METHOD OF DETECTING A NEED FOR REGENERATION OF AN EXHAUST PARTICULATE FILTER, AND EXHAUST SYSTEM

Abstract

A method of detecting a need for regeneration of an exhaust particulate filter is described. A first pressure drop is detected in a flow section of an exhaust system which includes the exhaust particulate filter. In addition, an exhaust gas temperature is determined. An exhaust gas mass flow flowing through the exhaust particulate filter is then calculated on the basis of the exhaust gas temperature and the pressure drop. Furthermore, a second pressure drop at the exhaust particulate filter is determined. A need for regeneration is detected when the second pressure drop exceeds a predefined pressure limit value that is dependent on the exhaust gas mass flow. Moreover, an exhaust system for an internal combustion engine is presented which includes an exhaust particulate filter.

Claims

1. A method of detecting a need for regeneration of an exhaust particulate filter, comprising the steps of: (a) detecting a first pressure drop in a flow section of an exhaust system comprising the exhaust particulate filter, the flow section being connected to the exhaust particulate filter in a fluidically unbranched manner; (b) sensing an exhaust gas temperature; (c) calculating an exhaust gas mass flow flowing through the exhaust particulate filter on the basis of the first pressure drop and the exhaust gas temperature; (d) determining a second pressure drop across the exhaust particulate filter; and (e) identifying the need for regeneration when the second pressure drop exceeds a predefined pressure limit value dependent on the exhaust gas mass flow.

2. The method according to claim 1, wherein the predefined pressure limit value depends on a further exhaust gas temperature prevailing at the exhaust particulate filter.

3. The method according to claim 1, wherein the flow section comprises at least one of an SCR catalytic converter and an oxidation catalytic converter, and the first pressure drop is determined across at least one of the SCR catalytic converter and the oxidation catalytic converter.

4. The method according to claim 3, wherein the exhaust gas temperature is an exhaust gas temperature prevailing at at least one of the SCR catalytic converter and the oxidation catalytic converter.

5. The method according to claim 1, wherein the predefined pressure limit value is provided in a form of a characteristic map.

6. The method according to claim 1, wherein a future need for regeneration is identified when the second pressure drop exceeds a predefined pressure warning value, the predefined pressure warning value being smaller than the predefined pressure limit value.

7. An exhaust system for an internal combustion engine, comprising an exhaust particulate filter; a flow section connected to the exhaust particulate filter in a fluidic ally unbranched manner; a first pressure sensor arrangement for sensing a first pressure drop across the flow section, a second pressure sensor arrangement for sensing a second pressure drop at the exhaust particulate filter; a temperature sensor for sensing an exhaust gas temperature; and a control device which is coupled to the first pressure sensor arrangement (48), the second pressure sensor arrangement and the temperature sensor in terms of signaling, the control device being configured to (a) determine an exhaust gas mass flow flowing through the exhaust particulate filter on a basis of the first pressure drop detected by the first pressure sensor arrangement and the exhaust gas temperature sensed by the temperature sensor; and (b) identify a need for regeneration of the exhaust particulate filter when the second pressure drop detected by the second pressure sensor arrangement exceeds a predefined pressure limit value dependent on the exhaust gas mass flow.

8. The exhaust system according to claim 7, including a further temperature sensor which is arranged in or on the exhaust particulate filter and is connected to the control device in terms of signaling.

9. The exhaust system according to claim 7, wherein at least one of an SCR catalytic converter and an oxidation catalytic converter is arranged in the flow section, the flow section being positioned downstream of the exhaust particulate filter.

Description

DESCRIPTION OF THE DRAWINGS

[0037] The disclosure will be explained below with reference to an exemplary embodiment, which is illustrated in the accompanying drawings, in which: [0038] (h) schematically shows an exhaust system according to the disclosure, by which a method according to the disclosure can be carried out; and [0039] (i) shows a characteristic map in which pressure limit values and pressure warning values, which are dependent on an exhaust gas volume flow rate, for a pressure drop across the exhaust particulate filter of the exhaust system of FIG. 1 are plotted.

[0040] FIG. 1 shows an exhaust system 10 for an internal combustion engine.

[0041] Here, an exhaust gas mass flow 12, symbolized by an arrow, can flow into the exhaust system 10 on an inlet side 14 and flow out of it on an outlet side 16.

[0042] Along the flow direction from the inlet side 14 to the outlet side 16, the exhaust system 10 comprises an exhaust particulate filter 18, a reducing agent dosing device 20 and a mixing section 22, which is configured to mix the exhaust gas mass flow 12 with a volume flow 24 of reducing agent.

[0043] The mixing section 22 is adjoined downstream by a flow section 25 of the exhaust system 10, in which an SCR catalytic converter 26, i.e. a catalytic converter the effect of which is based on selective catalytic reduction, and an oxidation catalytic converter 28 are arranged.

[0044] Here, the SCR catalytic converter 26 and the oxidation catalytic converter 28 are arranged in a shared housing.

[0045] The flow section 25 is connected to the exhaust particulate filter 18 in a fluidically unbranched manner here.

[0046] Such exhaust systems 10 are frequently used in combination with internal combustion engines that operate on the diesel principle. In this connection, the exhaust particulate filter 18 is also referred to as a diesel particulate filter (DPF).

[0047] The exhaust system 10 is further equipped with numerous sensors.

[0048] In this context, a first sensor arrangement 30 is positioned at the exhaust particulate filter 18 on an upstream side, which comprises a temperature sensor 32, a nitrogen oxide concentration sensor 34, and a pressure sensor 36.

[0049] A further pressure sensor 38 is positioned downstream at the exhaust particulate filter 18.

[0050] A further sensor arrangement 40 is provided at an upstream end of the SCR catalytic converter 26 and comprises a temperature sensor 42 and a pressure sensor 44.

[0051] A further pressure sensor 46 is positioned downstream of the oxidation catalytic converter 28.

[0052] In this context, the pressure sensor 44 and the pressure sensor 46 constitute a first pressure sensor arrangement 48 for sensing a first pressure drop Δp.sub.1 across the flow section 25.

[0053] In this context, a respective absolute pressure can be sensed by the pressure sensors 44, 46. The first pressure drop Δp.sub.1 is then determined by calculating a difference between these absolute pressures.

[0054] Alternatively, the pressure sensors 44, 46 can form a differential pressure sensor of which the first pressure drop Δp.sub.1 can be sensed directly.

[0055] The pressure sensors 36 and 38 constitute a second pressure sensor arrangement 50 for sensing a second pressure drop Δp.sub.2 across the exhaust particulate filter 18.

[0056] The pressure sensors 36, 38 can also each sense an absolute pressure. The second pressure drop Δp.sub.2 is then determined by calculating a difference between these absolute pressures.

[0057] Likewise, it is possible for the pressure sensors 36, 38 to form a differential pressure sensor, via which the second pressure drop Δp.sub.2 can be directly sensed.

[0058] The exhaust system 10 further comprises a control device 52.

[0059] The control device is coupled to all of the aforementioned sensors in terms of signaling.

[0060] This means that in terms of signaling, the control device 52 is coupled to the pressure sensors 36, 38, 44, 46, the temperature sensors 32, 42 and the nitrogen oxide concentration sensor 34.

[0061] Here, the control device 52 comprises a first arithmetic unit 54, which is configured to determine an exhaust gas mass flow 12 flowing through the exhaust particulate filter 18 on the basis of the first pressure drop Δp.sub.1 determined by the first pressure sensor arrangement 48 and an exhaust gas temperature T.sub.1 sensed by the temperature sensor 44.

[0062] To this end, first the pressure drop Δp.sub.1 is measured by the pressure sensor arrangement 48.

[0063] Based on the temperature T.sub.1 determined by the temperature sensor 42, a density of the exhaust gas mass flow 12 can be calculated. Here, temperature-dependent density values of exhaust gas are stored on the arithmetic unit 54.

[0064] The values for the first pressure drop Api and the density can be inserted into the above-mentioned equations (1) and (2) so that the exhaust gas mass flow 12 can be determined.

[0065] Furthermore, the second pressure drop Ape can be detected by the control device 52, in particular by the arithmetic unit 54. The pressure sensor arrangement 50 is used for this purpose.

[0066] In addition, an exhaust gas volume flow 56 flowing through the exhaust particulate filter 18 can be determined by using the control device 52.

[0067] To this end, a temperature T.sub.2 sensed by the temperature sensor 32 is used to determine a density of the exhaust gas stream flowing into the exhaust particulate filter 18. Again, the density values stored on the control device 52 are made use of for this purpose.

[0068] In addition, the exhaust gas mass flow 12 is used, which was calculated using the first pressure drop Δp.sub.1 in the flow section 25 and the temperature T.sub.1 sensed by the temperature sensor 42.

[0069] On the basis of the exhaust gas mass flow 12 and the density, the exhaust gas volume flow 56 can now be determined.

[0070] The control device 52, in particular the arithmetic unit 54, is also configured to detect a need for regeneration of the exhaust particulate filter 18.

[0071] For this purpose, the characteristic map according to FIG. 2 is stored on the arithmetic unit 54.

[0072] In this connection, the characteristic map comprises, in an exhaust gas volume flow-second pressure drop diagram, a first curve which represents a pressure limit value p.sub.G as a function of the exhaust gas volume flow {dot over (V)}, 56.

[0073] Furthermore, the characteristic map comprises a second curve that represents a pressure warning value pw as a function of the exhaust gas volume flow {dot over (V)}, 56.

[0074] Since, as discussed above, the exhaust gas volume flow 56 can be calculated on the basis of the exhaust gas mass flow 12 and the temperature T.sub.2 detected by the temperature sensor 32, the curves for the pressure limit value p.sub.G and the pressure warning value pw are thus also plotted as a function of the exhaust gas mass flow 12 and the temperature T.sub.2. This is equivalent to a dependence on the exhaust gas volume flow {dot over (V)}, 56.

[0075] Therefore, during operation of the exhaust system 10, a future need for regeneration is detected when, at an exhaust gas volume flow {dot over (V)}, 56, the second pressure drop 4.sub.2 exceeds the predefined pressure warning value pw represented by the second curve.

[0076] When a future need for regeneration is identified, depending on further operating parameters of the exhaust system 10 a regeneration may be carried out immediately, in which particulate matter collected by the exhaust particulate filter 18 is burned off in a controlled manner.

[0077] Alternatively, such a regeneration may also be held off for a certain period of time.

[0078] In operation of the exhaust system 10, a need for regeneration is further detected when at an exhaust gas volume flow {dot over (V)}, 56, the second pressure drop Δp.sub.2 exceeds the predefined pressure limit value p.sub.G represented by the second curve. In such a case, regeneration of the exhaust particulate filter 18 is necessary immediately or at least within a short time.

[0079] Such a need for regeneration may also be referred to as an acute need for regeneration.

[0080] To further illustrate the detection of the need for regeneration, four operating points have been drawn into the characteristic map of FIG. 2 by way of example.

[0081] Here, with the respectively associated volume flows {dot over (V)}.sub.1 and {dot over (V)}.sub.4, the second pressure drop Δp.sub.2,1 and the second pressure drop Δp.sub.2,4 are below the curve representing the pressure warning value p.sub.w. Thus, for these operating points, there is neither a future nor an acute need for regeneration.

[0082] The second pressure drop Δp.sub.2,2 which is determined at the exhaust gas volume flow {dot over (V)}.sub.2, is above the curve representing the pressure warning value pw but below the curve representing the pressure limit value p.sub.G. Thus, in this operating point, a future need for regeneration is detected.

[0083] The second pressure drop Δp.sub.2,3, which is measured at the exhaust gas volume flow {dot over (V)}.sub.3, is above the curve representing the pressure limit value p.sub.G. Therefore, an acute need for regeneration is detected here.

[0084] With reference to the above equation (1), this means that a regeneration is recognized as being necessary if those components of the pressure coefficient ζ which are brought about by soot particles and ash particles have increased to such an extent that, for a given exhaust gas mass flow 12 or a given exhaust gas volume flow {dot over (V)}, 56, an associated second pressure drop Δp.sub.2 ensues which is above the pressure limit value p.sub.G.

[0085] The control device 52 furthermore comprises a second arithmetic unit 58, which is configured to control the volume flow 24 of reducing agent, that is, to provide a volume flow 24 of reducing agent suitable for the exhaust gas mass flow 12.

[0086] The arithmetic unit 58 is therefore coupled to the reducing agent dosing device 20 in terms of signaling.

[0087] In addition, the control device 52, more specifically the second arithmetic unit 58, is coupled to the nitrogen oxide concentration sensor 34 in terms of signaling. Furthermore, the already determined value for the exhaust gas mass flow 12 is available to the arithmetic unit 58.

[0088] Based on these characteristic values, a mass flow of nitrogen oxides can be determined.

[0089] This also allows a suitable volume flow 24 of reducing agent that is to be injected into the mixing section 22 to be adjusted.

[0090] Although various embodiments have been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this disclosure. For that reason, the following claims should be studied to determine the true scope and content of this disclosure.