Abstract:
A vehicle includes an engine, an exhaust system having a particulate filter which removes soot from the exhaust stream, a sensor, and a controller. The sensor measures instantaneous differential pressure across the filter. The controller executes a method to selectively enable or disable execution of an efficiency diagnostic of the filter as a function of a learned differential pressure offset value. The controller may also compare the differential pressure to a calibrated threshold and execute a control action when the differential pressure falls within an allowable range of the threshold. This may include applying the differential pressure offset value and enabling execution of the diagnostic using measurements from the zeroed sensor. Another control action may be executed when the measured differential pressure is not within the allowable range of the threshold, including disabling the execution of the diagnostic and setting a diagnostic code indicating that the sensor may be faulty.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates to a system and method for enabling a diagnostic of a particulate filter using differential pressure measurements. 
       BACKGROUND 
       [0002]    The exhaust stream of a diesel engine is typically filtered using a diesel particulate filter (DPF). The DPF, which is positioned in the exhaust stream downstream of a catalyst, captures engine soot and other suspended particulate matter before it can be discharged via the tailpipe into the surrounding atmosphere. Soot production is heavily influenced by engine operation, for instance EGR valve position, turbo position, fuel injection timing, etc. Over time, soot loading accumulates in the porous media of the DPF. In-situ thermal regeneration of the DPF is therefore conducted periodically to burn off accumulated particulate matter. 
         [0003]    DPF regeneration is typically performed by temporarily elevating the temperature of the exhaust stream passing through the DPF. A metered stream of fuel is injected into the exhaust stream. The exothermic reaction with a diesel oxidation catalyst (DOC) quickly raises exhaust temperatures to 600° C. or higher, thereby incinerating accumulated soot. Over time, substrate within the DPF may become cracked, melted, or pitted from repeated exposure to thermal stress and other factors. As a result, a DPF diagnostic is ordinarily performed in order to verify satisfactory performance of the DPF. 
       SUMMARY 
       [0004]    A vehicle is disclosed herein that includes an engine, an exhaust system, and a controller. The exhaust system includes a particulate filter, e.g., a diesel particulate filter (DPF), that receives an exhaust stream discharged by the engine. A differential pressure (ΔP) sensor is in communication with the controller. The ΔP sensor measures the instantaneous differential pressure across the filter and transmits the measured instantaneous ΔP value to the controller. The controller then selectively enables a subsequent efficiency diagnostic of the filter as a function of received instantaneous ΔP values. 
         [0005]    To determine when to enable/disable the diagnostic, the controller may execute a set of recorded instructions whenever a key-off event of the engine is detected. The engine shuts off in response to such a key-off event. After a calibrated settling time, the controller compares the received instantaneous ΔP value to a calibrated ΔP threshold. If the instantaneous ΔP value is less than or equal to the ΔP threshold, the controller zeros the ΔP sensor, e.g., by applying an offset that is equal and opposite in magnitude to the measured ΔP value. The controller then enables execution of the efficiency diagnostic using the zeroed value. However, if the instantaneous ΔP value exceeds the threshold, the controller automatically disables or postpones execution of the diagnostic. The controller may also set a diagnostic code in memory to signal a required repair or replacement of the ΔP sensor. 
         [0006]    A method is also disclosed herein that includes measuring an instantaneous differential pressure across a particulate filter in an exhaust stream of an engine using a sensor, receiving, via a controller, the measured instantaneous differential pressure from the sensor, and selectively enabling or disabling execution of a diagnostic of the particulate filter as a function of the instantaneous differential pressure. 
         [0007]    In another embodiment, the method includes measuring an instantaneous differential pressure across a diesel particulate filter (DPF) in an exhaust stream of a diesel engine using a sensor, and receiving, via a controller, the measured instantaneous differential pressure from the sensor. The method also includes detecting a key-off event of the engine and selectively enabling or disabling execution of a diagnostic of the DPF as a function of the measured instantaneous differential pressure only when the key-off event is detected. 
         [0008]    Enabling/disabling includes waiting through a calibrated settling time after detecting the key-off event, comparing the measured instantaneous differential pressure to a calibrated threshold, and executing a first control action when the measured instantaneous differential pressure is within an allowable range of the calibrated threshold. The first control action may include applying a differential pressure offset value to the measured differential pressure to thereby zero the sensor, and enabling the execution of the particulate filter efficiency diagnostic using measurements from the zeroed sensor. 
         [0009]    The method may include executing a second control action when the measured instantaneous differential pressure is not within the allowable range of the threshold, including disabling the execution of the DPF efficiency diagnostic and setting a diagnostic code indicating that the sensor is faulty. 
         [0010]    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 
         [0011]      FIG. 1  is a schematic illustration of a vehicle having an exhaust system with a diesel particulate filter (DPF) and a differential pressure (ΔP) sensor, as well as a controller that executes a method using instantaneous ΔP values from the sensor to selectively enable/disable a DPF efficiency diagnostic. 
           [0012]      FIG. 2  is an example plot of measured instantaneous ΔP values vs. the volumetric flow rate of the exhaust stream flowing through the DPF shown in  FIG. 1 . 
           [0013]      FIG. 3  is a block diagram of an example set of linear regression logic used by the controller of  FIG. 1  as part of a DPF efficiency diagnostic. 
           [0014]      FIG. 4  is a diagram of filtered regression factors output by the linear regression logic shown in  FIG. 3 , with the horizontal axis indicating the sample number and the vertical axis corresponding to the filtered factor value. 
           [0015]      FIG. 5  is a flow chart describing an example method for enabling/disabling execution of a DPF efficiency diagnostic using instantaneous ΔP signals. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Referring to the drawings, wherein like reference numbers represent like components throughout the several figures, an example vehicle  10  is shown in  FIG. 1 . The vehicle  10  includes an internal combustion engine  12 . The engine  12  is a diesel engine in the examples that follow, although direct injection-type gasoline combustion engines or other engine types may be used without departing from the intended inventive scope. 
         [0017]    Engine torque from the engine  12  is transferred to a rotatable input member  36  of a transmission  38 , which may include one or more planetary gear sets, clutches, and fluid control devices (not shown) as is well understood in the art. The transmission  38  ultimately transfers output torque (T O ) to a transmission output member  40  to propel the vehicle  10 . 
         [0018]    The engine  12  generates an exhaust stream  13  as a product of the fuel combustion process. The exhaust stream  13  is discharged from the engine  12  through an exhaust manifold  34  and into an exhaust system  14 . The exhaust stream  13  is processed using various components of the exhaust system  14  in order to remove any entrained particulate matter, nitrogen oxide (NOx) gases, carbon monoxide gas, suspended hydrocarbons, and the like. 
         [0019]    The various components of the exhaust system  14  include a particulate filter, which in keeping with the example diesel engine embodiment is referred to hereinafter as a diesel particulate filter (DPF)  24 . The DPF  24  may be configured as a block of sintered ceramic foam, metal mesh, pelletized alumina, and/or any other suitable material or combination of materials. A controller  50  periodically executes recorded instructions embodying a method  100 , an example of which is shown in  FIG. 5 . As explained in detail below, execution of the method  100  by the controller  50  selectively enables/disables subsequent execution of DPF diagnostic logic  55  as a function of differential pressure across the DPF  24 . 
         [0020]    The exhaust system  14  shown in  FIG. 1  may also include a selective catalytic reduction (SCR) device  16 . The SCR device  16  converts NOx gases into water and nitrogen as inert byproducts using an active catalyst. The SCR device  16  may be configured as a ceramic brick or a ceramic honeycomb structure, a plate structure, or any other suitable design having a sufficient thermal mass. NOx gases in the exhaust stream  13  react with urea or ammonia (NH 3 ) stored in or delivered to the SCR device  16 , thereby reducing levels of NOx gases in the exhaust stream  13 . 
         [0021]    In addition to the SCR device  16  and the DPF  24  noted above, the exhaust system  14  may also include an oxidation catalyst  22 . The oxidation catalyst  22  is in communication with a fuel injector device  23  that delivers a calibrated amount of fuel into the oxidation catalyst  22 . Ignition of the injected fuel rapidly increases the temperature of the exhaust stream  13 , typically to 600° C. or more, in order to enable thermal regeneration of the DPF  24 . Use of the oxidation catalyst  22  in the exhaust system  14  is intended to reduce hydrocarbon and carbon monoxide levels in the exhaust stream  13 , and allows for exhaust temperatures to be achieved at levels suitable for regeneration of the DPF  24 . 
         [0022]    The controller  50  that is shown schematically in  FIG. 1  may be embodied as a general-purpose digital computer in communication with a plurality of exhaust temperature sensors  20 , as well as with NOx sensors  21 . The controller  50  may include a processor  52 , along with tangible, non-transitory memory  54 , e.g., read-only memory (ROM), flash memory, optical memory, additional magnetic memory, etc. The controller  50  may also include random access memory (RAM), electrically programmable read only memory (EPROM), a high-speed clock, analog-to-digital (A/D) and/or digital-to-analog (D/A) circuitry, and any input/output circuitry or devices, as well as any appropriate signal conditioning and buffer circuitry. 
         [0023]    The controller  50  of  FIG. 1  receives a measured engine speed (arrow N E ), whether from the engine  12  or from a separate engine control module (not shown). The controller  50  also receives temperature signals (arrows T) from the various temperature sensors  20 , and NOx readings (arrows NOx) from the NOx sensors  21 . Instantaneous differential pressure ΔP values (arrow ΔP) are received as signals measured by a ΔP sensor  25 . The ΔP sensor  25 , as is well understood in the art, measures and/or calculates a pressure differential between the inlet and outlet sides of a filter housing, in this instance the DPF  24 , i.e., ΔP=P IN −P OUT . The ΔP sensor  25  may be a unitary sensor or gauge connected to the DPF  24 , or it may be embodied as a pair of pressure taps that individually read the inlet and outlet pressures and calculate the differential pressure across the DPF  24 . 
         [0024]    The controller  50  shown in  FIG. 1 , in the execution of the DPF efficiency diagnostic logic  55 , may use various weighted regression factors such as the volumetric flow of the exhaust stream  13 , the measured instantaneous ΔP across the DPF  24 , the temperature of the exhaust stream  13  upstream and downstream of the DPF  24 , and the temperature gradient across the DPF  24 . The controller  50  may also calculate or otherwise determine the amount of soot discharged from the engine  12 , a value that may be obtained from a calibrated soot model  56  stored in a lookup table in memory  54 . Other regression factors may include the engine speed (arrow  27 ), the amount of fuel injected into the exhaust stream  13  by the fuel injection device  23 , and the distance traveled, elapsed time, and total volume of fuel consumed by the engine  12  since execution of a prior regeneration of the DPF  24 . 
         [0025]    Each of the regression factors may be assigned a corresponding weight based on the relative importance of that particular factor to an ultimate decision as to whether or not the DPF  24  is functioning properly. In the present approach, the instantaneous ΔP values (arrow ΔP) from the ΔP sensor  25  may be weighted more heavily than the remaining factors, particularly at areas of greater separation between a nominal or “good” DPF  24  and a malfunctioning one, e.g., at the end of a thermal regeneration cycle. The term “separation” as used herein is described immediately hereinbelow with reference to  FIG. 2 . Additionally, the instantaneous ΔP values (arrow ΔP) are used by the controller  50  in the execution of the method  100  in order to determine whether or not to proceed with use of a subsequent DPF efficiency diagnostic, during a subsequent engine-on cycle, using the DPF efficiency diagnostic logic  55 . 
         [0026]    Referring to  FIG. 2 , an example plot  60  represents, on the horizontal axis, the volumetric flow rate (F) of the exhaust stream  13  as it passes through the DPF  24 . The corresponding instantaneous differential pressure value (ΔP) is represented on the vertical axis. Raw data  62  corresponds to the performance of a nominal DPF  24 , i.e., a properly functioning/validated or new DPF  24  having no discernible flaws or any appreciable damage to the internal filter media. Raw data  64  represents a damaged DPF  24  having a known set of flaws, e.g., a set of holes having a variety of sizes. Such flaws may be representative of damage that the internal media of the DPF  24  might incur over time during extended operation and thermal regeneration, most often due to thermal shock, i.e., extreme localized heating and melting of the internal media or an over-accumulation of soot and subsequent regeneration of the DPF  24 . 
         [0027]    As shown in  FIG. 2 , very little separation exists between the raw data  62  and  64  when using instantaneous ΔP values to evaluate the performance of a DPF  24  in the conventional threshold comparison manner. As a result, sensor error or offset value of the ΔP sensor  25  of  FIG. 1 , if excessive, can greatly affect the overall accuracy of any subsequent DPF performance analysis. For instance, false failures of the DPF  24  may result if the ΔP offset value is excessive. That is, a relatively expensive DPF  24  may be diagnosed as failing when in fact the ΔP offset value of the relatively inexpensive ΔP sensor  25  is the root cause of the failing diagnosis. Successful diagnosis of the ΔP sensor  25  is therefore performed herein via the method  100  of  FIG. 5  as a precursor to continued execution/use of the DPF regression logic  55 . 
         [0028]    Referring to  FIG. 3 , the recorded DPF efficiency diagnostic logic  55  used by the controller  50  of  FIG. 1  may include a linearization block  70  and a filter block  74 , e.g., a Kalman filter of the type know in the art. The diagnostic logic  55  first creates linearized data from the instantaneous ΔP values measured by the ΔP sensor  25  of  FIG. 1 . The linearized ΔP data is represented herein as ΔP′. Therefore, the linearization block  70  receives the measured instantaneous ΔP value as an input, as well as the calculated/measured volumetric flow rate (F) and measured temperature (T) of the exhaust stream  13 . The linearization block  70  then processes the inputs using the processor  52  shown in  FIG. 1  to linearize the raw data (see  FIG. 2 ) via any suitable linear transformation technique, e.g., using the formula ΔP′=R·F+B, where R is the flow resistance through the DPF  24  and B is a constant. 
         [0029]    The linearized data (arrow  72 ) is then output to the filter block  74 . The filter block  74  is used to generate a diagnostic detection parameter, which is referred to hereinafter as a regression factor, i.e., arrow  76 . The regression factor (arrow  76 ) may be calculated by the controller  50  as 
         [0000]    
       
         
           
             
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                   P 
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         [0030]    Referring to  FIG. 4 , the regression factor  76  noted above may be represented as data clusters  78  and  79 . Note that a regression factor  76  having a larger value corresponds to a larger/more severe fault, in this example a fault of the ΔP sensor  25 . The controller  50  may use a calibrated threshold  80  to evaluate each of the regression factors, with values recorded below the threshold  80  being passing/desirable results, and those falling above the threshold  80  corresponding to failing/undesirable results. Data cluster  79  corresponds to the raw data  62  shown in  FIG. 2 . Likewise, data cluster  78  corresponds to the raw data  64  shown in the same Figure. Whereas the raw data  63  and  64  shows minimal separation in  FIG. 2 , improved separation is provided between results in  FIG. 4  due to the use of the DPF efficiency diagnostic logic  55  shown in  FIG. 3 . 
         [0031]    Referring to  FIG. 5 , the method  100  uses instantaneous ΔP values as measured by the ΔP sensor  25  to enable the subsequent execution of DPF efficiency diagnostics, e.g., using the DPF efficiency diagnostic logic  55  described above. The method  100  begins at step  102 , wherein the controller  50  of  FIG. 1  detects an ignition state of the vehicle  10 , whether by measuring current through a starter switch, detecting a key/switch position, or by any other suitable steps. The method  100  proceeds to step  104  once the ignition state has been detected. 
         [0032]    At step  104 , the controller  50  next determines whether the ignition state detected at step  102  corresponds to a key-off or engine-off state. If so, the method  100  proceeds to step  106 . Otherwise, the controller  50  repeats step  102 . 
         [0033]    At step  106 , the controller  50  of  FIG. 1  may initiate a timer to allow a sufficient amount of settling time to elapse after shutdown of the engine  12 . The settling time provided by step  106  should be sufficient for any residual exhaust flow in the exhaust system  14  of  FIG. 1  to stop flowing. The method  100  proceeds to step  108  once the calibrated settling time has elapsed. 
         [0034]    At step  108 , the controller  50  of  FIG. 1  next receives the instantaneous ΔP measurement, i.e., arrow ΔP of  FIG. 1 , from the ΔP sensor  25  shown in the same Figure. The controller  50  then temporarily records the received value in memory  54  before proceeding to step  110 . 
         [0035]    At step  110 , the controller  50  of  FIG. 1  compares the value received in step  108  to a calibrated ΔP offset value. In a typical embodiment, the calibrated ΔP offset value is a tolerance of a validated/new ΔP sensor  25 , e.g., less than about ±1-2 hecto Pascal (hPa). If the received value is within an allowable range of the calibrated offset value, such as within 10 hPa of this value, the method  100  proceeds to step  112 . In another embodiment, the method  100  proceeds to step  112  only if the instantaneous ΔP value is within the tolerance of the ΔP sensor  25 . Use of a maximum ΔP offset value at step  110  is intended to reduce the risk of using inaccurate measurements from the ΔP sensor  25  of  FIG. 1  as an input in any subsequent DPF regression analysis. The method  100  proceeds to step  114  only if the received value of the ΔP signal is not within an allowable range of the calibrated ΔP offset value. 
         [0036]    At step  112 , the controller  50  learns and applies a ΔP offset value, thereby effectively zeroing the ΔP sensor  25 , and then proceeds to use the DPF efficiency diagnostic logic  55  of  FIG. 3  as explained above. The results of step  112  may include a determination that the DPF  24  of  FIG. 1  is or is not functioning properly, as well as any suitable control actions stemming from such a determination, e.g., recoding of a passing or failing diagnostic code, etc. 
         [0037]    At step  114 , the controller  50  records a suitable diagnostic code in memory  54  indicating that the ΔP sensor  25  of  FIG. 1  is potentially faulty or functioning out of tolerance, and may optionally include illuminating a warning lamp on the instrument panel of the vehicle  10  of  FIG. 1 . Additionally, step  114  may entail disabling further of execution of the DPF efficiency diagnostic logic  55  until service can be performed on the exhaust system  14 . 
         [0038]    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.