Abstract:
A vehicle includes an engine, a regenerable exhaust stream particulate filter, and a host machine. The host machine has a pair of soot models providing respective actual and modeled soot mass values for the soot contained in the particulate filter, calculates a ratio of a change in the actual and modeled soot masses, and executes a control action when the ratio exceeds a calibrated threshold. A diagnostic code and/or activation of an indicator device may be part of the control action. A system includes the particulate filter and host machine noted above. A method for use aboard the vehicle includes determining the actual and modeled soot mass values using first and second soot models, respectively, calculating a ratio of a change in the actual and modeled soot mass, comparing the ratio to a calibrated threshold, and executing a control action when the ratio exceeds the threshold.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an apparatus and method for monitoring the regeneration frequency of a particulate filter adapted for removing soot from a vehicle exhaust stream. 
       BACKGROUND 
       [0002]    Particulate filters are designed to remove microscopic particles of soot, ash, metal, and other suspended matter from an exhaust stream of a vehicle. Over time, the particulate matter accumulates on a substrate within the filter. In order to extend the life of the particulate filter and to further optimize engine functionality, some filters are designed to be selectively regenerated using heat. 
         [0003]    Temperatures within the particulate filter can be temporarily increased to between approximately 450° C. to 600° C. by directly injecting and igniting fuel, either in the engine&#39;s cylinder chambers or in the exhaust stream upstream of the filter. The spike in exhaust gas temperature may be used in conjunction with a suitable catalyst, e.g., palladium or platinum, wherein the catalyst and heat act together to reduce the accumulated particulate matter to relatively inert carbon soot via a simple exothermic oxidation process. 
       SUMMARY 
       [0004]    A vehicle as disclosed herein includes an engine, a particulate filter that is regenerable using heat, and a host machine. The host machine accesses a first soot model to determine an actual soot mass in the particulate filter, e.g., a lookup table indexed by a calculated or measured differential pressure across the filter, and a second soot model to determine a modeled soot mass in the filter. The second soot model provides the modeled soot mass relative to a set of current vehicle operating points or conditions. The host machine then calculates a ratio of a change in the actual soot mass to a change in the modeled soot mass. The host machine compares the calculated ratio to a calibrated threshold, and automatically executes a control action when the calculated ratio exceeds the calibrated threshold. 
         [0005]    The method may be embodied as an algorithm executable by the host machine. By executing the algorithm as disclosed herein, the host machine can account for varying filter regeneration trigger points, i.e., sets of generated or related signals initiating a heat-based regeneration of the particulate filter. The host machine can also account for the varying soot masses remaining in the particulate filter subsequent to an immediately prior filter regeneration event. 
         [0006]    Suitable control actions may include setting a first diagnostic code when the calculated ratio exceeds the calibrated threshold, activating an indicator device, transmitting a message, etc. As the actual and modeled soot values can vary with vehicle operating conditions, conventional monitoring methods that set an arbitrary threshold to cover a worst case scenario may be less than optimal. The present method may therefore improve the robustness of any regeneration frequency monitoring algorithm. 
         [0007]    A system is also provided for use aboard the vehicle noted above. The system includes a host machine and a particulate filter, which is regenerable using heat. The host machine accesses a first soot model which provides an actual soot mass remaining in the particulate filter, and a second soot model which provides a modeled soot mass remaining in the filter using a set of current vehicle operating conditions. The host machine also calculates a ratio of a change in the measured soot mass to a change in the modeled soot mass. The host machine then compares the calculated ratio to a calibrated threshold, and executes a suitable control action when the ratio exceeds the threshold. 
         [0008]    A method is also provided that may be embodied as an algorithm and used aboard the vehicle noted above. The method includes using a first soot model to determine an actual soot mass remaining in the particulate filter, and using a second soot model to determine a modeled soot mass remaining in the filter, with the second soot model using a set of current vehicle operating conditions. The method also includes calculating a ratio of a change in the actual soot mass to a change in the modeled soot mass, comparing the ratio to a calibrated threshold, and executing a control action when the ratio exceeds the calibrated threshold. 
         [0009]    The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a schematic illustration of a vehicle having an internal combustion engine and a regenerable particulate filter; and 
           [0011]      FIG. 2  is a flow chart describing a method for monitoring filter regeneration frequency aboard the vehicle shown in  FIG. 1 . 
       
    
    
     DESCRIPTION 
       [0012]    Referring to the drawings, wherein like reference numbers correspond to like or similar components throughout the several figures, a vehicle  10  is shown schematically in  FIG. 1 . The vehicle  10  includes a host machine  40  having an algorithm  100  adapted to monitor a frequency of regeneration of a heat-regenerable particulate filter  34  as explained below, and to execute a control action as needed depending on the frequency of regeneration. Algorithm  100  is explained in detail below with reference to  FIG. 2 . 
         [0013]    Vehicle  10  includes an internal combustion engine  12 , such as a diesel engine or a direct injection gasoline engine, an oxidation catalyst (OC) system  13  having the particulate filter  34 , and a transmission  14 . The engine  12  combusts fuel  16  drawn from a fuel tank  18 . In one possible embodiment, the fuel  16  is diesel fuel, the oxidation catalyst system  13  is a diesel oxidation catalyst (DOC) system, and the particulate filter  34  is a diesel particulate filter (DPF), although gasoline or other fuel types may be used depending on the design of engine  12 . 
         [0014]    As noted above, algorithm  100  is executed by the host machine  40  in order to detect a condition in which a frequency of regeneration of the particulate filter  34  is higher than a threshold level required by design standards, doing so using first and second soot models  50  and  60 , respectively, as set forth herein. In particular, host machine  40  directly monitors regeneration frequency using a calculated ratio of the difference in a measured or actual soot level to a simulated or modeled soot level from the first and second soot models  50  and  60 , respectively, with the two models determining soot levels remaining in the particulate filter  34  in different ways, and by comparing the calculated ratio to a calibrated threshold as explained below with reference to  FIG. 2 . 
         [0015]    Host machine  40  may be configured as a digital computer acting as a vehicle controller, and/or as a proportional-integral-derivative (PID) controller device having a microprocessor or central processing unit (CPU), read-only memory (ROM), random access memory (RAM), electrically erasable programmable read only memory (EEPROM), a high-speed clock, analog-to-digital (A/D) and/or digital-to-analog (D/A) circuitry, and any required input/output circuitry and associated devices, as well as any required signal conditioning and/or signal buffering circuitry. Algorithm  100  and any required reference calibrations are stored within or readily accessed by host machine  40  to provide the functions described below with reference to  FIG. 2 . 
         [0016]    Vehicle  10  also includes a throttle  20  which selectively admits a predetermined amount of the fuel  16  and air into engine  12  as needed. Combustion of fuel  16  by the engine  12  generates an exhaust stream  22 , which passes through the exhaust system of the vehicle before it is ultimately discharged into the surrounding atmosphere as shown. Energy released by the combustion of fuel  16  ultimately produces torque on an input member  24  of transmission  14 . The transmission  14  in turn transfers torque from the engine  12  to an output member  26  in order to propel the vehicle  10  via a set of wheels  28 , only one of which is shown in  FIG. 1  for simplicity. 
         [0017]    The OC system  13  as shown in  FIG. 1  cleans and conditions the exhaust stream  22  as it passes from exhaust ports  17  of engine  12  through the vehicle&#39;s exhaust system. To this end, OC system  13  may include an oxidation catalyst  30 , a selective catalytic reduction (SCR) device  32 , and the particulate filter  34  noted above. SCR device  32  may be positioned between the oxidation catalyst  30  and the particulate filter  34 . As understood in the art, an SCR device converts nitrogen oxide (NOx) gasses into water and nitrogen as inert byproducts using an active catalyst. SCR device  32  may be configured as a ceramic brick or a ceramic honeycomb structure, a plate structure, or any other suitable design. 
         [0018]    Regeneration of the particulate filter  34  may be active or passive. As understood in the art, passive regeneration requires no additional control action for regeneration. Instead, the particulate filter is installed in place of the muffler, and at idle or low power operations, particulate matter is collected on the filter. As the engine exhaust temperatures increase, the collected material is then burned or oxidized by the exhaust stream  22 . Active regeneration adds an external source of heat to complete the regeneration, along with additional control methodology. 
         [0019]    However configured, the particulate filter  34  may be constructed of a suitable substrate constructed of, by way of example, ceramic, metal mesh, pelletized alumina, or any other temperature and application-suitable material(s). As the temperature of the exhaust stream  22  increases, particulate matter previously entrapped within the particulate filter  34  is burned or oxidized by the hot exhaust gas to form soot within the particulate filter. 
         [0020]    Vehicle  10  may also include a fuel injection device  36  in electronic communication with the host machine  40  via control signals  15 , and in fluid communication with fuel tank  18 . Fuel injection device  36  selectively injects fuel  16  into the oxidation catalyst  30  or engine cylinders (not shown) when determined by the host machine  40 . The injected fuel  16  is then ignited and burned in a controlled manner to generate the increased levels of heat necessary for regenerating the particulate filter  34 . 
         [0021]    Still referring got  FIG. 1 , the respective first and second soot models  50 ,  60  may be in the form of lookup tables and/or a series of calculations suitable for determining in different respective manners the remaining mass of soot in the particulate filter  34 . In one embodiment, the first soot model  50  provides a measured or actual soot mass value using the measured or calculated differential pressure across the particulate filter  34 , with the first soot model indexing a differential pressure across the particulate filter to the actual soot mass. 
         [0022]    The second soot model  60  provides the modeled soot mass in a different manner, i.e., doing so using a set of current vehicle operating conditions and not using the differential pressure across the particulate filter  34 . Second soot model  60  uses feedback signals  44  describing the operating point of engine  12  and other suitable vehicle operating data points. Such points may include oxygen levels, throttle position, engine speed, accelerator pedal position, fueling quantity, requested engine torque, exhaust temperatures, elapsed time since the start of the last regeneration event, the particular driving mode such as highway driving, city driving, and/or other recognized modes or combinations of modes as determined by monitoring parameters such as engine speed, engine loading, braking, etc. 
         [0023]    Host machine  40  also receives signals  11  from various sensors  42  positioned throughout the vehicle  10  describing various measured values, e.g., exhaust temperatures, pressure, oxygen levels, etc., at different locations within the OC system  13 , including directly upstream and downstream of the oxidation catalyst  30  and directly upstream and downstream of the particulate filter  34 . These signals  11  are each transmitted by or relayed to the host machine  40 . Host machine  40  is also in communication with the engine  12  to receive the feedback signals  44  indentifying the operating point of the engine, values which are used in particular by the second soot model  60  as described below. 
         [0024]    Referring to  FIG. 2 , the host machine  40  executes algorithm  100  aboard the vehicle  10  of  FIG. 1  to monitor regeneration frequency of the particulate filter  34 . In general, the host machine  40  determines a measured or actual soot mass using the first soot model  50 , with the actual soot mass being based on a differential pressure across the particulate filter  34  according to one possible embodiment. The host machine  40  then determines a modeled soot mass in the particulate filter  34 , e.g., by referencing the second soot model  60  using vehicle operating data. Next, a ratio of a change in the actual soot mass is calculated and compared to a change in the modeled soot mass, with the ratio compared to a calibrated threshold. Host machine  40  can execute a control action when the ratio exceeds the threshold. 
         [0025]    In particular, beginning at step  102  the host machine  40  first determines whether a set of initialization conditions are present, i.e., whether a regeneration event is presently commanded. Step  102  may be satisfied by detecting a discrete on/off regeneration trigger signal generated internally by the host machine if the host machine is configured to control the regeneration process, or by another vehicle controller if configured otherwise. The algorithm  100  proceeds to step  104  after detection of the regeneration trigger signal or other initialization condition. 
         [0026]    At step  104 , the host machine  40  determines the actual soot mass in the particulate filter  34 . In one possible embodiment, the host machine  40  directly reads or calculates the differential pressure across the particulate filter  34  using signals  11  from the sensors  42  positioned at the inlet and outlet sides of the particulate filter, in this case configured as temperature transducers or other suitable temperature sensors, and then references the first soot model  50  using the pressure drop to determine an actual soot mass value. This value is temporarily recorded in memory, and the algorithm  100  proceeds to step  106 . 
         [0027]    At step  106 , the host machine  40  processes the feedback signals  44  and any other required signals  11  to calculate a change in the modeled soot mass, with the modeled soot mass determined with reference to the second soot model  60  described above. This change occurs over the time interval between the present regeneration trigger signal and the initiation of the immediately prior filter regeneration event. Host machine  40  also calculates the change in actual soot mass within the particulate filter  34  over the same time interval, this time with reference to first soot model  50 , and then proceeds to step  108  after temporarily recording the two change values in memory. 
         [0028]    At step  108 , the host machine  40  calculates a ratio of the change values calculated at step  106 , i.e., the change in modeled soot mass and the change in actual soot mass in the elapsed interval since the last regeneration event, and temporarily records the value of this ratio in memory before proceeding to step  110 . 
         [0029]    At step  110 , the host machine  40  compares the ratio from step  108  to a calibrated threshold. If the recorded ratio exceeds the calibrated threshold, the host machine  40  proceeds to step  112 , and otherwise proceeds to step  114 . 
         [0030]    At step  112 , host machine  40  sets a first diagnostic code indicating that the ratio exceeds the calibrated threshold. Such a result could mean that there is more soot present within the particulate filter  34  than expected by the second soot model  60 , a result which may be caused by an air leak or an engine malfunction, and which therefore warrants further investigation. Additional control actions at step  112  may include activating an indicator device  38  to alert an operator, transmitting a message within vehicle  10 , transmitting a message outside of the vehicle using a vehicle telematics unit, and/or taking any other action suitable for signaling the need to inspect, maintain, or replace the particulate filter  34 . 
         [0031]    At step  114 , the host machine  40  sets a second diagnostic code indicating that the calculated ratio does not exceed the calibrated threshold. Algorithm  100  may continue to execute in a suitable control loop to minimize variability, i.e., all regeneration events must maintain at least a minimum level of efficiency, thus making the algorithm robust for any given control system calibration, as well as a wider variety of control system calibrations. 
         [0032]    While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.