Closed loop exhaust gas recirculation control system

A closed loop exhaust gas recirculation (EGR) control system in which the exhaust system and intake system of an internal combustion engine are operatively coupled to each other by a conduit so as to recirculate part of the exhaust gas from the exhaust system to the intake system for inhibiting the generation and emission of oxides of nitrogen and for regulating drivability and the like by selectively adjusting the position of an EGR valve disposed at least partially within said conduit, said closed loop EGR control system comprising:

• a first memory means pre-programmed for storing a predetermined optimal set of EGR values for a particular set of conditions representing the desired positions of said EGR valve as a function of engine speed and throttle position, one of each set of EGR values being accessible by addressing a first memory dimension with a first address word indicative of engine speed and a second memory dimension with a second address word indicative of throttle position;
• a second memory means pre-programmed for storing a predetermined optimal set of EGR values for said particular set of conditions representing the desired positions of said EGR valve as a function of engine speed and absolute manifold pressure, one of each set of EGR values being accessible by addressing a first memory dimension with said first address word indicative of engine speed and a second memory dimension with a third address word indicative of absolute manifold pressure;
• means associated with said engine for measuring an actual engine speed operating parameter and for generating a first multi-bit binary word indicative thereof, said first multi-bit binary word having "m" most significant bits (MSB) and "p" least significant bits (LSB);
• the intake system of said internal combustion engine including the throttle for regulating the air flow therein and said control system further including means responsive to the relative position of said throttle for generating a second multi-bit binary word indicative of the actual throttle position, said second multi-bit binary word having "n" MSB and "q" LSB;
• means coupled to said intake system of said internal combustion engine and responsive to the actual absolute manifold pressure existing therein for generating a third multi-bit binary word indicative thereof, said third multi-bit binary word having "r" MSB and "s" LSB;
• means for temporarily storing said first, second and third multi-bit binary words;
• timing means for controlling the sequence of operation of said EGR control system;
• memory address means responsive to the most significant bits of a selected first pair of the words contained in said temporary storage means and to said timing means and then to a selected second pair of the stored words and said timing means for addressing said first memory dimension and said second memory dimension of a selected one of said first and second memory means for accessing the EGR values stored therein;
• means for performing a double linear interpolation between stored EGR values by sequentially addressing adjacent EGR values stored in a selected one of said first and second memory means and using the least significant bits of said first and second stored words for first computing a first EGR value accurately corresponding to the actual measured values of engine speed and throttle position and for then computing the second EGR value accurately corresponding to the actuall measured values of engine speed and absolute manifold pressure;
• means responsive to said interpolation means and said timing means for modifying the most significant bits of said selected temporarily stored multi-bit binary words for sequentially addressing adjacent stored EGR values required for said interpolation computations;
• said memory means and said interpolation means being responsive to said timing means for initially selecting said first and second multi-bit binary words and utilizing the MSB thereof for addressing said first memory means and the LSB thereof for performing said interpolation computations to determine said first EGR value and then selecting said first and third multi-bit binary words utilizing the MSB thereof for addressing said second memory means and the LSB thereof for performing said interpolation computations to determine said second EGR value;
• means for subtracting said second EGR value from said first EGR value to determine a current EGR error value indicative of the current deviation in the position of said EGR valve from the desired pre-programmed position;
• means for storing the prior EGR error value used to perform the last EGR valve position adjustment;
• means for subtracting said prior EGR error value from said current EGR error value for computing the difference therebetween which is representative of the total EGR valve position correction required for restoring said pre-programmed EGR at the next valve position adjustment;
• means for algebraically adding only a predetermined fractional portion of said computed difference to said previously stored EGR error value for updating same so as to avoid rapid valve position changes which tend to cause engine roughness and the like;
• means for converting said updated EGR error value into an EGR valve position control signal;
• and
• means responsive to said EGR valve position control signal for adjusting the position of said EGR valve to increase or decrease EGR flow in a smooth and gradual manner conducive to optimal drivability.

In an internal combustion engine having an intake system, an exhaust system, a conduit coupling the exhaust system to the intake system and an exhaust gas recirculation (EGR) valve associated with said conduit for controlling the quantity of exhaust gases fed back to said intake system, a closed loop method of accurately controlling the position of said EGR valve for regulating EGR flow to obtain optimal drivability while simultaneously reducing noxious emissions below some predetermined acceptable level comprising the steps of:

• determining a first EGR value indicative of a desired EGR valve position for actual values of first and second engine operating parameters;
• determining a second EGR value indicative of a desired EGR valve position for actual values of third and fourth engine operating parameters;
• subtracting one of said first and second EGR values from the other of said first and second EGR values to obtain a current EGR correction for valve position error;
• comparing said current EGR correction with a previously computed EGR correction used to make the last EGR valve position adjustment to determine the change in EGR correction required for the next EGR valve position adjustment;
• alebraically adding a predetermined portion of said change in EGR correction for valve position error to said previously computed EGR correction to generate a new rate-limited EGR correction for controlling the rate at which EGR valve position corrections are made;
• and
• adjusting the position of said EGR valve in response to said new EGR correction for maintaining a desired EGR flow while avoiding engine roughness and the like.

In an internal combustion engine having an intake system, an exhaust system, a conduit coupling the exhaust system to the intake system and an EGR valve disposed at least partially within said conduit for controlling the amount of exhaust gas fed back to said intake system, a closed loop method for controlling the positioning of said valve means for regulating exhaust gas recirculation (EGR) to obtain optimal drivability while simultaneously reducing noxious emissions below some predetermined acceptable level comprising the steps of:

• preprogramming a first schedule of EGR values representing the desired position of said EGR valve as a function of first and second engine operating parameters into a first memory section;
• programming a second schedule of desired EGR values representing the desired position of said EGR valve as a function of third and fourth engine operating parameters into a second memory section;
• measuring the actual operating values of said first, second, third and fourth engine operating parameters at least one between each valve position adjustment;
• generating a first desired EGR value corresponding to said first and second actual measured values of engine operating parameters utilizing said first and second values of engine operating parameters and the values stored in said first memory section;
• generating a second desired EGR value corresponding to said third and fourth actual measured values of engine operating parameters utilizing said third and fourth actual measured values of engine operating parameters and the value stored in said second memory section;
• comparing said first generated EGR value with said second generated EGR value for obtaining a current EGR error value indicative of the present actual error in the position of said EGR valve;
• subtracting a previously stored EGR error value representing the past history of positional error corrections used to perform the previous positional adjustment of said EGR valve from said currently obtained EGR error value to obtain the change in EGR error value required for correcting the position of said EGR valve at the next positional adjustment of said EGR valve;
• selectively adding only a predetermined portion of said change in EGR error value to said previously stored EGR error value to obtain an updated EGR error value to control the rate at which EGR corrections are made to the position of the EGR valve at said next positional adjustment so as to avoid engine roughness and the like;
• generating an EGR valve position adjustment signal from said updated EGR error value;
• and
• adjusting the position of said EGR valve in response to said EGR valve position adjustment signal so that only a predetermined portion of the desired correction is applied with each positional adjustment to improve drivability while simultaneously reducing noxious emissions to below said predetermined acceptable level.