Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 60/972,946, filed on Sep. 17, 2007. 
     This application is related to U.S. Provisional Patent Application No. 60/955,743 filed on Aug. 14, 2007 and U.S. patent application 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 
     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 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 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 includes a particulate matter (PM) filter that includes an upstream end for receiving exhaust gas and a downstream end. A zoned resistive heater is arranged spaced from said upstream end and includes N zones, where N is an integer greater than one, wherein each of the N zones includes M sub-zones, where M is an integer greater than or equal to one, and wherein the heater includes an electrically insulating material. A control module selectively activates at least a selected one of the N zones to initiate regeneration in downstream portions of the PM filter from the one of the N zones and deactivates non-selected ones of the N zones. 
     A method includes providing a particulate matter (PM) filter including an upstream end for receiving exhaust gas and a downstream end, arranging a zoned resistive heater spaced from the upstream end that includes N zones, where N is an integer greater than one, wherein each of the N zones comprises M sub-zones, where M is an integer greater than or equal to one, and wherein the heater includes an electrically insulating material, and selectively activating at least a selected one of the N zones to initiate regeneration in downstream portions of the PM filter from the one of the N zones and deactivates non-selected ones of the 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 that is spaced from the PM filter; 
         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. 3A  illustrates a second exemplary zoning of the zoned inlet heater of the electrically heated PM filter of  FIG. 1  in further detail; 
         FIG. 3B  illustrates an exemplary resistive heater in one of the zones of the zoned inlet heater of  FIG. 3A ; 
         FIG. 4A  illustrates a second exemplary zoning of the zoned inlet heater of the electrically heated PM filter of  FIG. 1  in further detail; 
         FIG. 4B  illustrates an exemplary resistive heater in one of the zones of the zoned inlet heater of  FIG. 4A ; 
         FIG. 5  illustrates the electrically heated PM filter having a zoned electric heater that is spaced from the PM filter; 
         FIG. 6  illustrates heating within the zoned electric heater; 
         FIG. 7  is a flowchart illustrating steps performed by the control module to regenerate the PM filter; 
         FIG. 8  illustrates a zoned resistive heater grid; 
         FIG. 9  illustrates a zoned resistive heater grid that include an insulating material; and 
         FIG. 10  illustrates a zoned resistive heater grid that includes an insulating buffer. 
     
    
    
     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 utilizes a heater with zones. The electrical heater is spaced from the PM filter. In other words, the electric heater is located in front of the PM filter but is not in contact with the downstream PM filter. The heater selectively heats portions of the PM filter. The PM heater may be mounted close enough to the front of the PM filter to control the heating pattern. The length of the heater is set to optimize the exhaust gas temperature. 
     Thermal energy is transmitted from the heater to the PM filter by the exhaust gas. Therefore the PM filter is predominantly heated by convection. The electrical heater is divided into 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 is 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 is 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. In other words, the heater may be activated only long enough to start the soot ignition and is then shut off. Other regeneration systems typically use both conduction and convection and maintain power to the heater (at lower temperatures such as 600 degrees Celsius) throughout the soot burning process. As a result, these systems tend to use more power than the system proposed in the present disclosure. 
     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 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. 
     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. 
     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 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 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 zoned inlet heater  35  is 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 is 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 zoned heater  35  during the regeneration process. More specifically, the energy heats 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. The remainder of the regeneration process is achieved using the heat generated by the heated exhaust passing through the PM filter. 
     Referring now to  FIG. 2 , an exemplary zoned inlet heater  35  for the PM filter assembly  34  is shown in further detail. The zoned inlet heater  35  is arranged spaced from 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  10  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  10  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  10 . 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. 3A , another exemplary zoned inlet heater arrangement is shown. A center portion may be surrounded by a middle portion 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. 3B , an exemplary resistive heater  100  arranged adjacent to one of the zones (e.g. zone  3 ) from the first circumferential band of zones in  FIG. 3A  is shown. The resistive heater  100  may comprise one or more coils that cover the respective zone to provide sufficient heating. 
     Referring now to  FIG. 4A , another exemplary zoned inlet heater arrangement is shown. A center portion may be surrounded by an outer portion including a circumferential band of zones. In this example, the center portion includes zone  1 . The circumferential band of zones includes zones  2 ,  3 ,  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. In other implementations, multiple zones may be activated at the same time. For example, complementary zones (e.g. zones  2  and  4  or zones  3  and  5 ) may be activated at the same time. 
     Referring now to  FIG. 4B , an exemplary resistive heater  110  arranged adjacent to one of the zones (e.g. zone  2 ) from the first circumferential band of zones in  FIG. 4A  is shown. The resistive heater  110  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 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 spaced from the filter  202  such that the heating is predominantly convection 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 travels a distance and is received by the filter  202 . The heater  35  may be spaced from and not in contact with 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 . 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 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 , steps for regenerating the PM filter are shown. In step  300 , control begins and proceeds to step  304 . If control determines that regeneration is needed in step  304 , control selects one or more zones in step  308  and activates the heater for the selected zone in step  312 . In step  316 , 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  320  to step  316 , 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  324 , control determines whether the heating period is up. If step  324  is true, control determines whether additional zones need to be regenerated in step  326 . If step  326  is true, control returns to step  308 . Otherwise control ends. 
     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 or more of the zones at a time to initiate regeneration within the associated downstream portion of the PM filter. After the zone or zones are regenerated, one or more other zones are 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. 
     Referring now to  FIG. 8 , a zoned resistive heater grid  400  that corresponds to the zoned inlet heat arrangement of  FIG. 4A  is shown. The heater grid  400  includes a center portion  402  corresponding to zone  1  and an outer portion  404  corresponding to zones  2 ,  3 ,  4 , and  5 . Zones of the heater grid  400  may be selectively activated and deactivated as described above with respect to  FIGS. 1-7 . 
     Resistive coils in individual zones of the heater grid  400  may expand while activated (i.e. due to thermal expansion). Consequently, a selected (activated) zone may expand and come into contact with adjacent non-selected (deactivated) zones. For example, a portion of the heater grid  400  corresponding to zone  2  may expand and come into contact with one or more of zones  1 ,  4 , and  5 . When an activated zone contacts an adjacent deactivated zone, the current applied to the activated zone flows into the adjacent deactivated zone. In other words, the activated zone is short circuited. When the activated zone is short circuited, the corresponding zone of the filter does not reach the desired minimum filter face temperature and proper filter regeneration is prevented. 
     Referring now to  FIG. 9 , resistive coils of the zoned resistive heater grid  400  are coated with an insulating material  410 . The insulating material  410  prevents the resistive coils of a selected zone from contacting adjacent zones. In other words, even when the resistive coils experience thermal expansion, the insulating material  410  prevents short circuiting in the selected zone. The insulating material  410  is thermally conductive to allow the heat from the heater grid  400  to heat the exhaust gas. Conversely, the insulating material  410  is not electrically conductive. As such, current flowing through the resistive coil of a selected zone is prevented from flowing into an adjacent zone. Further, the insulating material  410  may be selected to thermally expand at a rate consistent with thermal expansion of the heater grid  400 . For example only, the insulating material  410  may include aluminum oxide. 
     Referring now to  FIG. 10 , the zoned resistive heater grid  400  includes an insulating buffer  420 . The insulating buffer  420  is located between each of the zones of the heater grid  400 . For example, the insulating buffer  420  may include a center portion  422  that surrounds zone  1  of the heater grid  400  and a plurality of spokes  424  that extend outward from the center portion  422 . Each of the plurality of spokes extends between adjacent ones of the zones in the outer portion of the heater grid  400 . 
     As described above with respect to  FIG. 9 , the insulating buffer  420  is thermally conductive but is not electrically conductive. As such, current flowing through the resistive coil of a selected zone is prevented from flowing into an adjacent zone and short circuiting is avoided. For example only, the insulating buffer  420  may include aluminum oxide. 
     In another implementation, the control module  44  (as shown in  FIG. 1 ) may detect short circuits due to thermal expansion. For example, the control module  44  may detect short circuits when the zoned resistive heater grid  400  does not include one of the insulating material  410  and the insulating buffer  420  and/or when one of the insulating material  410  and the insulating buffer  420  is damaged. For example, the control module  44  may measure a voltage across at least a portion of non-selected (deactivated) zones of the heater grid  400 . When a voltage is detected (e.g. when the voltage across one or more of the deactivated zones is greater than a threshold), the control module  44  determines that the activated zone is in contact with an adjacent one of the deactivated zones and, thus, is short circuited. Consequently, the control module  44  may deactivate the activated zone and activate a non adjacent zone. For example, when a short circuit is detected when zone  2  is activated, the control module  44  may deactivate zone  2  and activate zone  3 . Further, the control module  44  may indicate a fault that indicates that one of the heater grid  400 , the insulating material  410 , and the insulating buffer  420  needs to be replaced. 
     The present disclosure may substantially reduce the fuel economy penalty, decrease tailpipe temperatures, and improve system robustness due to the smaller regeneration time.

Technology Category: 2