Abstract:
A control system comprising a current control module and a force control module. The current control module selectively supplies a current to a turbine bypass valve (TBV) to adjust the TBV to a predetermined position. The force control module selectively adjusts the current in response to a determination that an actual TBV position is less than a predetermined distance from the predetermined position.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/084,816, filed on Jul. 30, 2008. 
     
    
     FIELD 
       [0002]    The present disclosure relates to valve position control and more particularly to valve position control in an engine system. 
       BACKGROUND 
       [0003]    The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
         [0004]    An engine combusts an air/fuel mixture to produce drive torque for a vehicle. Opening of a throttle valve is regulated to control the amount of air drawn into an intake manifold. Air from the intake manifold is drawn into cylinders. A fuel system may inject fuel into the intake manifold or may inject fuel directly into the cylinders. 
         [0005]    The byproducts of combustion are exhausted from the vehicle via an exhaust manifold. A high-pressure (HP) turbocharger and a low-pressure (LP) turbocharger are powered by exhaust gases flowing through the exhaust manifold and provide an HP compressed air charge and an LP compressed air charge, respectively, to the intake manifold. A turbine bypass valve (TBV) may allow exhaust gas to bypass the HP turbocharger, thereby reducing the restriction imposed by the HP turbocharger, but increasing the total amount of air charge provided to the intake manifold. 
         [0006]    Engine control systems have been developed to control the TBV. Traditional engine control systems, however, do not control the TBV as accurately as desired. For example, an engine control system may determine a position of the TBV using a proportional-integral-derivative (PID) control scheme and a TBV position signal measured by a TBV position sensor. However, variations in the TBV position signal, exhaust pressure, PID control inaccuracies, and/or thermal deformation of the TBV may cause different leaks of the TBV at the closed position. The different leaks result in incorrect calculations and control of exhaust gas that flows through the turbochargers and of the output of the turbochargers, decreasing their efficiency. 
       SUMMARY 
       [0007]    A control system comprising a current control module and a force control module. The current control module selectively supplies a current to a turbine bypass valve (TBV) to adjust the TBV to a predetermined position. The force control module selectively adjusts the current in response to a determination that an actual TBV position is less than a predetermined distance from the predetermined position. 
         [0008]    In other features, the predetermined position is one of a predetermined fully open position and a predetermined fully closed position. 
         [0009]    In still other features, the force control module selectively increases the current in response to the determination when the predetermined position is the predetermined fully closed position. 
         [0010]    In further features, the force control module increases the current starting a predetermined delay period after the determination. 
         [0011]    In still further features, the current control module decreases the current after the increase when a desired TBV position is less than a second predetermined position that is less closed than the predetermined position. 
         [0012]    In other features, the current control module decreases the current after the increase when the actual TBV position is less than a second predetermined position that is less closed than the predetermined position. 
         [0013]    In still other features, the force control module decreases the current in response to the determination when the predetermined position is the predetermined fully open position. 
         [0014]    In further features, the force control module decreases the current starting a predetermined delay period after the determination. 
         [0015]    In still further features, the current control module increases the current after the decrease when a desired TBV position is greater than a second predetermined position that is less open than the predetermined position. 
         [0016]    In other features, the current control module increases the current after the decrease when the actual TBV position is greater than a second predetermined position that is less open than the predetermined position. 
         [0017]    A control method comprises selectively supplying a current to a turbine bypass valve (TBV) to adjust the TBV to a predetermined position and selectively adjusting the current in response to a determination that an actual TBV position is less than a predetermined distance from the predetermined position. 
         [0018]    In other features, the predetermined position is one of a predetermined fully open position and a predetermined fully closed position. 
         [0019]    In still other features, the control method further comprises selectively increasing the current in response to the determination when the predetermined position is the predetermined fully closed position. 
         [0020]    In further features, the control method further comprises increasing the current starting a predetermined delay period after the determination. 
         [0021]    In still further features, the control method further comprises decreasing the current after the increasing the current when a desired TBV position is less than a second predetermined position that is less closed than the predetermined position. 
         [0022]    In other features, the control method further comprises decreasing the current after the increasing the current when the actual TBV position is less than a second predetermined position that is less closed than the predetermined position. 
         [0023]    In still other features, the control method further comprises decreasing the current in response to the determination when the predetermined position is the predetermined fully open position. 
         [0024]    In further features, the control method further comprises decreasing the current starting a predetermined delay period after the determination. 
         [0025]    In still further features, the control method further comprises increasing the current after the decreasing the current when a desired TBV position is greater than a second predetermined position that is less open than the predetermined position. 
         [0026]    In other features, the control method further comprises increasing the current after the decreasing the current when the actual TBV position is greater than a second predetermined position that is less open than the predetermined position. 
         [0027]    Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]    The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0029]      FIG. 1  is a functional block diagram of an exemplary engine system according to the principles of the present disclosure; 
           [0030]      FIG. 2  is a functional block diagram of an exemplary engine control module according to the principles of the present disclosure; 
           [0031]      FIG. 3  is a functional block diagram of an exemplary force control module according to the principles of the present disclosure; 
           [0032]      FIG. 4A  is a flowchart depicting exemplary steps of an engine control method according to the principles of the present disclosure; 
           [0033]      FIG. 4B  is a portion of the flowchart of  FIG. 4A ; 
           [0034]      FIG. 5  is a graph depicting three operating modes of the engine control module that are predetermined based on an engine load and an engine speed according to the principles of the present disclosure; and 
           [0035]      FIG. 6  is a graph depicting a time versus a desired current, an Q output, a delayed Q output, an Q′ output, a filtered Q′ output, and a position control module disable signal of the engine control module according to the principles of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0036]    The following description is merely exemplary in nature and is in no way intended to limit the disclosure, 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 phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical or. It should be understood that steps within a method may be executed in different order without altering the principles of the present disclosure. 
         [0037]    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 execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. 
         [0038]    To accurately control a turbine bypass valve (TBV) of an engine system, the engine control system of the present disclosure includes a force control module. The force control module determines whether the engine control system is to be set to a force close mode, set to a force open mode, or reset from the force close mode or the force open mode based on a desired position and an actual position of the TBV. When the engine control system is set to the force close mode, the force control module accurately determines a force position that forces the TBV to be fully closed and disables a proportional-integral-derivative (PID) control scheme that typically determines the position of the TBV. When the engine control system is set to the force open mode, the force control module accurately determines the force position that forces the TBV to be fully open and disables the PID control scheme. When the engine control system is reset from the force close mode or the force open mode, the force control module determines the force position to be an initial position for the PID control scheme and quickly enables the PID control scheme. 
         [0039]    Referring now to  FIG. 1 , a functional block diagram of an exemplary engine system  100  is shown. The engine system  100  includes an engine  102  that combusts an air/fuel mixture to produce drive torque for a vehicle. For example only, the engine  102  may include, but is not limited to, an internal combustion engine and/or a diesel engine. The engine  102  includes cylinders  104 . For illustration purposes, six cylinders are shown. For example only, the engine  102  may include, but is not limited to, 2, 3, 4, 5, 6, 8, 10, and/or 12 cylinders. 
         [0040]    The engine system  100  further includes an intake manifold  106 , a throttle valve  108 , an engine control module  110 , a throttle actuator module  112 , a fuel system  114 , an ignition system  116 , and an exhaust manifold  118 . The engine system  100  further includes a high-pressure (HP) turbocharger  120 , a low-pressure (LP) turbocharger  122 , an outlet  124 , an outlet  126 , an inlet  128 , a wastegate  132 , a boost actuator module  134 , and an engine speed (RPM) sensor  136 . The engine system  100  further includes an TBV  138  and a solenoid actuator module  140 . 
         [0041]    Air is drawn into the intake manifold  106  through the throttle valve  108 . The engine control module  110  commands the throttle actuator module  112  to regulate opening of the throttle valve  108  to control the amount of air drawn into the intake manifold  106 . Air from the intake manifold  106  is drawn into the cylinders  104 . 
         [0042]    The engine control module  110  controls the amount of fuel injected by the fuel system  114 . The fuel system  114  may inject fuel into the intake manifold  106  at a central location or may inject fuel into the intake manifold  106  at multiple locations. Alternatively, the fuel system  114  may inject fuel directly into the cylinders  104 . 
         [0043]    The injected fuel mixes with the air and creates the air/fuel mixture in the cylinders  104 . Pistons (not shown) within the cylinders  104  compress the air/fuel mixture. Based upon a signal from the engine control module  110 , the ignition system  116  ignites the air/fuel mixture. In various engine systems, the air/fuel mixture may be ignited by heat produced by compression. 
         [0044]    The combustion of the air/fuel mixture drives the pistons down, thereby driving a crankshaft (not shown). The pistons then begin moving up again and expel the byproducts of combustion through the exhaust manifold  118 . The byproducts of combustion are exhausted from the vehicle via the exhaust manifold  118 . 
         [0045]    The HP turbocharger  120  and the LP turbocharger  122  are powered by exhaust gases flowing through the exhaust manifold  118  and provide an HP compressed air charge and an LP compressed air charge, respectively, to the intake manifold  106 . The HP compressed air charge and the LP compressed air charge are provided to the intake manifold  106  through the outlets  124  and  126 , respectively. The LP turbocharger  122  may also supply air for compression to the HP turbocharger  120  via the outlet  126 . The total compressed air charge may be provided upstream of the throttle valve  108 . The air used to produce the compressed air charges may be drawn in via the inlet  128 . 
         [0046]    The wastegate  132  may allow exhaust gas to bypass the LP turbocharger  122  and/or the HP turbocharger  120 , thereby reducing the output (i.e., boost) of the LP turbocharger  122  and/or the HP turbocharger  120 . The engine control module  110  controls the LP turbocharger  122  and/or the HP turbocharger  120  via the boost actuator module  134 . The boost actuator module  134  may modulate the boost of the LP turbocharger  122  and/or the HP turbocharger  120  by controlling, for example, the position of the wastegate  132  and/or the turbocharger positions. For example only, the boost actuator module  134  may control vane or nozzle position of the turbochargers  120  and  122  when the LP turbocharger  122  and/or the HP turbocharger  120  is a variable geometry turbocharger (VGT) or a variable nozzle turbocharger (VNT), respectively. 
         [0047]    The engine control module  110  regulates operation of the engine system  100  based on various engine operating parameters. For example, the engine control module  110  controls and communicates with the engine  102 . The control module  110  further communicates with the RPM sensor  136  that generates an RPM signal based on a speed of the engine  102 . The RPM sensor  136  may be located within the engine  102  or at other locations, such as on the crankshaft (not shown). 
         [0048]    The TBV  138  may allow exhaust gas to bypass the HP turbocharger  120 , thereby reducing the boost of the HP turbocharger  120 . The TBV  138  includes a solenoid valve that is controlled by running or stopping an electrical current through a solenoid, thus opening or closing the solenoid valve. The engine control module  110  commands the solenoid actuator module  140  to regulate opening of the TBV  138  to control the amount of exhaust gas released to the HP turbocharger  120 . In addition, the solenoid actuator module  140  may measure the position of the TBV  138  and output a signal based on the position to the engine control module  110 . The engine control module  110  determines the commands to the solenoid actuator module  140  as described herein. 
         [0049]    Referring now to  FIG. 2 , a functional block diagram of the engine control module  110  is shown. The engine control module  110  includes a desired position determination module  202 , a subtraction module  204 , a position control module  206 , a force control module  208 , a position-to-current conversion module  210 , a summation module  212 , and a current control module  214 . The desired position determination module  202  receives data on engine operating conditions from sensors of the engine system  100 . For example only, the engine operating conditions may include, but are not limited, to an engine load, the RPM, an actual pressure within the intake manifold  106  (not shown), and/or a desired pressure within the intake manifold  106  to be reached by the turbochargers  120  and  122  (not shown). The desired position determination module  202  determines a desired position of the TBV  138  based on models that relate the desired position to the engine operating conditions. For example only, a position of the TBV  138  may be in units of percentage and may include a predetermined range of values from −100% (e.g., fully open) to 100% (e.g., fully closed). 
         [0050]    The subtraction module  204  receives the desired position and an actual position of the TBV  138  from the solenoid actuator module  140 . The subtraction module  204  subtracts the actual position from the desired position to determine a position error. The position control module  206  receives the position error and determines a position correction factor based on the position error. The position control module  206  uses a proportional-integral-derivative (PID) control scheme to determine the position correction factor. 
         [0051]    The force control module  208  receives the desired position and the actual position. The force control module  208  determines whether the engine control module  110  is to be set to a force close mode, set to a force open mode, or reset to a position control mode based on the desired and the actual positions. When the engine control module  110  is set to the force close mode, the force control module  208  forces the TBV  138  to fully close by determining a force position based on the actual position and disabling the position control module  206 . When the engine control module  110  is set to the force open mode, the force control module  208  forces the TBV  138  to fully open by determining the force position based on the actual position and disabling the position control module  206 . When the engine control module  110  is reset to the position control mode, the force control module  208  initializes the position control module  206  by determining the force position based on predetermined initial positions and enabling the position control module  206  to control the position of the TBV  138 . 
         [0052]    The position-to-current conversion module  210  receives the position correction factor and the force position. When the position-to-current conversion module  210  receives the force position, the position-to-current conversion module  210  converts the force position to a current correction factor based on a model that relates a position to the current correction factor. Otherwise, the position-to-current conversion module  210  converts the position correction factor to the current correction factor based on the model. For example only, a current through the solenoid of the TBV  138  may be in units of amperes (A) and may include a predetermined range of values from 0 A to 1 A. For example only, when a position of the TBV  138  is equal to zero, a current through the solenoid of the TBV  138  may be equal to 0.5 A. 
         [0053]    The summation module  212  receives the current correction factor and a current offset from data memory (not shown). The current offset is the amount of current when the TBV  138  is at a null position (i.e., an initial position) and is determined based on the type of the solenoid at engine startup. The summation module  212  sums the current correction factor and the current offset to determine a desired current through the solenoid of the TBV  138 . 
         [0054]    The current control module  214  receives a battery voltage from a battery (not shown) that creates the electrical current for the solenoid and the desired current. The current control module  214  determines (i.e., predicts) a pulse-width modulation of a duty cycle of the desired current (i.e., a PWM duty cycle). The current control module  214  determines the PWM duty cycle further based on the battery voltage. The solenoid actuator module  140  receives the PWM duty cycle and regulates opening of the TBV  138  based on the PWM duty cycle. 
         [0055]    Referring now to  FIG. 3 , a functional block diagram of the force control module  208  is shown. The force control module  208  includes a force close determination module  302 , an SR latch  304 , a delay module  306 , a filter module  308 , an initial position selection module  310 , a force position determination module  312 , a force close reset module  314 , and a position control initialization module  316 . The force control module  208  further includes a force open determination module  318 , an SR latch  320 , a delay module  322 , a filter module  324 , an initial position selection module  326 , a force position determination module  328 , a force open reset module  330 , and a position control initialization module  332 . 
         [0056]    The force close determination module  302  receives the desired position and the actual position and determines whether the engine control module  110  is to be set to the force close mode. When the desired position is greater than or equal to a first predetermined position (e.g., 99.9%) and the actual position is greater than a second predetermined position (e.g., 99.5%), the engine control module  110  is determined to be set to the force close mode. The force close determination module  302  sets a set input (i.e., an S) of the SR latch  304  to high. If a reset input (i.e., an R) of the SR latch  304  is low, the SR latch  304  sets an Q output (i.e., an Q) to high and holds an Q′ output (i.e., an Q′), or the complement of Q, at low. 
         [0057]    When the Q output is initially set to high, the delay module  306  receives and delays the Q output for a predetermined time period (e.g., greater than 0.5 seconds). The Q output is delayed to account for TBV response delay and noise in the actual position signal from the solenoid actuator module  140 . This assures that the actual position is stable and that the determination to set the engine control module  110  to the force close mode is accurate. 
         [0058]    The filter module  308  receives and outputs the Q′ output to the initial position selection module  310 . The initial position selection module  310  further receives the actual position. When the Q′ output is low, the initial position selection module  310  determines an initial position for the TBV  138  based on the actual position. 
         [0059]    When the force position determination module  312  receives the delayed Q output that is high, the force position determination module  312  receives the initial position and sets the engine control module  110  to the force close mode. The force position determination module  312  determines the force position based on the initial position and ramps the force position to a predetermined closed holding position (e.g., 40%). The closed holding position corresponds to a position required to fully close the TBV  138  and that is independent of closed position offsets that may be erroneous and/or too excessive in value (i.e., damaging to the TBV  138 ). 
         [0060]    The force position is ramped based on a predetermined positive rate (e.g., 200%/second) or a predetermined negative rate (e.g., −200%/second). The force position is ramped to ensure a smooth transition to the closed holding position. The force position determination module  312  disables the position control module  206  (i.e., sets a proportional gain and a derivative gain of the position control module  206  to zero). 
         [0061]    The force close reset module  314  receives the desired position and the actual position and determines whether the engine control module  110  is to be reset from the force close mode (i.e., set back to the position control mode). When the desired position is less than a third predetermined position (e.g., 99.8%) or the actual position is less than or equal to a fourth predetermined position (e.g., 99%), the engine control module  110  is determined to be reset from the force close mode. The force close reset module  314  sets the reset input to high, and if the set input is low, the SR latch  304  sets the Q output to low and sets the Q′ output to high. 
         [0062]    The force close reset module  314  outputs a signal that indicates whether the desired position is less than the third predetermined position. The position control initialization module  316  receives the signal and determines an initial position for the position control mode (i.e., a position control initial position) based on the signal. When the signal indicates that the desired position is less than the third predetermined position, the position control initialization module  316  determines the position control initial position based on a fifth predetermined position. The fifth predetermined position is less than or equal to a predetermined null position (i.e., a maximum initial position for the position control mode) to open the TBV  138  (e.g., 0%). 
         [0063]    When the signal indicates that the desired position is greater than or equal to the third predetermined position, the position control initial position is determined based on a sixth predetermined position that is greater than or equal to the closed holding position. The sixth predetermined position may be greater than the closed holding position because when the desired position is greater than or equal the third predetermined position but the actual position is less than or equal to the fourth predetermined position, the closed holding position is not enough to hold the TBV  138  closed. For example only, exhaust pressure may be pushing the TBV  138  open. 
         [0064]    When the Q output is set to low, the delay module  306  receives and outputs the Q output to the force position determination module  312 . When the Q′ output is initially set to high, the filter module  308  receives and filters the Q′ output into a pulse of a predetermined time period. The initial position selection module  310  receives the filtered Q′ output and the position control initial position. When the filtered Q′ output is high, the initial position selection module  310  determines the initial position based on the position control initial position. 
         [0065]    When the force position determination module  312  receives the filtered Q′ output that is high, the force position determination module  312  receives the initial position and determines the force position based on the initial position. When the filtered Q′ output returns to low and the Q output is low, the force position determination module  312  sets the engine control module  110  to the position control mode. The force position determination module  312  enables the position control module  206  (i.e., sets the proportional and the derivative gains to predetermined initial values). 
         [0066]    The force open determination module  318  receives the desired position and the actual position and determines whether the engine control module  110  is to be set to the force open mode. When the desired position is less than or equal to a seventh predetermined position (e.g., −99.9%) and the actual position is less than an eighth predetermined position (e.g., −99.5%), the engine control module  110  is determined to be set to the force open mode. The force open determination module  318  sets a set input (i.e., an S) of the SR latch  320  to high. If a reset input (i.e., an R) of the SR latch  320  is low, the SR latch  320  sets an Q output (i.e., an Q) to high and holds an Q′ output (i.e., an Q′), or the complement of Q, at low. 
         [0067]    When the Q output is initially set to high, the delay module  322  receives and delays the Q output for a predetermined time period (e.g., greater than 0.5 seconds). This assures that the actual position is stable and that the determination to set the engine control module  110  to the force open mode is accurate. The filter module  324  receives and outputs the Q′ output to the initial position selection module  326 . The initial position selection module  326  further receives the actual position. When the Q′ output is low, the initial position selection module  326  determines an initial position for the TBV  138  based on the actual position. 
         [0068]    When the force position determination module  328  receives the delayed Q output that is high, the force position determination module  328  receives the initial position and sets the engine control module  110  to the force open mode. The force position determination module  328  determines the force position based on the initial position and ramps the force position to a predetermined open holding position (e.g., −40%). The open holding position corresponds to a position required to fully open the TBV  138  and that is independent of open position offsets. The force position is ramped based on a predetermined positive rate (e.g., 200%/second) or a predetermined negative rate (e.g., −200%/second). The force position determination module  328  disables the position control module  206 . 
         [0069]    The force close reset module  330  receives the desired position and the actual position and determines whether the engine control module  110  is to be reset from the force open mode (i.e., set back to the position control mode). When the desired position is greater than a ninth predetermined position (e.g., −99.8%) or the actual position is greater than or equal to a tenth predetermined position (e.g., −99%), the engine control module  110  is determined to be reset from the force open mode. The force close reset module  330  sets the reset input to high, and if the set input is low, the SR latch  332  sets the Q output to low and sets the Q′ output to high. 
         [0070]    The force close reset module  330  outputs a signal that indicates whether the desired position is greater than the ninth predetermined position. The position control initialization module  332  receives the signal and determines an initial position for the position control mode (i.e., a position control initial position) based on the signal. When the signal indicates that the desired position is greater than the ninth predetermined position, the position control initialization module  332  determines the position control initial position based on an eleventh predetermined position. The eleventh predetermined position is greater than or equal to the null position to close the TBV  138 . 
         [0071]    When the signal indicates that the desired position is less than or equal to the ninth predetermined position, the position control initial position is determined based on a twelfth predetermined position that is less than or equal to the open holding position. The twelfth predetermined position may be less than the open holding position. When the desired position is less than or equal the ninth predetermined position but the actual position is greater than or equal to the tenth predetermined position, the open holding position is not enough to hold the TBV  138  open. 
         [0072]    When the Q output is set to low, the delay module  322  receives and outputs the Q output to the force position determination module  328 . When the Q′ output is initially set to high, the filter module  324  receives and filters the Q′ output into a pulse of a predetermined time period. The initial position selection module  326  receives the filtered Q′ output and the position control initial position. When the filtered Q′ output is high, the initial position selection module  326  determines the initial position based on the position control initial position. 
         [0073]    When the force position determination module  328  receives the filtered Q′ output that is high, the force position determination module  328  receives the initial position and determines the force position based on the initial position. When the filtered Q′ output returns to low and the Q output is low, the force position determination module  328  sets the engine control module  110  to the position control mode. The force position determination module  328  enables the position control module  206 . 
         [0074]    Referring now to  FIGS. 4A and 4B , a flowchart depicting exemplary steps of an engine control method is shown. Control begins in step  402 . In step  404 , the desired and the actual positions are determined. In step  406 , control determines whether the engine control module  110  is to be set to the force close mode based on the desired and the actual positions. If true, control continues in step  408 . If false, control continues in step  410 . 
         [0075]    In step  408 , the initial position is determined based on the actual position. In step  412 , the force position is determined based on the initial position. In step  414 , the position control module  206  is disabled. Control returns to step  404 . 
         [0076]    In step  410 , control determines whether the engine control module  110  is to be reset from the force close mode based on the desired and the actual positions. If true, control continues in step  416 . If false, control continues in step  418 . 
         [0077]    In step  416 , control determines whether the desired position caused the force close mode to be reset. If true, control continues in step  420 . If false, control continues in step  422 . In step  420 , the initial position is determined based on the null position. 
         [0078]    In step  422 , the initial position is determined based on the closed holding position. In step  424 , the force position is determined based on the initial position. In step  426 , the position control module  206  is enabled. Control returns to step  404 . 
         [0079]    In step  418 , control determines whether the engine control module  110  is to be set to the force open mode based on the desired and the actual positions. If true, control continues in step  428 . If false, control continues in step  430 . 
         [0080]    In step  428 , the initial position is determined based on the actual position. In step  432 , the force position is determined based on the initial position. In step  434 , the position control module  206  is disabled. Control returns to step  404 . 
         [0081]    In step  430 , control determines whether the engine control module  110  is to be reset from the force open mode based on the desired and the actual positions. If true, control continues in step  436 . If false, control returns to step  404 . 
         [0082]    In step  436 , control determines whether the desired position caused the force open mode to be reset. If true, control continues in step  438 . If false, control continues in step  440 . In step  438 , the initial position is determined based on the null position. 
         [0083]    In step  440 , the initial position is determined based on the open holding position. In step  442 , the force position is determined based on the initial position. In step  444 , the position control module  206  is enabled. Control returns to step  404 . 
         [0084]    Referring now to  FIG. 5 , a graph depicting three operating modes of the engine control module  110  that are predetermined based on the engine load and the RPM is shown. The operating modes include a force close mode  502 , a force open mode  504 , and a position control mode  506 . When the engine load and the RPM are low in value, the engine control module  110  determines a desired position of the TBV  138  (not shown) that results in the engine control module  110  operating in the force close mode  502 . When the engine load and the RPM are high in value, the desired position is determined that results in the engine control module  110  operating in the force open mode  504 . When the engine load and the RPM are within a range of values, the desired position is determined that results in the engine control module  110  operating the position control mode. 
         [0085]    Referring now to  FIG. 6 , a graph depicting a time versus a desired current  602 , an Q output  604 , a delayed Q output (i.e., a delayed Q)  606 , an Q′ output  608 , a filtered Q′ output (i.e., a filtered Q′)  610 , and a position control module disable signal (i.e., position control module disable)  612  of the engine control module  110  is shown. When the Q output  604  is set to high, the Q′ output  608  is set to low. When the delayed Q output  606  is set to high, engine control module  110  is set to the force close mode  614 . The desired current  602  is initialized to an actual current and ramped down to a holding current. The position control module disable signal  612  is set to high, which indicates that the position control module  206  is disabled. 
         [0086]    When the Q output  604  is reset to low, the Q′ output  608  is reset to high. The filtered Q′  610  is set to high and is a pulse of a predetermined time period. The desired current  602  is set to a null current. When the filtered Q′ falls to low, the position control module  206  is enabled and the desired current  602  is controlled by the position control module  206 . 
         [0087]    Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification, and the following claims.