Abstract:
A system comprising an injector for injecting fuel directly into the exhaust system. A control module supplies fuel using the injector to burn particulate matter in the particulate filter when the control module determines that regeneration is needed. The control module selectively supplies fuel to exercise the injector during periods when the control module determines that regeneration is not needed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/932,927, filed on Jun. 1, 2007. The disclosure of the above application is incorporated herein by reference in its entirety. 
     
    
     FIELD 
       [0002]    The present disclosure relates to anti-coking control systems for vehicles that perform regeneration using fuel injectors that inject fuel into the exhaust system. 
       BACKGROUND 
       [0003]    The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
         [0004]    Engines such as diesel engines produce particulates that are typically filtered from exhaust gas by a particulate filter (PF). The PF is disposed in an exhaust system of the engine. The PF reduces emission of particulate matter that is generated during combustion. Over time, the PF becomes full and the trapped particulate matter needs to be removed. During regeneration, the particulate matter is burned within the PF. 
         [0005]    An engine control system can estimate accumulation of the particulate matter and determine when the filter needs regeneration. Once regeneration is needed, the control system enables regeneration by injecting fuel into the exhaust system. The heat released during combustion of the injected fuel in the diesel oxidation catalyst increases the exhaust temperature, which burns the trapped particulate matter in the PF. In some systems, the injectors of the engine are used to increase fuel by temporarily enriching the air/fuel mixture. The excess fuel in the exhaust gas after combustion is used to increase the temperature of the PF. 
         [0006]    Other systems use a fuel injector that is separate from the injectors associated with the fuel system. The injector injects fuel into the exhaust system. Performance issues may arise due to coking or deposit formation in fuel injection devices that are exposed to exhaust conditions. As a result, the fuel injection devices may experience poor durability. 
       SUMMARY 
       [0007]    A system comprises an injector for injecting fuel directly into an exhaust system. A control module supplies fuel using the injector to burn particulate matter in the particulate filter when the control module determines that regeneration is needed. The control module selectively supplies fuel to exercise the injector during periods when the control module determines that regeneration is not needed. 
         [0008]    In other features, an exhaust temperature sensor senses an exhaust temperature. A timer determines a period since a last injection using the at least one second injector. A degradation module determines degradation of the at least one second injector based on the exhaust temperature and the period since a last injection using the at least one second injector. The control module selectively enables exercise of the at least one second injector based on enabling conditions. The enabling conditions include at least one of exhaust temperature, engine mode, and a period since a last use of the at least one second injector. 
         [0009]    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 
         [0010]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0011]      FIG. 1  is a functional block diagram of an exemplary engine system according to the present disclosure; 
           [0012]      FIG. 2  is a functional block diagram of a regeneration system according to the present disclosure; 
           [0013]      FIG. 3  illustrates an exemplary regeneration injector; 
           [0014]      FIG. 4  illustrates a method for reducing coking deposits; and 
           [0015]      FIG. 5  illustrates injection quantity as a function of temperature and time. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    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. 
         [0017]    Coking and deposit formation described herein may be particularly challenging with fuel injection devices that are exposed to exhaust conditions and that are used relatively infrequently. For these fuel injection devices, there may be time intervals of inactivity where residual fuel oxidation and polymerization may occur. 
         [0018]    For example, injection devices may be used to facilitate or assist diesel particulate filter (PF) regeneration. The regeneration interval may be infrequent. For example only, the regeneration interval can be as long as several hundred miles. For example only, the injector device may be operated only when needed. Typically, the injector may be used about 15-30 minutes every 8-10 operating hours. The regeneration intervals described above provide time periods during which deposit formation or fuel coking issues may occur. 
         [0019]    The present disclosure reduces deterioration of fuel injection devices used in the exhaust systems of automotive products. The present disclosure monitors and models the conditions in the vehicle exhaust system. The present disclosure determines an appropriate schedule for the fuel injection system to exercise the injector that will minimize fuel consumption and emission control issues while improving fuel injection system durability. As a result, lower cost hardware and fuel injection components may be used. As can be appreciated, while the present disclosure describes a diesel engine application, the present disclosure may also be applied to internal combustion engines with a particulate filter as well as Hydrocarbon (HC) Selective Catalyst Reduction (SCR). 
         [0020]    Referring now to  FIG. 1 , a vehicle  10  includes an engine control system. The engine control system  12  includes an engine  14 , an intake manifold  16 , a common rail fuel injection system  18  and a turbocharger  27 . The engine  14  includes six cylinders  22  configured in adjacent cylinder banks  24  and  26  and in a V-type layout. Although  FIG. 1  depicts six cylinders  22 , it can be appreciated that the engine  14  may include additional or fewer cylinders  22 . For example, engines having 2, 3, 4, 5, 8, 10, 12 and 16 cylinders are contemplated. It is also anticipated that the engine  14  can have an inline-type cylinder configuration. While a turbocharged diesel engine is shown, the present disclosure also applies to other engines such as naturally aspirated or supercharged engines. 
         [0021]    Air is drawn into the intake manifold  16  by the inlet vacuum created by an engine turbocharger  27 . Air is ducted into the individual cylinders  22  from the intake manifold  16  and is compressed therein. Fuel is injected by the common rail injection system  18  and the heat of the compressed air ignites the air/fuel mixture. Exhaust gas is exhausted from the cylinders through exhaust conduits  28 . The exhaust gas drives the turbocharger  27 , which delivers additional air into the cylinders  22  for combustion. 
         [0022]    The exhaust gas enters a diesel oxidation catalyst (DOC)  30 , which facilitates chemical reactions with excess fuel in the exhaust gases. Exhaust gases from the DOC  30  pass through a particulate matter (PM) filter  31 , which extracts PM from the exhaust stream. The exhaust gases exit the PM filter  31 . 
         [0023]    A control module  32  controls operation of the engine control system  12 . More specifically, the control module  32  controls engine system operations based on various parameters. For example, the control module  32  may be implemented in an engine control module (ECM), a vehicle computer, or may be an independent controller. 
         [0024]    The control module  32  may also perform engine system diagnostics. For example, the control module  32  may verify proper operation of the DOC  30 . Additionally, the control module  32  may initiate a post-fuel injection process to heat the exhaust gases to the PM filter  31  by oxidizing fuel in the DOC  30 . The control module  32  may receive a temperature signal from an inlet temperature sensor  34  that senses the temperature of exhaust gases at the opening of the DOC  30 . The control module  32  may also receive a temperature signal from an outlet temperature sensor  36  that senses the temperature of exhaust gases that exit the DOC  30 . The control module  32  may receive a pressure signal from an exhaust pressure sensor  37  that senses the air pressure in the exhaust system. 
         [0025]    The control module  32  may receive a speed signal from a speed sensor  38  in the engine  14 . The control module  32  may receive a temperature signal from an engine coolant sensor  39  that senses a temperature of coolant in the engine  14 . The control module  32  may receive a temperature signal from an inlet air temperature sensor  40  that detects an inlet air temperature of the engine  14 . The control module  32  may receive a pressure signal from an ambient pressure sensor  41  that senses a pressure of the air outside of the engine  14 . The control module  32  may receive an airflow signal from a mass airflow sensor  42  that detects a rate that air flows into the engine  14 . Still other inputs may be provided. 
         [0026]    At various times, the control module  32  sends a command to an injector  50  to inject fuel into the exhaust system. A valve  52  such as a poppet valve may be used. The control module  32  may command fuel when regeneration of the PF  31  is needed. The control module  32  may also command fuel when regeneration is not needed to exercise the injector  50 . 
         [0027]    Referring now to  FIG. 2 , a conduit from a supply of fuel may supply fuel to the injector  50 . Another conduit  62  may connect an output of the injector to the valve  52 , which is arranged adjacent to the exhaust system. The valve  52  and the injector  50  may be spaced a distance D that is sufficient to allow cooling and to prevent damage to the injector  50  due to high exhaust gas temperatures. 
         [0028]    Any suitable valve or injector may be used including a low spray nozzle valve or injector such as the one shown in  FIG. 3 . In  FIG. 3 , an exemplary valve  52  is shown. For example only, the valve  52  may include an upper housing  70 , an upper guide  72 , a valve body  73 , a spring  74 , a needle  76  and a lower guide  78 . 
         [0029]    Referring now to  FIGS. 4 and 5 , control begins in step  200 . In step  204 , control looks up a fuel degradation factor as a function of exhaust temperature and a period since last injection event. For example, an exemplary relationship between injection amount, time and temperature is shown in  FIG. 5 . In step  208 , the degradation factor is integrated. A new degradation factor is set equal to an old degradation factor plus a new lookup value. The time since the last injection is incremented. 
         [0030]    In step  210 , control determines whether the degradation factor is greater than a degradation minimum. If false, control returns to step  204 . Otherwise control continues with step  214 . In step  214 , control determines whether the time or the integrated time since last exercise is greater than a predetermined period tmin. If false, control returns to step  204 . Otherwise control continues with step  218  and checks enabling conditions for injector exercise. Exemplary enabling conditions include exhaust temperature, ambient temperature and catalyst temperature. Other exemplary enabling conditions may be based on an engine operating mode. 
         [0031]    Control continues from step  218  and control determines whether the exhaust temperature is greater than a predetermined temperature tempmin in step  222 . If step  222  is false, control returns to step  218 . If step  222  is true, control delivers a predetermined amount of fuel (such as Q grams) to exercise the injector (despite the fact that regeneration is not needed). Control continues with step  230  and fuel degradation factor, injector quantity, and time since last injection to zero. Control continues with step  204 . 
         [0032]    This approach provides an optimal balance between durability, fuel consumption, and emission control. This control approach reduces coking by exercising the injector during the period in time when it is normally not used or needed. The frequency of exercise is dependent on operating time, temperature, and exhaust flow rate, among other items. Exercise is more frequent under particularly challenging conditions. Total fuel use and emission impact are negligible, while improving durability of the injection device.