Patent Abstract:
An exhaust system that processes exhaust generated by an engine is provided. The system includes: a particulate filter (PF) that filters particulates from the exhaust wherein an upstream end of the PF receives exhaust from the engine; and a grid of electrically resistive material that is applied to an exterior upstream surface of the PF and that selectively heats exhaust passing through the grid to initiate combustion of particulates within the PF.

Full Description:
STATEMENT OF GOVERNMENT RIGHTS 
     Certain of the subject matter of the present application was developed under Contract Number DE-FC-04-03AL67635 awarded by the Department of Energy. The U.S. government has certain rights in this invention. 
    
    
     CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/786,059, filed on Mar. 24, 2006. The disclosure of the above application is incorporated herein by reference. 
     FIELD 
     The present disclosure relates to methods and systems for heating particulate filters. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Diesel engines typically have higher efficiency than gasoline engines due to an increased compression ratio and a higher energy density of diesel fuel. A diesel combustion cycle produces particulates that are typically filtered from diesel exhaust gas by a particulate filter (PF) that is disposed in the exhaust stream. Over time, the PF becomes full and the trapped diesel particulates must be removed. During regeneration, the diesel particulates are burned within the PF. 
     Conventional regeneration methods inject fuel into the exhaust stream after the main combustion event. The post-combustion injected fuel is combusted over one or more catalysts placed in the exhaust stream. The heat released during the fuel combustion on the catalysts increases the exhaust temperature, which burns the trapped soot particles in the PF. This approach, however, can result in higher temperature excursions than desired, which can be detrimental to exhaust system components including the PF. 
     SUMMARY 
     Accordingly, an exhaust system that processes exhaust generated by an engine is provided. The system includes: a particulate filter (PF) that filters particulates from the exhaust wherein an upstream end of the PF receives exhaust from the engine; and a grid of electrically resistive material that is applied to an exterior upstream surface of the PF and that selectively heats exhaust passing through the grid to initiate combustion of particulates within the PF. 
     In other features, a method of regenerating a particulate filter (PF) of an exhaust system is provided. The method includes: applying a grid of electrically resistive material to a front exterior surface of the PF; heating the grid by supplying current to the electrically resistive material; inducing combustion of particulates present on the front surface of the PF via the heated grid; and directing heat generated by combustion of the particulates into the PF to induce combustion of particulates within the PF. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a functional block diagram of a vehicle including a particulate filter. 
         FIG. 2  is a cross-sectional view of a wall-flow monolith particulate filter. 
         FIG. 3  includes perspective views of front faces of PFs illustrating various patterns of resistive paths. 
         FIG. 4  is a perspective view of a front face of the PF and a heater insert. 
         FIG. 5  is a cross-sectional view of a portion of the PF of  FIG. 2  including a conductive coating. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. As used herein, the term module refers to 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. 
     Referring now to  FIG. 1 , an exemplary diesel engine system  10  is schematically illustrated in accordance with the present invention. It is appreciated that the diesel engine system  10  is merely exemplary in nature and that the particulate filter regeneration system described herein can be implemented in various engine systems implementing a particulate filter. Such engine systems may include, but are not limited to, gasoline direct injection engine systems and homogeneous charge compression ignition engine systems. For ease of the discussion, the disclosure will be discussed in the context of a diesel engine system. 
     A turbocharged diesel engine system  10  includes an engine  12  that combusts an air and fuel mixture to produce drive torque. Air enters the system by passing through an air filter  14 . Air passes through the air filter  14  and is drawn into a turbocharger  18 . The turbocharger  18  compresses the fresh air entering the system  10 . The greater the compression of the air generally, the greater the output of the engine  12 . Compressed air then passes through an air cooler  20  before entering into an intake manifold  22 . 
     Air within the intake manifold  22  is distributed into cylinders  26 . Although four cylinders  26  are illustrated, it is appreciated that the systems and methods of the present invention can be implemented in engines having a plurality of cylinders including, but not limited to, 2, 3, 4, 5, 6, 8, 10 and 12 cylinders. It is also appreciated that the systems and methods of the present invention can be implemented in a v-type cylinder configuration. Fuel is injected into the cylinders  26  by fuel injectors  28 . Heat from the compressed air ignites the air/fuel mixture. Combustion of the air/fuel mixture creates exhaust. Exhaust exits the cylinders  26  into the exhaust system. 
     The exhaust system includes an exhaust manifold  30 , a diesel oxidation catalyst (DOC)  32 , and a particulate filter (PF)  34 . Optionally, an EGR valve (not shown) recirculates a portion of the exhaust back into the intake manifold  22 . The remainder of the exhaust is directed into the turbocharger  18  to drive a turbine. The turbine facilitates the compression of the fresh air received from the air filter  14 . Exhaust flows from the turbocharger  18  through the DOC  32  and the PF  34 . The DOC  32  oxidizes the exhaust based on the post combustion air/fuel ratio. The amount of oxidation increases the temperature of the exhaust. The PF  34  receives exhaust from the DOC  32  and filters any soot particulates present in the exhaust. 
     A control module  44  controls the engine and PF regeneration based on various sensed information. More specifically, the control module  44  estimates loading of the PF  34 . When the estimated loading achieves a threshold level (e.g. 5 grams/liter of particulate matter) and the exhaust flow rate is within a desired range, current is controlled to the PF  34  via a power source  46  to initiate the regeneration process. The duration of the regeneration process varies based upon the amount of particulate matter within the PF  34 . It is anticipated, that the regeneration process can last between 4-6 minutes. Current is only applied, however, during an initial portion of the regeneration process. More specifically, the electric energy heats the face of the PF for a threshold period (e.g., 1-2 minutes). Exhaust passing through the front face is heated. The remainder of the regeneration process is achieved using the heat generated by combustion of particulate matter present near the heated face of the PF  34  or by the heated exhaust passing through the PF. 
     With particular reference to  FIG. 2 , the PF  34  is preferably a monolith particulate trap and includes alternating closed cells/channels  50  and opened cells/channels  52 . The cells/channels  50 , 52  are typically square cross-sections, running axially through the part. Walls  58  of the PF  34  are preferably comprised of a porous ceramic honeycomb wall of cordierite material. It is appreciated that any ceramic comb material is considered within the scope of the present invention. Adjacent channels are alternatively plugged at each end as shown at  56 . This forces the diesel aerosol through the porous substrate walls which act as a mechanical filter. Particulate matter is deposited within the closed channels  50  and exhaust exits through the opened channels  52 . Soot particles  59  flow into the PF  34  and are trapped therein. 
     For regeneration purposes, a grid  64  including an electrically resistive material is attached to the front exterior surface referred to as the front face of the PF  34 . Current is supplied to the resistive material to generate thermal energy. It is appreciated that thick film heating technology may be used to attach the grid  64  to the PF  34 . For example, a heating material such as Silver or Nichrome may be coated then etched or applied with a mask to the front face of the PF  34 . In various other embodiments, the grid is composed of electrically resistive material such as stainless steel and attached to the PF using a ceramic adhesive. 
     It is also appreciated that the resistive material may be applied in various single or multi-path patterns as shown in  FIG. 3 . Segments of resistive material can be removed to generate the pathways. In various embodiments a perforated heater insert  70  as shown in  FIG. 4  may be attached to the front face of the PF  34 . In any of the above mentioned embodiments, exhaust passing through the PF  34  carries thermal energy generated at the front face of the PF  34  a short distance down the channels  50 , 52 . The increased thermal energy ignites particulate matter present near the inlet of the PF  34 . The heat generated from the combustion of the particulates is then directed through the PF to induce combustion of the remaining particulates within the PF. 
     With particular reference to  FIG. 5 , a thermally conductive coating  72  can be additionally applied at the inlets  62  of the channels  50 , 52 . The coating  72  can extend a short distance down the opened ends of the closed channels  50 . In various embodiments, the conductive coating extends within an inch of the front face of the PF. The resistive material of the grid  64  contacts the conductive coating  72 . Thermal energy is transferred to the conductive coating  72  when electrical energy passes through the resistive material. Heat from the conductive coating  72  ignites particulate matter present near the inlet of the PF  34 . 
     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present disclosure can be implemented in a variety of forms. Therefore, while this disclosure has been described in connection with particular examples thereof, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, specification, and the following claims.

Technology Classification (CPC): 5