Method for regenerating a gasoline particulate filter of a spark-ignition internal combustion engine and control unit of a spark-ignition internal combustion engine

Abstract

Method for regenerating a gasoline particulate filter of a spark-ignition internal combustion engine with an exhaust system in which the gasoline particulate filter is arranged, wherein oxygen-containing gas is supplied to the gasoline particulate filter (14), wherein the internal combustion engine with reaction-warm gasoline particulate filter is shut down (10) and the supplied oxygen-containing gas is held without flow in the gasoline particulate filter for a residence time period (16), characterized by that at least part of the exhaust system in which the gasoline particulate filter is located is closed in a fluid-tight manner after the supply of the oxygen-containing gas (14) and before the start of the residence time.

Description

[0001] The invention relates to a method for regenerating a gasoline particulate filter of a spark-ignition internal combustion engine with the features according to the preamble of claim 1. Furthermore, the invention relates to a control unit of a spark-ignition internal combustion engine with the features according to the preamble of claim 9.

[0002] Combustion processes in a spark-ignition internal combustion engine produce soot particles, which are separated from the exhaust gas by a gasoline particulate filter (GPF) located in the engine's exhaust system during operation. To prevent the exhaust backpressure upstream of the GPF from increasing too much, the GPF is continuously or periodically regenerated. This means that the soot load in the GPF is reduced by creating reaction conditions for the thermal oxidation of the soot with oxygen. For this purpose, a sufficiently high temperature in the GPF is necessary, along with a simultaneous supply of oxygen in the exhaust gas.

[0003] For example, document DE 10 2012 022 153 A1 discloses a method and a control device for regenerating a soot-laden gasoline particulate filter (GPF) of an exhaust system for a gasoline engine. Temperatures of the GPF and the exhaust gas flow are determined. As long as the temperatures are below a predetermined minimum temperature for the oxidation of the soot particles in the GPF, the ignition timing of the gasoline engine is retarded. When the minimum temperature is reached, the oxygen content of the exhaust gas is increased by further opening the throttle of the gasoline engine during overrun, by increasing the lambda value to a value greater than 1, or by shutting off the fuel supply to the gasoline engine.

[0004] Furthermore, document DE 39 12 301 A1 describes a method for regenerating a diesel particulate filter, in which, to avoid damage to the diesel filter body during the transition to overrun operation, the control device of the intake pipe cross-section is first moved from an open position to a minimal reduction position and then continuously back to an open position.

[0005] From DE 10 2010 046 899 A1, a system and a method for controlling the regeneration of a particulate filter downstream of an internal combustion engine in a vehicle are known. The method comprises, during first engine shutdown conditions, increasing the excess oxygen to the particulate filter and regenerating the particulate filter, at least during one engine shutdown. The method further comprises, during second engine shutdown conditions, decreasing the excess oxygen to the particulate filter, at least during part of an engine shutdown.

[0006] It has been found that in newly installed gasoline particulate filters (GPFs), soot initially deposits in the filter substrate wall and subsequently accumulates on the surface. A typical substrate wall is 8 mil (approximately 0.2032 mm) thick and exhibits a fine pore structure with a mean pore diameter of about 20 µm. Given a typical particle diameter in the soot from spark-ignition combustion engines of approximately 20 to 150 nm, the soot particles can penetrate the pore structure of the wall and clog it. Tests show that a quantity of soot in the substrate wall causes a significantly greater pressure drop than an equivalent quantity of soot on the surface.Due to the high temperatures during the operation of a gasoline engine compared to other combustion processes, and the comparatively low soot masses emitted, it can be observed that in a newly installed gasoline particulate filter, until a certain ash accumulation mass is reached on the substrate wall (where the ash itself acts as a filtering porous material), soot is initially deposited deep within the substrate wall. The difficulty in accessing the soot deep within the substrate wall poses a problem for regeneration. Conventional regeneration methods primarily reduce the soot on the surface of the substrate wall, while a significant amount of soot remains within the substrate wall, due to its influence on the backpressure behavior of the gasoline particulate filter.

[0007] The object of the present invention is to achieve a regeneration of the gasoline particulate filter.

[0008] This problem is solved according to the invention by a method for regenerating a gasoline particulate filter with the features according to claim 1. Advantageous embodiments of the invention are characterized in the dependent claims.

[0009] In the inventive method for regenerating a gasoline particulate filter of a spark-ignition internal combustion engine with an exhaust system in which the gasoline particulate filter is arranged, oxygen-containing gas is supplied to the gasoline particulate filter. The internal combustion engine is shut down with the gasoline particulate filter at operating temperature. The supplied oxygen-containing gas is held in the gasoline particulate filter without flow for a specified residence time.

[0010] The steps of the method according to the invention can follow the operation of the spark-ignition internal combustion engine, particularly in a steady state. The method can also include providing the spark-ignition internal combustion engine. To achieve a sufficient temperature in the gasoline particulate filter, measures can be taken before carrying out the described steps of the method according to the invention, as described in document DE 10 2012 022 153 A1. The disclosure content of document DE 10 2012 022 153 A1 is hereby incorporated in its entirety into this presentation by reference.

[0011] In the context of the invention, the term "flowless" means that the oxygen-containing gas does not flow through the exhaust system in a directed flow - be it laminar or turbulent - but at most performs stationary movements within the gasoline particulate filter, such as convection or Brownian molecular motion.

[0012] In the context of the invention, the term "reaction-warm" means that the gasoline particulate filter has a sufficiently high temperature for regeneration, so that the regeneration reaction, in particular, proceeds at an appropriate rate. The temperature can be higher than 500 degrees Celsius, particularly 580 degrees Celsius, preferably 650 degrees Celsius.

[0013] The process can be initiated during motorized driving or generated in workshop mode.

[0014] While oxygen-based regeneration of a gasoline particulate filter (GPF) via overrun operation following high-temperature operation of the spark-ignition engine reduces the soot on the substrate wall, it has been surprisingly found that a static residence time of the oxygen-containing gas in the GPF also leads to enhanced regeneration, particularly beneficial at depth within the substrate wall. The mechanism of action is thought to be based on a time-controlled diffusion of oxygen into the substrate wall and of the reaction products out of the substrate wall. A sufficiently high reaction rate of oxygen at depth within the substrate wall appears to be unattainable at non-zero, and especially higher, flow velocities of the oxygen-containing gas through the GPF.The inventive method allows for an acceleration of the reaction kinetics due to the temperature in the gasoline particulate filter and the oxygen supply.

[0015] As a consequence of applying the method according to the invention, it is possible to keep the amount of soot deposited deep within the substrate wall of newly installed gasoline particulate filters as low as possible, until the ash accumulation, which increases with the duration of filter operation, dominates the pressure drop in the gasoline particulate filter. In this way, the increase in back pressure is reduced or delayed, preferably minimized, so that no negative effects on the performance or responsiveness and / or the carbon dioxide emissions of the internal combustion engine result.

[0016] In the inventive method for regenerating a gasoline particulate filter, it is advantageous if, during the shutdown of the internal combustion engine, a throttle valve of the internal combustion engine is opened and the fuel supply is interrupted. In this simple way, the exhaust system and, in particular, the gasoline particulate filter can be flooded with fresh air as an oxygen-containing gas.

[0017] In order to supply oxygen-containing gas to the gasoline particulate filter, in the method according to the invention the oxygen-containing gas can be flushed to the gasoline particulate filter via the combustion chambers by means of a compressor - for example an electric or mechanical compressor or a compressor of an exhaust gas turbocharger - and / or pumped from a fresh gas system to the exhaust system by means of a secondary air pump via a fluid connection.

[0018] Furthermore, in the method according to the invention, before the internal combustion engine is taken out of service, it can be checked, in particular by a control unit or a workshop test device, whether at least one physical parameter of the gasoline particulate filter lies within a defined range of values, and that the decommissioning only takes place if the at least one physical parameter of the gasoline particulate filter lies within the defined range of values. Specifically, the at least one physical parameter of the gasoline particulate filter can be its temperature and / or its previous operating time or a measure of the previous operating stress.

[0019] Alternatively or furthermore, in the inventive method, a measure of the operating stress of the internal combustion engine can be determined from the engine's ongoing operation. The gasoline particulate filter can then be regenerated before this measure exceeds a limit value. This limit value is preferably designed such that the ash deposit in the gasoline particulate filter remains below a tolerable threshold. In other words, the limit is set at the value up to which only the soot deposit in the gasoline particulate filter, more precisely the soot deposit deep within the substrate wall of the gasoline particulate filter, determines the pressure drop. Specifically, this measure can be a running distance or operating time of the internal combustion engine, or a pressure in the exhaust system.

[0020] After driving with high exhaust gas temperatures, for example on the motorway under heavy load, the throttle valve can be fully opened during the shutdown process of the spark-ignition engine. This allows fresh air to be drawn through the combustion chambers after the injection system shuts off and during the shutdown phase, entering the exhaust system and thus the gasoline particulate filter (GPF). The still-hot GPF, combined with the available oxygen, can initiate soot oxidation. Due to the lack of convection from the switched-off spark-ignition engine, the GPF cools down only slowly. Alternatively or additionally, this process can be carried out during a service interval for the spark-ignition engine, for example, during the first service at 30,000 km (10,000 miles) in a motor vehicle.

[0021] According to the invention, at least a part of the exhaust system, in which the gasoline particulate filter is located, is closed or sealed in a fluid-tight manner after the oxygen-containing gas has been introduced and before the start of the residence time. This prevents flow through the gasoline particulate filter and / or the escape of heated gas.

[0022] Furthermore, or alternatively, it can be advantageous in the inventive method to supply oxygen-containing gas to the gasoline particulate filter at a pressure greater than atmospheric pressure and to maintain the gas at a pressure greater than atmospheric pressure within the gasoline particulate filter. The pressure greater than atmospheric pressure can be achieved by means of a compressor in a turbocharging unit of the internal combustion engine. In this way, a large quantity or a high concentration of oxygen-containing gas can be achieved in the gasoline particulate filter.

[0023] In a preferred embodiment of the method according to the invention, air is used as the oxygen-containing gas and / or the residence time is longer than 25 minutes, in particular longer than 90 minutes, preferably longer than 120 minutes.

[0024] Since the operation of the spark-ignition internal combustion engine takes precedence over the regeneration of the gasoline particulate filter, a further development of the inventive method provides that the retention of the oxygen-containing gas during the residence time is interrupted if the internal combustion engine is started. An error signal is then generated, in particular by a control unit. This error signal can be stored in an error memory. Alternatively, or in addition, an error signal can also be brought to the attention of the operator of the internal combustion engine, in particular in acoustic or visual form. The error signal can be used to decide whether to repeat the inventive method and to carry it out again at a later time, when the opportunity arises.

[0025] Also related to the inventive concept is a control unit for a spark-ignition internal combustion engine, wherein the control unit comprises at least one computer and a (computer-readable) memory element. According to the invention, a program is stored in the memory element of the control unit which, when at least partially executed in the computer, performs the steps of the method for regenerating a gasoline particulate filter with the features or a combination of the features as described in this description.

[0026] Further advantages and advantageous embodiments and developments of the invention are presented in the following description with reference to the figures. Specifically, it shows: Fig. 1 a schematic representation of the process of a preferred embodiment of the method according to the invention, and Fig. 2 a qualitative representation of the pressure loss as a function of the running distance of a gasoline particulate filter.

[0027] In the Fig. Figure 1 schematically illustrates the sequence of a preferred embodiment of the method according to the invention. In step 10, the spark-ignition internal combustion engine with a reaction-warm gasoline particulate filter (GPF) at a temperature greater than 650 degrees Celsius is shut down. In option 12, during the shutdown of the internal combustion engine, a throttle valve of the engine is opened and the fuel supply is interrupted. In step 14, oxygen-containing gas is supplied to the GPF by means of a compressor that forces the oxygen-containing gas through the combustion chambers to the GPF. In step 16, the supplied oxygen-containing gas is held in the GPF without flow for a residence time of more than 2 hours. During this time, a portion of the exhaust system containing the GPF is sealed in a fluid-tight manner.

[0028] The Fig.Figure 2 serves to illustrate the effects of the method according to the invention. The pressure loss 18 is qualitatively plotted in a diagram as a function of the operating distance 20 of a gasoline particulate filter. The pressure loss 18 can be measured, for example, by the pressure difference between a point upstream of the gasoline particulate filter and a point downstream of the gasoline particulate filter in the exhaust system. For the preferred embodiment of a spark-ignition internal combustion engine in a motor vehicle, the distance traveled by the motor vehicle serves as the measure of the operating distance 20.

[0029] Without regeneration, the pressure loss 18 follows the curve 22 (solid line): For a newly installed gasoline particulate filter, the pressure loss 18 increases approximately linearly with the running distance 20 for low values ​​of the running distance 20. A point is then reached where the slope decreases significantly and the pressure loss 18 assumes a proportional or linear course with increasing running distance 20. This is thought to be because at this point, the deposition of soot in the substrate wall – clogging of the pores – is saturated, and the deposition of soot on the substrate wall – thickening of the wall – increasingly determines the pressure loss.

[0030] While for short distances traveled, soot deposition in the substrate wall and soot deposition on the substrate wall initially dominate the pressure loss 18, for longer distances 20 ash deposition on the substrate wall also begins: For this range of distance 20, with an increasing number of kilometers, there is a proportion 26 of the pressure loss 18 due to ash deposition, the course of which is also disproportionately high and increasingly increasing (dashed line).

[0031] Using the regeneration method according to the invention, the following profile 26 (dashed line) can now be achieved in the ideal case of complete regeneration of the gasoline particulate filter: By way of example, and without limiting the implementation of the method at a different running distance 20, the method according to the invention is carried out at the described point where the proportionally increasing pressure loss 18 of the profile 22 transitions into a less steeply rising section. Thanks to the complete regeneration, the pressure loss 18 is reduced, ideally essentially equal to the minimum pressure loss of the gasoline particulate filter in its unused, new state. With increasing running distance 20, a proportional increase is then observed again, generally with a different slope than the previous increase.Since the ash contained in the gasoline particulate filter cannot be expelled in this way, the regime is nevertheless reached in which ash accumulation shows an increasingly significant proportion of the pressure loss 18. Advantageously, however, the total pressure loss is considerably lower than would be expected according to the curve 22 without regeneration.

[0032] The regeneration process according to the invention can also be carried out partially and / or multiple times for a gasoline particulate filter at different values ​​of the running distance 20, so that a pressure loss curve 18 as a function of the running distance 20 can result, which is composed section by section of proportional degree segments, before the proportion of ash deposition increasingly determines the course and transforms it into a linear, longer section. REFERENCE MARK LIST 10. Decommissioning the internal combustion engine 12. Opening the throttle valve and interrupting the fuel supply 14. Supply of oxygen-containing gas 16. Flowless dwell time in the gasoline particulate filter 18 Pressure loss 20 running distance 22 Course without regeneration 24% due to ash deposition 26 Course with regeneration according to the invention

Claims

[1] Method for regenerating a gasoline particulate filter of a spark-ignition internal combustion engine with an exhaust system in which the gasoline particulate filter is arranged, wherein oxygen-containing gas is supplied to the gasoline particulate filter (14), wherein the internal combustion engine with reaction-warm gasoline particulate filter is shut down (10) and the supplied oxygen-containing gas is held without flow in the gasoline particulate filter for a residence time period (16), characterized by , that at least part of the exhaust system in which the gasoline particulate filter is located is closed in a fluid-tight manner after the supply of the oxygen-containing gas (14) and before the start of the residence time. [2] Method for regenerating a gasoline particulate filter according to claim 1, characterized by, that during the shutdown (10) of the internal combustion engine a throttle valve of the internal combustion engine is opened and the fuel supply is interrupted (12). [3] Method for regenerating a gasoline particulate filter according to claim 1 or 2, characterized by , that the oxygen-containing gas is purged via a compressor through the combustion chambers to the Otto particulate filter and / or pumped from a fresh gas system to the exhaust system via a fluid connection using a secondary air pump. [4] Method for regenerating a gasoline particulate filter according to any one of the preceding claims, characterized by , that before the internal combustion engine is taken out of service (10) it is checked whether at least one physical parameter of the gasoline particulate filter is within a specified range of values, and that the taking out of service (10) only takes place if the at least one physical parameter of the gasoline particulate filter is within the specified range of values. [5] Method for regenerating a gasoline particulate filter according to any one of the preceding claims, characterized by , that a measure of the operational stress of the internal combustion engine is determined from the ongoing operation of the internal combustion engine and the gasoline particulate filter is regenerated before the measure exceeds a limit value. [6] Method for regenerating a gasoline particulate filter according to any one of the preceding claims, characterized by , that oxygen-containing gas is supplied to the gasoline particulate filter up to a pressure greater than atmospheric pressure (14) and that the gas is held in the gasoline particulate filter at a pressure greater than atmospheric pressure. [7] Method for regenerating a gasoline particulate filter according to any one of the preceding claims, characterized by that air is used as the oxygen-containing gas and / or that the residence time is longer than 25 minutes. [8] Method for regenerating a gasoline particulate filter according to any one of the preceding claims, characterized by , that the retention of the oxygen-containing gas during the residence time is terminated if the internal combustion engine is started, and an error signal is generated. [9] Control unit of a spark-ignited internal combustion engine, wherein the control unit comprises at least a computer and a storage element, characterized by , that a program is stored in the memory element which, when at least partially executed in the computer, performs the steps of the method for regenerating a gasoline particulate filter according to one of the preceding claims.

Images