Patent Publication Number: US-7901475-B2

Title: Diesel particulate filter with zoned resistive heater

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/022,047, filed on Jan. 18, 2008. The disclosure of the above application is incorporated herein by reference in its entirety. 
    
    
     STATEMENT OF GOVERNMENT RIGHTS 
     This invention 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 invention. 
    
    
     FIELD 
     The present disclosure relates to vehicle emissions and more particularly to diesel particulate filters. 
     BACKGROUND 
     The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
     Diesel engines typically produce torque more efficiently than gasoline engines. This increase in efficiency may be due to an increased compression ratio and/or the combustion of diesel fuel, which has a higher energy density than that of gasoline. The combustion of diesel fuel produces particulate. The particulate is filtered from exhaust gas using a diesel particulate filter (DPF). With time, the DPF may fill with particulate, thereby restricting the flow of the exhaust gas. The particulate may be combusted by a process referred to as regeneration. 
     Regeneration may be accomplished, for example, by injecting fuel into the exhaust gas after the combustion of the diesel fuel. One or more catalysts may be disposed in the stream of the exhaust gas and may combust the injected fuel. The combustion of the fuel by the catalysts generates heat, thereby increasing the temperature of the exhaust gas. The increased temperature of the exhaust gas may burn the remainder of the particulate trapped in the DPF. 
     SUMMARY 
     A diesel particulate filter assembly comprises a diesel particulate filter (DPF) and a heater assembly. The DPF filters a particulate from exhaust produced by an engine. The heater assembly has a first metallic layer that is applied to the DPF, a resistive layer that is applied to the first metallic layer, and a second metallic layer that is applied to the resistive layer. The second metallic layer is etched to form a plurality of zones. 
     In other features, the diesel particulate filter assembly further comprises an end plug that is inserted into the second metallic layer to close a channel of the DPF. The resistive layer is disposed downstream of the end plug. 
     In further features, the first metallic layer is applied to the DPF by dip-coating. The first metallic layer is embedded into a wall of the DPF. 
     In still further features, the resistive layer is applied to the first metallic layer by dip-coating. 
     In other features, the second metallic layer is applied to the resistive layer by dip-coating. 
     A system comprises the diesel particulate filter assembly and a heater power module. The heater power module is in electrical communication with each of the zones and selectively applies at least one of a voltage and a current to selected ones of the zones. 
     A method comprises applying a first metallic layer to a diesel particulate filter (DPF), applying a resistive layer to the first metallic layer, applying a second metallic layer to the resistive layer, and etching the second metallic layer into a plurality of zones. 
     In further features, the method further comprises inserting an end plug into the second metallic layer to close a channel of the DPF. The resistive layer is disposed downstream of the end plug. 
     In still further features, the first metallic layer is applied to the DPF by dip-coating. The applying the first metallic layer to the DPF embeds the first metallic layer into a wall of the DPF. 
     In other features, the resistive layer is applied to the first metallic layer by dip-coating. 
     In still other features, the second metallic layer is applied to the resistive layer by dip-coating. 
     In further features, the method further comprises selecting ones of the zones and selectively applying at least one of a voltage and a current to the selected ones of the zones. 
     Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a functional block diagram of an exemplary engine system and exhaust system according to the principles of the present disclosure; 
         FIG. 2A  is a cross-sectional view of an exemplary diesel particulate filter assembly according to the principles of the present disclosure; 
         FIG. 2B  is an enlarged, cross-sectional view of an exemplary heater assembly according to the principles of the present disclosure; 
         FIG. 2C  is an enlarged view of an exemplary zone arrangement of the heater assembly according to the principles of the present disclosure; 
         FIG. 3  is another cross-sectional view of a diesel particulate filter with a zoned resistive heater assembly according to the principles of the present disclosure; and 
         FIGS. 4-5  are illustrated exemplary methods for making the diesel particulate filter with the zoned resistive heater assembly according to the principles of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is in no way intended to limit the disclosure, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical or. It should be understood that steps within a method may be executed in different order without altering the principles of the present disclosure. 
     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. 
     Referring now to  FIG. 1 , a functional block diagram of an exemplary engine and exhaust system  100  for a vehicle is presented. The vehicle includes a diesel engine system  102 . While the diesel engine system  102  is described, the present disclosure is applicable to gasoline engine systems, homogenous charge compression ignition engine systems, and/or other engine systems. 
     The diesel engine system  102  includes an engine  104  and an exhaust system  106 . The engine  104  combusts a mixture of air and diesel fuel to produce torque. Resulting exhaust gas is expelled from the engine  104  into the exhaust system  106 . The exhaust system  106  includes an exhaust manifold  108 , a diesel oxidation catalyst (DOC)  110 , a reductant injector  112 , a mixer  114 , and a diesel particulate filter (DPF) assembly  116 . The exhaust system  106  may also include an exhaust gas recirculation (EGR) valve (not shown) that may recirculate a portion of the exhaust gas back to the engine  104 . 
     The exhaust gas flows from the engine  104  through the exhaust manifold  108  to the DOC  110 . The DOC  110  oxidizes particulate in the exhaust gas as the exhaust gas flows through the DOC  110 . For example only, the DOC  110  may oxidize particulate such as hydrocarbons and/or carbon oxides. The reductant injector  112  may inject a reductant, such as ammonia or urea, into the exhaust system  106 . The mixer  114 , which may be implemented as a baffle, agitates the exhaust gas and/or the injected reductant. In this manner, the mixer  114  may create a reductant-exhaust aerosol by mixing the reductant with the exhaust gas. 
     The DPF assembly  116  filters particulate from the exhaust gas passing through it. This particulate may accumulate within the DPF assembly  116  and may restrict the flow of exhaust gas through the DPF assembly  116 . The particulate may be removed from the DPF assembly  116  by a process referred to as regeneration. Discussion of a DPF assembly and the regeneration process can be found in commonly assigned U.S. patent application Ser. No. 11/233,450, filed Nov. 22, 2005, which is herein incorporated by reference in its entirety. 
     Referring now to  FIG. 2A , a cross-sectional view of an exemplary implementation of the DPF assembly  116  is presented. The DPF assembly  116  includes a heater assembly  220  and a diesel particulate filter (DPF) element  222 . The exhaust gas enters the DPF assembly  116  through an inlet  224  and flows through the heater assembly  220  and then the DPF element  222 . The exhaust gas exits the DPF assembly  116  though an outlet  226 . 
     The exhaust gas enters the DPF element  222  through a front section  227  of the DPF element  222 . The DPF element  222  may include alternating open channels  228  and closed channels  230  that force the exhaust gas through walls  232  of the DPF element  222 . The arrangement of the closed channels  230  and the open channels  228  may be chosen to make the flow of the exhaust gas through the DPF element  222  more laminar (i.e., straighter). 
     The walls  232  of the DPF element  222  may be porous, may be arranged in a honeycomb fashion, and may be made of, for example, a ceramic or cordierite material. The walls  232  of the DPF element  222  filter particulate from the exhaust gas. As particulate is filtered, the particulate may accumulate within the DPF element  222 , as shown at  236 . The exhaust gas exits the DPF element  222  via a rear section  238 . 
     The regeneration process (i.e., combustion of particulate) may begin once the heater assembly temperature reaches a threshold temperature, such as 800° C. Particulate on and/or passing the heater assembly  220  is then combusted, generating heat. The exhaust gas carries this heat from the front section  227  to the rear section  238 , thereby combusting particulate throughout the DPF element  222 . 
     A selective catalytic reductant (SCR) catalyst (not shown) may be applied to all of or a portion of the DPF element  222 . For example only, the SCR catalyst may be applied to the front section  227 , the walls  232 , and/or the rear section  238  of the DPF element  222 . The SCR catalyst may be applied to the DPF element  222  in any pattern, such as striped, and the SCR catalyst may be applied in varying degrees. For example only, the SCR catalyst may be applied more heavily toward the rear section  238  of the DPF element  222 . 
     The SCR catalyst absorbs reductant injected by the reductant injector  112  and reacts with nitrogen oxides (NO X ) and/or other pollutants in the exhaust gas. In this manner, the SCR catalyst reduces the NO X  emissions of the vehicle. The SCR catalyst may be effective in reducing (reacting with) NO X  once the temperature of the SCR catalyst exceeds a threshold. For example only, the threshold may be 200° C. If the reductant is injected when the SCR temperature is below the threshold, the reductant may compromise the function of the SCR catalyst. Heat provided by the heater assembly  220  may be used to warm the SCR catalyst. 
     Referring now to  FIG. 2B , an exemplary enlarged, cross-sectional view of the heater assembly  220  is presented. The heater assembly  220  includes a first metallic layer  240 , a second metallic layer  242 , and a resistive layer  244 . The first metallic layer  240 , the second metallic layer  242 , and the resistive layer  244  may be any suitable thickness. While the layers are shown in  FIG. 2B  as being approximately equal in thickness, the thickness of each of the layers may vary. 
     The first metallic layer  240  is applied to the front section  227  of the DPF element  222 . The first metallic layer  240  may be applied to the front section  227  in any suitable manner, such as by dip-coating. As the walls  232  of the DPF element  222  may be porous, the first metallic layer  240  may be partially embedded or infused in the walls  232 . The metallic substance of the first metallic layer  240  may be any suitable electrically-conductive metallic substance and may be applied in any suitable thickness. 
     The resistive layer  244  is applied to the first metallic layer  240 . The resistive layer  244  may be applied to the first metallic layer  240  in any suitable manner, such as by dip-coating. The resistive layer  244  may include any suitable electrically-resistive substance and may be applied in any suitable thickness. 
     The second metallic layer  242  is applied to the resistive layer  244 . In this manner, the second metallic layer  242  is electrically connected to the first metallic layer  240  via the resistive layer  244 . The second metallic layer  242  may be applied to the resistive layer  244  in any suitable manner, such as by dip-coating. The metallic substance of the second metallic layer  242  may be any suitable electrically-conductive metallic substance and may be applied in any suitable thickness. 
     Referring again to  FIG. 2A , the closed channels  230  are closed by end plugs  234 . The end plugs  234  may be inserted into the second metallic layer  242  to create the closed channels  230 . The thickness of the second metallic layer  242  may be specified relative to the length of the end plugs  234 . For example only, as shown in  FIG. 2A , the thickness of the second metallic layer  242  may be greater than the length of the end plugs  234 . In other implementations the thickness of the second metallic layer  242  may be equal to the length of the end plugs  234 . Accordingly, the resistive layer  244  is disposed downstream of the end plugs  234 . 
     Referring now to  FIG. 2C , an enlarged view of an exemplary zone arrangement of the heater assembly  220  is presented. The second metallic layer  242  is formed into a plurality of zones  246 . For example only, the second metallic layer  242  may be formed into N zones,  246 - 1 ,  246 - 2 , . . . ,  246 -N, collectively. While the second metallic layer  242  is depicted in  FIG. 2C  as being formed into five zones (N=5)  246 - 1 - 246 - 5 , the second metallic layer  242  may be formed into any suitable number of zones and the zones  246  may be arranged in any suitable configuration. 
     The zones  246  may be formed in any suitable manner, such as by etching the zones  246  into the second metallic layer  242 . Etching the second metallic layer  242  into the zones  246  creates a void  248 , which separates each of the zones  246  from each of the other zones. In this manner, each of the zones  246  is electrically isolated from each other zone of the heater assembly  220 . 
     The dimensions (width and depth) of the void  248  may be specified to ensure that each of the zones  246  is electrically isolated from each other zone. For example, the void  248  is etched completely through the second metallic layer  242 . Accordingly, the depth of the void  248  is greater than or equal to the thickness of the second metallic layer  242 . The width of the void  248  may be specified to ensure that power applied to one of the zones  246  cannot transfer to any other zone. 
     Referring now to  FIG. 3 , a cross-sectional view of an exemplary diesel particulate filter with the heater assembly  220  is presented. Each of the zones  246  of the heater assembly  220  is connected to a heater power module  350 . The first metallic layer  240  is connected to a ground source. 
     The heater power module  350  selectively applies power from a power source  352  to one or more selected zones. For example only, the power source  352  may include an alternator and/or a battery. Applying power to selected zones instead of to the heater assembly  220  as a whole may limit the amount of power that is drawn from the power source  352  at any one time. In various implementations, the heater power module  350  may be implemented in an engine control module (not shown). 
     Power applied to a zone of the second metallic layer  242  flows from that zone of the second metallic layer  242  to the first metallic layer  240  via the resistive layer  244 . Heat (resistive heat) is generated as power flows through the resistive layer  244 . This heat may be used to, for example, warm the SCR catalyst and/or to warm that zone to the threshold temperature to begin the regeneration process. Additionally, the heat may warm the other zones of the heater assembly  220 . 
     As stated above, the resistive layer  244  is downstream of the end plugs  234 . In this manner, the zones  246  provide heat downstream of the end plugs  234 . Providing heat downstream of the end plugs  234  may help minimize heat losses attributable to flow of the exhaust gas as the flow of the exhaust gas may be more turbulent near the end plugs  234 . 
     The heater power module  350  may apply power to the zones  246  in any suitable order. For example only, the heater power module  350  may apply power to the zones  246  in a predetermined order or pattern. The predetermined order or pattern may be specified to, for example, minimize the time necessary to complete the regeneration process. For example only, the heater power module  350  may first apply power to the zone  246 - 5 . As the zone  246 - 5  is depicted in  FIG. 2C  as being in a central location, heat generated by the zone  246 - 5  may warm the other zones  246 - 1 - 246 - 4 . This warming may reduce the time necessary for the other zones  246 - 1 - 246 - 4  to reach the threshold temperature. 
     Referring now to  FIG. 4 , an exemplary method for making the diesel particulate filter with the zoned resistive heater assembly is presented. Diagram  402  depicts an exemplary illustration of the DPF element  222 . First, the first metallic layer  240  is applied to the DPF element  222 . More specifically, the first metallic layer  240  is applied to the front section  227  of the DPF element  222 . 
     The first metallic layer  240  may be applied in any suitable manner. For example only, the metallic substance of the first metallic layer  240  may be dip-coated onto the front section  227  of the DPF element  222 . As the walls  232  of the DPF element  222  may be porous, the first metallic layer  240  may be partially infused into the walls  232 . The first metallic substance may be any suitable electrically-conductive metallic substance. 
     In various implementations, a buffer substance (not shown), may be used to isolate the first metallic layer  240  from the second metallic layer  242 . For example only, the buffer substance may be a silicone substance. In various implementations, the buffer substance may be disposed between the first metallic layer  240  and the resistive layer  244 . The buffer substance is later removed by, for example, calcination. 
     Diagram  404  depicts an exemplary illustration of the DPF element  222  with the first metallic layer  240  applied. After the first metallic layer  240  is applied, the resistive layer  244  is applied to the first metallic layer  240 . The resistive substance of the resistive layer  244  may be applied to the first metallic layer  240  in any suitable manner. For example only, the resistive substance of the resistive layer  244  may be dip-coated onto the first metallic layer  240 . The resistive substance of the resistive layer  244  may be any suitable electrically-resistive substance. 
     Diagram  406  depicts an exemplary illustration of the DPF element  222  with the first metallic layer  240  and the resistive layer  244  applied. The second metallic layer  242  is applied to the resistive layer  244 . In this manner, the second metallic layer  242  is in electrical communication with the first metallic layer  240  via the resistive layer  244 . 
     The metallic substance of the second metallic layer  242  may be applied to the resistive layer  244  in any suitable manner. For example only, the metallic substance of the second metallic layer  242  may be dip-coated onto the resistive layer  244 . The metallic substance of the second metallic layer  242  may be any suitable electrically-conductive metallic substance. The metallic substance of the second metallic layer  232  may be similar or identical to the metallic substance of the first metallic layer  240 . 
     Diagram  408  depicts an exemplary an exemplary zone arrangement of the heater assembly  220 . The second metallic layer  242  is formed into zones, such as the zones  246 . The zones  246  may be arranged in any suitable configuration. The zones  246  may be formed in any suitable manner, such as by etching the zones  246  into the second metallic layer  242 . Forming of the zones  246  creates one or more voids in the second metallic layer  242 , such as the void  248 . The void  248  electrically isolates each of the zones  246  from each other zone. In various arrangements, one or more additional voids may be formed to create a zone arrangement. 
     Referring now to  FIG. 5 , a flowchart depicting an exemplary method for making the diesel particulate filter with the zoned resistive heater assembly is presented. The method begins in step  502  where the first metallic layer  240  is applied to the DPF element  222 . More specifically, the first metallic layer  240  is applied to the front section  227  of the DPF element  222 . The first metallic layer  240  may be applied in any suitable manner, such as by dip-coating. 
     The method continues in step  504  where the resistive layer  244  is applied to the first metallic layer  240 . The resistive layer  244  may be applied in any suitable manner, such as by dip-coating. The method continues in step  506  where the second metallic layer  242  is applied to the resistive layer  244 . The second metallic layer  242  may be applied in any suitable manner, such as by dip-coating. 
     The method continues in step  508  where the zones  246  are formed. More specifically, the zones  246  are etched in the second metallic layer  242 . The configuration and design of the zones  246  may be any suitable design or configuration. Etching the zones  246  into the second metallic layer  242  creates the void  248 . The void  248  electrically isolates each of the zones  246  from each other zone. 
     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, 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, the specification, and the following claims.