Adaptive air/fuel ratio control method

Claim 1

A method of controlling air/fuel ratio for an engine control system of an internal combustion engine having a learning control correction factor for altering the air/fuel ratio including the steps of: establishing an upper and a lower limit for the air/fuel ratio; determining the time period difference between a first time period during which the air/fuel ratio is greater than the upper limit and a second time period during which the air/fuel ratio is less than a lower limit during a rich and lean cycle; determining the system is rich if the first time period is greater than the second time period; and determining the system is lean if the second time period is greater than the first time period.

Claim 2

A method of controlling air/fuel ratio for an engine control system of an internal combustion engine having a learning control correction factor for altering the air/fuel ratio including the steps of: establishing an upper and a lower limit for the air/fuel ratio; determining the time period difference between a first time period during which the air/fuel ratio is greater than the upper limit and a second time period during which the air/fuel ratio is less than a lower limit during a rich and lean cycle; determining the system is rich if the first time period is greater than the second time period; and determining the system is lean if the second time period is greater than the first time period.

Claim 13

A method of controlling air/fuel ratio for an engine control system with an adaptive keep-alive memory having an update routine for changing the value stored in the keep-alive memory cell corresponding to the operating point so that system operation can be adaptively adjusted by changing a learning control correction factor for altering air/fuel ratio, the method including the steps of: determining whether or not it is time to update the value stored in the keep-alive memory cell; establishing a time to update if the EGO switch count is greater than a predetermined number indicating a predetermined number of rich and lean cycles have elapsed; if it is not time to update, the routine is ended; if it is time to update, determining whether or not the system is biased towards rich operation; if it is biased toward rich operation, subtracting an adaptive amount from the value stored in the keep-alive memory in the cell, resetting a rich/lean difference timer and an EGO switch counter to zero and setting the previous memory cell number to the current memory cell number; if the system is not biased toward rich operation, determining whether the system is biased towards lean operation; if it is biased toward lean operation, adding an adaptive amount to the value stored in the keep-alive memory cell; and if it is not biased toward lean operation or if the keep-alive memory cell has been updated, clearing and setting to zero the rich/lean difference timer and the EGO switch counter, and setting the previous memory cell number to the current memory cell number.

Claim 14

A method of controlling air/fuel ratio for an engine control system with an adaptive keep-alive memory having an update routine for changing the value stored in the keep-alive memory cell corresponding to the operating point so that system operation can be adaptively adjusted by changing a learning control correction factor for altering air/fuel ratio, the method including the steps of: determining whether or not it is time to update the value stored in the keep-alive memory cell; establishing a time to update if the EGO switch count is greater than a predetermined number indicating a predetermined number of rich and lean cycles have elapsed; if it is not time to update, the routine is ended; if it is time to update, determining whether or not the system is biased towards rich operation; if it is biased toward rich operation, subtracting an adaptive amount from the value stored in the keep-alive memory in the cell, resetting a rich/lean difference timer and an EGO switch counter to zero and setting the previous memory cell number to the current memory cell number; if the system is not biased toward rich operation, determining whether the system is biased towards lean operation; if it is biased toward lean operation, adding an adaptive amount to the value stored in the keep-alive memory cell; and if it is not biased toward lean operation or if the keep-alive memory cell has been updated, clearing and setting to zero the rich/lean difference timer and the EGO switch counter, and setting the previous memory cell number to the current memory cell number.

Claim 15

A method controlling air/fuel ratio for an engine control system of an internal combustion engine having a learning control correction factor for altering the air/fuel ratio including the steps of: determining whether it is appropriate to enter an adaptive learning routine; determining whether to set a rich/lean time flag routine by determining whether it is time to update a difference timer and setting the timer flag to one if it is time to update and setting the timer flag to zero if it is not time to update; updating an adaptive learning control correction factor, L c , which can be used to determine a corrected fuel pulse time duration; and wherein determining whether to enter the adaptive learning routine includes periodically activating a foreground interrupt service routine includes checking the timer flag; if the timer flag is zero, not updating a difference timer indicating the difference between rich and lean air/fuel ratio operating time; if the timer flag is one, updating the difference timer indicating the difference between rich and lean air/fuel ratio operating time and determining a normalized air/fuel ratio LAMBDA; if LAMBDA is greater than an upper limit, the difference timer is incremented by one; if LAMBDA is not greater than an upper limit LAMBDA is checked to see if it is less than a lower limit; and if LAMBDA is less than a lower limit, the difference timer is decremented by one, otherwise the foreground routine is terminated.

Claim 16

A method controlling air/fuel ratio for an engine control system of an internal combustion engine having a learning control correction factor for altering the air/fuel ratio including the steps of: determining whether it is appropriate to enter an adaptive learning routine; determining whether to set a rich/lean time flag routine by determining whether it is time to update a difference timer and setting the timer flag to one if it is time to update and setting the timer flag to zero if it is not time to update; updating an adaptive learning control correction factor, L c , which can be used to determine a corrected fuel pulse time duration; and wherein determining whether to enter the adaptive learning routine includes periodically activating a foreground interrupt service routine includes checking the timer flag; if the timer flag is zero, not updating a difference timer indicating the difference between rich and lean air/fuel ratio operating time; if the timer flag is one, updating the difference timer indicating the difference between rich and lean air/fuel ratio operating time and determining a normalized air/fuel ratio LAMBDA; if LAMBDA is greater than an upper limit, the difference timer is incremented by one; if LAMBDA is not greater than an upper limit LAMBDA is checked to see if it is less than a lower limit; and if LAMBDA is less than a lower limit, the difference timer is decremented by one, otherwise the foreground routine is terminated.

Claim 21

A method of controlling air/fuel ratio for an engine control system of an internal combustion engine having a learning control correction factor for altering the air/fuel ratio including the steps of: determining whether it is appropriate to enter an adaptive learning routine; if the learning entry condition is not satisfied, a rich/lean difference timer, an EGO counter, and a timer flag are set to zero and the learning processes is discontinued; if the learning condition has been satisfied determining a current adaptive keep-alive memory cell number; determining the difference between the current memory cell number and a previously recorded memory cell number; comparing the difference between the current memory cell number and the previous recorded memory cell number to a predetermined cell number variance parameter; if the difference is larger than the predetermined cell number variance parameter, setting a rich/lean difference timer, an EGO counter, and a timer flag to zero and setting the value of the last cell number to the present cell number; if the difference between the current memory cell number and the previous recorded memory cell number is not greater than the predetermined cell number variance parameter, determining if an exhaust gas oxygen (EGO) sensor has switched or not; if the EGO sensor has switched, incrementing an EGO switching count; determining whether to set a rich/lean time flag by determining whether it is time to update a difference timer and setting the timer flag to one if it is time to update and setting the timer flag to zero if it is not time to update; updating an adaptive learning control correction factor, L c , which can be used to determine a corrected fuel pulse time duration, including the steps of: establishing an upper and lower limit for the air/fuel ratio; periodically activating a foreground interrupt service routine includes checking the timer flag; if the timer flag is zero, not updating a difference timer indicating the difference between rich and lean air/fuel ratio operating time; if the timer flag is one, updating the difference timer indicating the difference between rich and lean air/fuel ratio operating time based on the value of a normalized air/fuel ratio LAMBDA; if LAMBDA is greater than an upper limit, the difference timer is incremented by one; if LAMBDA is not greater than an upper limit LAMBDA is checked to see if it is less than a lower limit; if LAMBDA is less than a lower limit, the difference timer is decremented by one, otherwise the foreground routine is terminated; determining the time period difference between a first time period during which the air/fuel ratio is greater than the upper limit and a second time period during which the air/fuel ratio is less than a lower limit during one or more complete rich and lean cycle; determining the system is rich if the first time period is greater than the second time period; determining the system is lean if the second time period is greater than the first time period; determining the degree that the system is too rich or too lean; adjusting the amount of the learning control correction factor by making it proportional to the time period difference; clipping the value of the stored learning correction factor so as not to exceed a maximum value; and clipping the stored learning correction factor so that the learning factor is not less than the minimum value.

Claim 22

A method of controlling air/fuel ratio for an engine control system of an internal combustion engine having a learning control correction factor for altering the air/fuel ratio including the steps of: determining whether it is appropriate to enter an adaptive learning routine; if the learning entry condition is not satisfied, a rich/lean difference timer, an EGO counter, and a timer flag are set to zero and the learning processes is discontinued; if the learning condition has been satisfied determining a current adaptive keep-alive memory cell number; determining the difference between the current memory cell number and a previously recorded memory cell number; comparing the difference between the current memory cell number and the previous recorded memory cell number to a predetermined cell number variance parameter; if the difference is larger than the predetermined cell number variance parameter, setting a rich/lean difference timer, an EGO counter, and a timer flag to zero and setting the value of the last cell number to the present cell number; if the difference between the current memory cell number and the previous recorded memory cell number is not greater than the predetermined cell number variance parameter, determining if an exhaust gas oxygen (EGO) sensor has switched or not; if the EGO sensor has switched, incrementing an EGO switching count; determining whether to set a rich/lean time flag by determining whether it is time to update a difference timer and setting the timer flag to one if it is time to update and setting the timer flag to zero if it is not time to update; updating an adaptive learning control correction factor, L c , which can be used to determine a corrected fuel pulse time duration, including the steps of: establishing an upper and lower limit for the air/fuel ratio; periodically activating a foreground interrupt service routine includes checking the timer flag; if the timer flag is zero, not updating a difference timer indicating the difference between rich and lean air/fuel ratio operating time; if the timer flag is one, updating the difference timer indicating the difference between rich and lean air/fuel ratio operating time based on the value of a normalized air/fuel ratio LAMBDA; if LAMBDA is greater than an upper limit, the difference timer is incremented by one; if LAMBDA is not greater than an upper limit LAMBDA is checked to see if it is less than a lower limit; if LAMBDA is less than a lower limit, the difference timer is decremented by one, otherwise the foreground routine is terminated; determining the time period difference between a first time period during which the air/fuel ratio is greater than the upper limit and a second time period during which the air/fuel ratio is less than a lower limit during one or more complete rich and lean cycle; determining the system is rich if the first time period is greater than the second time period; determining the system is lean if the second time period is greater than the first time period; determining the degree that the system is too rich or too lean; adjusting the amount of the learning control correction factor by making it proportional to the time period difference; clipping the value of the stored learning correction factor so as not to exceed a maximum value; and clipping the stored learning correction factor so that the learning factor is not less than the minimum value.