Abstract:
A system comprises a particulate matter (PM) filter comprising an inlet for receiving exhaust gas. A zoned heater is arranged in the inlet and comprises a resistive heater comprising N zones, where N is an integer greater than one. Each of the N zones comprises M sub-zones, where M is an integer greater than one. A control module selectively activates one of the N zones to initiate regeneration in downstream portions of the PM filter from the one of the N zones and deactivates others of the N zones.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 60/955,743, filed on Aug. 14, 2007. 
         [0002]    This application is related to U.S. patent application Ser. Nos. 11/561,100 filed on Nov. 17, 2006, 11/561,108 filed on Nov. 17, 2006, and 11/557,715 filed on Nov. 8, 2006. The disclosures of the above applications are incorporated herein by reference in their entirety. 
     
    
     STATEMENT OF GOVERNMENT RIGHTS 
       [0003]    This disclosure was produced pursuant to U.S. Government Contract No. DE-FC-04-03 AL67635 with the Department of Energy (DoE). The U.S. Government has certain rights in this disclosure. 
     
    
     FIELD 
       [0004]    The present disclosure relates to particulate matter (PM) filters, and more particularly to ash reduction systems for PM filters. 
       BACKGROUND 
       [0005]    The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
         [0006]    Engines such as diesel engines produce particulate matter (PM) that is filtered from exhaust gas by a PM filter. The PM filter is disposed in an exhaust system of the engine. The PM filter reduces emission of PM that is generated during combustion. 
         [0007]    Over time, the PM filter becomes full. During regeneration, the PM may be burned within the PM filter. Regeneration may involve heating the PM filter to a combustion temperature of the PM. There are various ways to perform regeneration including modifying engine management, using a fuel burner, using a catalytic oxidizer to increase the exhaust temperature with after injection of fuel, using resistive heating coils, and/or using microwave energy. 
         [0008]    Diesel PM combusts when temperatures above a combustion temperature such as 600° C. are attained. The start of combustion causes a further increase in temperature. While spark-ignited engines typically have low oxygen levels in the exhaust gas stream, diesel engines have significantly higher oxygen levels. While the increased oxygen levels make fast regeneration of the PM filter possible, it may also pose some problems. 
         [0009]    PM reduction systems that use fuel tend to decrease fuel economy. For example, many fuel-based PM reduction systems decrease fuel economy by 5%. Electrically heated PM reduction systems reduce fuel economy by a negligible amount. However, durability of the electrically heated PM reduction systems has been difficult to achieve. 
       SUMMARY 
       [0010]    A system comprises a particulate matter (PM) filter comprising an inlet for receiving exhaust gas. A zoned heater is arranged in the inlet and comprises a resistive heater comprising N zones, where N is an integer greater than one. Each of the N zones comprises M sub-zones, where M is an integer greater than one. A control module selectively activates one of the N zones to initiate regeneration in downstream portions of the PM filter from the one of the N zones and deactivates others of the N zones. 
         [0011]    In other features, the others of the N zones provide stress mitigation zones. The N zones are arranged in a center portion, a first circumferential portion radially outside of the center portion and a second circumferential portion radially outside of the first circumferential portion. The center portion comprises a first zone. The second circumferential portion comprises the first zone, a second zone and a third zone. The first, second and third zones alternate around the second circumferential portion. The first circumferential portion comprises fourth and fifth zones that alternate. 
         [0012]    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 
         [0013]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0014]      FIG. 1  is a functional block diagram of an exemplary engine including an electrically heated particulate matter (PM) filter with a zoned inlet heater; 
           [0015]      FIG. 2  illustrates exemplary zoning of the zoned inlet heater of the electrically heated particulate matter (PM) filter of  FIG. 1  in further detail; 
           [0016]      FIG. 3  illustrates exemplary zoning of the zoned inlet heater of the electrically heated PM filter of  FIG. 1  in further detail; and 
           [0017]      FIG. 4  illustrates an exemplary resistive heater in one of the zones of the zoned inlet heater of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    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. 
         [0019]    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 execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. 
         [0020]    The present disclosure utilizes heater zones distributed throughout an inlet of an electrically heated PM filter. The heater zones are spaced in a manner such that thermal stress is mitigated between active heaters. Therefore, the overall stress forces due to heating are smaller and distributed over the volume of the entire electrically heated PM filter. This approach allows regeneration in larger segments of the electrically heated PM filter without creating thermal stresses that damage the electrically heated PM filter. 
         [0021]    A largest temperature gradient occurs at edges of the heaters. Therefore, activating one heater past the localized stress zone of another heater enables more actively heated regeneration volume without an increase in overall stress. This tends to improve the regeneration opportunity within a drive cycle and reduces cost and complexity since the system does not need to regenerate as many zones independently. 
         [0022]    Referring now to  FIG. 1 , an exemplary diesel engine system  10  is schematically illustrated in accordance with the present disclosure. It is appreciated that the diesel engine system  10  is merely exemplary in nature and that the zone heated 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. 
         [0023]    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 . 
         [0024]    Air within the intake manifold  22  is distributed into cylinders  26 . Although four cylinders  26  are illustrated, the systems and methods of the present disclosure 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 disclosure 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. 
         [0025]    The exhaust system includes an exhaust manifold  30 , a diesel oxidation catalyst (DOC)  32 , and a particulate filter (PF)  34  with a zoned inlet heater  35 . Optionally, an EGR valve (not shown) re-circulates 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 , through the zoned inlet heater  35  and into 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. The zoned inlet heater  35  heats the exhaust to a regeneration temperature as will be described below. 
         [0026]    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 predetermined level 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 may be varied based upon the estimated amount of particulate matter within the PF  34 . 
         [0027]    Current is applied to the zoned inlet heater  35  during the regeneration process. More specifically, the electric energy heats selected portions of the zoned inlet portion  35  of the PF  34  for predetermined periods, respectively. Exhaust passing through the front face is heated by the activated zones. 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. 
         [0028]    Referring now to  FIG. 2 , an exemplary zoned inlet heater  35  for the PM filter  34  is shown in further detail. The electrically heated PM filter  34  includes multiple spaced heater zones including zone  1  (with sub-zones  1 A,  1 B and  1 C), zone  2  (with sub-zones  2 A,  2 B and  2 C) and zone  3  (with sub-zones  3 A,  3 B and  3 C). The zones  1 ,  2  and  3  are activated during different respective periods. 
         [0029]    As exhaust gas flows through the activated zones, regeneration occurs in the corresponding portions of the PF that are downstream from the activated zones. The corresponding portions of the PF that are not downstream from an activated zone act as stress mitigation zones. For example in  FIG. 2 , sub-zones  1 A,  1 B and  1 C are activated and sub-zones  2 A,  2 B,  2 C,  3 A,  3 B, and  3 C act as stress mitigation zones. 
         [0030]    The corresponding portions of the PM filter downstream from the active heater sub-zones  1 A,  1 B and  1 C thermally expand and contract during heating and cooling. The stress mitigation sub-zones  2 A and  3 A,  2 B and  3 B, and  2 C and  3 C mitigate stress caused by the expansion and contraction of the heater sub-zones  1 A,  1 B and  1 C. After zone  1  has completed regeneration, zone  2  can be activated and zones  1  and  3  act as stress mitigation zones. After zone  2  has completed regeneration, zone  3  can be activated and zones  1  and  2  act as stress mitigation zones. 
         [0031]    Referring now to  FIG. 3 , another exemplary zoned inlet heater arrangement is shown. A center portion may be surrounded by a middle zone including a first circumferential band of zones. The middle portion may be surrounded by an outer portion including a second circumferential band of zones. 
         [0032]    In this example, the center portion includes zone  1 . The first circumferential band of zones includes zones  2  and  3 . The second circumferential band of zones comprises zones  1 ,  4  and  5 . As with the embodiment described above, downstream portions from active zones are regenerated while downstream portions from inactive zones provide stress mitigation. As can be appreciated, one of the zones  1 ,  2 ,  3 ,  4  and  5  can be activated at a time. Others of the zones remain inactivated. 
         [0033]    Referring now to  FIG. 4 , an exemplary resistive heater  200  arranged adjacent to one of the zones (e.g. zone  3 ) from the first circumferential band of zones in  FIG. 3  is shown. The resistive heater  200  may comprise one or more coils that cover the respective zone to provide sufficient heating. 
         [0034]    In use, the control module determines when the PM filter requires regeneration. Alternately, regeneration can be performed periodically or on an event basis. The control module may estimate when the entire PM filter needs regeneration or when zones within the PM filter need regeneration. When the control module determines that the entire PM filter needs regeneration, the control module sequentially activates one of the zones at a time to initiate regeneration within the associated downstream portion of the PM filter. After the one zone is regenerated, another zone is activated while the others are deactivated. This approach continues until all of the zones have been activated. When the control module determines that one of the zones needs regeneration, the control module activates the zone corresponding to the associated downstream portion of the PM filter needing regeneration.