the diameter of the soot particle filter 13 at the respective location. On the other hand, however, the impedance is also dependent on the dielectric constant of the material located between the measuring electrodes 31, 32. Owing to the comparatively high dielectric constant of soot deposited in the soot particle filter 13, the soot charge in the volume region measured by the impedance measurement can be measured with high accuracy. There is provision here for the electrical impedance to be evaluated both with respect to its virtual part and to its real part and in terms of absolute value and phase. The aforesaid measurement variables are referred to below as a measurement signal for the sake of simplification. In this context, the evaluation of the measurement signal can be performed by the impedance measuring arrangement 24 or by a separate evaluation device (not illustrated).

In this context it is advantageous for the measurement frequency for determining the impedance to be suitably selected, and if appropriate varied, with the aim of obtaining the largest possible measurement signal and the most reliable possible information about the charge. The frequency of the measurement voltage is advantageously set in the range between 1 kHz and approximately 30 MHz. A frequency range from approximately 1 kHz to approximately 20 MHz is preferred, and the measurement frequency is particularly preferably approximately 10 MHz. It is also advantageous to perform simultaneous measurements of the temperature in the most significant soot particle filter region or in the region of the measuring electrodes 31, 32. As a result, temperature dependencies of the impedance measured value can be corrected or a temperature compensation of the measurement signal can be performed.

The measuring electrodes 31, 32 can, for example, be provided on the surface of the soot particle filter 13 by way of thick film technology or else by an electrically conductive material being sprayed or painted on. It is also advantageous to apply metal-containing films with the filter body, for example by sintering in close contact. The measuring electrodes 31, 32 can also be secured positionally on the filter body by the pressing force of the mounting mat 33 which occurs in the installed state.

FIG. 11 illustrates a further advantageous arrangement in which the functionally identical components to those in FIG. 10 are provided with the same reference symbols. In contrast to the arrangement illustrated in FIG. 10, the measuring electrodes 31, 32 according to FIG. 11 are not arranged directly in contact with the soot particle filter 13 but rather at a short distance from the surface of the soot particle filter 13. For example, owing to the low thermal loading it may be advantageous to arrange the measuring electrodes 31, 32 in the outer region of the mounting mat 33, or to embed them in the mounting mat 33. Depending on the thickness of the mounting mat 33, the measuring electrodes 31, 32 are typically arranged at a distance in the millimeter range from the surface of the particle filter body. For this arrangement it is advantageous to construct the measuring electrodes 31, 32 in film form.

According to the present invention, at least two, and preferably more, measuring electrodes 31, 32 can be provided at different locations, which permits the charge in the soot particle filter 13 to be determined with spatial resolution. The partial volume regions which are measured by the impedance measurement can overlap here or be separated from one another. In this way, the charge of the soot particle filter 13 can be determined locally. Depending on the size of the soot particle filter 13 and after the aimed-at spatial resolution, three, four or more electrode arrangements can be arranged, preferably in the direction of flow of the exhaust gas with an offset. Since in particular the outflow end region of the soot particle filter 13 is susceptible to blockage, it is advantageous when there are a plurality of measured partial volume regions to arrange them increasingly densely in the direction of flow of the exhaust gas, which improves the accuracy of the determination of the charge.

FIG. 12 is illustrates an electrode arrangement of two pairs of electrodes 31, 32 and 31′, 32′ developed onto a plane. The electrodes 31, 32 and 31′, 32′ are preferably applied as a layer on a thin and flexible carrier 36 which is mounted resting on the soot particle filter 13 or on the mounting mat 33. Feed lines 34 to the electrodes 31, 32 and 31′, 32′ are provided on the carrier 36 and lead to connecting contacts 35 which are preferably arranged at an end region of the carrier 36. This thus easily permits connection to the impedance measuring device 24 by a plug contact or clamping contact (not illustrated). This arrangement additionally has the advantage that only a single through-contact with the housing which surrounds the soot particle filter 13 has to be implemented for the connection to the impedance measuring device 24.

It is advantageous to arrange the electrodes 31, 32 and 31′, 32′ at a distance A on the carrier 36 with respect to their central longitudinal axis, which distance a corresponds approximately to half the circumference of the soot particle filter 13. In this way, in the mounted state of the carrier 36 the electrodes 31, 32 and 31′, 32′ are arranged approximately diametrically opposite one another. In addition, it is advantageous to arrange the electrodes 31, 32 and 31′, 32′ on the carrier 36 with an offset in the lateral or longitudinal direction of the carrier 36.

FIG. 13 illustrates a detail of a segment of a soot particle filter 13. Here, the components which correspond to those in FIG. 3 are identified by the same reference symbols.

The soot particle filter 13 is provided with a measuring arrangement with an electrode structure which can be used to determine the charge of the soot particle filter 13. Here, the electrode structure is formed by way of example by a first, approximately rectangular, planar electrode 22, and a second electrode 23 which is arranged diametrically opposite the latter and has the same shape. The electrodes 22, 23 are preferably arranged as illustrated in such a way that the imaginary connecting line which extends between their respective center points is oriented perpendicularly with respect to the longitudinal direction of the ducts 14, 15 of the soot particle filter 13. The electrodes 22, 23 thus form the end faces of a coherent, approximately cylindrical partial volume region of the soot particle filter 13, this partial volume region having an approximately rectangular cross section overall here. The longitudinal dimensions of the cylindrical partial volume region correspond here to the lateral dimensions of the soot particle filter 13 or of the filter segment, and the electrodes 22, 23 each rest on the outside of the particle filter. The electrodes 22, 23 in this way form the plates of a plate capacitor whose dielectric is formed by the material located between the electrodes 22, 23.

The above is illustrated once more in FIG. 14, and the impedance measuring device 24 and the associated feed lines have not again been illustrated. In addition, the soot and/or ash charge 38 which is present on the inside of the blind ducts 14 and is usually in layer form is illustrated schematically.

It is advantageous to use a soot particle filter 13 which is composed of a plurality of segments which are connected in parallel in terms of flow. Here, particle filter segments with a rectangular or square cross section are preferred. In total, external rounding of a soot particle filter which is composed of individual segments still makes it possible to obtain a filter body with a round or oval cross section. The individual segments are connected to one another mechanically in a flush fashion using a partially elastic joining compound. In this configuration, it is advantageous to provide the electrodes 22, 23 at the joint between the two respectively abutting segments so that they rest on the outside of a respective segment and are surrounded by the joining compound. A partial volume region of the soot particle filter 13 which is measured by the measuring arrangement can, with the described measuring arrangement, also be arranged completely in the interior of the filter body and surrounded by particle filter material. In the way described above, a dependence of the filter charge in the radial direction can be determined with respect to the flow direction A of flow of the exhaust gas.

According to the invention, the electrical capacitance or the complex electrical impedance of the capacitor which is formed via the electrodes 22, 23 is determined by the impedance measuring device 24. Here, the symbolic field lines 37 represent in schematic form the partial volume region, measured via the impedance measurement, of the soot particle filter 13.

In the device illustrated in FIG. 15, a soot particle filter 13 is shown with a measuring arrangement with a coil 39 as the conductor structure, with which the charge of the soot particle filter 13 can be determined. The windings of the coil 39 surround a section of the soot particle filter 13. The windings of the coil 39 preferably rest on the surface of the soot particle filter 13 or are at a short distance from it.

The measuring arrangement also comprises an impedance measuring device 24 which is connected to the coil 39 by feed lines. The coil 39 is supplied with a measurement voltage, preferably in the form of an alternating voltage, via the impedance measuring device 24. The section of the soot particle filter 13 which is surrounded by the coil 39 forms the core of the coil, for which reason its inductance L is determined essentially by the material acting as the coil core, or its permeability constant μr. Owing to the different permeability constants μr of soot and of mineral-like ashes, the soot charge and the ash charge can be differentiated by the measured inductance L in this context. The measured inductance here is linked to the complex electrical impedance of the conductor structure 39 and there is provision to evaluate the latter with respect to its virtual part and/or its real part or according to its absolute value and phase. In addition to the inductance L, the electrical losses, such as the ohmic losses or eddy current losses, can also be measured and evaluated. With respect to the aforesaid measurement variables, the term measurement signal is used below for the sake of simplification. There is provision for the impedance measuring device 24 to be used both for supplying the voltage and current and for evaluating the measurement signal. However, the measurement signal can also be evaluated by a separate measuring device.

In this context it is advantageous, when determining the inductance, to suitably select and if appropriate vary, the measurement frequency with the aim of obtaining the largest possible measurement signal and the most reliable possible information about the charge. The frequency of the measurement voltage is preferably set in the range between 1 kHz and approximately 30 MHz. A frequency range from approximately 100 kHz to approximately 10 MHz is preferred, and the measurement frequency is particularly preferably approximately 1 MHz. The amplitude of the supply voltage which is applied to the coil 39 by the impedance measuring device 24 is preferably selected in a range between 1 V and 1000 V. Since the inductance L of the coil 39 is also dependent on its geometry or number of turns, the sensitivity can also be suitably adapted by adapting these variables. It is also advantageous simultaneously to measure the temperature in the most significant filter region or in the region of the conductor structure 39 in order to be able to correct temperature dependencies of the inductance measured value or impedance measured value.

At least two coil-shaped conductor structures can be placed at different locations, which permits the charge in the soot particle filter 13 to be determined with spatial resolution. FIG. 16 is a schematic illustration of an arrangement with a first coil 39 and a second coil 39′ which is arranged opposite it with an axial offset with respect to the particle filter. For reasons of clarity, the impedance measuring device and the feed lines to the coils 39, 39′ are not also illustrated. Functionally identical components to those in FIG. 15 are provided with the same reference symbols. As a result of the offset arrangement of the coils 39, 39′, the charge of the soot particle filter 13 can be determined locally. Depending on the size of the soot particle filter 13 and according to the aimed-at spatial resolution, three, four or more conductor structures can be arranged, preferably with an offset with respect to one another, in the direction of the exhaust gas flow. Since in particular the outflow end region of the soot particle filter 13 is susceptible to blocking, at least one conductor structure is advantageously arranged at the outflow region of the soot particle filter 13.

As well as directly winding the coil-shaped conductor structure 39 around the filter body, further arrangements, which are obtained through simple modifications and are therefore not illustrated in more detail, are contemplated within the scope of the claimed invention. For example, the conductor structure 39 can be in the form of a coil on the internal surface of a housing which surrounds the soot particle filter 13. Furthermore a coil-shaped conductor structure can be advantageously arranged completely in the interior of the soot particle filter 13 parallel to or else transversely with respect to the flow direction A of the exhaust gas. An overlapping arrangement of coils with different diameters permits a coupled coil arrangement with a predefinable coupling to be provided.

When there are a plurality of coils which, in particular, are arranged with an offset with respect to one another, a variable which correlates to the mutual inductance of a coil can be advantageously measured, for example the mutual inductance of a coil with respect to another coil, and evaluates with respect to the filter charge. In one particularly advantageous embodiment (also not illustrated), three coils are arranged one behind the other in the direction of the exhaust gas flow and are, for example, wound around the filter body or surround volume regions of the filter body which lie one behind the other. The central coil can be operated as a transmitter, while the two other coils are respectively operated as receivers for the magnetic field induced in them by the central coil. With such an arrangement, asymmetries with respect to the axial distribution of the filter charge can be advantageously arranged. In this way, an ash charge or filter blockage which originates for the most part from the outflow side of the soot particle filter can be detected and evaluated.

In order to clarify the measuring effect which is measured by means of a measuring arrangement according to FIG. 15, FIG. 17 illustrates the measured inductance L of a coil 39 is illustrated as a function of the volume-related soot charge m/V of the particle filter. The soot-particle-containing exhaust gas of a diesel engine has been applied to the soot particle filter 13 and the measuring arrangement shown in FIG. 15 has been operated continuously under conditions which are close to reality. In this context, inductance values L in the region of several micro-Henrys have been measured for soot charges m/V in the range from several grams of soot per liter filter volume. As is apparent from FIG. 17, the dependence of the inductance L which is evaluated as a measurement signal on the soot charge m/V is approximately linear so that the charge state of the soot particle filter 13 can be determined reliably. The change in inductance which occurs owing to the filter charge can be determined, for example, by the change in the resonant frequency of an oscillatory circuit, which change is determined by the inductance of the conductor structure 39.

The above-explained devices make it is possible to measure accumulations of soot with spatial resolution, and regeneration of the soot particle filter can be initiated if the soot charge exceeds a predefinable limiting value in at least one of the measured partial volume regions. This prevents the soot particle filter being charged locally with soot beyond a permissible minimum degree, and as a result being destroyed at this location by excessive release of heat when regeneration is carried out through the burning off of soot. Of course, regeneration is also triggered if it is detected that the integral overall charge of the soot particle filter exceeds a predefinable threshold value. In addition it is advantageous, if appropriate, to adapt the limiting value which triggers the regeneration in order, for example, to react to changing regeneration conditions. This avoids an unacceptable rise in the counterpressure caused by the particle filter charge. The triggering of the particle filter regeneration in a way which is matched to requirements and adapted to the actual soot charge, limits the number of regeneration processes to a minimum and thus the thermal loading of the soot particle filter and of further exhaust gas cleaning units which may be present is kept low.

The limiting values for the local charge or the integral charge which are most significant for the triggering of regeneration are expediently stored in a control unit. The operation of a diesel engine is preferably controlled by this control unit and reset for regeneration of the soot particle filter. A person skilled in the art is familiar with operating modes which are suitable for this and they therefore do not require any further explanation here.

It is advantageous if the regeneration time of the soot particle filter is defined as a function of the local and/or integral charge, determined before the triggering of the regeneration, for example by a predefined characteristic-diagram-based regeneration time. In this context the temperature in the soot particle filter can be advantageously measured and the regeneration time defined as a function of previously stored soot burning-off rates for the respective temperature. The success of the regeneration is expediently checked by determining the charge again after the regeneration has ended. The predefined regeneration time can be appropriately corrected by evaluating a comparison between the determined charge before and after the regeneration. This avoids the operating state, which is necessary for the regeneration, being maintained for longer than necessary, and the expenditure of energy or additional consumption of fuel for the regeneration is thus kept small. In order to reliably define the duration of the regeneration process it is expedient here to perform averaging over the corresponding values before and after a plurality of regeneration processes.

It is particularly advantageous if the charge of the soot particle filter is also monitored during the regeneration process. The regeneration operating mode is then preferably maintained until the charge in each of the partial volume regions measured by the corresponding pairs of electrodes has dropped below a predefinable lower limiting value. This avoids incomplete particle filter regeneration processes and maximizes the absorption capacity of the soot particle filter for the subsequent normal operating mode of the diesel engine.

The determination of the particle filter charge in two or more partial volume regions of the soot particle filter is advantageously also used to differentiate between a soot charge component and an ash charge component. For this purpose, the fact that the measurement signal of a respective pair of electrodes is composed in an additive fashion from a component which is caused by the soot charge and a component which is caused by the ash charge, and the ash charge grows continuously is utilized. Although the contribution of the ash charge to the overall measurement signal is small, the ash charge component can, if appropriate, be determined if the time profile of the measurement signal is measured and a signal component which grows continuously within the course of the period of use of the soot particle filter 13 is determined and taken into account. In this context it is also advantageous to vary the measurement frequency.

In particular when the ash charge forms a very small component of the measurement signal, the ash charge is advantageously determined indirectly by evaluating the measurement signal in terms of its time profile and spatial profile. In particular, on the basis of the possibly different profile of the measurement signal, to what extent part of the soot particle filter has a greater soot charge than another can be determined, or whether only a small degree of soot charge, or none at all, occurs due to a high degree of deposition of ash in a partial volume region.

Since the absorption capacity for soot particles drops as the ash charge increases, it is advantageous to adapt or define the duration of the regeneration process and/or the time intervals between two regeneration processes as a function of the determined ash charge.

Specifically total blockage as a result of deposition of ash can be determined if there is no further accumulation of soot in one of the measured partial volume regions of the soot particle filter, that is an at least approximately stable measurement signal is present. In particular, when the charge is measured in a multiplicity of regions of the soot particle filter a degree of filling with ash can be determined with respect to the overall volume of the soot particle filter. As a result, the possibility of such particle filter becoming unusable owing to an excessive ash charge can be detected in good time and an appropriate warning message can be issued. It is advantageous in this context to carry out a predictive calculation about the further profile of the deposition of ash and to issue a warning message if the remaining residual running time up to the point when the soot particle filter becomes unusable drops below a predefinable value.

In the case of a wall flow filter, the filter may also become unusable owing to a stopper breakage. As a result, there is no longer any filter effect in the respective region. This can advantageously be detected by a separate soot sensor arranged downstream of the soot particle filter. However, this type of damage can also be detected if there is no longer any appreciable rise in the charge in a respective region over a predefinable time period. There is also provision for a fault message to be issued for this type of damage.

A further improvement in the reliability when the charge state is determined and when the soot particle filter is operated is obtained if, in addition to the measuring arrangement according to the invention, a pressure sensor or differential pressure sensor is used to measure the ram pressure upstream of the soot particle filter. The charge of the particle filter is also characterized on the basis of the corresponding pressure signal. Pressure sensors and signal evaluation methods with which a person skilled in the art is familiar can be used for this, for which reason further information in this regard can be dispensed with.

The pressure sensor permits the reliability and efficiency of the operation of the particle filter to be improved further. It is advantageous for this, for example, to subject the particle filter charge which is determined by the impedance measuring device to checking, plausibility checking or correction by means of the pressure signal. It is advantageous, for example, to use an interrelation of the manner of a cross-correlation to reconcile the values obtained from the measurement signals of the impedance measuring device for the soot charge or for the charge limiting values which are most significant for the process of particle filter regeneration if appropriate with the pressure signal values, or to correct them. The additional pressure sensor can also be used to carry out diagnostics of the impedance measuring device in order to detect faults or defects and if appropriate indicate them.

Claims

1-28. (canceled)

29. A device for determining the state of a soot particle filter of an internal combustion engine, comprising an electrical measuring arrangement configured as a soot sensor for measuring a soot deposit of the soot particle filter, including an electrical component with a conductor structure for exciting an electrical or magnetic field influenceable by the soot deposit and characterizes an electrical or magnetic characteristic variable of the component as a measure of a quantity of the soot deposit, wherein the conductor structure is arranged such that a partial volume region of the soot particle filter is penetrated by the electrical field and the partial volume region forms part of the component, and the electrical component is a coil or a capacitor.

30. The device as claimed in claim 29, wherein the soot deposit is measurable in partial volume regions of the soot particle filter that are different from one another.

31. The device as claimed in claim 29, wherein the measuring means measures a characteristic variable of the component which is linked to the electrical impedance.

32. The device as claimed in claim 31, wherein at least one of the absolute value and phase of the electrical impedance is measurable.

33. The device as claimed in claim 31, wherein at least one of the ohmic resistance, the capacitance and the inductance of the component is measurable.

34. The device as claimed in claim 32, wherein at least one of the ohmic resistance, the capacitance and the inductance of the component is measurable.

35. The device as claimed in claim 29, wherein switching means are provided for automatically initiating regeneration of the filter when a predefinable triggering measured value is reached.

36. The device as claimed in claim 29, wherein switching means are provided for automatically ending the regeneration of the filter when a predefinable limiting measured value is reached.

37. The device as claimed in claim 29, wherein means are provided for at least one of measuring the temperature of the filter and performing temperature compensation on the measurement signal.

38. The device as claimed in claim 29, wherein a coil-shaped conductor structure is arranged at least partially in the interior of the soot particle filter.

39. The device as claimed in claim 29, wherein a coil-shaped conductor structure is arranged outside the soot particle filter.

40. The device as claimed in claim 38, wherein the soot particle filter is of cylindrical configuration, and a coil longitudinal axis of the coil-shaped conductor structure is oriented one of approximately parallel and approximately perpendicular to a longitudinal axis of the soot particle filter.

41. The device as claimed in claim 39, wherein the soot particle filter is of cylindrical configuration, and a coil longitudinal axis of the coil-shaped conductor structure is oriented one of approximately parallel and approximately perpendicular to a longitudinal axis of the soot particle filter.

42. The device as claimed in claim 38, wherein the measuring arrangement further comprises a second conductor structure, the coil-shaped conductor structure being operatively connected to the second conductor structure which has an electrical characteristic variable influenceable by the soot deposit and measurable by the measuring means.

43. The device as claimed in claim 42, wherein the measuring arrangement further comprises a second conductor structure, the coil-shaped conductor structure being operatively connected to the second conductor structure which has an electrical characteristic variable influenceable by the soot deposit and measurable by the measuring means.

44. The device as claimed in claim 42, wherein the second conductor structure is a second coil-shaped conductor structure, and a variable which correlates to the mutual inductance which is effective between the coil-shaped conductor structures is measurable by the measuring means.

45. The device as claimed in claim 43, wherein the second conductor structure is a second coil-shaped conductor structure, and a variable which correlates to the mutual inductance which is effective between the coil-shaped conductor structures is measurable by the measuring means.

46. The device as claimed in claim 42, wherein the coil-shaped conductor structure is arranged in an exhaust gas flow direction with an offset with respect to the second conductor structure.

47. The device as claimed in claim 43, wherein the coil-shaped conductor structure is arranged in an exhaust gas flow direction with an offset with respect to the second conductor structure.

48. The device as claimed in claim 44, wherein the coil-shaped conductor structure is arranged in an exhaust gas flow direction with an offset with respect to the second conductor structure.

49. The device as claimed in claim 44, wherein the coil-shaped conductor structure is arranged in an exhaust gas flow direction with an offset with respect to the second conductor structure.

50. The device as claimed in claim 29, wherein the conductor structure comprises a pair of electrodes with a first electrode and a second electrode spaced from the first electrode, the partial volume region being arranged between the first electrode and the second electrode.

51. The device as claimed in claim 50, wherein at least the first electrode and the second electrode is arranged on or a short distance from an outer surface of the soot particle filter.

52. The device as claimed in claim 50, wherein the measuring arrangement further comprises at least two pairs of electrodes.

53. The device as claimed in claim 51, wherein the measuring arrangement further comprises at least two pairs of electrodes.

54. The device as claimed in claim 52, wherein the first pair of electrodes is arranged in the exhaust gas flow offset from the second pair of electrodes.

55. The device as claimed in claim 53, wherein the first pair of electrodes is arranged in the exhaust gas flow offset from the second pair of electrodes.

56. The device as claimed in claim 29, further comprising a second electrical measuring arrangement operative as a soot sensor for measuring a soot deposit is arranged downstream of the soot particle filter with respect to a flow direction through the soot particle filter.