Abstract:
A particulate filter regeneration method for an internal combustion engine system is provided. The method includes: receiving an outlet temperature signal corresponding to a temperature at an outlet of a particulate filter; receiving an oxygen signal corresponding to an oxygen level in exhaust flowing from said particulate filter; and controlling at least one of airflow and fuel based on said oxygen level such that said outlet temperature is within a desired range.

Description:
FIELD OF THE INVENTION 
     The present invention relates to particulate filters and more particularly to methods and systems for controlling the temperature of a particulate filter during regeneration. 
     BACKGROUND OF THE INVENTION 
     Diesel Particulate Filters (DPF) are used on diesel engines to reduce emissions of particulate matter (soot) generated during a heterogeneous combustion process. These filters must be cleaned or “regenerated” when the filter is determined full of soot. An engine control system can estimate the DPF accumulation, and determine when the filter needs regeneration. Once the filter is determined to be full, the control system will enable regeneration by modifying the combustion process and/or injecting fuel into the exhaust system to increase the temperature of exhaust flowing into the DPF. The elevated exhaust temperatures will initiate oxidation of the stored soot within the DPF. 
     Normally, this process is well controlled, and results in acceptable filter temperatures and durability. However, under some conditions the filter can be overloaded with particulates or regenerated during conditions that result in run-away temperatures. These excessively high temperatures can result in filter failure due to cracking from thermal stress, or even melting of the filter substrate. 
     In order to improve DPF durability, peak temperatures within the DPF should be controlled. One method of controlling peak temperatures includes limiting particulate loading. This cannot always be guaranteed due to customer driving cycles, ambient conditions, and/or variations in engine operating modes. Another method includes limiting the heat input into the DPF by the fuel injection process. This too is not always effective, since the stored particulate mass is often sufficient to lead to highly exothermic reactions that can damage the DPF material. 
     SUMMARY OF THE INVENTION 
     Accordingly, a particulate filter regeneration method for an internal combustion engine system is provided. The method includes: receiving an outlet temperature signal corresponding to a temperature at an outlet of a particulate filter; receiving an oxygen signal corresponding to an oxygen level in exhaust flowing from said particulate filter; and controlling at least one of airflow and fuel based on said oxygen level such that said outlet temperature is within a desired range. 
     In other features, a system for controlling regeneration of a particulate filter is provided. The system includes: an outlet temperature sensor that senses a temperature at an outlet of the particulate filter and that generates a temperature signal based on said outlet temperature; an air fuel sensor that senses an oxygen level in exhaust flowing from the particulate filter and generates an oxygen signal based on said oxygen level; and a control module that receives said outlet temperature signal and said oxygen signal and controls regeneration of said particulate filter based on said outlet temperature signal and said oxygen signal. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a schematic view of an exemplary diesel engine system that includes a particular filter regeneration system according to the present invention; 
         FIG. 2  is flow chart illustrating the oxygen based particulate fitter regeneration method according to the present invention; and 
         FIG. 3  is a graph illustrating a control band of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, 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 term module refers to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that executes 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  an exemplary diesel engine system  10  is schematically illustrated in accordance with the present invention. It is appreciated that the diesel engine system  10  is merely exemplary in nature and that the 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. 
     The diesel engine system  10  includes a diesel engine  12 , an intake manifold  14 , a common rail fuel injection system  16  and an exhaust system  18 . The exemplary engine  12  includes eight cylinders  20  configured in adjacent cylinder banks  22 , 24  in V-type layout. Although  FIG. 1  depicts eight cylinders (N=8), it can be appreciated that the engine  12  may include additional or fewer cylinders  20 . For example, engines having 2, 4, 5, 6, 8, 10, 12 and 16 cylinders are contemplated. It is also anticipated that the particulate filter regeneration control of the present invention can be implemented in an inline-type cylinder configuration. 
     Air is drawn into the intake manifold  14  through a throttle (not shown). Air is drawn into the cylinders  20  from the intake manifold  14  and is compressed therein. Fuel is injected into cylinder  20  by the common rail injection system  16  and the heat of the compressed air ignites the air/fuel mixture. The exhaust gases are exhausted from the cylinders  20  into the exhaust system  18 . In some instances, the diesel engine system  10  can include a turbocharger that uses an exhaust driven turbine  26  to drive a compressor  27  that compresses the air entering the intake manifold  14 . The compressed air typically passes through an air cooler (not shown) before entering into the intake manifold  14 . 
     The exhaust system  18  includes exhaust manifolds  28 , 30 , exhaust conduits  29 , 31 , and  36 , a diesel oxidizing catalyst (DOC)  38 , and a diesel particulate filter (DPF)  40 . The exhaust manifolds  28 , 30  direct the exhaust exiting corresponding cylinder banks  22 , 24  into the exhaust conduits  29 , 31 . The exhaust is directed into the turbocharger to drive the turbine  26 . A combined exhaust stream flows from the turbocharger through the exhaust conduit  36 , the DOC  38 , and the DPF  40 . The DPF  40  filters particulates from the combined exhaust stream as it flows to the atmosphere. 
     A control module  42  regulates operation of the diesel engine system  10  according to the oxygen based particulate filter regeneration method of the present invention. More particularly, the control module  42  communicates with a DPF outlet temperature sensor, a wide-range air fuel sensor  46 , and a DPF inlet temperature sensor  48 . The DPF outlet temperature sensor generates a signal indicating a temperature at the outlet of the DPF  40 . In various embodiments, the DPF outlet temperature sensor senses a temperature of the DPF substrate as shown by temperature sensor  44  and generates a substrate temperature signal. In various embodiments, the DPF outlet temperature sensor senses a temperature of gases exiting the DPF as shown by temperature sensor  45  and generates a gas temperature signal. The wide-range air fuel sensor  46  generates a signal indicating the amount of oxygen (O 2 ) in the exhaust. The DPF inlet temperature sensor  48  generates a signal indicating the temperature of exhaust flowing into the DPF  40 . 
     The control module  42  determines when regeneration is needed and controls engine operation to allow regeneration to occur. Based on the outlet temperature signal and the oxygen signal, control continues to control engine operation at regeneration levels until regeneration is complete. 
     Referring now to  FIG. 2 , a flowchart illustrates steps performed by the oxygen based particulate filter regeneration method. In step  100 , control estimates soot accumulation in the DPF and determines whether regeneration is needed based on an accumulation threshold. If the DPF is full, control determines whether engine operating conditions are sufficient to permit regeneration in step  110 . If the DPF is not full, control proceeds to the end. If regeneration is permitted, control enables regeneration by modifying the combustion process and/or injecting fuel into the exhaust stream to raise the DPF inlet temperature above a soot light-off threshold in step  120 . The elevated exhaust temperature initiates oxidation of the stored soot within the DPF. If regeneration is not permitted, control proceeds to the end. 
     If regeneration has begun and the temperature signal indicates a substrate temperature of greater than a selectable threshold in step  130 , the proper temperature for regeneration is maintained by commanding air and/or fuel such that the oxygen level indicated by the air fuel sensor is within a pre-defined control band. In an exemplary embodiment, the selectable threshold can be five hundred degrees Celsius.  FIG. 3  illustrates an exemplary control band. The oxygen level is indicated along the y-axis at  200  and ranges from zero percent to ten percent. The DPF outlet temperature is indicated along the x-axis at  210  and ranges from three hundred degrees Celsius to nine hundred degrees Celsius. An exemplary control band is indicated at  220 . The control band indicates the range at which the oxygen levels should be maintained in order to control the temperature of the DPF and to completely burn the accumulated soot. 
     Referring back to  FIG. 2 , as regeneration occurs in step  140 , the soot mass is reduced over a period of time. The time for complete regeneration of the stored soot mass can be estimated from the known DPF conditions. A maximum regeneration time can be pre-determined for the particular system. If the DPF outlet temperature in step  150  remains above a minimum temperature (e.g., 550 degrees Celsius) and the regeneration time in step  160  is greater than the regeneration time max (e.g., 7 minutes), the filter is clean and regeneration is complete. Control proceeds to the end. If the DPF outlet temperature is above the minimum temperature, but for insufficient time, control loops back to step  100  and regeneration will continue to complete the soot oxidation process. 
     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, specification, and the following claims.