Electronic exhaust gas recirculation valve control

An EGR valve position control method controls a position of an EGR valve according to a pressure change across the valve and a desired EGR valve position. The method calculates a desired EGR valve position and generates one or more duty cycle control terms based on a difference between the desired EGR valve position and an actual EGR valve position. Additionally, the method provides feedforward control based on the pressure change and the desired EGR valve position in order to generate feedforward duty cycle control terms. The method controls the position of the EGR valve based on the duty cycle control terms.

FIELD OF THE INVENTION

The present invention relates to exhaust gas recirculation valves, and more particularly to electronically controlling a position of an exhaust gas recirculation valve based on a desired EGR valve position and a pressure across the valve.

BACKGROUND OF THE INVENTION

Exhaust gas recirculation (EGR) is used to reduce emissions and increase fuel economy in internal combustion engines. Exhaust gas is forced from the engine cylinders into the exhaust manifold after combustion. The exhaust gas includes non-burnable gas and other emissions that are otherwise released into the environment. Conventionally, EGR is used while the engine is running to reduce emissions and increase fuel economy.

The exhaust gas is mixed with intake air before entering the engine cylinders. Because the exhaust gas is non-burnable and takes up volume, the throttle has to open further in order to maintain a desired power level. A larger throttle opening reduces pumping losses and increases engine fuel efficiency.

SUMMARY OF THE INVENTION

A position control system for an EGR valve that includes a solenoid actuator comprises a desired EGR valve position module that calculates a desired EGR valve position. An actual EGR valve position module communicates with the EGR valve and calculates an actual EGR valve position. An EGR valve pressure change module determines a pressure change across the EGR valve. A first lookup table communicates with the EGR valve position module and determines a first duty cycle control term indicative of the desired EGR valve position. A second lookup table communicates with the EGR valve pressure change module and determines a second duty cycle control term indicative of the pressure change. A control module communicates with the desired EGR valve position module, the actual EGR valve position module, and the first and second lookup tables. The control module generates an error signal based on the desired EGR valve position and the actual EGR valve position, calculates at least one third duty cycle control term based on the error signal, and controls a duty cycle of the solenoid actuator according to the first, second, and third duty cycle control terms.

In another aspect of the invention, a position control method for an EGR valve comprises calculating a desired EGR valve position. An EGR valve position error is calculated according to the desired EGR valve position and an actual EGR valve position. At least one duty cycle control term is calculated based on the EGR valve position error. At least one duty cycle feedforward term is calculated. An output duty cycle is calculated based on the at least one duty cycle feedforward term and the at least one duty cycle control term. A duty cycle of the solenoid actuator is controlled based on the output duty cycle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring toFIG. 1, an engine control system10includes an engine12, an intake manifold14, an exhaust manifold16, a fuel system18, an EGR valve20, an ignition system22, an engine speed sensor24, an engine controller26, and a throttle position sensor (TPS)28. The engine speed sensor24determines a speed of the engine12and generates an engine speed signal30. The TPS28communicates with the throttle32and generates a throttle position signal34. The engine controller26monitors and adjusts engine performance based on various input signals. For example, the controller26receives the engine speed signal30from the engine speed sensor24and the throttle position signal34from the TPS28. The controller26calculates air flow into the engine12and fuel delivery from a fuel system18to the engine12based on variables such as engine speed and manifold absolute pressure. The controller26communicates with the ignition system22to determine ignition spark timing.

The controller26adjusts the EGR valve20to reduce certain emissions. Higher combustion temperatures in the engine12increase levels of the emissions in exhaust gas. Directing a portion of the exhaust gas back into the engine12along with intake air reduces the combustion temperatures. The EGR valve20controls the amount of exhaust gas that is recirculated with the intake air. The recirculated exhaust gases lower the combustion temperatures, which reduces emissions. The controller26determines the position of the EGR valve20based on engine conditions such as engine speed and desired air per cylinder. A conduit36connects the exhaust manifold16to the intake manifold14. The EGR valve20is positioned along the conduit36and meters EGR according to input from the controller26.

The EGR valve20is operable to actuate between a fully open and fully closed position. The controller26controls the position of the EGR valve20with an EGR valve voltage signal38. For example, the EGR valve20includes a linear solenoid actuator that is responsive to the EGR valve voltage signal38. In other words, the controller26regulates current through the solenoid in order to open and close the EGR valve20. The controller26generates the EGR valve voltage signal38according to inputs from the system10. In the preferred embodiment, the controller26calculates a desired flow rate of exhaust gas through the EGR valve20according to one or more inputs, including, but not limited to, engine speed, throttle position, mass air flow, ambient temperature, and vehicle speed. The controller26calculates a desired EGR valve position according to the desired flow rate. The controller26controls the EGR valve position according to the desired EGR valve position as described below.

The controller utilizes a control scheme40to continually adjust the EGR valve position as shown inFIG. 2. The control scheme40receives a desired EGR valve position42and an actual EGR valve position44at node46. The control scheme40calculates a EGR valve position error48at node46based on the desired EGR valve position42and the actual EGR valve position44. In the preferred embodiment, the control scheme40performs PID control operations on the EGR valve position error48. For example, the control scheme40performs proportional, integral, and derivative operations50,52, and54on the EGR valve position error48. The outputs56,58, and60of the derivative operations50,52, and54, respectively, are duty cycle control terms.

Additionally, the control scheme40includes one or more feedforward terms. The control scheme determines a duty cycle control term as a function of the desired EGR valve position42according to a lookup table, which is represented schematically at62. The control scheme40uses the lookup table62to select and output a duty cycle control term64based on the desired EGR valve position42. The lookup table62is populated with calibratable duty cycle control terms associated with the desired EGR valve position42according to one or more observed conditions. For example, the duty cycle control term64may be selected to correspond to a particular EGR valve position based on observable dynamometer data.

The control scheme40determines an additional feedforward term according to a change in pressure across the EGR valve. The control scheme40determines a duty cycle control term as a function of intake manifold pressure66and upstream exhaust pressure68at a lookup table, which is represented schematically at70. In the preferred embodiment, the intake manifold pressure66is physically measured, while the upstream exhaust pressure68is modeled based on one or more engine conditions, such as mass air flow. The difference between the intake manifold pressure66and the upstream exhaust pressure68is indicative of the change in pressure ΔP across the EGR valve. The control scheme40uses the lookup table70to select and output a duty cycle control term72based on the change in pressure across the EGR valve. The lookup table70is populated with calibratable duty cycle control terms associated with the change in pressure across the EGR valve according to one or more observed conditions.

The control scheme40performs a summing operation, which is represented schematically at74. The control scheme40sums the duty cycle control terms56,58,60,64, and72, and outputs a final EGR valve duty cycle control term76. The output process of the control scheme40is the solenoid actuator of the EGR valve, represented schematically at78. The actuator78opens and closes the EGR valve according to the EGR valve duty cycle control term76. Additionally, the actuator78includes a feedback sensor. The feedback sensor generates a feedback signal that is indicative of the position of the EGR valve. The feedback signal is represented schematically as the actual EGR valve position44. In this manner, the control scheme40determines the position of the EGR valve based on PID control of the desired and actual EGR valve positions42and44, including feedforward control62based on the desired EGR valve position and feedforward control70based on change in pressure across the EGR valve.

An EGR valve control algorithm90is shown inFIG. 3. At step92, the algorithm90calculates a desired EGR valve position. The algorithm90calculates the desired EGR valve position according to one or more system variables, including, but not limited to, a desired EGR valve flow rate. At step94, the algorithm90calculates an EGR valve position error. The algorithm90calculates the EGR valve position error according to the desired EGR valve position and an actual EGR valve position. At step96, the algorithm90calculates one or more duty cycle control terms for controlling a solenoid actuator of the EGR valve. For example, the algorithm90performs PID control on the EGR valve position error in order to generate duty cycle control terms indicative of the proportional, integral, and derivate control. Additionally, the algorithm90calculates one or more feedforward duty cycle control terms. The feedforward duty cycle control terms include a duty cycle control term indicative of the desired EGR valve position and a duty cycle control term indicative of a change of pressure across the EGR valve. At step98, the algorithm90determines an output duty cycle control term based on the PID control duty cycle control terms and the one or more feedforward duty cycle control terms. For example the algorithm sums the duty cycle control terms calculated at step96. At step100, the algorithm control the duty cycle of the solenoid actuator according to the output duty cycle control term.