EP0654121A1

EP0654121A1 - Process and device for determining the load level of particle filters

Info

Publication number: EP0654121A1
Application number: EP94906764A
Authority: EP
Inventors: Wolfgang Pfister; Walter Blaschke; Erwin Burner; Heinrich Wacker; Peter Steiner
Original assignee: J Eberspaecher GmbH and Co KG
Current assignee: Eberspaecher Climate Control Systems GmbH and Co KG
Priority date: 1992-08-06
Filing date: 1993-08-06
Publication date: 1995-05-24
Also published as: WO1994003711A1; DE4226055C1

Abstract

A process and device are disclosed for determining the load level of a particle filter (10) provided in the exhaust gas system (11) of a Diesel engine. The pressure drop Δ pfilter across the particle filter (10) is measured by a first differential pressure measurement device (21). The pressure drop Δ p¿throttle? across a cross-sectional reduction (15) of the exhaust gas system (11) is measured by a second differential pressure measurement device (22). The pressure value measured in the first differential pressure measurement device (21) is correlated with the pressure value measured in the second differential pressure measurement device (22) in order to form a real characteristic value (IK), and the real characteristic value (IK) is compared with a limit characteristic value (GK), so that when the difference is sufficiently small a regeneration process is initiated.

Description

METHOD AND DEVICE FOR DETERMINING THE LOADING CONDITION OF PARTICLE FILTERS

The invention relates to a method for determining the loading state of a particle filter provided in the exhaust system of a diesel engine, and to a device for carrying out the method. This is preferably a diesel engine which is used in a motor vehicle.

The particle filters increasingly used for exhaust gas cleaning in diesel engines, which, in addition to filtering out other harmful gas components of the engine exhaust gas, in particular for filtering out soot particles carried in the exhaust gas, must be subjected to frequent cleaning (regeneration) in order to maintain their functionality. Here, in particular, the thermal regeneration of particle filters has proven to be effective in the high temperature-controlled through the introduction of hot gases (about 700 ° C to ^'900 ° C) will ignite the "in the particulate filter soot particles contained and incinerated.

There are essentially three methods known for carrying out the thermal regeneration of particle filters, namely stationary regeneration, alternating regeneration and full-flow regeneration. In the stationary regeneration, the particulate filter is burned out when the motor vehicle engine is at a standstill by means of a motor-independent heating device provided for this purpose. The alternating regeneration enables thermal Regeneration of the particle filter during vehicle operation. For this purpose, two particle filters are connected in parallel, whereby one particle filter is alternately flowed through by the engine exhaust gas, and the other particle filter decoupled from the exhaust system is flowed through by a heating gas heated by a motor-independent heating device for the time of thermal regeneration. In the case of full-flow regeneration, in which the regeneration also takes place during motor vehicle operation, a heating gas flow generated by an engine-independent heating device is mixed with the engine gas in the particle filter which is permanently in the exhaust gas flow for the time of regeneration and is fed together with this into the particle filter Tet in order to achieve the above-mentioned gas temperature required for regeneration.

Irrespective of the choice of the regeneration process carried out, it is of course only necessary to carry out a thermal regeneration when a certain loading state of the particle filter has been reached, in which either the filter is no longer effective, or the Exhaust gas back pressure generated by the added filter has a disadvantageous effect on the engine output, or the filter would be thermally destroyed by further loading during the next regeneration due to the heat released during the soot combustion.

Since previously practicable options for continuously monitoring the loading status of a particle filter during operation are not known, the manufacturers of particle filters specify specific, fixed operating intervals in which a thermal rain is to be carried out. In the absence of knowledge of the actual loading condition, the regeneration intervals are selected so that even under extreme operating conditions of the engine, for example frequent short-distance operation with extreme soot formation in the engine exhaust gases, sufficient security is provided in the intervals so that the regeneration in any case can take place in good time before the described harmful effects occur. Thus, the regeneration of a particle filter inevitably takes place in a low-soot engine operation at a point in time when it would not be necessary at all.

It is true that the regeneration intervals have been adapted to the particular operating conditions of a particle filter by taking into account the predominantly prevailing operating conditions, that is to say, for example, short-haul or long-haul operations, but this refined screening of the regeneration intervals has also proven to be too coarse in practice .

The generally known relationship between the pressure drop in a flow medium when flowing through a filter and the degree of clogging or the loading of the filter, which thus readily applies only to filters with a steady flow, cannot be determined because of the largely unsteady operation of an internal combustion engine the loading state of a particle filter. Rather, the volume flow through the filter, which changes depending on the engine speed, has to be taken into account.

The invention is based on the object of proposing a method and a device which or which enables a simple determination of the actually given loading state of a particle filter, taking into account the given engine operating conditions.

This object is solved by the features of claim 1.

In the method according to the invention, use is made, on the one hand, of the known relationship, described above, between the loading state of the filter and a pressure drop in a medium flowing through it. In addition, a further pressure drop in the flow medium is measured at a suitable point with a cross-sectional constriction in the flow medium in order to determine the current operating state of the engine based on the known fluidic connection between the pressure drop at a throttle point and the volume flow flowing through the throttle point to obtain reproducing flow parameters. This gives, on the one hand, a differential pressure value reflecting the loading condition of the particle filter and a differential pressure value reflecting the volume flow given in the exhaust system, which changes depending on the transient operating states of the engine.

According to the invention, taking into account the two differential pressure values, an actual characteristic value is defined which is compared with a given limit characteristic value in order to initiate a regeneration process if the difference between the actual characteristic value and the limit characteristic value is sufficiently small, for example if the values match . In this case, the limit characteristic value can be specified, for example, as a limit characteristic curve determined in test bench tests, taking into account various loading conditions and volume flows. The level of the limit values depends on the level of the permitted torque drop due to the exhaust gas back pressure caused by the particle filter and the throttle point in the exhaust system.

As a throttle point for the measurement of the second differential pressure value, an already existing, that is to say design-related, cross-sectional constriction in the exhaust system can preferably be used; in this case, the method according to the invention can be carried out without the installation of an additional throttle point in the exhaust gas duct of the exhaust gas system. All that is required on the exhaust gas system itself is the installation of the sensors that are required for recording the differential pressures.

In a preferred embodiment of the method according to the invention, the differential pressure in the exhaust system is measured in the region of a cross-sectional constriction, which results when the relatively large flow cross section of the particle filter is passed to the downstream part of the exhaust system, for example a pipe section .

When the existence of a sufficiently small difference between an actual characteristic value and a corresponding limit characteristic value is determined, a display device is preferably activated which, for example when the method according to the invention is used in a motor vehicle, notifies the motor vehicle driver of the critical loading state of the particle filter. This can then regenerate the particle filter according to one of the above Start the described regeneration process.

A further possibility is to couple the display device to a start device for automatically triggering one of the described regeneration methods, or to trigger the start device immediately if a critical difference value is determined, without first displaying the value .

If a display device is provided, it proves to be particularly advantageous to display the actual characteristic value determined by the method according to the invention on the basis of an initial characteristic value having a defined difference from the limit characteristic value, continuously or at predetermined time intervals in order to progress to make the loading state visible from the outside, so that the necessity of carrying out a particle filter regeneration can be recognized in advance.

The device according to the invention for determining the loading state of a particle filter used in the exhaust system of a diesel engine, in particular used in a motor vehicle, has the features of claim 5.

A first differential pressure measuring device is provided in the area of the particle filter and a second differential pressure measuring device is provided in the area of a cross-sectional constriction present in the exhaust gas system. Furthermore, a computing device is provided which is used to form an actual characteristic value, starting from the two measured values measured by the pressure measuring devices, and for comparison of the actual characteristic value is determined with a predetermined limit characteristic value.

The second pressure measuring device is preferably arranged in the region of a throttle point which is already present in the exhaust system, which leads to the device according to the invention being implemented with a minimum of expenditure on equipment.

The determined actual characteristic value and / or its difference to the relevant limit characteristic value can be displayed by means of a display device, so that suitable measures for regeneration of the particle filter can be taken in good time.

Alternatively, it is also possible, in addition to or instead of the display device, to provide a starting device which can be actuated as a function of the difference between the actual characteristic value and the limiting characteristic value and which, for example, starts a burner device for thermal regeneration of the particle filter.

It proves to be particularly advantageous if the first differential pressure measuring device is arranged in the area of the particle filter and the second differential pressure measuring device in the transition area from the particle filter to a region of the exhaust system that is narrowed in cross-section and follows the particle filter, since the required pressure measuring devices are thus all in one relatively small area of the exhaust system can be summarized. In particular, there is the advantageous possibility of installing the differential pressure measuring devices, each having two measuring sensors, in such a way that the second measuring sensor of the first pressure measuring device tig can be used as the first measuring device of the second pressure measuring device, so that the measurement of two differential pressures is carried out with only three sensors.

The method according to the invention and a device suitable for carrying out the method are explained in more detail below with reference to the drawings. Show it:

Fig. 1 a between components of a system installed Abgas¬ particulate filter having a first and a second measuring section for determining the differential pressure ^ ^ Pfilter ^unci ^there differential pressure at a subsequent throttling point

• ΔP throttle ^;

2 shows a diagram showing an exemplary limit characteristic curve;

Fig. 3 is a flowchart showing the determination of the load state in a particle filter.

1 shows a particle filter 10 which is installed in an exhaust system 11 of a motor vehicle (not shown in more detail) which is operated with a diesel engine. The particle filter 10 is connected via flange connections 12, 13 on its input side to a prechamber 14 and on its output side to a reducer 15. On the flow side, ie in the direction of the drive motor (not shown in more detail), the prechamber 14 is connected to an exhaust pipe 17 via a flange connection 16. The reducing piece 15 is on the flow side, towards the end of the exhaust gas pipe leading to the outside. Systems 11 out, connected to an exhaust pipe 19 via a flange connection 18.

A combustion chamber 19 is provided for the regeneration of the particle filter 10 and is used to heat a gas stream introduced into it through a feed 20. In the case of regeneration, the gas stream introduced into the pre-chamber 14 through the feed 20 is mixed with the exhaust gas stream flowing into the pre-chamber 14 through the exhaust pipe 17 to achieve the exhaust gas temperature necessary for the regeneration.

In order to be able to determine on the installed particle filter 10 when the loading state of the particle filter requires regeneration, two differential pressure measuring devices 21, 22 are provided in the area of the particle filter 10 and the reducer 15, which, in the case of the differential pressure measuring device 21, for determining the pressure drop across the particulate filter 10, so Pfilter ^ ^'s ° as in the case of the differential pressure measuring means 22 for determining the pressure drop across the throttling point representing a reducer 15 so PDrossel' are used. The differential pressure measuring device 21 has two sensors 23, 24, which are arranged immediately before or immediately after the particle filter 10. The differential pressure measuring device 22 also has two sensors, namely the sensor 24 common to the differential pressure measuring device 21 in the gas inlet area of the reducer 15, and the sensor 25 in the gas outlet area of the reducer 15.

In the diagram according to FIG. 2, the pressure drop across the particle filter is 10 AP filters' over the pressure drop. case over the reducer 15 ΔPDrossel 'applied. As can be seen from the illustration in FIG. 2, there is a linear relationship between the differential pressures. The upper function line represents a limit characteristic, for example ascertained in test bench tests, for a particle filter with the highest permissible loading state, the lower characteristic line stands for a particle filter in an unloaded, ie clean, state.

Because of the linear relationship between

ΔP filter ^and Δ P ^{throttle is the} quotient of the pressure differences, that is to say the slope of the function line is given by a constant value. The limit characteristic value GK for the critical loading state of the particle filter, from which regeneration must take place, is defined by the limit characteristic. The actual characteristic value IK derived from the current in the operation of the particulate filter 10 renzdruckmeßeinrichtungen means of the differential 21, 22 determined Diffe¬ Renz pressure values / \ Pfilter ^and pD ι _horses or their quotient formation.

3 shows a possible procedure for determining the current loading state of a particle filter using a flow chart as an example.

The sensors 23, 24, 25 of the differential pressure measuring devices 21, 22 arranged as shown in FIG. 1 supply the differential pressure values as input variables for a computing device 26

ΔP filter ^and PD throttle • ^To determine the actual characteristic value IK, quotient formation is carried out in the computing device 26 ^and the actual characteristic value IK determined in this way is subtracted from the limit characteristic value GK in order to calculate an actual differential value DI. The The actual difference value DI is then subjected to a comparison with a target difference value DS, which, shown in FIG. 2 by the cross-hatched area, represents a freely selectable tolerance offset from the limit characteristic.

In the event that the actual difference DI is smaller than the tolerable target difference DS, a start signal is given to a start device for the regeneration burner (not shown here).

In order to obtain information about the current loading condition in relation to the maximum possible loading condition, it is provided that the actual difference DI is displayed on a display device, not shown here, so that a permanent display of the loading condition or whose change is possible over time.

Of course, it is also possible to create the display device as a warning device and to activate the display device without forming a difference only if the actual characteristic value IK is equal to the limit characteristic value GK. The same applies to the starting device, which, contrary to the illustration in FIG. 3, can be activated if the actual characteristic value IK is also equal to the limit characteristic value GK.

Claims

PATENT CLAIMS

1. A method for determining the loading state of a particle filter (10) provided in the exhaust system (11) of a diesel engine, characterized in that

- The pressure drop by means of a first differential pressure measuring device (21)

ΔP filter is measured via the particle filter (10);

- The pressure drop by means of a second differential pressure measuring device (22)

ΔP throttle is measured via a cross-sectional constriction (15) in the exhaust system (11); an actual characteristic value (IK) is formed taking into account the pressure value measured in the first differential pressure measuring device (21) and the pressure value measured in the second differential pressure measuring device (22); and

- A comparison of the actual characteristic value (IK) with a limit characteristic value (GK) is carried out in order to initiate a regeneration process with a sufficiently small difference.

2. The method according to claim 1, characterized in that the second differential pressure measuring device (22) takes place in the region of a particle filter (10) in the exhaust system (11) on the flow side subsequent cross-sectional constriction (15).

Method according to one of claims 1 or 2, characterized in that that when there is a sufficiently small difference between the actual characteristic value (IK) and the limit characteristic value (GK), a display device and / or a starting device is actuated to start the regeneration process.

4. The method according to claim 3, characterized in that the display device, starting from a fixed difference (target difference DS) to the limit characteristic value (GK) having the initial characteristic value, for displaying the loading progress until the limit value (GK) is reached. is used.

5. Device for determining the loading status of a particle filter (10) provided in the exhaust system (11) of a diesel engine, characterized by a first differential pressure measuring device () in the area of the particle filter (10) that detects the pressure drop ppiiter via the particle filter (10). 21); - a second differential pressure measuring device (22) in the area of a cross-sectional constriction (15) of the exhaust system (11) which detects the pressure drop pDrossel via the cross-sectional constriction (15); - A computing device to form a

Actual characteristic value (IK) from pressure values determined by the first differential pressure measuring device (21) and the second differential pressure measuring device (22) and for comparing the actual characteristic value (IK) with a predetermined limit characteristic value (GK); and a display device for displaying the actual characteristic value (IK) and / or its difference (DI) to the limit characteristic value (GK).

6. The device according to claim 5, characterized in that in addition to the display device or instead of this one depending on the difference (DI) between the actual characteristic value (IK) and the limit characteristic value (GK) actuatable starting device for starting a regeneration device, in particular a burner device for thermal regeneration, is provided.

7. Apparatus according to claim 5 or 6, characterized in that the first differential pressure measuring device (21) in the area of the particle filter (10) and the second differential pressure measuring device (22) in the transition area from the particle filter (10) to a subsequent one, relative to the particle filter (10 ) cross-sectionally narrowed region of the exhaust system (11) is arranged.

8. The device according to claim 7, characterized in that the first differential pressure measuring device (21) and the second differential pressure measuring device (22) each have two sensors (23, 24; 24, 25), the second sensor (24) being the first Differential pressure measuring device (21) simultaneously forms the first sensor (24) of the second differential pressure measuring device (22).