US20080155967A1

US20080155967A1 - Method for Operating a Particle Trap and Device for Carrying Out the Method

Info

Publication number: US20080155967A1
Application number: US11/963,901
Authority: US
Inventors: Wolfgang Maus; Rolf Bruck
Original assignee: Emitec Gesellschaft fuer Emissionstechnologie mbH; Toyota Motor Corp
Current assignee: Vitesco Technologies Lohmar Verwaltungs GmbH; Toyota Motor Corp
Priority date: 2005-06-24
Filing date: 2007-12-24
Publication date: 2008-07-03
Also published as: JP2008544149A; EP1893853B1; CN101248258B; KR20080019298A; KR100918604B1; DE502006005351D1; DE102005029338A1; CN101248258A; PL1893853T3; EP1893853A1; WO2006136431A1; ES2336701T3; RU2008101806A

Abstract

A method for operating a particle trap, in particular an open particle trap, in an exhaust gas system of an internal combustion engine, includes determining a first point in time in which the particle trap falls below a first effectiveness limiting value, increasing the effectiveness of the particle trap by adjusting at least one specific operating parameter of the internal combustion engine, while exhaust gas produced by the internal combustion engine does not exceed a temperature of 500° C. in the vicinity of the particle trap, determining a second point in time in which the particle trap exceeds a second effectiveness limiting value, and activating normal operation of the internal combustion engine. The method and an associated device ensure operation of an exhaust gas system of an internal combustion engine, with conservation of fuel, savings of materials and simultaneous high effectiveness of the particle trap integrated into the exhaust gas system.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuing application, under 35 U.S.C. § 120, of copending International Application No. PCT/EP2006/006054, filed Jun. 23, 2006, which designated the United States; this application also claims the priority, under 35 U.S.C. § 119, of German Patent Application DE 10 2005 029 338.7, filed Jun. 24, 2005; the prior applications are herewith incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a method for operating a particle trap, in particular an open particle trap, in an exhaust gas system of an internal combustion engine. A device for carrying out the method is also described. The method and the device preferably find application in the automotive industry.
The exhaust gas produced by an internal combustion engine, in addition to gaseous components, in many cases also contains solid particles having emissions to the environment which are prohibited or limited. In order to comply with such requirements, it is known to lead the exhaust gas through a filter, wherein the particles contained in the exhaust gas are retained, at least temporarily, in a porous wall structure. In order to prevent the wall structure from becoming completely clogged, such filters must be repeatedly regenerated. The soot particles are combusted during such a regeneration. In order to combust the particles, temperatures above approximately 600° C. must be provided. That may be achieved by temporarily raising the temperature of the filter or of the exhaust gas, and/or by the addition of additives. It is known for such a regeneration, for example, to displace the load-point of the engine by using an engine control so that significantly hotter exhaust gas reaches the filter. By misfiring a cylinder in the engine, it is also possible to supply a quantity of fuel to the exhaust gas system so that an increased concentration of unsaturated hydrocarbons impinges on a catalytic converter. Combustion occurs upon contact with the catalytic converter, which results in the desired increase in the exhaust gas temperature. Such regeneration methods, however, generally entail increased fuel consumption and significantly higher loads on the filter.
In addition to the aforementioned filters, which have alternatingly sealed channels to ensure that the entire quantity of exhaust gas flows through the walls of the filter, other devices are known for retaining particles contained in an exhaust gas stream. Particular reference is made to a so-called “open” particle trap, which is distinguished by having flow paths or channels that allow the exhaust gas to pass through the particle trap without flowing through the filter material which at least partially adjoins the flow walls. German Utility Model DE 201 17 873, corresponding to U.S. Patent Application Publication No. US 2004/0013580 A1, may be mentioned as an example of such an open particle trap and gives numerous parameters of such a particle trap. Whenever reference is made below to a particle trap, in particular an open particle trap, the contents of German Utility Model DE 201 17 873, corresponding to U.S. Patent Application Publication No. US 2004/0013580 A1, may be consistently and fully drawn upon.
In contrast to the closed filter, which always has a relatively constant effectiveness because all particles must flow through the filter walls, the effectiveness of open particle traps varies. In this context, “effectiveness” refers to the ratio of retained particles to incoming particles (E=Pretained/Pincoming). Thus, if all particles are retained the effectiveness is 100%, whereas if only two-thirds of the particles are retained and the remainder flow out, the effectiveness is 67%.
In the case of open particle traps, the effectiveness is primarily determined by pressure conditions in the interior and surroundings of the particle trap. In this regard it must be noted that particles collect in or on the filter material with increasing operating time, so that the pores or cavities of the filter material through which exhaust gas can flow become at least reduced or diminished in size. This causes a pressure differential between adjoining channels to rise, with the result that for extended operating times the inflowing particles increasingly select the open flow paths to the outside and are no longer trapped, thereby lowering the effectiveness.

BRIEF SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide a method for operating a particle trap and a device for carrying out the method, which overcome or at least partially alleviate the hereinafore-mentioned disadvantages or problems of the heretofore-known methods and devices of this general type, which counteract the above-described loss in effectiveness and which conserve fuel and save on materials as compared to the filters used heretofore.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for operating a particle trap, in particular an open particle trap, in an exhaust gas system of an internal combustion engine. The method comprises:
a) determining a first point in time of the particle trap in which the particle trap falls below a first effectiveness limiting value;
b) increasing an effectiveness of the particle trap by adjusting at least one specific operating parameter of the internal combustion engine, while exhaust gas produced by the internal combustion engine has a sufficiently low temperature in vicinity of the particle trap to ensure that substantially no thermal regeneration of particles occurs;
c) determining a second point in time of the particle trap in which the particle trap exceeds a second effectiveness limiting value; and
d) activating normal operation of the internal combustion engine.
It is particularly preferred to use this method for operating an open particle trap as described above or in German Utility Model DE 201 17 873, corresponding to U.S. Patent Application Publication No. US 2004/0013580 A1. With regard to use of the method in the exhaust gas system of an internal combustion engine, the exhaust gas system of a spark ignition or diesel engine as encountered in the automotive industry is preferred. The special suitability of an open particle trap results from the fact that in this instance a noticeable drop in effectiveness may occur in the course of operation which may be reduced or eliminated according to the invention. Nevertheless, in principle it is possible to also operate closed filters in the manner described herein, since a conversion of the embedded particles is carried out which conserves fuel and saves on materials. The following discussion focuses primarily on an open particle trap which, however, does not limit the method according to the invention to operation of only an open system.
According to step a), at the outset a first point in time is determined, in which the effectiveness of the particle trap falls below a first limiting value. This first effectiveness limiting value is not the same for all applications but, rather, depends on the type of internal combustion engine and the construction of the particle trap itself, for example, in particular on the geometry or alignment of the flow paths in the particle trap. The previously described open particle traps generally have an effectiveness of approximately 80% when new. After a certain operating time, due to embedded particles, the effectiveness fluctuates in an approximate range of 60% for trucks and 30% for passenger vehicles, which is still sufficient to meet regulatory emissions limits over the next few decades. Particular environmental conditions must be present for the conversion of the particles that flow through or become embedded in the particle trap, but typically do not permanently prevail during operation. The driving cycle of the vehicle operator, for example, at least on a temporary basis, is not suitable for ensuring these external conditions. This includes short trips and city driving. During such trips an increased number of particles are generally entrained in the exhaust gas, and they may be present at temperatures that do not support conversion of soot, for example, into gaseous components. As a result, a relatively large quantity of particles accumulates on or in the filter material in the open particle trap, which normally leads to a drop in effectiveness. However, as soon as the effectiveness has fallen below a first effectiveness limiting value, an increase in effectiveness is initiated according to step b) of the invention.
According to step b), the effectiveness is increased by adjusting at least one specific operating parameter of the internal combustion engine. In other words, the internal combustion engine changes from its normal mode to another mode which results in conditions that are favorable for conversion in the particle trap. This is preferably achieved in such a way that no significant additional fuel consumption is detectable, and the temperature of the exhaust gas in the vicinity of the particle trap remains below the limiting temperature required for thermal regeneration. In particular, the exhaust gas in the vicinity of the particle trap does not exceed a temperature of 500° C., and very particularly preferably a temperature of 400° C. The specific operating parameters of the internal combustion engine that may be varied in this case to achieve this increase in effectiveness of the particle trap are further discussed in detail below. The increase in effectiveness causes more particles to be converted or retained, as would be the case during normal operation of the internal combustion engine. Preferably, so many particles are converted that the first effectiveness limiting value is again exceeded.
According to step c), a second point in time for the particle trap is then determined in which the particle trap exceeds a second effectiveness limiting value. The second effectiveness limiting value preferably is greater than the first effectiveness limiting value, optionally even greater than the effectiveness of the particle trap during normal operation. When this second effectiveness limiting value is exceeded, the normal operation of the internal combustion engine is then activated according to step d).
As a basic principle, it is noted that the soot mass flow (m soot) in the exhaust gas system produced by the internal combustion engine is expressed with respect to its behavior in an open particle trap, namely, the soot mass flow that is regenerated ({dot over (m)}_regenerated), the soot mass flow that is embedded in the filter material (m embedded), and the soot mass flow that bypasses the filter material and is emitted to the surroundings ({dot over (m)}_bypass).
{dot over (m)} _soot ={dot over (m)} _regenerated +{dot over (m)} _embedded +{dot over (m)} _bypass (1)
For the case in which during unchanged conditions the regenerated soot mass flow ({dot over (m)}_regenerated) remains the same, as the load in the particle trap increases the embedded soot mass flow ({dot over (m)}_embedded) decreases. As a result, the soot mass flow bypassing the particle trap ({dot over (m)}_bypass) automatically becomes greater. This effect may be eliminated by use of the proposed method, which conserves energy, saves on materials, and with respect to pollutant conversion is particularly effective. It is very particularly preferred to operate the method in conjunction with an open particle trap installed in the exhaust gas system of a diesel engine.
In accordance with another feature of the invention, step a) includes determining an instantaneous loading state of the particle trap with particles. In particular, this is understood to mean that information is obtained on the quantity of particles stored inside the particle trap. In the following discussion, “particles” are understood to mean the following solids in particular: soot particles, ash and combustion products adhering to these solids.
Soot particles are of primary interest in this discussion. In principle, it is possible for the loading state to be directly (quantitatively, for example) determined, but it is also possible to use related (indirect) measured values or characteristic values. Step a) is preferably carried out continuously, at least during normal operation of the internal combustion engine, but a determination at short time intervals may also be practical. In accordance with a further feature of the invention, in this regard it is particularly advantageous to calculate the instantaneous loading state. Such a calculation is preferably made from the starting products which form the exhaust gas, as well as the external environmental conditions in the vicinity of the particle trap. For example, the conversion rate of the exhaust gas as a function of the operating state of the internal combustion engine is also used. In other words, the exhaust gas composition, for example, in particular the nitrogen oxides formation, and its effect on particle removal is taken into account. In each case, specific conversion rates are achieved by reduction of nitrogen dioxide. As an illustration, this conversion of soot particles by nitrogen dioxide is considered in greater detail below. This chemical reaction may be approximately described by the following equation:
C+NO₂→CO₂+½N₂,
where C stands for soot particles, NO₂for nitrogen dioxide, CO₂for carbon dioxide, and N₂for nitrogen. The reaction rate may be expressed by the following relationships:
$\begin{matrix} r^{'} = \frac{1}{A} \cdot \dot{ζ} = \frac{1}{A} \cdot \frac{{\dot{ζ}}_{m}}{M_{C}} = κ^{'} \cdot c_{{NO}_{2}} = κ^{'} \cdot x_{{NO}_{2}} \cdot \frac{P_{total}}{R \cdot T} [\frac{mol}{m^{2} s}] & (2) \end{matrix}$
where


Symbol	Term/value	Units

R′	Reaction rate	mol/m²/s
A	Available surface of soot particle	m²
ζ	Reaction run number	mol/s
ζ _m	Reaction run number	kg/s
	(relative to the mass of soot particles)
M_c	Molar mass of soot particles (0.012	kg/mol
	g/mol)
K′	Reaction rate constant	m/s
C_NO ₂	Concentration of NO₂	mol/m³
X_NO ₂	Molar quantity of NO₂	—
P_total	Total pressure	N/m²
R	Gas constant (8.314 J/mol/K)	J/mol/K
T	Temperature	K

This is based on an absolute surface of the soot particle (A), which is composed of the configuration of the dispersed soot particle on the surface of the particle trap (A_{particle trap}or the filter material of the particle trap A_fleece), the soot particle loading in the particle trap (k_soot), and a mass-specific soot particle surface (A′_specific: specific surface of the particle itself: for soot, approximately 350 m²/kg). The mass-specific soot particle surface itself is ordinarily a function of the soot particle loading in the particle trap, since with increasing loading the soot particles are superimposed and the mass-specific soot particle surface decreases. Thus, depending on the specific construction of the particle trap and in particular for increased soot particle loading in the particle trap, it cannot be assumed that the entire surface of the soot particle is available to the reactants, and that it can therefore be used for the calculation. Rather, it turns out that some regions of the particle trap receive better flow and a greater supply of soot particles and nitrogen dioxide than other regions, and/or as a result of interlayering of soot particles, active areas of the soot particles in principle are covered and therefore unavailable to reactants.
For these reasons, for the particle trap in use it is customary to assume an available soot particle surface (A) that depends on the loading and construction, and that may vary, for example, between a maximum value (corresponding to a maximum dispersion of the soot particles, linear increase in the absolute surface of the soot particle with a linear increase in the soot particles embedded in the particle trap) and a minimum value (constant absolute surface of the soot particles despite increasing embedding of soot particles in the particle trap). These relationships are described by the following equation:
(3) A=A′_specific·M_soot=A′_specific·K_soot·A_fleece[m²],
where


Symbol	Term/value	Units

A′_specific	Mass-specific soot particle surface	m²/kg
	(350,000 m²/kg)
m_soot	Mass of soot particles embedded in the	kg
	particle trap
K_soot	Soot particle loading in the particle trap	kg/m²
	(mass of soot per filter area)
A_fleece	Geometric filter area	m²
	(in this instance, filter area is formed by
	fleece)

Equation (2) also specifies the rate constant (κ′), which may be described as follows:
$\begin{matrix} κ^{'} = \frac{1}{4} \sqrt{\frac{8 \cdot R \cdot T}{π \cdot M_{{NO}_{2}}}} \cdot 1.1 \cdot 10^{4} \exp (- \frac{49800}{R \cdot T}) [\frac{m}{s}], & (4) \end{matrix}$
where


Symbol	Term/value	Units

M_NO2	Molar mass of NO₂(0.046 kg/mol)	kg/mol

If the information from Equations (3) and (4) is used in Equation (2), the following relationship is obtained for the mass-dependent reaction run number for soot:
$\begin{matrix} {\dot{ζ}}_{m} = κ_{_{{NO}_{2}}}^{'} \cdot \frac{P_{total}}{R \cdot T} \cdot A_{specific}^{'} \cdot m_{soot} \cdot M_{c} [\frac{kg}{s}] . & (4) \end{matrix}$
Using this relationship and the indicated expressions for soot embedding, a mass balance may be set up which allows the soot loading in the particle trap present at any point in time to be determined relatively accurately, taking into consideration the boundary conditions of the engine (particle concentration, temperature, nitrogen dioxide concentration, exhaust gas flow rate) and the boundary conditions of the particle trap (length, diameter, cell density, filter area, filter thickness, permeability, filter geometry). In the present case, the reaction sequences have been described with special attention to the NO₂conversion. However, it is clear that other influences on the behavior patterns of the particle trap must also be taken into account, such as the soot burnoff (resulting from a high engine load, for example), for which appropriate computing models may be provided. Thus, a method using very simple equipment is proposed for determining the point in time for increasing the effectiveness of the particle trap.
In this manner, the behavior of the particle trap may be characterized relatively accurately, so that when the necessary information or actual values are provided for the exhaust gas system and/or the internal combustion engine, the quantity of particles produced and converted may be determined at any point in time. The loading state may also be determined from this information. Thus, a method using very simple equipment is proposed for determining the point in time for increasing the effectiveness of the particle trap.
In accordance with an added feature of the invention, it is proposed to determine the instantaneous loading state based on a pressure differential in the exhaust gas system between a first position upstream of the particle trap and a second position downstream of the particle trap. “Upstream” and “downstream” of the particle trap are understood to refer to a position relative to the direction of extension of the exhaust gas. The filter material and the flow paths or channels in the particle trap represent a flow resistance for the exhaust gas, resulting in a pressure drop. It is possible to obtain information on the loading state by monitoring the pressure differential over the particle trap. It is noted that such monitoring of the pressure differential is not necessary particularly when the calculation method under all conditions provides a sufficiently accurate instantaneous loading state for the method according to the invention. For the case in which the pressure differential is nevertheless monitored, for example as a check, this is preferably carried out continuously.
In accordance with an additional feature of the invention, during step b) the effectiveness of the particle trap with respect to particles contained in the exhaust gas is increased by at least 20% compared to normal operation of the internal combustion engine. It is very particularly preferred for the increase in effectiveness in the particle trap during step b) to range from 20% to 30%. The time period over which the increase in effectiveness takes place is substantially determined by the external environmental conditions or the operating mode of the internal combustion engine (the driving cycle, for example). It is not uncommon for step b) to be maintained over a time period of several minutes, longer than 10 or 30 minutes, for example, and if necessary, even longer than 60 minutes. The effectiveness is increased until sufficient free filter area is once again available, so that the ratio of the prevailing pressure difference between the flow through the filter material and the unfiltered discharge to the surroundings is sufficiently low.
In accordance with yet another feature of the invention, it is proposed to determine the duration of step b) as a function of the underlying loading state. This is understood in particular to mean that the increase in effectiveness according to step b) lasts for different periods of time, depending on the quantity of particles stored in the particle trap. In particular, this means that for a larger quantity of particles in the particle trap, step b) is carried out over a longer period of time.
In accordance with yet a further feature of the invention, it is likewise advantageous to determine the duration of step b) as a function of the exhaust gas temperature during the effectiveness increase. Even if a temperature for thermal regeneration of the particles is not reached in the method proposed herein, the influence of the exhaust gas temperature is still of considerable importance. If, for example, one considers the conversion of soot using nitrogen dioxide, minimum temperatures of approximately 200° to 230° C., for example, must be provided. If the temperature at least temporarily falls below this value in the course of step b), the process of the effectiveness increase is generally extended. A reaction in the range of the above-referenced limiting temperature is not as “willing” or dynamic, so to speak, as at temperatures of approximately 300° C., for example. Therefore, it is advantageous to select the duration of step b) as a function of the exhaust gas temperature. The temperature of the exhaust gas may be determined in a known manner, for example by integrating at least one temperature sensor into the exhaust gas system of the internal combustion engine and/or into the particle trap.
In accordance with yet an added feature of the invention, it is also proposed to determine the duration of step b) as a function of the nitrogen dioxide concentration in the exhaust gas during the effectiveness increase. In other words, the nitrogen dioxide concentration in the exhaust gas is calculated or monitored during step b), and the duration is varied depending on this nitrogen dioxide concentration. Thus, for high nitrogen dioxide concentrations the duration may be shortened, since a greater number of reactants are supplied for the particles.
In accordance with yet an additional feature of the invention, it is also advantageous to determine the duration of step b) as a function of the concentration of water in the exhaust gas during the efficiency increase. This is understood to mean, among other things, that the water or water vapor concentration in the exhaust gas is monitored or determined. The water concentration has a considerable influence on the conversion characteristics of soot, whereby the effectiveness of the particle trap increases with increasing water concentration, in particular in a concentration range of up to 5% water in the exhaust gas.
In accordance with still another feature of the invention, the duration of step b) is determined as a function of the concentration of ozone in the exhaust gas during the effectiveness increase. It has been shown that specifically at relatively low temperatures (up to approximately 300° C., for example), the presence of ozone has an effect on the soot conversion similar to that of nitrogen dioxide. Thus, it is particularly advantageous (especially for temperatures up to 300° C.) to provide an increased ozone concentration.
In accordance with still a further feature of the invention, the at least one operating parameter of the internal combustion engine is adjusted during step b) so as to increase the nitrogen dioxide concentration in the exhaust gas produced. This means, for example, that on the engine side the engine characteristic map is modified until the exhaust gas produced has an increased nitrogen dioxide concentration compared to normal operation. However, as an alternative or cumulative approach, the internal combustion engine may be operated in such a way, for example, that an increased nitric oxide concentration is generated. This exhaust gas enriched with nitric oxide (NO) is then led over an oxidation catalytic converter so that increased nitrogen dioxide (NO₂) is formed by reaction with the oxygen (O₂) contained in the exhaust gas. It is also conceivable to appropriately modify an exhaust gas recirculation system to achieve the objective described herein.
In accordance with still an added feature of the invention, the at least one operating parameter of the internal combustion engine is adjusted during step b) so as to increase the oxygen concentration in the exhaust gas produced. The presence of oxygen has a critical effect on the conversion characteristics of soot, or for the conversion of nitric oxide to nitrogen dioxide. For this reason it is advantageous to supply as much oxygen as possible. For exhaust gas systems having exhaust gas recirculation, the proportion of the recirculated exhaust gas is advantageously kept as low as possible so that an increased oxygen concentration greater than that for normal operation is present during step b).
At this point it should be noted that it is also possible to optionally operate the internal combustion engine so that a proportion of water up to 5% and/or an increased proportion of ozone is present.
In accordance with still an additional feature of the invention, the at least one operating parameter of the internal combustion engine is adjusted during step b) so as to increase the temperature of the produced exhaust gas by a maximum of 50° C. in the vicinity of the particle trap. Preferably, the temperature increase is even much less than this value, such as 20° C., for example. Thus, it is clear that in this case a high thermal load on the particle trap is avoided. With regard to the conversion of soot by nitrogen dioxide, specifically in the range of the limiting temperature, such a small temperature increase may result in significantly improved conversion rates, which accompanies the desired increase in effectiveness of the particle trap. The temperature increase is particularly advantageous when, before step b) is initiated, the exhaust gas temperature in the vicinity of the particle trap is below the temperature for a chemical reaction of nitrogen dioxide with soot, i.e., below 230° C., for example. If the temperature in the vicinity of the particle trap is already greatly above this limiting temperature, preferably other specific operating parameters of the internal combustion engine should be modified.
The above-referenced specific operating parameters of the internal combustion engine may be easily carried out by an appropriate modification of the characteristic map of the internal combustion engine through the use of a so-called engine control.
With the objects of the invention in view, there is also provided a device for operating a particle trap. The device comprises a vehicle having an internal combustion engine and an exhaust gas system. An engine control operates the internal combustion engine. At least one, in particular open, particle trap is disposed in the exhaust gas system. A device determines an effectiveness of the at least one particle trap according to the invention.
The vehicle preferably is a ground transportation vehicle such as a passenger vehicle or truck, for example. These vehicles typically have a spark ignition or diesel engine as an internal combustion engine. The exhaust gas produced thereby is emitted to the surroundings through (at least) one exhaust gas system. For operating such internal combustion engines it is common to use an engine control which, for example, varies the quantities of air and/or fuel supplied, the ignition points of the fuel-air mixture, the pressures in the internal combustion engine, and many other specific operating parameters as a function of the load state of the internal combustion engine. In this regard, the engine control or operation of the internal combustion engine in normal operation is determined starting from a predetermined driving cycle (for example, the so-called NEFZ cycle for Europe, or the FTP cycle for the United States, both of which are known to those skilled in the art in this field), so that for specified load states the engine control also typically regulates the same operating parameters in a corresponding manner.
In addition to (at least) one particle trap, the exhaust gas system may also include additional components for exhaust gas treatment, such as for example an oxidation catalytic converter, mixer, addition of additives, filter, adsorber, etc. In order to implement the aforementioned method, a device for determining the effectiveness of the at least one particle trap is also provided by the device. In this regard, the device may be a part of the engine control, or separate sensors, or the like. For the case in which the device is a part of the engine control, it is preferably integrated into the engine control as a computer program. This computer program causes a deviation from normal operation of the internal combustion engine during step b), with the at least one specific operating parameter of the internal combustion engine being adjusted so that the effectiveness of the particle trap is increased.
In accordance with a concomitant feature of the invention, in this regard it is particularly advantageous for the device to be equipped with an exhaust gas system that includes exhaust gas recirculation. Such an exhaust gas recirculation device enables specific operating parameters of the internal combustion engine to be influenced in a relatively simple manner, so that the desired increase in effectiveness occurs. Preferably, it is possible for the recirculated exhaust gas stream to be variably adjustable by the engine control.
The invention and the technical field are explained in greater detail below, with reference to the figures. It is noted that, although the figures illustrate particularly preferred embodiments of the method and/or of the device according to the invention, the invention is not limited thereto. In particular, the proportionate dimensions illustrated with reference to the drawings as a rule are not transferable to actual conditions.
Other features which are considered as characteristic for the invention are set forth in the appended claims, noting that the features individually recited in the claims may be combined in any given, technically feasible manner and describe further embodiments of the method or the device, and noting that reference may be made to supplementary features or parameters contained in the description herein.
Although the invention is illustrated and described herein as embodied in a method for operating a particle trap and a device for carrying out the method, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a diagrammatic, perspective view of a motor vehicle having an exhaust gas system;

FIG. 2 is an enlarged, perspective view of a portion of an open particle trap;

FIG. 3 is a further enlarged, longitudinal-sectional view of an open particle trap;

FIG. 4 is a graph showing an effectiveness curve for a particle trap;

FIG. 5 is a graph showing a variation of a specific operating parameter of the internal combustion engine; and

FIG. 6 is a graph showing an effect of nitrogen dioxide concentration on a soot conversion rate.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the figures of the drawings in detail and first, particularly, to FIG. 1 thereof, there is seen a diagrammatic, perspective illustration of a vehicle 5 that has an internal combustion engine 3. The exhaust gas produced by the internal combustion engine 3 flows through an exhaust gas system 2 to the ambient surroundings, with the pollutants present therein having been previously treated inside the exhaust gas system 2. The internal combustion engine 3 is operated by an engine control or management system 6 which, for example, regulates ignition characteristics of the internal combustion engine as well as a proportion of exhaust gas that is recirculated through an exhaust gas recirculation device 7 of the internal combustion engine 3. In the exhaust gas system 2, the exhaust gas first impinges on a catalytic converter 8, for example a catalytic converter 8 that is suitable for forming nitrogen dioxide (oxidation catalytic converter). The exhaust gas enriched with nitrogen dioxide then flows further to a particle trap 1. The exhaust gas system 2 is equipped with non-illustrated pressure sensors at a first position P1 and a second position P2, thus enabling a pressure difference over the particle trap 1 to be determined. The measured values obtained from the sensors in the exhaust gas system preferably are provided to the engine control or engine timing or speed control 6. The pressure difference may be used, for example, as a measure of an effectiveness of the particle trap 1.
FIG. 2 diagrammatically shows the structure of an embodiment variant of an open particle trap 1. The particle trap 1 includes a plurality of channels 11 aligned substantially in parallel. The channels 11 are formed by an alternating configuration of at least one smooth or flat layer 9 and at least one corrugated layer 10. The smooth layer 9 and the corrugated layer 10 may be subsequently joined or wound together, thereby forming the particle trap 1. The smooth layer 9 preferably is composed of a filter material such as a metallic non-woven fleece, for example. The exhaust gas inside the channels 11, which is to be cleaned, is diverted toward this filter material by providing projections 12 (provided only in the corrugated layers 10 in this case, although that need not be the case) that extend into the channels 11. These projections 12 partially close off the channels 11 while still allowing the exhaust gas to flow through. The exhaust gas now flows in a flow direction 13 into the channels 11, and is diverted at least in some locations by the projections 12 to the smooth layer 9 composed of filter material. When the exhaust gas contacts the smooth layer 9 having the filter material, the soot particles become embedded or retained, so that conversion with the nitrogen dioxide contained in the exhaust gas may now take place. The smooth layer 9 and/or the corrugated layer 10 may be provided with openings 14 to improve the flow exchange in adjoining channels 11.
FIG. 3 shows adjoining channels 11 of a particle trap 1 in detail, in order to illustrate the flow direction 13 of the exhaust gas and/or the flow characteristics inside the particle trap 1. The smooth layer 9 is represented herein by hatched lines, and is intended to include a filter material. The corrugated layer 10 is formed by a metal foil, for example, having a plurality of projections 12 that are produced, for example, by pressing sections of the metal foil into the channel 11, or by punching out guide vanes from the metal foil. The projections 12 are shaped so as to form a bypass 15 for the flowing exhaust gas. The orientation of the projections 12 may be adapted to the particular application. In principle, materials used in the construction of the particle trap 1 should be resistant to high temperatures and corrosion.
The exhaust gas containing particles 4 is forced through the bypass 15 or the smooth layer 9 including the filter material (as indicated by arrows). The flow resistances necessary for this purpose are illustrated by a pressure difference shown in the right-hand section of FIG. 3. When the exhaust gas flows through the bypass 15, the partial exhaust gas stream is subjected to a bypass pressure change Δp2. A filter pressure change Δp1 is observed when the exhaust gas flows through the smooth layer 9 including the filter material. Increasing loading of the filter material causes the value Δp1 to rise, thereby increasing the tendency for the partial exhaust gas streams to flow through the bypass 15 instead of through the smooth layer 9. This is associated with a drop in effectiveness, which may at least be significantly limited by the method according to the invention.
FIG. 4 diagrammatically shows a curve of effectiveness E for an open particle trap. The effectiveness E of the particle trap fluctuates about an average effectiveness value Em when conditions are sufficient for the conversion of soot. For city driving in particular, however, the low exhaust gas temperature and the intensified soot formation cause increased embedding of soot particles in the filter material, thus increasingly impeding the flow of exhaust gas. This causes the effectiveness E of the particle trap to drop. When a first point in time t1 is reached in the particle trap at which the effectiveness reaches or falls below a first effectiveness limiting value E1, an effectiveness increase for the particle trap is carried out. FIG. 4 shows a “normal” curve of the effectiveness E, without the intervention according to the invention, as a dashed-dotted line. After the effectiveness increase according to the invention is activated, however, the effectiveness E of the particle trap is initially maintained, and ultimately may even be increased to a second effectiveness limiting value E2. When the second effectiveness limiting value E2 is reached at a second point in time t2, the normal operation of the internal combustion engine is re-activated and the effectiveness E of the particle trap fluctuates about the average effectiveness value Em.
FIG. 5 likewise diagrammatically illustrates a curve of an operating parameter B during normal operation (Bn) over time t. The operating parameter B is modified at a point in time t1, i.e. when the effectiveness increase is begun (see curve Be). After the second effectiveness limiting value E2 is reached at a second point in time t2, the normal operation of the internal combustion engine is re-activated. It is noted that the curve Be need not be constant, and may have a variable value even during the effectiveness increase. Furthermore, this diagrammatic illustration of a specific operating parameter B is not to be construed in such a way that only one operating parameter B is always modified. Rather, it is possible to modify multiple operating parameters B, simultaneously or staggered over time, for an effectiveness increase of the particle trap.
FIG. 6 diagrammatically shows the effect of a nitrogen dioxide concentration N on a converted particle mass M at identical time intervals. It can be seen that as the value of the nitrogen dioxide concentration (see N1, N2, N3) rises, the quantity of converted particles increases (see ΔM1, ΔM2, ΔM3). Use is made of this effect in the effectiveness increase so that, for example, for a high loading, i.e. a large quantity of soot particles embedded in the particle trap, the nitrogen dioxide supply may be selected in such a way that at a predetermined time interval the particle trap is freed of embedded soot particles, accompanied by a certain adjustment of the exhaust gas recirculation, etc.
Through the use of the method described herein and the associated device, operation of an exhaust gas system of an internal combustion engine may be ensured, with conservation of fuel and savings of materials and simultaneous high effectiveness of the particle trap which is integrated into the exhaust gas system.

Claims

1. A method for operating a particle trap in an exhaust gas system of an internal combustion engine, the method comprising the following steps:

a) determining a first point in time in which the particle trap falls below a first effectiveness limiting value;

b) increasing an effectiveness of the particle trap by adjusting at least one specific operating parameter of the internal combustion engine, while exhaust gas produced by the internal combustion engine has a sufficiently low temperature in vicinity of the particle trap to ensure that substantially no thermal regeneration of particles occurs;

c) determining a second point in time in which the particle trap exceeds a second effectiveness limiting value; and

d) activating normal operation of the internal combustion engine.

2. The method according to claim 1, wherein the particle trap is an open particle trap.

3. The method according to claim 1, wherein step a) includes determining an instantaneous particle loading state of the particle trap with particles.

4. The method according to claim 2, which further comprises calculating the instantaneous loading state.

5. The method according to claim 2, which further comprises determining the instantaneous loading state based on a pressure differential in the exhaust gas system between a first position upstream of the particle trap and a second position downstream of the particle trap.

6. The method according to claim 1, which further comprises, during step b), increasing the effectiveness of the particle trap with respect to particles contained in the exhaust gas by at least 20% compared to normal operation of the internal combustion engine.

7. The method according to claim 1, which further comprises determining a duration of step b) as a function of an underlying loading state.

8. The method according to claim 1, which further comprises determining a duration of step b) as a function of a temperature of the exhaust gas during the effectiveness increase.

9. The method according to claim 1, which further comprises determining a duration of step b) as a function of a nitrogen dioxide concentration in the exhaust gas during the effectiveness increase.

10. The method according to claim 1, which further comprises determining a duration of step b) as a function of a concentration of water in the exhaust gas during the efficiency increase.

11. The method according to claim 1, which further comprises determining a duration of step b) as a function of a concentration of ozone in the exhaust gas during the effectiveness increase.

12. The method according to claim 1, which further comprises adjusting the at least one specific operating parameter of the internal combustion engine during step b) to increase a nitrogen dioxide concentration in the exhaust gas being produced.

13. The method according to claim 1, which further comprises adjusting the at least one specific operating parameter of the internal combustion engine during step b) to increase an oxygen concentration in the exhaust gas being produced.

14. The method according to claim 1, which further comprises adjusting the at least one specific operating parameter of the internal combustion engine during step b) to increase a temperature of the exhaust gas being produced by a maximum of 50° C. in vicinity of the particle trap.

15. A device for operating a particle trap, the device comprising:

a vehicle having an internal combustion engine and an exhaust gas system;

an engine control operating said internal combustion engine;

at least one particle trap disposed in said exhaust gas system; and

a device for determining an effectiveness of said at least one particle trap according to claim 1.

16. The device according to claim 15, wherein said particle trap is open.

17. The device according to claim 15, wherein said exhaust gas system includes an exhaust gas recirculation device.

18. A vehicle, comprising:

an internal combustion engine;

an engine control operating said internal combustion engine;

an exhaust gas system connected to said internal combustion engine;

at least one particle trap disposed in said exhaust gas system; and

19. The vehicle according to claim 18, wherein said particle trap is open.

20. The vehicle according to claim 18, wherein said exhaust gas system includes an exhaust gas recirculation device.