Abstract:
A method to control a wastegate valve actuator by determining a NOx deadband with hysteresis for an engine controller is disclosed. This NOx deadband defines an outer band and an inner band. In this method, a NOx sensor keep sensing the NOx level in the exhaust gases and accordingly the engine controller sends commands to the wastegate valve actuator. At the NOx level less than inner band and the outer band, engine controller remains at deactivated state. When the NOx level goes outside the outer band, the engine controller sends dither command to the wastegate valve actuator and continues to send the dither command until the NOx level does not reach inside the NOx inner band. This method improves life of the wastegate valve assembly as separate activating and deactivating bands for the engine controller ensures less command fluctuations for the wastegate valve actuator.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates to a wastegate valve of an exhaust system of an engine. More particularly, the present disclosure relates to a method of controlling a wastegate valve actuator of an exhaust system based on NOx emissions in the engine. 
       BACKGROUND 
       [0002]    Exhaust gases released by the internal combustion engines contains a complex mixture of air pollutants. These air pollutants may include solid unburnt Hydrocarbon particles, carbon mono oxide (CO), oxides of nitrogen (NOx), and the like. NOx emission standards have grown more stringent because NOx is the most harmful among all air pollutants in the exhaust of the internal combustion engine. Different NOx emission control techniques, such as the engine controller and the intake manifold pressure control by operating the wastegate valve are being adapted. These mechanisms result in significant control of the NOx emissions. 
         [0003]    Continuous commands, from the engine controller, to operate the wastegate valve thereby to adjust the air-fuel ratio, produce oscillations in the wastegate valve. To control these oscillations, continuous dithering is applied to the wastegate valve. Continuous dithering may damage the waste gate valve actuation assembly and reduces the component&#39;s lifespan. 
         [0004]    U.S. Pat. No. 7,168,411 discloses an engine controller using an active wastegate valve to adjust the air-fuel ratio to achieve desired NOx set point based on the intake manifold pressure. 
         [0005]    Given description covers one or more above-mentioned problems and discloses a method to solve the problem. 
       SUMMARY OF THE DISCLOSURE 
       [0006]    Various aspects of the present disclosure describe a method to control a wastegate valve actuator. This method incorporates, determining a NOx level deadband with predetermined hysteresis values for the engine controller. Based on the NOx level with respect to the NOx level deadband, the wastegate valve actuator receives commands to control the wastegate valve from the engine controller. The deadband includes two bands i.e. an inner band and an outer band. The NOx level determined by a NOx sensor is compared with the inner band and the outer band by the engine controller. At the NOx level less than the inner hand, the engine controller gets deactivated and sends a constant output to the wastegate valve actuator. In this case, the wastegate valve remains at its previous position with no oscillations and thus no dither command is required. If NOx level goes outside the inner band and remains inside the outer band, the deactivated state of the controller is maintained and no dither command is sent to the wastegate valve actuator. At NOx level outside the outer band, the engine controller gets activated and enables the dither command for the wastegate valve actuator. The wastegate valve actuator, during changing position of the wastegate valve, applies dithering to the wastegate valve and control oscillations, With change in position of the wastegate valve, the turbocharger unit increases or reduces the air quantity in the air inlet manifold, reducing or increasing the NOx level. After the NOx level reduction, at NOx level more than the inner hand and less than the outer band, activated state of the engine controller is maintained and the dither command is continuously sent to the wastegate valve actuator to avoid command fluctuations in case of oscillating NOx levels. The engine controller gets deactivated and does not send the dither command to the wastegate valve actuator as the NOx level reaches in the inner band. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a schematic view, showing a power generation assembly, in accordance with the concepts of the present disclosure; 
           [0008]      FIG. 2  is a schematic showing a turbocharger assembly connected to an engine system of  FIG. 1  and a wastegate valve assembly of the power generation system, in accordance with the concepts of the present disclosure; 
           [0009]      FIG. 3  is a graphical representation of a NOx deadhand with hysteresis pre-stored in an engine controller, with the corresponding position of a wastegate valve of the wastegate valve assembly, in accordance with the concepts of the present disclosure; and 
           [0010]      FIG. 4  is a flow chart for a method to control a wastegate valve actuator of the wastegate valve assembly of  FIG. 2 , in accordance with the concepts of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    Referring to  FIG. 1 , a power generation assembly of a vehicle is shown, referred to as a power assembly  10  hereinafter. The power assembly  10  includes a fuel rail  12 , an engine system  14 , a turbocharger assembly  16 , and a wastegate assembly  18 . The fuel rail  12  supplies fuel to the engine system  14 . 
         [0012]    The engine system  14  includes an intake manifold  20 , a cylinder  22 , and an exhaust manifold  24 . The cylinder  22  may include a pre-combustion chamber (not show in figure) and/or a combustion chamber (not shown in figure) facilitating combustion of air-fuel mixture received through the intake manifold  20 . The exhaust manifold  24  directs exhaust gases, generated during the combustion in the cylinder  22 . 
         [0013]    The turbocharger assembly  16  supplies compressed air to the engine system  14  for the air-fuel mixture, via the intake manifold  20 . The turbocharger assembly  16  includes a turbocharger turbine  26  coupled with a turbocharger compressor  28 . The turbocharger turbine  26  is powered by exhaust gases flowing out of the exhaust manifold  24  of the engine system  14 . 
         [0014]    The wastegate assembly  18  includes a wastegate valve  30  and a wastegate valve actuator  32 . The wastegate valve  30  of the wastegate assembly  18  regulates flow of exhaust gases into the turbocharger turbine  26 . In one embodiment, the wastegate valve  30  can be a diverter valve or a spool valve configured to regulate the flow of exhaust gases to the turbocharger assembly  16  by diverting the exhaust gases to the turbocharger turbine  26  or vent the exhaust gases to the atmosphere/an exhaust after treatment system. The flow of exhaust gases is controlled by controlling the position of a gate element (not shown in figures) of the wastegate valve  30 . The gate element (not shown in figures) of the wastegate valve  30  is actuated by the wastegate valve actuator  32 . The wastegate valve actuator  32  is connected to the gate element and controls its position. In one embodiment, the wastegate valve actuator  32  can be a stepper motor, or a solenoid controlled actuation mechanism configured to selectively adjust the position, and opening/closing of the gate element of the wastegate valve  30 . The wastegate valve  30  directs exhaust gases towards the turbocharger turbine  26  as well as vents it to the atmosphere  34  depending on the position of the gate element. The exhaust gases flowing out of the wastegate valve  30  may be recirculated into the intake manifold  20  by an EGR system (not shown in the figure) or may be directed to an after-treatment system (not shown in the figure), before emitting into the atmosphere. 
         [0015]    Referring to  FIG. 2 , the turbocharger assembly  16  is shown connected to the engine system  14  via a NOx sensor  36 , an engine controller  38  and the wastegate assembly  18 . The NOx sensor  36  is mounted downstream of the exhaust manifold  24 . As an exemplary embodiment of the concept, the NOx sensor  36  is mounted downstream of the turbocharger turbine  26  and the wastegate valve  30 . The NOx sensor  36  determines the NOx level  42  in the exhaust gases flowing out of the exhaust manifold  24 . 
         [0016]    The engine controller  38  receives a determined value of the NOx level  42  (shown in  FIG. 3 ) from the NOx sensor  36  and generates a control command. The control command is communicated to the wastegate valve actuator  32  accordingly. Based on the control command received from the engine controller  38 , the wastegate valve actuator  32  adjusts the position of the wastegate valve  30  and controls oscillations by dithering. 
         [0017]    It may be noted that the determined value of NOx level  42  in the exhaust gases governs the position of the gate element in the wastegate valve  30 . In one embodiment, if a high value of NOx level  42  is determined by the NOx sensor  36 , the command signal may cause the gate element of the wastegate valve  30  to close more and divert more exhaust gases towards the turbocharger turbine  26 . This may lead to increase in the speed of the turbocharger turbine  26  and hence more air is provided to the cylinder  22  by the turbocharger compressor  28 . 
         [0018]    It may be noted that in one embodiment, the wastegate assembly  18  can be in-built within the turbocharger assembly  16 . In another embodiment, the wastegate assembly  18  can be an external standalone unit functioning in communication with the engine system  14  and the turbocharger assembly  16 . In the current disclosure either of the two in-built or standalone wastegate assembly  18  is compatible. 
         [0019]    Further  FIG. 3  shows a graph  40 , describing a NOx deadband with hysteresis. The graph  40  elaborates the corresponding position of the wastegate valve  30  with the changing NOx levels. 
         [0020]    The vertical axis (Y-axis) of the graph  40  indicates the NOx level  42  in the exhaust gases as determined by the NOx sensor  36 . The horizontal axis (X-axis) indicates the time as the NOx level  42  changes during running of the engine system  14 . A solid line  42  indicates the changing value of the NOx level  42  as determined by the NOx sensor  36  over duration of time. 
         [0021]    A point on the vertical axis indicates a standard NOx level  44 . The standard NOx level  44  is the expected level of NOx as per the type of engine system  14 . In other words, during normal operation, the engine system  14  is expecting to produce NOx as per the standard NOx level  44 . On either side of the standard NOx level  44 , a NOx deadband with hysteresis is provided. The NOx deadband includes a NOx inner band  46  and a NOx outer band  48 . The NOx inner band  46  stretches on both sides of the standard NOx level  44 . The NOx inner band  46  is further enveloped by the NOx outer band  48 . The outer band stretches starting from the outer edge of the NOx inner band  46 . As shown in the graph  40 , the NOx inner band  46  expanses a range area between  46   a  and  46   b  and the NOx outer band  48  expanses a range area between  48   a  and  48   b.  The NOx inner band  46   a  and  46   b  and the NOx outer band  48   a  and  48   b  are determined with respect to a standard NOx level  44  as per NOx regulations. 
         [0022]    The total expanse of the NOx inner band  46  and the NOx outer band  48  is defined as the NOx deadband with hysteresis. 
         [0023]    Further, a chart  40   a  indicating the position of the gate element of the wastegate valve  30  is shown below the graph  40 . The position of the gate element, corresponding to the NOx level  42  in the graph  40 , is indicated by a solid line  50 . A section  50   a  of the solid line  50  indicates no movement of the gate element, whereas the section  50   b  of the solid line  50  indicates the opening or closing of the gate element. 
         [0024]      FIG. 3  in conjunction with  FIG. 2 , indicate the changing value of the NOx level  42 , as determined by the NOx sensor  36 . The determined value of the NOx in the exhaust gases is further communicated to the engine controller  38 . As shown, the NOx level  42  is indicated on the graph  40  by a section  42   a,    42   b,    42   bb,  and  42   c  of the solid line  42 . Further as shown, the section  42   a  indicates the determined NOx level  42  within the NOx inner band  46 , the section  42   b  and  42   bb  indicates the determined NOx level  42  within the NOx outer band  48 , and the section  42   c  indicates the determined NOx level  42  beyond the NOx outer band  48 . The determined value of the NOx level  42  is compared to the range area of the NOx inner band  46   a  and  46   h  and NOx outer band  48   a  and  48   b.  The engine controller  38  then generates the command signal for the wastegate valve actuator  32  to accordingly control oscillation of the wastegate valve  30 . The control signal may correspond to freezing the engine controller  38  at a deactivated state and disabling a dither command to the wastegate valve actuator  32 , when the NOx level  42  is within the NOx inner band  46 . This is depicted by the section  42   a  on graph  40  and section  50   a.  on the chart  40   a.  Further, the control signal may correspond to maintaining a preceding state of the engine controller  38  and disabling the dither command to the wastegate valve actuator  32  when the NOx level  42  is more than the NOx inner band  46  and less than the NOx outer band  48 . This is depicted by section  42   b  and  42   bb  on the graph  40 , and section  50   a  on the chart  40   a.  Furthermore, the control signal may also correspond to unfreezing the engine controller  38  from the deactivated state to an activated state at the NOx level  42  more than the NOx outer band  48  and enabling the dither command to the wastegate valve actuator  32 . This state is depicted by the section  42   c  and  50   b  of the graph  40  and the chart  40   a,  respectively. 
         [0025]    Referring to  FIG. 4 , a flow chart for a method  52  to control the wastegate valve actuator  32  of the wastegate assembly  18  is described. The method  52  includes a step  54  to determine the NOx inner band  46  with range area between  46   a,    46   h  and the NOx outer band  48  with range area between  48   a  and  48   b  with respect to the standard NOx level  44 . The determined NOx inner band  46  and the NOx outer band  48  are pre-stored in the engine controller  38 . In other words, the engine controller  38  may determine the range area of the NOx inner band  46  and the NOx outer band  48  and store for a later reference. In one embodiment, the engine controller  38  may include a memory unit (not shown in figures) to store the range area of the NOx inner band  46  and the NOx outer band  48 . It may be noted that the range area of the NOx inner band  46  and the NOx outer band  48  may be updated and uploaded by an operator of the engine system  14 . 
         [0026]    At step  56 , the NOx sensor  36  determines the NOx level  42  including the NOx level  42   a.    42   b,    42   bb,  or  42   c  in the exhaust gases flowing out of the exhaust manifold  24 . The NOx sensor  36  communicates the determined NOx level  42 ,  42   a,    42   b,    42   bb,  or  42   c  to the engine controller  38  for comparing as per the stored values in the NOx deadband. with hysteresis. 
         [0027]    At step  58 , the engine controller  38  compares the NOx level  42 ,  42   a,    42   b,    42   bb,  or  42   c  with the NOx inner band  46 . If the NOx level  42   a  is between the NOx inner band  46   a  and  46   b  of the NOx inner band  46 , then the method  52  proceeds to step  60 . If the NOx level  42   b  or  42   bb  is outside the NOx inner band  46   a  and  46   b,  then the method  52  proceeds to step  62 . 
         [0028]    At step  60 , the engine controller  38  is deactivated and the dither command for the wastegate valve actuator  32  is disabled. 
         [0029]    At step  62 , the engine controller  38  compares the NOx value  42   b  or  42   bb  with the NOx outer band  48 . If the NOx level  42   h  or  42   bb  exceeds the NOx inner band  46   a  and  46   b  of the NOx inner band  46  and is within the NOx outer band  48   a  and  48   b  of the NOx outer band  48  then the method  52  proceeds to step  64 , else step  66  is followed. 
         [0030]    At step  64 , the engine controller  38  remains in a preceding state, that is, remain activated if the engine controller  38  was activated earlier or remain deactivated if the engine controller  38  was deactivated. 
         [0031]    In the event of NOx level  42   c  exceeding the NOx outer band  48   a  and  48   b  of the NOx outer band  48 , the method  52  follows the step  66  and the engine controller  38  is activated and enables the dither command for the wastegate valve actuator  32 . The method  52  to control the wastegate valve actuator  32  based on the determined value of the NOx level  42 ,  42   a,    42   b,    42   bb,  and  42   c  is further explained in description below. 
       Industrial Applicability 
       [0032]    As shown in  FIG. 1 , the fuel rail  12  supplies the fuel to the engine system  14  for ignition of a flame in the cylinder  22 . The flame generated in the pre-combustion chamber (not shown in the figures) of the cylinder  22  expands in the combustion chamber (not shown in the figures) and combustion of the air-fuel mixture occurs. The air-fuel mixture flows into the cylinder  22 , through the intake manifold  20 , The intake manifold  20  receives the fuel from the fuel rail  12  and the intake air from the turbocharger assembly  16 . The exhaust gases produced during the combustion exits the cylinder  22  from the exhaust manifold  24 . The NOx sensor  36  is mounted downstream of the exhaust manifold  24 . As the preferred exemplary embodiment. the NOx sensor  36  is mounted downstream of the turbocharger turbine  26  and the wastegate valve  30 . The NOx sensor  36  is configured to determine the value of the NOx level  42  in the exhaust gases exiting the cylinder  22  via the exhaust manifold  24 . 
         [0033]    The exhaust gases exiting from the exhaust manifold  24  is directed to the wastegate valve  30  of the wastegate assembly  18 . The wastegate valve  30  regulates the flow of the exhaust gases towards the atmosphere  34  as well as to the turbocharger assembly  16 . The wastegate valve actuator  32  controls the opening and closing i.e. the position of the gate element of the wastegate valve  30 . The exhaust gases flowing through the wastegate valve  30  powers the turbocharger turbine  26  that generates compression pressure at the turbocharger compressor  28 . With changing compression pressure, the density of the intake air supplied to the cylinder  22  changes and richness of air-fuel mixture varies thereby affecting the NOx level  42  in the exhaust gases. 
         [0034]    Referring to  FIG. 2  and  FIG. 3 , the wastegate valve actuator  32  is linked to the engine controller  38 . The engine controller  38  is configured to receive determined value of NOx level  42 ,  42   a,    42   b,    42   bb,  and  42   c  from the NOx sensor  36 . Further, the NOx inner band  46   a  and  46   b  and the NOx outer band  48   a  and  48   b  are pre-stored in the engine controller  38 . On receiving the determined value of NOx level  42  from the NOx sensor  36 , the engine controller  38  compares the NOx level  42 ,  42   a,    42   b,    42   bb,  and  42   c  with the NOx inner band  46  and the NOx outer band  48 . Thereafter, the engine controller  38  communicates a control signal accordingly to the wastegate valve actuator  32  to control the wastegate valve  30 . 
         [0035]    Further referring to  FIG. 4  in view of  FIG. 2  and  FIG. 3 , the enabling function of the present concept is described by the method  52 . The control signal from the engine controller  38  may correspond to freezing the engine controller  38  at a deactivated state and disabling a dither command to the wastegate valve actuator  32 . When the NOx level  42  is within the range of the NOx inner band  46 . This is depicted by the section  42   a  of the section  40  and  50   a  of the chart  40   a.  Further, the control signal may correspond to maintaining a preceding state of the engine controller  38  and disabling the dither command to the wastegate valve actuator  32  when the NOx level  42  is more than the NOx inner band  46  and within the NOx outer band  48   a  and  48   b  of the NOx outer band  48 . This is depicted by section  42   bb  and  50   a.  In other words, the engine controller  38  continues to remain in the frozen state and disables any dither command, when the determined value of the NOx level  42  exceeds the NOx inner band  46 , but is within the NOx outer band  48 . Furthermore, the control signal may also correspond to unfreezing the engine controller  38  from the deactivated state to an activated state at the NOx level  42  more than the NOx outer band  48  and enabling the dither command to the wastegate valve actuator  32 . This state is depicted by the section  42   c  and  50   b.    
         [0036]    At NOx level  42   a,  the NOx level  42  of the exhaust gases is between the NOx inner band  46   a  and  46   b.  Hence, at NOx level  42   a,  the engine controller  38  is deactivated and does not send any command to the wastegate valve  30 . Thereby, the wastegate valve actuator  32  does not change the position of the wastegate valve  30  (that is, the wastegate valve  30  remains in a stable position  48   a ). With NOx level  42   b,  outside the NOx inner band  46  and inside the NOx outer band  48   a  and  48   b  of the NOx outer band  48 , the engine controller  38  remains deactivated and the constant command is sent to the wastegate valve actuator  32 . 
         [0037]    As the NOx level  42   c  increases beyond the NOx outer band  48 , the engine controller  38  becomes activate, and sends the dither command to the wastegate valve actuator  32 . The wastegate valve actuator  32  applies dithering to control the oscillations of the wastegate valve  30  as long as the NOx level  42  remains outside the NOx outer band  48 . This is depicted by the changing position section  50   b  in the chart  40   a.  With controlled oscillations and changed exhaust gas flow in the turbocharger turbine  26 , a lean air-fuel mixture is supplied to the engine that reduces the NOx level  42  in the exhaust gases. 
         [0038]    With reducing NOx levels, the NOx sensor  36  again detects the NOx level  42   bb  and the engine controller  38  compares the NOx level  42   bb  with the NOx inner band  46  and the NOx outer band  48 . As the NOx level  42   bb  is inside the NOx outer band  48   a  and  48   b,  but remains outside the NOx inner band  46   a  and  46   b,  the engine controller  38  remains activated and continue to send dither commands to the wastegate valve actuator  32  until the NOx level  42   a  is achieved. 
         [0039]    The many features and advantages of the disclosure are apparent from the detailed specification, and thus, it is intended by the appended claims to cover all such features and advantages of the disclosure that fall within the true spirit and scope thereof. Further, since numerous modifications and variations will readily occur to those skilled in the art. It is not desired to limit the disclosure to the exact construction and operation illustrated and described, and, accordingly, all suitable modifications and equivalents may be resorted to that fall within the scope of the disclosure.