Method for regenerating a particle filter

Abstract

The invention relates to a method for regenerating a particulate filter in the exhaust gas channel of an internal combustion engine. Here, the particulate filter is divided into several zones for determining the loading state, and, at the same time, a temperature distribution over the cross section of the particulate filter is determined. In order to prevent the soot retained in the edge zones of in the particulate filter from being insufficiently oxidized, when it is ascertained that the edge zones have been sufficiently loaded, the exhaust gas temperature is raised to a temperature which, in spite of the heat losses in the edge areas, lies above the temperature at which oxidation of the soot particles can take place. The invention further relates to an internal combustion engine having an exhaust gas channel and a particulate filter arranged in the exhaust gas channel, said internal combustion engine being configured to carry out such a method.

Claims

1. A method for regenerating a particulate filter in an exhaust gas channel of a spark-ignited internal combustion engine according to the Otto principle, said method comprising the following steps: determining a loading state of the particulate filter by means of a loading model or by means of a sensor system, dividing the particulate filter into at least two zones for purposes of creating the loading model, determining a loading state and/or a temperature separately for each zone of the particulate filter, and when it is detected that there is a need for regenerating at least one zone of the at least two zones of the particulate filter, raising the temperature to such an extent that the temperature in all of the at least two zones of the particulate filter is above a regeneration temperature needed for oxidizing the soot that has been retained in the particulate filter, and wherein measures to protect components of the particulate filter are initiated when an unfavorable loading state of the particulate filter is detected, wherein, in an event of critical loading of the particulate filter, a combustion air ratio is shifted in a direction of sub-stoichiometric or overrun phases of the internal combustion engine are avoided or interrupted in order to avoid a simultaneous presence of high temperatures and excess oxygen in the exhaust gas channel.

2. The method according to claim 1, wherein dividing the particulate filter further comprises dividing a cross section of the particulate filter into at least two rings in a radial direction, and wherein each of said at least two rings forming one of the at least two zones whose loading condition and/or temperature is separately monitored or modeled.

3. The method according to claim 2, wherein determining a loading state and/or a temperature separately for each zone further comprises determining a loading state for each of the at least two rings.

4. The method according to claim 3, wherein regeneration of the particulate filter is initiated when a threshold value of the loading state is exceeded in a radially outermost ring of the at least two rings.

5. The method according to claim 2, wherein the loading state of each of the at least two rings is determined by a calculation model relating to particles entering the particulate filter and particles exiting from an appertaining ring of the at least two rings.

6. The method according to claim 1, wherein the temperature of the particulate filter is raised from a first threshold temperature to a second threshold temperature only if a non-uniform loading of the particulate filter is detected.

7. An internal combustion engine having: an exhaust gas channel, a particulate filter arranged in the exhaust gas channel of the internal combustion engine, and a control unit that has a non-transitory computer-readable program algorithm for carrying out the method according to claim 1.

8. The internal combustion engine according to claim 7, further comprising the sensor system for determining the loading state in the at least two zones of the particulate filter, wherein the sensor system is arranged on or in the exhaust gas channel.

9. The internal combustion engine according to claim 8, wherein the sensor system comprises a radio frequency sensor system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be explained below in embodiments with reference to the accompanying drawings. The following is shown:

(2) FIG. 1 an internal combustion engine having an exhaust gas channel and a particulate filter in which a method according to the invention for regenerating the particulate filter can be carried out,

(3) FIG. 2 a section through a particulate filter with which a method according to the invention is carried out,

(4) FIG. 3 a particulate filter in the exhaust gas channel of an internal combustion engine which is non-uniformly loaded with soot particles, and also showing an associated temperature profile over the cross section of the particulate filter, and

(5) FIG. 4 another particulate filter in the exhaust gas channel of an internal combustion engine in which the temperature was raised by a method according to the invention to such an extent that the temperature needed for the regeneration is reached in all of the zones of the particulate filter, and also showing an associated temperature profile over the cross section of the particulate filter.

(6) FIG. 1 shows an internal combustion engine 10 having an exhaust gas channel 12 and a particulate filter 20 arranged in the exhaust gas channel 12. The internal combustion engine 10 is preferably configured as an internal combustion engine to power a motor vehicle, especially preferably as a gasoline engine. The internal combustion engine 10 preferably has direct fuel injection by means of which the fuel is injected directly into the cylinders of the internal combustion engine 10. The combustion processes in the internal combustion engine 10 are controlled or regulated by means of a control unit 16. The internal combustion engine 10 is preferably configured as a turbocharged internal combustion engine that is supplied with air by means of a turbocharger 14 or a compressor. As an alternative, the internal combustion engine 10 can also be configured as a naturally aspirated engine or as an internal combustion engine 10 of some other type. A three-way catalytic converter 18 is preferably arranged in the exhaust gas channel 12 of the internal combustion engine 10.

DETAILED DESCRIPTION OF THE INVENTION

(7) During the operation of the internal combustion engine 10, the particulate filter 20 is loaded with particles from the combustion process of the internal combustion engine 10. This loading can be determined by means of modeling in the control unit 16 or else by means of a measurement, especially a differential measurement, over the particulate filter 20. In order to prevent the exhaust gas counter-pressure of the internal combustion engine 10 from rising excessively, the particulate filter 20 has to be continuously or periodically regenerated. The particulate filter 20 can also have a catalytically active coating, for example, a three-way catalytically active coating. In order to use oxygen to carry out a thermal oxidation of the soot particles retained in the particulate filter 20, a sufficient temperature level is needed, along with the concurrent presence of residual oxygen in the exhaust gas. The soot discharge from the particulate filter 20 can likewise be determined by means of modeling in the control unit 16. As an alternative, the loading state of the particulate filter 20 can also be measured by an appropriate sensor system 28, for example, by a sensor system 30 that emits radio waves.

(8) FIG. 2 shows a cross section through the body 36 of the particulate filter 20. As already mentioned, the decisive factors for regenerating the particles retained in the particulate filter 20 are an excess of oxygen and a sufficient temperature of the exhaust gas flowing through the particulate filter 20. Owing to the construction of the particulate filter 20, the temperature is necessarily distributed radially throughout the particulate filter 20 during operation, whereby the inner zone 22 facing the center axis 34 has a higher temperature than the edge zone 26. The zones 22, 24, 26 are arranged as concentric rings around the center axis 34 of the particulate filter 20. Owing to the heat losses through the wall of the particulate filter 20 and owing to a slower flow rate of the hot gas, the temperature decreases towards the wall of the particulate filter 20. The extent of this temperature drop is decisively influenced by the operating point and by the structural design of the opening funnel 38 and by the characteristic of the inflow against the body 36 of the particulate filter 20. In the edge areas, especially in the third zone 26, this temperature gradient can mean that the temperature prevailing there is no longer sufficient for an oxidation of the soot. As a result, there are zones 26 of the particulate filter 20 in which soot continues to accumulate while other hotter zones 22 are regularly regenerated. This leads to problems with the regenerability as well as with the counter-pressure behavior of the particulate filter 20. Moreover, an uncontrolled regeneration of the particulate filter 20 can cause the particulate filter 20 to be thermally damaged. This can especially be the case if an operating point is actuated at which a changeover is made from very high exhaust gas temperatures to overrun operation during numerous short-distance trips and the resultant soot accumulation in the particulate filter 20.

(9) In the method according to the invention, the regeneration temperature of the particulate filter 20 is regulated on the basis of the soot distribution in zones 22, 24, 26 of the body 36 of the particulate filter 20. If a non-uniform soot distribution is detected in the individual zones 22, 24, 26, then the regeneration temperature T.sub.reg is raised by the engine management system to such an extent that the temperature needed for regenerating the soot is also reached in the edge zone 26.

(10) FIG. 3 shows a particulate filter 20 of the type often used nowadays in motor vehicles with internal combustion engines 10. The particulate filter 20 has an opening funnel 38, a body 36 as well as a collecting funnel 40, whereby the diameter D.sub.2 of the body 36 provided with the filter material 42 is larger than the diameter D.sub.1 of the exhaust gas channel 12 upstream as well as downstream from the particulate filter 20. Along the center axis 34, there is a first concentric zone 22 that is hotter than a second zone 24 in the edge area of the particulate filter 20. The temperature distribution over the diameter D.sub.2 of the filter body 36 is shown in FIG. 3. Here, it can be seen that the temperature needed for oxidizing the soot is not reached in the second zone 24, whereas the temperature T in the first zone is raised to a first threshold temperature T.sub.S1 that lies above the regeneration temperature T.sub.reg. Here, owing to the generally known fluid-dynamic and thermodynamic laws, a higher flow rate and a lower heat loss occur in the first zone 22, whereas the flow is slower through the outer zone 24, in addition to which the outer zone 24 also has a higher heat loss through the outer wall of the particulate filter 20. As shown in FIG. 3, this can cause soot to accumulate in the outer zone 24, whereas a partial regeneration of the particulate filter 20 takes place in the inner zone 22. In this process, a soot ring is deposited in the outer zone 24 that can only be regenerated by raising the exhaust gas temperature. Here, it has to be ensured that the outer areas 24, 26 of the particulate filter are also above the regeneration temperature T.sub.reg of the particulate filter 20. If a higher load point with a very high exhaust gas temperature is implemented with such a soot ring, then component-damaging situations can occur in the particulate filter 20. This is possible, for example, if numerous city-traffic trips are followed by highway driving at full load, which is then followed by an overrun phase, during which large amounts of fresh air enter the exhaust gas channel 12 and thus the particulate filter 20.

(11) In order to determine the loading state of the particulate filter 20, an appropriate sensor system 28, especially a radio frequency sensor system 30, can be provided on the particulate filter 20 in order to determine the loading states of the individual zones of the particulate filter 20. As an alternative, this can also be carried out by a loading model stored in the control unit 16. Furthermore, at least one temperature sensor 32 is arranged in the collecting funnel 40 in order to determine the exhaust gas temperature downstream from the particulate filter 20 and to model a temperature distribution over the cross section of the particulate filter 20 on the basis of the determined temperature(s). As an alternative, the exhaust gas temperature can also be modeled by the appertaining parameters of the internal combustion engine 10 and by a corresponding calculation model stored in the control unit 16.

(12) According to the invention, the regeneration of the particulate filter now takes place as shown in FIG. 4. If a non-homogenous soot distribution is detected over zones 22, 24, 26 of the particulate filter 20, then the engine management system stored in the control unit 16 requests an elevated exhaust gas temperature T.sub.S2 that is selected in such a way that—for the current operating state of the particulate filter 20, that is to say, for the exhaust gas mass flow through the particulate filter 20 as well as for the soot loading—the temperature is also so high in the outer zones 24, 26 that the soot retained there can be oxidized. Once the regeneration of the particulate filter 20 has been completed in the outer zones 24, 26, which is ascertained by the sensor system 28 or by an appropriate loading model, the regeneration of the particulate filter 20 is terminated. This ensures a homogenous distribution of the subsequent soot loading.

(13) In this manner, it is ensured that each active regeneration of the particulate filter 20 is always only carried out at the required exhaust gas temperature T.sub.S1, T.sub.S2, thereby saving fuel. The target regeneration temperature of the particulate filter 20 can be variably influenced as a function of the loading states and of the operating point. This method can prevent that the particulate filter 20 is constantly, that is to say, during every single regeneration process, regenerated at an elevated regeneration temperature T.sub.S2, but rather that this only occurs when a given loading of the outer zones 24, 26 makes this necessary.

LIST OF REFERENCE NUMERALS

(14) 10 internal combustion engine 12 exhaust gas channel 14 turbocharger 16 control unit 18 three-way catalytic converter 20 particulate filter 22 first zone/first ring 24 second zone/second ring 26 third zone/third ring 28 sensor system 30 radio frequency sensor 32 temperature sensor 34 center axis 36 body of the particulate filter 38 opening funnel 40 collecting funnel 42 filter material D.sub.1 diameter of the exhaust gas channel D.sub.2 diameter of the particulate filter T temperature T.sub.S1 first threshold temperature T.sub.S2 second threshold temperature T.sub.reg regeneration temperature