Patent Publication Number: US-8109256-B2

Title: Solenoid current control with direct forward prediction and iterative backward state estimation

Description:
FIELD 
     The present disclosure relates to solenoid current control and more particularly to solenoid current control in an engine system. 
     BACKGROUND 
     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. 
     A diesel engine combusts an air/fuel mixture to produce drive torque for a vehicle. Air is drawn into cylinders through an intake manifold. A fuel system injects fuel directly into the cylinders. 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 bypass valve assembly may allow exhaust gas to bypass the HP turbocharger, thereby reducing the HP compressed air charge and an expansion ratio across the HP turbocharger. The bypass valve assembly typically includes a butterfly valve and a magnetic solenoid actuator. The magnetic solenoid actuator typically includes a solenoid coil and a magnetic core. The bypass valve is opened and closed by selectively supplying current through the solenoid coil. Control systems such as an engine control system may control the solenoid current to regulate opening of the bypass valve. 
     Traditional engine control systems, however, do not control the solenoid current as accurately or quickly as desired. For example, an engine control system may determine the solenoid current based on a solenoid temperature. However, solenoid variations and/or system aging may affect accuracy of the system. An engine control system may include a fast-response proportional-integral-derivative (PID) control scheme (e.g., 5 milliseconds) to control the solenoid current. However, a slow-response filter (e.g., 100 milliseconds) may be required to smooth the signal of feedback to remove short-term oscillations due to aliasing. 
     SUMMARY 
     An engine control system comprises a current control module and a solenoid actuator module. The current control module determines a duty cycle based on a desired current through a solenoid of an engine system and a resistance of the solenoid and corrects the resistance based on an actual current through the solenoid. The solenoid actuator module actuates the solenoid based on the duty cycle. 
     A method of operating an engine control system comprises determining a duty cycle based on a desired current through a solenoid of an engine system and a resistance of the solenoid; correcting the resistance based on an actual current through the solenoid; and actuating the solenoid based on the duty cycle. 
     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 
       The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a functional block diagram of an exemplary diesel engine system according to the principles of the present disclosure; 
         FIG. 2  is a functional block diagram of an exemplary engine control module according to the principles of the present disclosure; 
         FIG. 3  is a functional block diagram of an exemplary current control module according to the principles of the present disclosure; and 
         FIG. 4  is a flowchart depicting exemplary steps of an engine control method according to the principles of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     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. 
     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. 
     To accurately and rapidly control a solenoid current in a diesel engine system, the engine control system of the present disclosure predicts a duty cycle of a desired current through a solenoid. The duty cycle is predicted based on a slow-varying system parameter that defines a linear relationship between the duty cycle and an actual current through the solenoid. The engine control system corrects the slow-varying system parameter based on the predicted duty cycle, the desired current, and/or the resulting actual current. While the operation of the engine control system will be discussed as it relates to the bypass valve, the principles of the present disclosure are also applicable to any device that includes at least one solenoid. For example, devices may include, but are not limited to, a Variable Nozzle Turbine (VNT) of a turbocharger and/or metering valves of a common-rail direct fuel injection system. 
     Referring now to  FIG. 1 , a functional block diagram of an exemplary diesel engine system  100  is shown. The diesel engine system  100  includes a diesel engine  102  that combusts an air/fuel mixture to produce drive torque for a vehicle. The diesel engine  102  includes cylinders  104 . For illustration purposes, six cylinders are shown. For example only, the diesel engine  102  may include, but is not limited to, 2, 3, 4, 5, 6, 8, 10, and/or 12 cylinders. 
     The diesel engine system  100  further includes an air line  106 , an intake manifold  108 , an engine control module  110 , a fuel system  112 , an exhaust manifold  114 , and an exhaust line  116 . The diesel engine system  100  further includes a variable geometry turbocharger (VGT)  118 , a high-pressure (HP) turbocharger  120 , a low-pressure (LP) turbocharger  122 , a wastegate  124 , an intake air temperature (IAT) sensor  126 , and an engine coolant temperature (ECT) sensor  128 . The diesel engine system  100  further includes a bypass valve  130  and a bypass valve actuator module  132 . 
     Air is drawn into the intake manifold  108  through the air line  106 . Air from the intake manifold  108  is drawn into the cylinders  104 . The engine control module  110  controls the amount of fuel injected by the fuel system  112 . The fuel system  112  injects fuel directly into the cylinders  104 . 
     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. The compressed air/fuel mixture is auto-ignited near the top dead centre of the cylinders  104 . 
     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  114 . The byproducts of combustion are exhausted from the vehicle via the exhaust line  116 . 
     The HP turbocharger  120  and the LP turbocharger  122  are powered by exhaust gas flowing through the exhaust line  116  and provide an HP compressed air charge and an LP compressed air charge, respectively, to the intake manifold  108 . The HP compressed air charge and the LP compressed air charge are provided to the intake manifold  108  through the air line  106 . The air used to produce the compressed air charges is taken from the air line  106 . The VGT  118  receives exhaust gas and alters the output (i.e., the boost) of the HP turbocharger  120  based on the position (i.e., the aspect ratio) of the VGT  118 . The wastegate  124  may allow exhaust gas to bypass the LP turbocharger  122  to avoid placing too high of an exhaust pressure on the turbine of the LP turbocharger  122 . 
     An ambient temperature of air being drawn into the diesel engine system  100  (i.e., an IAT) may be measured using the IAT sensor  126 . A temperature of the engine coolant (i.e., an ECT) may be measured using the ECT sensor  128 . The ECT sensor  128  may be located within the diesel engine  102  or at other locations where the coolant is circulated, such as in a radiator (not shown). The engine control module  110  uses signals from the sensors  126  and  128  to make control decisions for the diesel engine system  100 . The engine control module  110  controls and communicates with the diesel engine  102 , the fuel system  112 , the VGT  118  (not shown), the turbochargers  120  and  122  (not shown), the wastegate  124 , and the bypass valve  130  as described herein. 
     The bypass valve  130  may allow exhaust gas to bypass the HP turbocharger  120 , thereby reducing the boost of the HP turbocharger  120  and an expansion ratio across the HP turbocharger  120 . The bypass valve  130  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 bypass valve actuator module  132  to regulate opening of the bypass valve  130  to control the amount of exhaust gas released to the HP turbocharger  120 . In addition, the bypass valve actuator module  132  may measure the position of the bypass valve  130  and output a signal based on the position to the engine control module  110 . The engine control module  110  determines the commands to the bypass valve actuator module  132  as described herein. 
     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 , and a position control module  206 . The engine control module  110  further includes a position-to-current conversion module  208 , a summation module  210 , a filter module  212 , and a current control module  214 . 
     The desired position determination module  202  receives data on engine operating conditions from sensors of the diesel engine system  100 . For example only, the engine operating conditions may include, but are not limited, to an engine speed, an actual pressure within the intake manifold  108 , and/or a desired pressure within the intake manifold  108  to be reached by the turbochargers  120  and  122 . The desired position determination module  202  determines a desired position of the bypass valve  130  based on models that relate the desired position to the engine operating conditions. The subtraction module  204  receives the desired position and an actual position of the bypass valve  130  from the bypass valve actuator module  132 . 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. For example only, the position correction factor may be in units of percentage and may include a predetermined range of values from −100% to 100%. 
     The position-to-current conversion module  208  receives the position correction factor. The position-to-current conversion module  208  converts the position correction factor to a current correction factor based on a model that relates the position correction factor to the current correction factor. For example only, the current correction factor 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 the position correction factor is equal to zero, the current correction factor may be equal to 0.5 A. 
     The summation module  210  receives the current correction factor and a current offset from data memory (not shown). The current offset is the amount of current when the bypass valve  130  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  210  sums the current correction factor and the current offset to determine a desired current for the solenoid of the bypass valve  130 . 
     The filter module  212  receives a battery voltage from a battery (not shown) that creates the electrical current for the solenoid. The filter module  212  filters the battery voltage for use by the current control module  214 . For example only, the filter module  212  may include a low-pass filter that smoothes the signal of the battery voltage to remove short-term oscillations. In addition, the filter module  212  determines an average of the battery voltage and filters the average to determine an average battery voltage (i.e., a battery voltage avg ). 
     The current control module  214  receives the battery voltage, the average battery voltage, 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 at least one the battery voltage and the average battery voltage. The bypass valve actuator module  132  receives the PWM duty cycle and regulates opening of the bypass valve  130  based on the PWM duty cycle. 
     Referring now to  FIG. 3 , a functional block diagram of the current control module  214  is shown. The current control module  214  includes a current correction module  302 , a filter module  304 , a duty cycle determination module  306 , and a driver module  308 . The current control module  214  further includes a filter module  310 , a filter module  312 , a current correction module  314 , and a resistance determination module  316 . 
     The current correction module  302  receives the desired current. The current correction module  302  determines a desired current correction factor (i.e., a current correction factor des ) based on a model that relates the desired current correction factor to the desired current. The desired current correction factor accounts for non-linearity in the relationship between the desired current and the duty cycle of the desired current. 
     At engine startup, the filter module  304  receives the IAT and the ECT and determines a resistance based on a model that relates the initial resistance to the IAT and the ECT. The resistance is a slow-varying system parameter that defines a linear relationship between the duty cycle of the desired current and an actual current through the solenoid of the bypass valve  130 . While the operation of the current control module  214  will be discussed as it relates to the resistance, the principles of the present disclosure are also applicable to any slow-varying system parameter that defines the linear relationship between the duty cycle and the actual current. For example, the slow-varying system parameter may include, but is not limited to, an impedance that is determined based on a temperature in the solenoid. 
     In addition, the filter module  304  determines an average of the resistance and filters the average to determine an average resistance (i.e., a resistance avg ). The resistance is averaged because it is a slow-varying system parameter, not an instantaneous one. For example only, the filter module  304  may include a low-pass filter that smoothes the signal of the average resistance to remove short-term oscillations. For example only, the filter module  304  may include a variable filter time constant that ramps from a smaller value to a predetermined value during a time period after engine start up. 
     The duty cycle determination module  306  receives the average resistance, the desired current correction factor, the desired current, and the battery voltage. The duty cycle determination module  306  determines (i.e., predicts) the duty cycle of the desired current based on the average resistance, the desired current correction factor, the desired current, and the battery voltage. The duty cycle DC is determined according to the following equation: 
                       D   ⁢           ⁢   C     =       K   ⁡     (     I   des     )       ⁢         I   des     ×     R   avg       V         ,           (   1   )               
where K(I des ) is the desired current correction factor, I des  is the desired current, R avg  is the average resistance, and V is the battery voltage. The duty cycle is determined instantly (e.g., in 5 milliseconds). This is because the duty cycle determination module  306  does not wait (e.g., 100 milliseconds) to receive feedback (e.g., the actual current that is changed due to the previous duty cycle) to determine the new duty cycle.
 
     The driver module  308  receives the duty cycle and modulates the duty cycle to determine the PWM duty cycle. The filter module  310  receives the duty cycle, determines an average of the duty cycle, and filters the average to determine an average duty cycle (i.e., a duty cycle avg ). The duty cycle is averaged because the resistance is a slow-varying system parameter, not an instantaneous one. For example only, the filter module  310  may include a low-pass filter that smoothes the signal of the average duty cycle to remove short-term oscillations. As can be appreciated, other signal conditioning such as reforming, filtering, amplification or other signal processing may be performed on any of the signals disclosed herein. 
     The driver module  308  includes a shunt (not shown) that is used to determine the actual current through the solenoid of the bypass valve  130 . The filter module  312  receives the actual current, determines an average of the actual current, and filters the average to determine an average actual current (i.e., an actual current avg ). The actual current is averaged because the resistance is a slow-varying system parameter, not an instantaneous one. For example only, the filter module  312  may include a low-pass filter that smoothes the signal of the average actual current to remove short-term oscillations. 
     The current correction module  314  receives the average actual current. The current correction module  314  determines an actual current correction factor (i.e., a current correction factor avg ) based on a model that relates the actual current correction factor to the actual current. The actual current correction factor accounts for non-linearity in the relationship between the actual current and the duty cycle of the desired current. 
     The resistance determination module  316  receives the actual current correction factor, the average battery voltage, the average actual current, and the average duty cycle. The resistance determination module  316  determines (i.e., corrects) the resistance based on the actual current correction factor, the average battery voltage, the average actual current, and the average duty cycle. The resistance R is determined according to the following equation: 
                     R   =         V   avg     ×   D   ⁢           ⁢     C   avg           K   ⁡     (     I     act   ⁢     -     ⁢   avg       )       ×     I     act   ⁢     -     ⁢   avg             ,           (   2   )               
where V avg  is the average battery voltage, DC avg  is the average duty cycle, K(I act-avg ) is the actual current correction factor, and I act-avg  is the average actual current.
 
     When the average actual current is equal to zero, the resistance determination module  316  may determine the resistance based on a small predetermined current instead of the average actual current. The small current does not affect the desired position. The corrected resistance is outputted to the filter module  304  where the corrected resistance is used to determine (i.e., correct) the average resistance for the duty cycle determination module  306 . This correction allows the duty cycle to be determined accurately and instantly even though the resistance is being corrected more slowly (e.g., 100 milliseconds). 
     For example only, the resistance may be initially determined to be less than its actual value. As a result, the duty cycle may be determined to be less than its desired value, and the actual current may be determined to be less than the desired current. However, since the actual current is in the denominator of the equation to correct the resistance, the underdetermined actual current may raise the resistance iteratively until the actual current equals the desired current. 
     In another implementation, the resistance determination module  316  receives the average actual current, the desired current (not shown), and a filtered average of the desired current (not shown). The resistance determination module  316  determines (i.e., corrects) the resistance based on the average actual current, the desired current, and the average desired current. The fresistance R i  is determined according to the following equation: 
                       R   i     =       R     i   -   1       [     1   +     α   ⁢         I     des   ⁢     -     ⁢   avg       -     I     act   ⁢     -     ⁢   avg           I   des           ]       ,           (   3   )               
where R i-1  is the resistance during the previous control loop, α is a predetermined smoothing factor, and I des-avg  is the average desired current. The resistance is corrected iteratively until the actual current equals the desired current.
 
     By determining the resistance, the engine control module  110  may determine a duty cycle offset (not shown) based on the resistance and the current offset. The duty cycle offset is the duty cycle of the actual current when the bypass valve  130  is at the null position. The duty cycle offset may be determined according to an equation similar to equation (1). Accordingly, determining the duty cycle offset based on the type of the solenoid at engine startup may be unnecessary. 
     Referring now to  FIG. 4 , a flowchart depicting exemplary steps of an engine control method is shown. Control begins in step  402 . In step  404 , the IAT is determined. In step  406 , the ECT is determined. In step  408 , the resistance is determined based on the IAT and the ECT. 
     In step  410 , the average resistance is determined based on the resistance. In step  412 , the desired current is determined. In step  414 , the desired current correction factor is determined based on the desired current. In step  416 , the battery voltage is determined. 
     In step  418 , the duty cycle is determined based on the average resistance, the desired current correction factor, the desired current, and the battery voltage. In step  420 , the PWM duty cycle is determined based on the duty cycle. In step  422 , the solenoid actuator module is commanded based on the PWM duty cycle. 
     In step  424 , control determines whether the engine is still on. If true, control continues in step  426 . If false, control continues in step  428 . In step  426 , the average duty cycle is determined based on the duty cycle. In step  430 , the actual current is determined. 
     In step  432 , the average actual current is determined based on the actual current. In step  434 , the actual current correction factor is determined based on the average actual current. In step  436 , the battery voltage is determined. In step  438 , the average battery voltage is determined based on the battery voltage. 
     In step  440 , the resistance is determined based on the actual current correction factor, the average battery voltage, the average actual current, and the average duty cycle. Control returns to step  410 . Control ends in step  428 . 
     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.