The present disclosure relates to an exhaust-gas aftertreatment system for an internal combustion engine, having an exhaust line and having provided therein a filter arrangement which comprises a first particle filter element and a second particle filter element, wherein the first particle filter element is equipped with an active regeneration device for restoring its filtration performance. The disclosure furthermore relates to a method for operating an exhaust-gas aftertreatment system of said type and to the use thereof.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to German Patent Application No. 102011085086.4, filed on Oct. 24, 2011, the entire contents of which are hereby incorporated by reference for all purposes.

TECHNICAL FIELD

The present disclosure relates to exhaust gas aftertreatment for diesel engines.

BACKGROUND AND SUMMARY

The lean operation and relatively cool operating temperatures of diesel engines create an environment where incomplete combustion produces particle emissions and soot build up that necessitates exhaust-gas aftertreatment including particle filters. This can also be true of direct injected spark ignition engines. This is especially the case with turbocharged engines that have higher NOx emissions. Exhaust-gas recirculation combats the higher NOx emissions but at the expense of soot production. More efficient particle filtration could provide both minimized particle emissions and maximized energy efficiency by reducing backpressure through the filtration device.

DE 40 04 424 A1 discloses a device for purification of the exhaust gases of diesel engines, in which device, the exhaust line of the engine is divided into two branch lines which can be alternately shut off by means of a switching device and one of which leads through a soot filter. Downstream of the branch line containing the soot filter, the other branch line, which serves as a bypass line, merges again to form an end line. The branch line that leads through the soot filter is opened above a predetermined partial engine load value, as well as at full engine load, by means of the switching device, which can be actuated as a function of the engine load. To be able to ensure practically complete purification of the exhaust gases, an oxidation catalytic converter is installed downstream of the switching device in the bypass line or in the end line. If the oxidation catalytic converter is installed in the end line, all of the exhaust gas flows through it.

DE 10 2004 049 511 A1 is concerned with a semi-active heat-exchanging silencer, downstream of which is positioned a catalytic converter. In order to prevent heat losses from the exhaust gases after starting of the internal combustion engine and to effect heat losses when the engine is at operating temperature, via a compact component, two different flow paths are provided in the silencer. One of said flow paths is of heat-insulated design whereas the other flow path is designed such that the exhaust gases are cooled.

DE 10 2005 019 466 A1 in turn discloses a diesel particle filter for an exhaust system of an internal combustion engine, said diesel particle filter having at least one housing and at least one filter body. The filter device comprises at least two filter bodies arranged fluidically in series. The filter bodies are arranged spaced apart from one another in a common housing. Between the filter bodies there are provided chambers into each of which externally connected lines open out.

Exhaust-gas aftertreatment devices in the form of particle filters or soot filters require periodic regeneration through burn-off of the captured soot particles. To be able to perform the regeneration, the exhaust-gas temperature is raised to a value above, for example, 550° C. in order to initiate the combustion of the captured soot particles. In the case of lean-burn internal combustion engines, for example, diesel engines, said temperature levels are attained during normal operation of the internal combustion engine under full load if the soot filter is in a close-coupled arrangement. Close-coupled means that the soot or particle filter is arranged so close to an exhaust-gas outlet of the internal combustion engine that heat losses of the exhaust gases are minimized, but also that a desired passive regeneration is attained. Since the soot filter is arranged very close to the exhaust-gas outlet where there is little installation space available, design parameters, that is to say the size and capacity of the soot filter, are restricted. Furthermore, the configuration of the exhaust lines (cones, bends) may lead to a sub-optimal flow distribution. This causes a considerable pressure drop across the soot filter resulting in high throughflow rates, which has an adverse effect on the fuel consumption of the internal combustion engine, in particular during, so-called, highway driving.

To, at least partially, eliminate said problems, DE 10 2009 029 259 A1 proposes an exhaust-gas aftertreatment system of the type mentioned in the technical field. In said exhaust-gas aftertreatment system, within a first soot filter, there is arranged a passage line which can be shut off via a control element, which is closed in the circumferential direction, is free from filter elements, and which extends all the way through the particle filter element of the first soot filter. Here, at least one second soot filter is positioned downstream of the first soot filter. It is thus the case that two soot filter elements are arranged in series in the exhaust line or in an exhaust section, such that a low pressure drop can be attained despite a high throughflow rate. Therefore, improved fuel consumption can be attained in conjunction with an increased back pressure caused by the one or more soot filters.

A disadvantage of such a system is that, with the “downsizing” of the swept volume of engines which has been increasingly pursued recently, the exhaust-gas temperature is often no longer adequate, in particular in the lower load range, to generate the exhaust-gas temperature required for the regeneration of the particle filter. At the same time, relatively high exhaust-gas temperatures, and therefore greater quantities of emissions, in particular of nitrogen oxides, are encountered in such engines at medium load and full load. To reduce nitrogen oxide emissions, increased exhaust-gas recirculation is performed, which comes at the expense of soot emissions. However, if the required regeneration temperatures of the soot particle filter are not exceeded at corresponding time intervals, the soot filters reach their capacity limit relatively quickly, and can then accommodate no further soot.

An increase in the soot accommodation capacity of such exhaust-gas aftertreatment systems by increasing the size thereof is however possible and expedient within certain limits. Firstly, this is generally associated with an increased space requirement, wherein the space availability in the under-floor region of passenger motor vehicles in particular is limited. Furthermore, this would also increase the dynamic pressure in the exhaust tract, which is likewise, acceptable within certain limits. Consequently, the exhaust-gas aftertreatment systems hitherto known from the prior art are often not capable of reducing the emissions of such engines to a satisfactory extent over the different operating states, in particular in light of the intensely fluctuating exhaust-gas temperatures and the resulting fluctuating emission profile.

It is an object of the present disclosure to modify an exhaust-gas aftertreatment system such that satisfactory exhaust-gas treatment is attained, in particular with regard to soot emissions, even in the case of engines of reduced swept volume. In one example, said object is achieved via an exhaust-gas aftertreatment system for an internal combustion engine, having an exhaust line containing a filter arrangement which comprises a first particle filter element and a second particle filter element, wherein the first particle filter element is equipped with an active regeneration device for restoring its filtration performance.

In this way, it is possible to provide particle filtration and regeneration of the particle filter element without the space constraints of a close-coupled particle filter. Additionally, because of the affixed active regeneration device on the first particle filter element, soot particle overloading can be reduced and there is no need for increased soot load capacity. The use of the two particle filter elements of the present disclosure furthermore decrease backpressure compared to a system with a single particle filter element.

DETAILED DESCRIPTION

The present disclosure is based on the realization that the abovementioned problems can be eliminated through the use of a particle filter element with an active regeneration device for restoring filtration performance. In contrast to the otherwise conventional passive particle filter elements, said actively regenerable particle filter element is not dependent on increased exhaust-gas temperatures for oxidizing the stored soot. The particle filter element can thus be regenerated even at exhaust-gas temperatures of less than 250° C. or 300° C. For this purpose, the particle filter element can be heated to above the required regeneration temperature through activation of the active regeneration device. For this purpose, the degree of loading of the first particle filter element may be estimated or measured based on engine operating conditions such as air-fuel ratio and exhaust-gas temperature. When a predetermined degree of soot loading has been reached, the regeneration device is activated and the particle filter is thereby regenerated. Aside from the above-described regeneration device, it is possible in principle for any particle filter to be used for the first particle filter element.

A further advantage is that the first particle filter element does not require such a high storage capacity because it can be actively regenerated at all times. Consequently, the first particle filter element can be of smaller dimensions than the second particle filter element. Specifically, in the case of such an embodiment, the maximum soot loading density of the first particle filter element may be at least 10% by weight lower, and in particular at least 20% by weight lower with respect to the soot quantity, than that of the second particle filter element.

The active regeneration device may be formed, for example, by an electric heating device or else also comprise known measures of the internal combustion engine such as engine-internal post-injection and/or direct fuel injection into the exhaust tract.

In a further embodiment of the exhaust-gas aftertreatment system according to the disclosure, a control element is provided therein, said control element being designed such that, by means thereof, the exhaust-gas flow can be conducted selectively through the first particle filter element, through the second particle filter element or through the first and second particle filter elements simultaneously. In this way, it is possible, through connection to the engine controller, for the exhaust-gas flow to be conducted selectively through the two particle filter elements. The control element may be for example a motor-actuable or pneumatically actuable flap or a valve. By means of the control element, it is furthermore likewise possible at high exhaust-gas temperatures for the exhaust-gas flow to be conducted through both particle filter elements, and to thereby also “passively” regenerate the actively regenerable particle filter element.

Here, the control element may particularly preferably be switched in a continuously variable fashion between a closed and an open position with respect to the first particle filter element. In this way, it is possible to realize highly variable control of the exhaust-gas flow through the two particle filter elements in order to ensure as optimum an elimination of soot as possible under all operating conditions and at all exhaust-gas temperatures.

Within the context of the present disclosure, the control element may be arranged upstream or downstream of the first and second particle filter elements. The control element is preferably situated at a pipe switch of the exhaust line, for example at a Y-shaped pipe switch. Here, one limb of the Y-shaped pipe switch constitutes the exhaust-gas inflow or exhaust-gas outflow, whereas the two other limbs form the inflows or outflows of the first and second particle filter elements.

In one particularly preferred embodiment of the exhaust-gas aftertreatment system according to the disclosure, the first particle filter element and the second particle filter element are connected in parallel with one another. This may be realized in numerous ways. For example, the exhaust line may have a Y-type pipe switch through which an exhaust-gas partial flow, or a fraction from 0 to 100% of the exhaust-gas volume flow, apportioned by means of the optional control element, is conducted to each of the particle filter elements. Here, the two particle filter elements are situated in separate housings and are fastened separately from one another, for example, under the vehicle floor.

As an alternative to the embodiment described above, the two particle filter elements may also be arranged in the same housing, wherein the exhaust-gas volume flow is variably apportioned to the particle filter elements, preferably by means of a control element. Here, the control element is arranged preferably so as to regulate the exhaust-gas flow through the first particle filter element alone. That is to say, here, there is a continuous exhaust-gas flow through the second particle filter element.

In a refinement of the exhaust-gas aftertreatment system according to the disclosure, the second particle filter element is a passive particle filter element which can be regenerated by means of exhaust-gas temperatures of 500° C. or higher. Such particle filters are known to a person skilled in the art.

The exhaust-gas aftertreatment system according to the disclosure may also have further exhaust-gas purification devices in addition to the two particle filter elements. For example, the exhaust-gas aftertreatment system may comprise at least one exhaust-gas aftertreatment device selected from oxidation catalytic converter, NOx catalytic converter and selective catalytic reduction (SCR) catalytic converter, wherein the exhaust-gas aftertreatment device is arranged, preferably, upstream of the first and second particle filter elements. Such exhaust-gas aftertreatment devices are known to a person skilled in the art.

A further subject matter of the present disclosure relates to a method for exhaust-gas aftertreatment by means of an exhaust-gas aftertreatment system for an internal combustion engine, which exhaust-gas aftertreatment system comprises an exhaust line and has provided therein a filter arrangement which has a first particle filter element and a second particle filter element, wherein the filtration performance of the first particle filter element is restored by means of an active regeneration device which is assigned to the first particle filter element.

In a further embodiment of the method according to the disclosure, the regeneration device is formed by an electric heating device by which the first particle filter element, when a predefined soot loading density is reached and exhaust-gas temperatures of less than 500° C. prevail, can be heated to the required regeneration temperature, in particular to a regeneration temperature of 500° C. or higher, preferably to at least 550° C. The control of said processes may be performed by the operation controller of the engine, because the required data, such as the composition of the exhaust gas, exhaust-gas temperature and so forth, are generally present therein.

Finally, the present disclosure relates to the use of an exhaust-gas aftertreatment system according to the disclosure for the exhaust-gas aftertreatment of an internal combustion engine. An example of such an engine is depicted inFIG. 1.

FIG. 1schematically shows aspects of an example engine system100including an engine2. In the depicted embodiment, engine2is a boosted engine coupled to a turbocharger113including a compressor4adriven by a turbine4b. Specifically, fresh air is introduced along intake passage142into engine2via air filter3and flows to compressor4a. A flow rate of ambient air that enters the intake system through intake air passage142can be controlled at least in part by adjusting throttle120. Compressor4amay be any suitable intake-air compressor, such as a motor-driven or driveshaft driven supercharger compressor. In engine system2, however, the compressor is a turbocharger compressor mechanically coupled to turbine4b, the turbine4bdriven by expanding engine exhaust.

As shown inFIG. 1, compressor4ais coupled, through charge-air cooler118to throttle valve120. Throttle valve120is coupled to engine intake manifold122. From the compressor, the compressed air charge flows through the charge-air cooler and the throttle valve to the intake manifold. The charge-air cooler may be an air-to-air or air-to-water heat exchanger, for example. In the embodiment shown inFIG. 1, the pressure of the air charge within the intake manifold is sensed by manifold absolute pressure (MAP) sensor124.

Intake manifold122is coupled to a series of combustion chambers130through a series of intake valves (not shown). The combustion chambers are further coupled to exhaust manifold136via a series of exhaust valves (not shown). In the depicted embodiment, a single exhaust manifold136is shown.

Combustion chambers130may be supplied one or more fuels, such as gasoline, alcohol fuel blends, diesel, biodiesel, compressed natural gas, etc. Each cylinder130may be serviced by one or more valves. In the present example, each cylinder130includes a corresponding intake valve162and an exhaust valve164. Fuel is supplied to the combustion chambers130via injector166.

In the depicted example, fuel injector166is configured for direct injection though in other embodiments, fuel injector166may be configured for port injection or throttle valve-body injection. Further, each combustion chamber may include one or more fuel injectors of different configurations to enable each cylinder to receive fuel via direct injection, port injection, throttle valve-body injection, or combinations thereof. In the combustion chambers, combustion may be initiated via spark ignition and/or compression ignition.

Exhaust from exhaust manifold136is directed to turbine4bto drive the turbine. When reduced turbine torque is desired, some exhaust may be directed instead through a waste gate (not shown), bypassing the turbine. The combined flow from the turbine and the waste gate then flows through emission control device6. In general, one or more emission control devices6may include one or more exhaust aftertreatment catalysts configured to catalytically treat the exhaust flow, and thereby reduce an amount of one or more substances in the exhaust flow. For example, one exhaust aftertreatment catalyst may be configured to trap NO from the exhaust flow when the exhaust flow is lean, and to reduce the trapped NOxwhen the exhaust flow is rich. In other examples, an exhaust aftertreatment catalyst may be configured to disproportionate NOxor to selectively reduce NOxwith the aid of a reducing agent. In still other examples, an exhaust after-treatment catalyst may be configured to oxidize residual hydrocarbons and/or carbon monoxide in the exhaust flow. Exhaust line135may continue on to additional exhaust-gas aftertreatment system1. Exhaust-gas temperature sensor128provides input on temperature of exhaust-gas in exhaust line135to controller138. Exhaust-gas flow to additional exhaust-gas aftertreatment may be controlled, dependent on operating conditions, such as exhaust gas temperature, by controller138. The exhaust-gas aftertreament that is the subject of the present disclosure will be discussed below.

Variations to the above engine need not be excluded from use with the exhaust-gas aftertreatment device of the present disclosure. For example, in another embodiment, engine2does not include a turbocharger.

Referring now toFIG. 2, the drawing schematically illustrates the layout of a diesel engine with connected exhaust-gas aftertreatment system1. The system comprises a reciprocating-piston engine2in the form of a diesel engine with turbocharging, which diesel engine draws in fresh air on its intake side via an air filter3, said fresh air being pre-compressed by a compressor4aof a turbocharger4. The compressor4aof the turbocharger4is driven by the turbine4bthereof, which is at the exhaust-gas side, via a common shaft.

The combustion gases of the reciprocating-piston engine2are discharged through an exhaust line5composed of multiple pipe segments. Arranged in the exhaust line5downstream of the turbocharger4is an oxidation catalytic converter6, at the outlet side of which in the downstream direction a Y-shaped pipe is situated in the exhaust line5. The two particle filter elements7,8are thus connected in parallel with one another in the present embodiment.

The first particle filter element7is equipped with an active regeneration device15. Active regeneration device15could be, for example, an electric heating device for restoring the filtration performance of said first particle filter element. When a predefined soot loading density is reached and exhaust-gas temperatures of less than 500° C. prevail, first particle filter element7can be heated to the required regeneration temperature, for example to a regeneration temperature of 500° C. or higher.

The first particle filter element7is smaller than the second particle filter element8and has an approximately 20% smaller soot storage capacity with respect to the weight of the soot. Furthermore, a control element10in the form of an electrically actuable valve is situated downstream of the first and second particle filter elements7,8in the region of the Y-shaped merging of the exhaust line12, said control element10being designed such that the exhaust-gas flow can be conducted selectively through the first particle filter element7(as shown inFIG. 2), the second particle filter element8(as shown inFIG. 3) or through the first and second particle filter elements7,8(as shown inFIG. 4). Here, the control element10can be switched in a continuously variable fashion between a closed and an open position with respect to the first particle filter element. Additionally, in the present embodiment control element10is located downstream of the first and second particle filter elements,7,8. In other embodiments a control element may be located upstream of the particle filter elements7,8, within exhaust line5.

Downstream of the first and second particle filter elements7,8, the exhaust-gas partial flows are merged again via a Y-shaped piece of the exhaust line12and conducted into a rear silencer9.

In the position of the control element10illustrated inFIG. 2, the exhaust-gas flow, which is indicated by a dashed line11, is conducted exclusively via the first particle filter element7. In the second operating state illustrated inFIG. 3, the outlet of the first particle filter element7is closed off by the control element10, as a result of which the exhaust-gas flow11flows exclusively through the second particle filter element8. Finally,FIG. 4shows a third operating state in which the control element10is situated in a central position, such that exhaust-gas flow11flows through both the first and the second particle filter element7,8.

FIG. 5illustrates an alternative embodiment of an exhaust-gas aftertreatment system20. Said embodiment differs from the design shown inFIGS. 2 to 4in that the first and second particle filter elements21,22are situated not in separate housings but rather in the same housing. More precisely, the first particle filter element21, and its associated active regeneration device15, are arranged concentrically within the second particle filter element22, wherein the control element23is provided at the outlet of the first particle filter element21. The other components are identical in principle and are therefore denoted by the same reference symbols.

In said embodiment, depicted inFIGS. 5 and 6, the control element23is assigned to the first particle filter element21, that is to say the control element23can regulate the exhaust-gas flow11which flows through the first particle filter element21. By contrast, the exhaust-gas flow11flows continuously through the second particle filter element22. InFIG. 5, the control element23is open, such that the exhaust-gas flow11flows both through the first, and through the second particle filter element21,22. By contrast, inFIG. 6, the control element23is closed, such that in this case, the exhaust-gas flow11flows through only the second particle filter element22.

The above configurations of the device are non limiting and additional configurations of the two filters, one with an affixed active regeneration device are possible. For example, the first and second particle filter element could share a housing, but may not be arranged concentrically in the shared housing.

Referring now toFIG. 7, the figure schematically depicts method700, an example method by which engine controller138instructs the exhaust-gas aftertreament device of the present disclosure. A default state of operation for an engine containing an embodiment of the exhaust-gas aftertreatment device of the present disclosure, as depicted inFIG. 2andFIG. 3, is for control element10to conduct exhaust-gas flow11through first particle filter element7containing an active regeneration device15. This default state is depicted at702. Engine operating conditions are estimated and/or measured at704. Engine operating conditions can be estimated and measure based on data from manifold absolute pressure (MAP) sensor124, load, RPM, air-fuel ratio, exhaust-gas temperature sensor128, and others. If, at706, the exhaust-gas temperature is above a threshold temperature based on above estimates and/or measurements (YES), method700proceeds to708. The threshold temperature is a temperature, for example 500° C., above which oxidation of soot loading in a particle filter element is favored. Threshold temperature is a predefined value based on known conditions for soot oxidation. This threshold temperature is consistent for a given system, but may vary for differing systems, for example those using different catalysts. At708control element10is adjusted to conduct exhaust-gas flow to the second particle filter element8. As depicted inFIG. 3control element10is a flap valve and here closes to the fork of exhaust line5that contains first particle filter element7, and is open to second particle filter element8. At712, exhaust-gas flow is conducted through second filter element7as a result of adjusted control element10, and this exhaust-gas flow is maintained until exhaust-gas temperature falls below threshold. In this embodiment routing exhaust-gas flow through the second particle filter element8is done above threshold potential because this particle filter element does not contain an active regeneration device and the higher than threshold temperatures passively regenerate the second filter element.

In other embodiments control element10could be partially open to conduct a portion of exhaust gas flow to first filter element7and the remainder to second filter element8. This could be advantageous in conditions where back pressure from conducting exhaust-gas flow to a single particle filter element is high.

If, at706, the exhaust-gas temperature is below threshold temperature (NO), or at712the temperature has fallen below threshold temperature, control element10retains, or adopts, its default state, wherein control element10, a flap valve, is open to conduct exhaust-gas flow11through the first particle filter element7. At714, exhaust-gas flow11flows through first particle filter element7. At temperatures below threshold, a particle filter element is unable to regenerate passively. First particle filter element7, contains active regeneration device15to allow for filter element regeneration at low temperatures. At716, soot loading in the first particle filter element7is monitored. If soot loading density is above a predetermined threshold at716(YES) active regeneration device15is activated, heating the first particle filter element to 500° C. or higher, preferably to at least 550° C., to regenerate first particle filter element7at718. Threshold for soot loading is a level above which first particle filter element7becomes inefficient as its catalytic abilities are inhibited or flow through is affected by soot accumulation. Soot loading can be estimated by backpressure in exhaust manifold136or by long-term engine operating conditions such as air-fuel ratio and manifold absolute pressure. Variations of the above method are compatible with alternate configurations of the present disclosure. For example first particle filter element21and second particle filter element22could be arranged as shown inFIG. 5andFIG. 6. Additionally, method700only includes two states of control element10. A third state, as depicted inFIG. 4, wherein exhaust-gas flow11, is conducted through both the first particle filter element7and the second particle filter element8simultaneously at sufficiently high temperature, is compatible with the device of the present disclosure but not shown inFIG. 7. This embodiment has the advantage of passively regenerating the first particle filter element7in addition to second particle filter element8. This configuration, in which exhaust gas flow can be directed towards both filer elements simultaneously, could be advantageous to reduce high exhaust back pressure.

Additionally, the default state of the present disclosure can differ. For example, by default control element10might be open to both the first and second particle filter element. Therein, engine controller38would instruct control element10to direct exhaust-gas flow through the first particle filter element, the second particle filter element, or both dependent on estimates and measurements of engine operating conditions. The present disclosure provides a system for reducing particle emissions while minimizing effects on engine efficiency. The system of the present disclosure is advantageous as a larger filter is available for capturing particle emissions that can be passively generated when engine conditions produce suitably high exhaust-gas temperatures. However, as this is not necessarily the case, especially in cooler operating diesel engines and/or when operating at low loads and RPMs an additional, smaller particle filter element is provided that is coupled to an active regeneration device. The active regeneration device allows for regeneration of the catalyst of the particle filter element by providing sufficient heat to promote the oxidation of soot particles even when engine operating conditions produce exhaust-gas below this temperature.