Abstract:
A method for detecting a closing time of an injector valve includes receiving a valve current profile of the injector valve, processing the valve current profile using at least a slope discriminator, determining a stuck status and a closing time (if applicable) of the injector valve based on an output of the slope discriminator. An engine control unit configured to detect a closing time of an injector valve is also provided. The engine control unit has a first control logic configured to receive a valve current profile of the injector valve, a second control logic configured to process the current profile using at least a slope discriminator, and a third control logic configured to determine a stuck status and a closing time of the injector valve based on an output of the slope discriminator. Further, a vehicle system including a controller configured to detecting a valve closing time is provided.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates generally to injector controls, and more specifically to a process, system, and apparatus for detecting a closing time and status of a solenoid injector. 
       BACKGROUND OF THE INVENTION 
       [0002]    The global drive to reduce NOx and CO2 emissions from diesel engine exhausts has led to the implementation of selective catalytic reduction systems in diesel engine vehicles to reduce the automotive emissions. Selective catalytic reduction systems operate by adding a gaseous or liquid reductant to the exhaust gas stream from an engine. The gaseous or liquid reductant is absorbed onto a catalyst where the reductant reacts with nitrogen oxides in the exhaust gas to form water vapor and nitrogen. 
         [0003]    This treatment requires the reducing agent to be administered at a precise concentration and with high quality. The solution must be accurately metered and injected into the exhaust gas stream, where it is hydrolyzed before converting the nitrogen oxide (NOx) to nitrogen (N2) and water (H2O). 
         [0004]    As the tailpipe NOx emission standard becomes increasingly stringent, it is desired to diagnose the injection faults to assist with the SCR DeNOx functionality and performance. For example, a stuck injector may cause under-dosing of urea and thus reduced DeNOx functionality. 
         [0005]    In order to properly interact with on-board diagnostic systems, such as OBD or OBDII, existing selective catalytic reduction systems include self-diagnostics to identify faults and enable pin point replacement while the vehicle is being serviced. For example, pressure changes may be monitored after commanding the pump to run or shut down. One drawback of this method, however, is that the emissions control process is disrupted. Accordingly, new systems and methods of detecting the SCR closing time are desired. 
         [0006]    In addition, determining closing time of injectors for direct fuel injection is also desired, in order to provide for better control and improved fuel economy. 
       SUMMARY OF THE INVENTION 
       [0007]    Disclosed is an apparatus, system, and method for detecting a closing time of a valve, such as an SCR valve or a direct injection valve, without additional hardware and without disrupting the emissions control process. The invention may include employing a digital filter and a slope discriminator is developed, which enables a diagnostic function to accurately detect injector closing time and reliably identify a stuck closing injector by monitoring injector current on an injection-to-injection basis. 
         [0008]    In one form, a method for detecting a closing time of an injector valve is provided. The method includes receiving a valve current profile of the injector valve, processing the valve current profile using at least a slope discriminator, determining a stuck status of the injector valve based on an output of the slope discriminator, and if the injector valve is not stuck, determining the closing time of the injector valve based on the output of the slope discriminator. 
         [0009]    In another form, an engine control unit configured to detect a closing time of an injector valve is provided. The engine control unit includes a first control logic configured to receive a valve current profile of the injector valve, a second control logic configured to process the valve current profile using at least a slope discriminator, and a third control logic configured to determine a stuck status and a closing time of the injector valve based on an output of the slope discriminator. 
         [0010]    In yet another form, a vehicle system is provided that includes an exhaust system including an injector and at least one sensor operable to detect a current draw of the injector. The vehicle system also includes a controller connected to the at least one sensor. The controller is operable to receive a profile of the current draw of the selective catalytic reduction injector and to process the profile using a slope discriminator. The controller is also operable to determine a stuck status and a closing time of the injector based on an output of the slope discriminator. 
         [0011]    In still another form, the present disclosure provides a non-transitory machine-readable medium that provides instructions, which when executed by a machine, cause the machine to perform operations. The operations include receiving a valve current profile of the injector valve, processing the valve current profile using at least a slope discriminator, and determining a stuck status and a closing time of the injector valve based on an output of the slope discriminator. 
         [0012]    In still another form, a method for controlling an injector is provided. The includes the steps of: instructing an injector to begin closing using a controller; receiving an injector current profile of the injector at the controller; processing the current profile using at least a slope discriminator in the controller; and determining stuck status and a closing of the injector based on an output of the slope discriminator. 
         [0013]    These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The following figures are provided for illustration purposes only, and are not intended to limit the scope of the present application and claims: 
           [0015]      FIG. 1  is a schematic side view of a vehicle including a selective catalytic reduction injector for reducing emissions, in accordance with the principles of the present disclosure; 
           [0016]      FIG. 2A  is a graph of a current profile of a selective catalytic reduction injector and a current profile of a stuck selective catalytic reduction injector with respect to time, according to the principles of the present disclosure; 
           [0017]      FIG. 2B  is a zoomed-in portion of the graph of  FIG. 2A , illustrating a current profile of a selective catalytic reduction injector and a stuck selective catalytic reduction injector at and around closing time, in accordance with the principles of the present disclosure; 
           [0018]      FIG. 3  is a block diagram illustrating a process for detecting a closing time and status of an injector, according to the principles of the present disclosure; 
           [0019]      FIG. 4  is a graph illustrating a slope discriminator scheme for the process of  FIG. 3 , in accordance with the principles of the present disclosure; and 
           [0020]      FIG. 5  is a graph illustrating an output chart of a slope discriminator, according to the principles of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]      FIG. 1  schematically illustrates a vehicle  10  including an exhaust system  20  for expelling exhaust  30  from an internal combustion engine of the vehicle  10 . The exhaust system  20  includes a selective catalytic reduction injector  40  that adds a gaseous or liquid reductant to the exhaust gas stream from the engine. The gaseous or liquid reductant is absorbed onto a catalyst where the reductant reacts with nitrogen oxides in the exhaust gas to form water vapor and nitrogen. The selective catalytic reduction injector  40  is controlled by a controller  50 , and includes a sensor package capable of sensing inputs to and outputs from the selective catalytic reduction injector  40 . In one example, the injector  40  is in the form of a solenoid valve. 
         [0022]    One of the inputs that the sensor package can detect, and communicate back to the controller  50 , is a current draw of the selective catalytic injector  40 . This current draw can be aggregated by the controller  50  to determine a current profile of the selective catalytic reduction injector  40 . Based on the current profile of the selective catalytic reduction injector  40 , the controller  50  can determine a precise injector closing time and whether the injector is stuck or unstuck using the below described process. 
         [0023]    The current profile of the selective catalytic reduction injector  40  is a function of battery voltage supplied to the injector, injector temperature and injector fluid pressure. At the conditions of low temperature, low pressure, and high voltage, the current profile of a nominal selective catalytic reduction injector  40  is almost the same as (superficially similar to) a stuck selective catalytic reduction injector, and a top level, or visual, inspection of the current profile is insufficient to identify a stuck injector or to precisely identify the closing time of the injector  40 . 
         [0024]    Though an SCR injector  40  is shown in  FIG. 1 , it should be understood that any type of solenoid injector could be used, such as a solenoid port fuel injector or a solenoid direct fuel injector. Solenoid fuel injectors also have a current draw, from which a current profile can be aggregated by a controller, such as controller  50 . Accordingly, the principles described here may apply to a solenoid fuel injector, as well as an SCR injector  40 , or any injector with an inductance reaction upon opening or closing. 
         [0025]    With continued reference to  FIG. 1 ,  FIGS. 2A-2B  illustrate a current profile  110  of a selective catalytic reduction injector  40  and a current profile  120  of a stuck selective catalytic reduction injector  40  with respect to time.  FIG. 2B  is an enlarged view of the end of injection. When the injector  40  is desired to be closed, the current is clamped and the injector begins to close at a time period c. After a delay period d, the non-stuck injector  40  has a post-clamp hump  112  in its current profile  110 , and the stuck injector  40  has a post-clamp hump  114  in its current profile  120 . The post-clamp hump  112  of the non-stuck injector is larger than the post-clamp hump  114  of the stuck injector, that is, the injector that does not fully close. The delay period d is a calibration value. The purpose of delay is to reduce the length of injector current data buffer, and avoid injector current clamp. 
         [0026]    A data collection window of a current profile  110 ,  120  is the window during which the analog-to-digital converter (ADC) of controller  50  collects injector current profile data for detecting the current drawn by the injector  40 . The ADC of controller  50  can be configured to read and filter injector closing data with a high sampling rate. During this window  116 , the injector closing current data is processed by the ADC of controller  50  and stored in a data buffer. The data in the buffer can be fed to a slope discriminator to determine the selective catalytic reduction injector  40  stuck status and closing time. The slope discriminator can be another controller, a software module stored in a memory of the controller  50 , or any other similar system. For example, the controller  50  can be configured to receive the valve current profile  110 ,  120 , process the valve current profile with the slope discriminator, and determine the stuck status and the closing time (if applicable) of the injector valve based on the output of the slope discriminator. 
         [0027]    With continued reference to  FIG. 1 ,  FIG. 3  illustrates a process  200  utilized by the controller  50  to detect the stuck status and closing time of the selective catalytic reduction injector  40 . As described above, the process  200  may alternatively apply to a solenoid fuel injector, rather than an SCR injector  40 . Initially, the controller  50  checks to see if injection has ended in an end of injection check step  210 . If injection has not ended, the process  200  loops back, and the end of injection check step  210  is performed again after any suitable delay. 
         [0028]    If injection has ended, the process  200  starts a delay timer in step  212 . The delay timer step  212  causes delay for a predetermined, calibrated period of time. As illustrated in  FIG. 2B , there is a delay period d between when the injection ends and when the detection window  116  opens. In the step  212 , the controller  50  waits the delay period between the end of injection and the beginning of the detection window  116  before moving on to detect the stuck status and closing time. 
         [0029]    Next, the process  200  moves to a check step  214  of whether the delay timer has expired. If the delay timer has not expired when the controller  50  performs the delay timer expired check  214 , the process  200  loops back to wait for the delay timer to expire and checks again at step  214 . The delay timer is updated every time when the function is executed. 
         [0030]    If, however, the delay timer has expired, the controller  50  begins collecting and filtering current data to construct an injector closing current profile of the injector  40  in a collect injector closing data step  218 . The current data can be processed using any acceptable sensor arrangement. In some examples, the current data is collected using an extremely high sampling rate. The sampling rate is the rate at which data samples are detected. By way of example, a sampling rate of 1 microsecond corresponds to one current detection occurring every microsecond, and this sampling rate may be used in the current application. 
         [0031]    After the collect injector closing data step  218 , the process moves to a check step  220  to determine whether data collection is complete. If data collection is not complete, the process  200  loops back around to the collect injector closing data step  218 , in the collection window  116 . After it is determined in step  220  that data collection is complete, the process  200  moves to step  222 . 
         [0032]    In order to reduce the detected current data to a manageable condition and amount, the detected data may be filtered by the controller  50  to remove high frequency noise using a standard digital filter. In example utilizing a high sampling rate, the data may be further downsampled using known downsampling techniques to reduce the amount of data in the current profile. The filtered and downsampled data forms an injector closing current profile, such as the current profiles  110 ,  120  illustrated in  FIGS. 2A-2B . The processed injector closing current profile data is stored in the injector closing data buffer. Once the current profile has been determined, the controller  50 , or another device, applies a slope discriminator process to the current profile in an apply slope discriminator step  222 . Because the injector closing current profile data has been stored in the buffer, the steps  222 ,  224  and  226  can be executed according to systems task scheduling. The process performed by the slope discriminator is described below in greater detail with regards to  FIG. 4 . 
         [0033]    The slope discriminator may utilize nonlinear digital filtering techniques to distinguish the difference in the slope between a stuck injector and a non-stuck injector during closing time. Thus, after the step  222  of applying the slope discriminator, the process  200  moves on to determine the injector closing time (if not stuck) and/or the stuck status of being stuck or not stuck in step  224 . 
         [0034]    Once the closing time and/or stuck status of the injector  40  has been determined, the controller  50  reports the stuck status and/or the closing time in a report closing time and status step  226 . The reporting can be to another separate controller, a subprogram within the controller  50 , or a diagnostic system, such as an OBD (On-Board Diagnostic) or OBDII (On-Board Diagnostic II). Alternately, the closing time and status can be reported to any other system where the opening time and status of the injector  40  is needed. 
         [0035]    With continued reference to  FIG. 1 ,  FIG. 4  is a graph  300  illustrating a current profile  302  of an injector  40 , which shows the principles of the slope discriminator. As described above, in order to determine the current profile  302 , the controller  50  may utilize a nonlinear digital filtering technique to remove noise and downsamples the data to decrease the amount of data, thereby decreasing the data buffer size. Once the current profile  302  has been determined, the controller  50  applies the slope discriminator. 
         [0036]    The slope discriminator utilizes a modified median filter to determine a slope of the injector profile  302 . The slope discriminator processes the current profile  302  entry by entry, replacing each entry with the centered value of neighboring entries falling within a median window  320  to determine a median current profile. The entries within the median window  320  are then sorted in increasing value. The slope discriminator further processes the current profile  302  entry by entry, replacing each entry with the mean value of neighboring entries falling with a mean window  310  to determine a mean current profile. 
         [0037]    As can be seen in  FIG. 4 , the mean window  310  is a smaller window (encompasses fewer neighboring data points) than the median window  320 . Further, the mean window  310  falls entirely within the median window  320 . The starting edge of the mean window  310  may be offset from the starting edge of the median window  320  by an offset value. The size of both the mean window  310  and the median window  320 , as well as the size of the offset, are calibration values that can be experimentally or mathematically determined for a particular selective catalytic reduction injector  40  by one of skill in the art having the benefit of this disclosure. Due to the required size of the windows  310 ,  320 , the initial output of the slope reflection detection process occurs at point  340 , and not at a start time  304  of the current profile  302 . In the illustrated example of  FIG. 4  the initial output  340  of the slope discriminator occurs at the end point of the initial mean window  310 . 
         [0038]    The value of the output at point  340 , and all output values  302 , is determined by the following relationship: 
         [0000]      Output=median term*gain factor for median term−(mean term*gain factor for mean term−offset term);
 
         [0039]    where Output is the output value; 
         [0040]    median term is the center value of the median window  320 , which is calculated in sliding window  320  entry by entry; 
         [0041]    mean term is the mean value of the mean window  310 , which is calculated in sliding window  310  entry by entry; 
         [0000]      gain factor for median term=1+abs(median term−mean term); and
 
         [0000]      gain factor for mean term=1−abs(median term−mean term);
 
         [0000]      offset term=abs(median term−mean term)/length of median sliding window  320 .
 
         [0042]    As known in mathematics, “abs” is the absolute value function. Thus, the gain factors are variable gain factors, which depend on the difference between the median term and the mean term. The gain factor for the median term is always greater than or equal to one; and the gain factor for the mean term is always less than or equal to one. The offset term is also related to the difference between the mean term and the median term. 
         [0043]    As a result of the above relationships, the bigger the difference between the value of the median window  320  and the mean window  310 , the greater the factor gain factor for the median term will be. Similarly, the bigger the difference between the value of the median window  320  and the mean window  310 , the smaller factor gain factor for the mean term will be. This difference in the gain factors results in an output term that greatly magnifies the slope, thus showing a separation between the stuck injector current profile and the non-stuck injector closing profile at closing time. 
         [0044]    With continued reference to  FIGS. 1 and 4 ,  FIG. 5  illustrates an output graph  400  showing outputs of the slope discriminator for non-stuck and stuck SCR injectors  40 . The outputs for a normal, non-stuck injector are graphed at line  410 , and the outputs for a stuck injector are graphed at line  420 . The location of the maximum value  422  of the normal injector output plot  410  indicates that the SCR injection needle is fully closed. Since there is a large separation between the stuck and non-stuck profiles  420 ,  410 , a predetermined calibrated threshold  424  can be determined, to which the profiles  410 ,  420  can be compared. For example, if any of the profile  410 ,  420  is above the threshold  424 , then the SCR injector can be determined to be non-stuck; and if any of the profile  410 ,  420  is below the threshold  424 , the SCR injector can be determined to be closed. Based on this difference, the controller  50  can detect when the selective catalytic reduction injector  40  is stuck (i.e. when any of the output profile  410 ,  420  exceeds the predetermined threshold  424 ). 
         [0045]    The precise injector closing time can be easily calculated based on the location of the maximum value  422 . The precise closing time of the selective catalytic reduction injector  40  is precise to within a time period of the downsampled data rate. Thus, if the downsampled data rate is 1 microsecond, the time of the maximum value point  422  can fall within 1 microsecond of the actual fully open time of the selective catalytic reduction injector  40 , depending on the system tolerances and slope discriminator filter calibration. 
         [0046]    By utilizing the above described process, the controller  50  can determine the precise closing time of a selective catalytic reduction injector and whether the selective catalytic reduction injector is stuck or non-stuck. As can be appreciated by one of skill in the art having the benefit of this disclosure, the above described process can be applied to any number of injector valves exhibiting similar slope reflection characteristics, and is not limited to selective catalytic reduction injectors. 
         [0047]    It is further understood that any of the above described concepts can be used alone or in combination with any or all of the other above described concepts. Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.