Abstract:
A system includes a particulate matter (PM) filter, an electric heater, and a control circuit. The electric heater includes multiple zones, which each correspond to longitudinal zones along a length of the PM filter. A first zone includes multiple discontinuous sub-zones. The control circuit determines whether regeneration is needed based on an estimated level of loading of the PM filter and an exhaust flow rate. In response to a determination that regeneration is needed, the control circuit: controls an operating parameter of an engine to increase an exhaust temperature to a first temperature during a first period; after the first period, activates the first zone; deactivates the first zone in response to a minimum filter face temperature being reached; subsequent to deactivating the first zone, activates a second zone; and deactivates the second zone in response to the minimum filter face temperature being reached.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 60/973,324, filed on Sep. 18, 2007. 
    
    
     STATEMENT OF GOVERNMENT RIGHTS 
     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 
     The present disclosure relates to particulate matter (PM) filters, and more particularly to high exhaust temperature, zoned electrically-heated PM filters. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     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. 
     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. The resistive heating coils are typically arranged in contact with the PM filter to allow heating by both conduction and convection. 
     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. 
     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 
     A system comprises a particulate matter (PM) filter including an upstream end for receiving exhaust gas and a downstream end. An electric heater is arranged one of spaced from and in contact with the upstream end. A control module increases an exhaust temperature above a soot oxidation temperature before activating the electric heater to regenerate downstream portions of the PM filter. 
     A method comprises providing a particulate matter (PM) filter comprises an upstream end for receiving exhaust gas and a downstream end; arranging an electric heater one of spaced from and in contact with said upstream end; increasing an exhaust temperature above a soot oxidation temperature before activating said electric heater to regenerate downstream portions of said PM filter from said one of said N zones. 
     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 an exemplary engine including a particulate matter (PM) filter with a zoned inlet heater; 
         FIG. 2  illustrates exemplary zoning of the zoned inlet heater of the electrically heated particulate matter (PM) filter of  FIG. 1  in further detail; 
         FIG. 3  illustrates exemplary zoning of the zoned inlet heater of the electrically heated PM filter of  FIG. 1  in further detail; 
         FIG. 4  illustrates an exemplary resistive heater in one of the zones of the zoned inlet heater of  FIG. 3 ; 
         FIG. 5  illustrates the electrically heated PM filter having a zoned electric heater; 
         FIG. 6  illustrates heating within the zoned electric heater; 
         FIG. 7  is a flowchart illustrating exemplary steps performed by the control module to increase exhaust temperature input to the electrically heated PM filter before starting regeneration; and 
         FIG. 8  is a flowchart illustrating exemplary steps for regenerating a zoned electric heater associated with a PM filter. 
     
    
    
     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 execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. 
     The present disclosure raises the exhaust temperature in any suitable manner before performing regeneration using an electrical heater to enable more robust PM filter regeneration. For example only, the inlet exhaust temperature may be raised above a soot oxidation temperature. The temperature of the exhaust gas entering an inlet of the PM filter may be increased by modifying engine management, using a fuel burner, using a catalytic oxidizer to increase the exhaust temperature with after injection of fuel, and/or using any other suitable approaches. 
     For example, the exhaust temperature may be raised to a temperature above 550 degrees Celsius. This temperature range is greater than or equal to a typical soot oxidation temperature and higher than the natural exhaust temperature. This temperature may be less than the regeneration temperature. 
     Once the temperature of the exhaust gas input to the PM filter is increased, the electrical heater initiates regeneration. For example, a zoned electric heater may activate heated zones, which causes a soot combustion wave to travel down the PM filter channel cleaning the filter. This process continues until all of the heater zones are regenerated. When PM filter regenerations are run with an inlet exhaust temperature in the increased temperature range described herein, the combustion flamefronts are less likely to be extinguished. The increased inlet exhaust temperature also creates a smaller temperature delta, which reduces thermal stress forces. Regeneration also occurs more quickly. 
     The electrical heater can be zoned or unzoned. The electrical heater may be in contact with or spaced from the PM filter. The heater selectively heats all or portions of the PM filter. The PM filter may be in contact with or mounted close enough to the front of the PM filter to control the heating pattern. The length of the heater may be set to optimize the exhaust gas temperature. 
     Thermal energy is transmitted from the heater to the PM filter. The PM filter may be heated by convection and/or conduction. The electrical heater may be divided in zones to reduce electrical power required to heat the PM filter. The zones also heat selected downstream portions within the PM filter. By heating only the selected portions of the filter, the magnitude of forces in the substrate is reduced due to thermal expansion. As a result, higher localized soot temperatures may be used during regeneration without damaging the PM filter. 
     The PM filter may be regenerated by selectively heating one or more of the zones in the front of the PM filter and igniting the soot using the heated exhaust gas. When a sufficient face temperature is reached, the heater may be turned off and the burning soot then cascades down the length of the PM filter channel, which is similar to a burning fuse on a firework. The burning soot is the fuel that continues the regeneration. This process is continued for each heating zone until the PM filter is completely regenerated. 
     The heater zones may be 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. 
     A largest temperature gradient tends to occur 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. 
     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. 
     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, 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. 
     The exhaust system includes an exhaust manifold  30 , a diesel oxidation catalyst (DOC)  32 , and a particulate filter (PM filter) assembly  34  with an inlet heater  35 . The heater  35  may be zoned. 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 heater  35  and into the PM filter assembly  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 PM filter assembly  34  receives exhaust from the DOC  32  and filters any soot particulates present in the exhaust. The inlet heater  35  is in contact with or spaced from the PM filter assembly  34  and heats the exhaust to a regeneration temperature as will be described below. 
     A control module  44  controls the engine and PM filter regeneration based on various sensed information. More specifically, the control module  44  estimates loading of the PM filter assembly  34 . When the estimated loading is at a predetermined level and the exhaust flow rate is within a desired range, current may be controlled to the PM filter assembly  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 PM filter assembly  34 . 
     Current is applied to the heater  35  during the regeneration process. More specifically, the energy may heat selected zones of the heater  35  of the PM filter assembly  34  for predetermined periods, respectively. Exhaust gas passing through the heater  35  is heated by the activated zones. The heated exhaust gas travels to the downstream filter of PM filter assembly  34  and heats the filter by convection and/or conduction. The remainder of the regeneration process is achieved using the heat generated by the heated exhaust passing through the PM filter. 
     The control module may increase the temperature of the exhaust gas entering an inlet of the PM filter using any suitable approach. For example, engine management may modify engine management such as the timing and/or amount of fuel supplied to the cylinders. Alternately, a fuel burner  47  may be used. The fuel burner  47  may be arranged in the exhaust and may selectively introduce fuel into the exhaust between the engine and PM filter. Alternately, the catalytic oxidizer may be used to increase the exhaust temperature with after injection of fuel. In other words, excess fuel may be injected during the exhaust part of the cycle. 
     Referring now to  FIG. 2 , an exemplary zoned inlet heater  35  for the PM filter assembly  34  is shown in further detail. The electrically heated PM filter assembly  34  is arranged spaced from or in contact with the PM filter assembly  34 . The PM filter assembly  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  may be activated during different respective periods. 
     As exhaust gas flows through the activated zones of the heater, regeneration occurs in the corresponding portions of the PM filter that initially received the heated exhaust gas (e.g. areas downstream from the activated zones) or downstream areas that are ignited by cascading burning soot. The corresponding portions of the PM filter 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. 
     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. 
     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. 
     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. 
     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. 
     Referring now to  FIG. 5 , the PM filter assembly  34  is shown in further detail. The PM filter assembly  34  includes a housing  200 , a filter  202 , and the zoned heater  35 . The filter  202  may include a rear endplug  208 . The heater  35  may be arranged between a laminar flow element  210  and a substrate of the filter  202 . An electrical connector  211  may provide current to the zones of the PM filter assembly  34  as described above. 
     As can be appreciated, the heater  35  may be in contact with or spaced from the filter  202  such that the heating is convection and/or conduction heating. Insulation  212  may be arranged between the heater  35  and the housing  200 . Exhaust gas enters the PM filter assembly  34  from an upstream inlet  214  and is heated by one or more zones of the PM filter assembly  34 . The heated exhaust gas is received by the filter  202 . 
     Referring now to  FIG. 6 , heating within the PM filter assembly  34  is shown in further detail. Exhaust gas  250  passes through the heater  35  and is heated by one or more zones of the heater  35 . If spaced from the filter  202 , the heated exhaust gas travels a distance “d” and is then received by the filter  202 . The distance “d” may be ½″ or less. The filter  202  may have a central inlet  240 , a channel  242 , filter material  244  and an outlet  246  located radially outside of the inlet. The filter may be catalyzed. The heated exhaust gas causes PM in the filter to burn, which regenerates the PM filter. The heater  35  transfers heat by convection and/or conduction to ignite a front portion of the filter  202 . When the soot in the front face portions reaches a sufficiently high temperature, the heater is turned off. Combustion of soot then cascades down a filter channel  254  without requiring power to be maintained to the heater. 
     Referring now to  FIG. 7 , control begins in step  300 . In step  304 , control determines whether regeneration is needed. If step  308 , control determines whether the input exhaust temperature to the PM filter is greater than a first temperature threshold T TH1 . The first temperature threshold T TH1  may be greater than a soot oxidation temperature. The first temperature threshold T TH1  may be less than regeneration temperature. For example only, the first temperature threshold T TH1  may be selected to be greater than or equal to 550 degrees Celsius. 
     If step  308  is false, the engine control module increases the exhaust temperature using any suitable approach in step  312 . Control continues from steps  312  and  308  (if true) with step  316 . If step  316  is true, control determines whether the PM filter temperature is greater than a second temperature threshold T TH2 . If step  316  is true, control executes PM filter regeneration control. Control continues from steps  316  (if false) and step  320  with step  324 . 
     For example only, the regeneration temperature in the PM filter may be set to approximately greater than or equal to 600 degrees Celsius. For example only, the regeneration temperature in the PM filter may be set to approximately greater than or equal to 700 degrees Celsius. For example only, the regeneration temperature in the PM filter may be set to approximately greater than or equal to 800 degrees Celsius. 
     Referring now to  FIG. 8 , exemplary steps for regenerating a zoned PM filter are shown. In step  400 , control begins and proceeds to step  404 . If control determines that regeneration is needed in step  404 , control selects one or more zones in step  408  and activates the heater for the selected zone in step  412 . In step  416 , control estimates a heating period sufficient to achieve a minimum filter face temperature based on at least one of current, voltage, exhaust flow and exhaust temperature. The minimum face temperature should be sufficient to start the soot burning and to create a cascade effect. For example only, the minimum face temperature may be set to 700 degrees Celsius or greater. In an alternate step  420  to step  416 , control estimates current and voltage needed to achieve minimum filter face temperature based on a predetermined heating period, exhaust flow and exhaust temperature. 
     In step  424 , control determines whether the heating period is up. If step  424  is true, control determines whether additional zones need to be regenerated in step  426 . If step  426  is true, control returns to step  408 . Otherwise control ends. 
     The present disclosure tends to improve regeneration of PM filters. The approach described herein tends to reduce thermal delta and therefore improves substrate durability. Force due to thermal expansion and contraction is defined as αΔTE(Area) where α is a coefficient of expansion, E is Young&#39;s Modulus, Area is perimeter area and is equal to πD, and ΔT is the temperature delta. As can be appreciated, increasing exhaust gas temperature before using the electrical heaters reduces ΔT, which reduces force due to thermal expansion and contraction. For example only, with the exhaust gas at the inlet of the PM filter at approximately 600 degrees C. and the heated zone at 800 degrees C., ΔT is approximately 200 degrees C. The reduced ΔT reduces thermal force and tends to increase durability. The present disclosure also tends to provide more consistent heating patterns and to reduce flameout.