FLOW CONTROLLED ELECTRICALLY ASSISTED DPF REGENERATION

A particulate filter assembly, an exhaust gas treatment system having a particulate filter assembly, and a control method for flow controlled zoned regeneration of the particulate filter assembly are provided. The particulate filter assembly is configured to receive an exhaust gas stream from an internal combustion engine and includes an inlet end configured to receive the exhaust gas stream, a filter configured to remove particulates from the exhaust gas stream, a heating device positioned upstream from the filter having a plurality of zones, each zone of the plurality of zones independently operable to heat a corresponding region of the filter and an exhaust flow valve positioned downstream from the filter configured to selectively restrict flow of the exhaust gas stream through the filter.

DESCRIPTION OF THE EMBODIMENTS

In accordance with an exemplary embodiment of the subject invention, and with reference toFIG. 1, an exhaust gas treatment system20is provided for the reduction of regulated exhaust gas constituents emitted by an internal combustion engine22. It is understood that the exhaust treatment system20described herein may be used in various engine systems utilizing an exhaust gas particulate filter. Such internal combustion engine systems may include, but are not limited to, diesel systems, gasoline systems and various homogeneous charge compression ignition engine systems.

The exhaust gas treatment system20includes at least one exhaust gas conduit30extending from the engine22. An exhaust gas stream25exits the engine22and flows into the exhaust gas conduit30. The exhaust gas treatment system20includes an oxidation catalyst (OC)32positioned within the exhaust gas conduit30in a flow path of the exhaust gas stream. The oxidation catalyst32may include a flow-through metal or ceramic monolith substrate that is packaged in a rigid shell or canister having an inlet and an outlet in fluid communication with the exhaust gas conduit. The substrate may include an oxidation catalyst compound (not shown) disposed thereon which may be applied as a wash coat and may contain platinum group metals such as platinum (Pt), palladium (Pd) rhodium (Rh) or other suitable oxidizing catalysts, or combination thereof. The oxidation catalyst32is useful in treating unburned gaseous and non-volatile HC and CO in the exhaust gas stream25, which are oxidized to form carbon dioxide and water.

An injector34may be positioned downstream from the oxidation catalyst32. The injector34is in fluid communication with the exhaust gas conduit30and is configured to periodically and selectively inject a reductant such as urea or ammonia, or a combination thereof, into the exhaust gas stream25. Other suitable methods of delivery of the reductant to the exhaust gas stream25may be used. The reductant is supplied from a reductant supply tank (not shown) through a supply conduit (not shown). The reductant may be in the form of a gas, a liquid or an aqueous urea solution and may be mixed with air in the injector34to aid in the dispersion of the injected spray in the exhaust gas.

The exhaust gas treatment system20further includes a selective catalytic reduction (SCR) device36disposed within the exhaust gas conduit30downstream from the oxidation catalyst32and injector34. The SCR device36is positioned in fluid communication with the exhaust gas stream25. Similar to the oxidation catalyst32, the SCR device36may also include a flow-through ceramic or metal monolith substrate which is packaged in a rigid shell or canister having an inlet and an outlet in fluid communication with the exhaust gas conduit. The substrate has an SCR catalyst composition (not shown) applied thereto. The SCR catalyst composition preferably contains a zeolite and one or more base metal components such as iron (“Fe”), cobalt (“Co”), copper (“Cu”) or vanadium (“V”) which can operate efficiently to convert NOx constituents in the exhaust gas in the presence of the reductant.

The exhaust gas treatment system20further includes a particulate filter assembly40. The particulate filter assembly40is in fluid communication with the exhaust gas stream25in the exhaust gas conduit30and is configured to receive the exhaust gas stream25. The particulate filter assembly40may be positioned downstream from the selective catalyst reduction device36and operates to filter the exhaust gas stream25of carbon and other particulates.

In an exemplary embodiment, the particulate filter assembly40includes an inlet end42, a heating device44, a filter46, an exhaust flow valve48and an outlet end50. The particulate filter assembly40may be formed as a section along the exhaust gas conduit30. The exhaust gas stream25is received through the inlet end42, passes through the heating device44, filter46, and exhaust flow valve48, and exits the particulate filter assembly at the outlet end50.

The heating device44is positioned within particulate filter assembly40and is configured to heat the filter46for regeneration purposes. The heating device44is disposed on or near a front face, i.e. a face disposed nearest the inlet end42, of the filter46. In an exemplary embodiment, the heating device44is an electrical heating device. The heating device44may be operated, for example, by supplying power to a resistive pathway of the heating device44.

Referring toFIG. 2, the heating device may be divided into a plurality of zones, Z1, Z2, Z3, Z4. It is understood that the four zones Z1, Z2, Z3, Z4 are illustrated and described herein for the purposes of example only, and the that a different or number, size and/or positioning of zones is envisioned as well. Each zone Z1, Z2, Z3, Z4 may be individually heated, independent of the other zones by supplying power to a resistive pathway in a particular zone. The heating of the zones Z1, Z2, Z3, Z4 may be selectively controlled. As such, the heating device44may be selectively operated to provide heat to filter46in stages based on operation of a particular zone Z1, Z2, Z3, Z4.

Referring again toFIG. 1, the filter46is positioned in the particulate filter assembly40. In an exemplary embodiment, the filter46may be formed using a ceramic wall flow monolith filter that is packaged in a rigid, heat resistant shell or canister having an inlet end and an outlet end in fluid communication with the exhaust gas conduit30. The ceramic wall flow monolith filter may be a monolith particulate trap, and include a plurality of longitudinally extending passages that are defined by longitudinally extending walls. The passages include a subset of inlet passages that have an open inlet end and a closed outlet end, and a subset of outlet passages having a closed inlet end and an open outlet end. Exhaust gas entering the filter through the inlet ends of the inlet passages is forced to migrate through adjacent longitudinally extending walls to the outlet passages due to adjacent inlet and outlet passages being plugged or closed at opposite ends. The exhaust gas stream25is filtered of carbon and other particulates through this wall flow mechanism. The filtered particulates are deposited on the longitudinally extending walls of the inlet passages and, over time, will have the effect of increasing the exhaust gas backpressure experienced by the engine22. The walls of the wall flow monolith filter may comprise a porous ceramic honeycomb wall of cordierite material. Any type of ceramic material suitable for the purpose set forth herein may be utilized. It is understood that the ceramic wall flow filter described above is merely exemplary in nature, and other suitable filters are envisioned. For example, particulate filter assembly40may include other filter devices such as wound or packed fiber filters, open cell foams, sintered metal fibers, etc., in addition to, or in place of the filter46described above.

The individual zones Z1, Z2, Z3, Z4 are configured to heat corresponding regions of the filter46. That is, a particular zone Z1, Z2, Z3, Z4 of the heating device44is configured to heat a region of the filter46that generally corresponds to the size, shape and position (radial and circumferential) of the particular zone. Accordingly, the filter46may be heated in stages based on operation of the heating device44, so that a staged regeneration may be performed.

Referring toFIG. 1, an exhaust flow valve48is positioned in the particulate filter assembly40adjacent to the outlet end50and downstream of the filter46. The exhaust flow valve48is in fluid communication with the exhaust gas stream25flowing from the filter46.

Referring toFIG. 3, in an exemplary embodiment, the exhaust flow valve48includes a plurality of valve plates52. The exhaust flow valve48may include, for example, four valve plates52. The valve plates52may be generally circular and positioned within the exhaust gas conduit30so as to selectively restrict flow of the exhaust gas stream25. It is understood, that the size, shape, number and/or position of the valve plates52is not limited to the example described above and shown inFIG. 3. Any suitable number of valve plates52may be implemented, and different shapes may be used for the valve plates52.

In an exemplary embodiment, each valve plate52is rotatably mounted and movable between an open position and a closed positioned. Referring toFIG. 1, in the open position, the valve plate52extends generally parallel to a direction of flow of the exhaust gas stream25in the exhaust gas conduit30. In the closed position, the valve plate52extends generally perpendicular to the direction of flow of the exhaust gas stream25in the exhaust gas conduit30so as to restrict the flow of the exhaust gas stream25.

Referring again toFIG. 1, the exhaust gas treatment system20includes a plurality of NOx sensors54,56. A first NOx sensor54may be positioned upstream of the selective catalyst reduction device36and a second NOx sensor56may be positioned downstream of the selective catalyst reduction device. The NOx sensors54,56may detect the amount of NOx in the exhaust gas stream25before and after the exhaust gas has passed through the SCR device36. Accordingly, an efficiency of the SCR device36may be determined. It is understood that additional NOx sensors may be included at various positions along the exhaust gas conduit30to measure the amount of NOx in the exhaust gas stream25.

In addition, at least one temperature sensor58may also be positioned in the exhaust gas conduit30. In an exemplary embodiment, the at least one temperature sensor58may be positioned at a downstream end of the particulate filter assembly40, adjacent to the outlet end50, downstream from the exhaust flow valve48. The at least one temperature sensor58is configured to measure a temperature of the exhaust gas stream25after passing through the particulate filter assembly40

A controller60such as a vehicle or engine controller is operably connected to, and monitors, the engine22and exhaust gas treatment system20through signal communication with various sensors, including the first and second NOx sensors54,56and at the least one temperature sensor58. The controller60may include, for example, an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated or group) and memory that executes one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. In addition, the controller60may be communicatively connected to the injector34, the heating device44and the exhaust flow valve48. Accordingly, the controller60may selectively operate the injector34, heating device44and exhaust flow valve48to control a staged regeneration of the filter46as described below. Controlling of the staged regeneration of the filter46may be in response, at least partially, to signals received from the various sensors, including the first and second NOx sensors54,56and at least one temperature sensor58.

In operation, an increase in exhaust backpressure caused by the accumulation of particulate matter requires that the filter46is periodically cleaned, or regenerated. Regeneration involves the oxidation or burning of the accumulated carbon and other particulates, in what is typically a high temperature (>600° C.) environment. According to an exemplary embodiment of the subject invention, the filter46may be regenerated in stages. That is, individual regions of the filter46may be regenerated in sequence. In an exemplary embodiment, the regions of the filter46correspond to the zones Z1, Z2, Z3 and Z4 of the heating device44. Thus, the filter46may include four regions corresponding to respective zones Z1, Z2, Z3 and Z4 of the heating device44. Accordingly, the staged regeneration may be selectively performed for each region of the filter46, such that one region is subsequently heated after another to ignite the particulate matter accumulated in that region and regenerate that region of the filter46. It is understood that the regions of the filter46described above are for exemplary purposes only, and that any other number of suitable regions are envisioned based on the number of zones of the heating element44. In various embodiments, the number, size, shape and position of the regions of the filter46corresponds to the number, size, shape and position of the zones of the heating device44. However, the number, size, shape and position of the regions may vary from the number, size, shape and position of the zones.

To regenerate a particular region of the filter46, at least one valve plate52of the exhaust flow valve48is moved to the closed position so as to restrict flow of the exhaust gas stream25. Power is supplied to a zone Z1, Z2, Z3, Z4 of the heating device44is positioned generally at a location where the exhaust gas stream25is limited due to the closed at least one valve plate52. Thus, a region of the filter46is heated by the operable zone Z1, Z2, Z3, Z4 in an area where the exhaust gas stream flow is limited or restricted. The accumulated particulate matter in the region of the filter46that is heated by a corresponding zone Z1, Z2, Z3, Z4 of the heating device and where the flow is restricted may then be ignited so that it may burn off. Accordingly, that region of the filter46may be regenerated. Because the flow of the exhaust gas stream25is restricted in that region, the ignited particulate matter is less susceptible to being extinguished. When regeneration of that region is complete, the at least one closed valve plate52is moved to an open position and the power is turned off to the operable zone of the heating device44so that the operable zone no longer provides heat to the filter sufficient for regeneration.

In an exemplary embodiment, the process above is carried out in stages, such that after one region of the filter46is regenerated, another zone Z1, Z2, Z2, Z4 of the heating device44is operated to provide heat to another correspond region of filter46. In addition, another valve plate52is closed to restrict the flow of the exhaust gas stream25in an area generally corresponding to the operable zone and region of the filter46to be regenerated. This process is carried out sequentially for each zone Z1, Z2, Z3, Z4 of the heating device44so that all of the corresponding regions of the filter46are regenerated. Accordingly, the filter46may be regenerated, as a whole, in stages, i.e., region-by-region, based on the selective operation of the zones Z1, Z2, Z3, Z4 of the heating device and the respective valve plates52.

FIG. 4shows a control method of carrying out a flow controlled zoned regeneration of the filter46, according to an exemplary embodiment of the subject invention. The exemplary method may be performed in a continuous loop. According to the exemplary method, at210the controller60determines if regeneration of the filter46is necessary. If regeneration is necessary, at220, the controller60determines the flow of the exhaust gas stream25based on exhaust temperatures of the exhaust gas stream25received from the at least one temperature sensor58. At230, the controller determines if the flow of the exhaust gas stream25corresponds to a target zone or region of the filter46to be regenerated. At240, the controller activates or energizes the heating device44if the flow of the exhaust gas stream25corresponds to a target zone or region of the filter46to be regenerated. In particular, the controller energizes a zone Z1, Z2, Z3, Z4 of the heating device44corresponding to a region of the filter46to be regenerated. For example, with reference toFIG. 2, if a central region of the filter46is to be regenerated, then a central zone Z1 of the heating device44is energized. That is, power is supplied to the central zone Z1 of the heating device so the heating device outputs heat to the central region of the filter46.

If the flow of the exhaust gas stream25does not correspond to a target zone or region of the filter46, the controller60adjusts the position of a valve plate or plates52at235, and continues the method at230.

That is, based on temperature information received from the at least one temperature sensor58, the controller60may determine which zone or region of the filter46is to be regenerated. The controller60operates the exhaust flow valve48to move a valve plate52to a closed position in a location that generally corresponds to a zone or region of the filter46to be regenerated, so as to restrict or limit the flow of exhaust gas through that zone or region to be regenerated.

At250, the controller60determines if accumulated particulate matter on the filter46has been ignited. If the accumulated particulate matter has been ignited, the heating device44, and in particular, the energized zone of the heating device44is turned off at255and the method continues at250. At260, if no accumulated particulate matter is ignited, the controller60determines that regeneration for the region of the filter46corresponding to the energized zone of the heating device is complete. At270, the controller60operates the exhaust flow valve48to open the closed valve plate52and carry out the regeneration in the next zone or region. That is, this process is then repeated to regenerate the filter46in other regions, by selectively closing the other valve plates52and energizing the other zones Z1, Z2, Z3, Z4 of the heating device44as described above. At280, the method is exited. If the controller60determines that the regeneration for the zone is not complete at260, the controller60exits the process at280, and begins a new loop for the process. Further, if the controller60determines that regeneration is not necessary at210, the controller exits the process at280and being a new loop for the process.

In the exemplary embodiments above, it is appreciated that filter46is heated in regions via the use of the heating device44. It is contemplated that the filter46may be segmented into a plurality of regions using a plurality of heating device44formats. Therefore, the present invention is not limited to the embodiments described above and shown inFIGS. 1-4.

In the exemplary embodiments above, fuel may be conserved as fuel is not required to be injected into the exhaust gas stream25to ignite the particulate matter. In addition, upward adjustment factors (UAF) emission penalties associated with the regeneration of the filter may be reduced or eliminated. Further still, by regenerating the filter in zones, the filter may be subjected to less thermal stress. Accordingly, the service life of the filter may be improved and warranty costs associated with regeneration may be reduced.