Method and system for controlling storage and release of exhaust gas constituents in an emission control device

• US 6,502,387 B1
• Filed: 06/19/2001
• Issued: 01/07/2003
• Est. Priority Date: 06/19/2001
• Status: Expired due to Fees

• Current Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Original Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Inventors: Meyer, Garth Michael, Asik, Joseph Richard
• Primary Examiner(s): Denion, Thomas
• Assistant Examiner(s): TRAN, BINH Q
• Application Number:
  US09/884,233
• Publication Number:
  US 20020194836A1
• Time in Patent Office: 567 Days
• Field of Search: 602/74, 602/76, 602/85, 602/95, 602/97, 602/86
• US Class Current: 60/277
• CPC Class Codes: F01N 11/002 the diagnostic devices measuring or estimating temperature or pressure in, or downstream of the exhaust apparatus
• CPC Class Codes: F01N 11/007 the diagnostic devices measuring oxygen or air concentration downstream of the exhaust apparatus
• CPC Class Codes: F01N 13/009 having two or more separate purifying devices arranged in series
• CPC Class Codes: F01N 13/0093 the purifying devices are of the same type
• CPC Class Codes: F01N 13/0097 the purifying devices are arranged in a single housing
• CPC Class Codes: F01N 2550/02 Catalytic activity of catalytic converters
• CPC Class Codes: F01N 2550/03 of sorbing activity of adsorbents or absorbents
• CPC Class Codes: F01N 2570/16 Oxygen
• CPC Class Codes: F01N 2900/0422 measuring the elapsed time
• CPC Class Codes: F01N 3/0842 Nitrogen oxides
• CPC Class Codes: F02D 2200/0808 NOx storage capacity, i.e. maximum amount of NOx that can be stored on NOx trap
• CPC Class Codes: F02D 2200/0814 Oxygen storage amount
• CPC Class Codes: F02D 41/0275 the exhaust gas treating apparatus being a NOx trap or adsorbent
• CPC Class Codes: F02D 41/1441 Plural sensors
• CPC Class Codes: F02D 41/1456 with sensor output signal being linear or quasi-linear with the concentration of oxygen
• CPC Class Codes: F02D 41/1474 by detecting the commutation time of the sensor
• CPC Class Codes: F02D 41/2441 characterised by the learning conditions
• CPC Class Codes: F02D 41/2451 characterised by what is learned or calibrated
• CPC Class Codes: F02D 41/2454 Learning of the air-fuel ratio control
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

A method and system are provided for adaptive control of a purge time and a fill time for an emission control device used to reduce emission of a selected constituent gas, such NO_x, of an engine'"'"'s generated exhaust gas, with optimization and adapting of stored values to reflect changes in device operating conditions. The invention determines a present value representative of the quantity of oxygen stored in the device, as well as a present value for the maximum device NO_x-storage capacity to provide real-time adjustment of purge and fill time to achieve optimum overall operation of the device. The invention also periodically determines actual fill times which corresponding to optimal fill times to generate adaptive values for use during normal open-loop control.

Claims

1. A method for controlling a purge time cycle and a fill time cycle of an emission control device that receives exhaust gas generated by an internal combustion engine, wherein the device is filled with a constituent gas of the exhaust gas during a first engine operating condition and is purged of constituent gas during a second engine operating condition, the method comprising:

selecting, in a normal open-loop mode of operation, a fill time and a purge time from a set of predetermined values as a function of an engine operating condition;

cyclically filling and purging the device based on the selected fill and purge times;

after a predetermined number of fill and purge cycles, determining a first value representative of current total device capacity, and a second value representative of a quantity of oxygen stored in the device;

updating at least one of the predetermined values as a function of the first and second values; and

periodically optimizing a selected purge time associated with a selected fill time by;

filling the device for the selected fill time;

purging the device for the selected purge time;

generating a third value representative of oxygen concentration present in the exhaust flowing through the device during a predetermined sampling period which includes at least an end portion of the purge time;

comparing the third value to a predetermined reference value, wherein the reference value is based on an optimized value for device capacity utilization; and

generating an adaption value for modifying the selected purge time as a function of any error between the third value and the reference value.

2. The method of claim 1, wherein generating the third value includes positioning a first oxygen sensor in the engine exhaust system so as to provide an output voltage representative of the oxygen concentration.

3. The method of claim 1, wherein the adaption value is generated as a function of either the generated third value if the third value is not greater than the reference value, and the adaption value is generated as a function of a length of time that the third value exceeds the reference value if the third value exceeds the reference value.

4. The method of claim 3, wherein generating the adaption value further includes linearly extrapolating the third value in proportion to the measured oxygen level when the generated value is below the reference value.

5. The method of claim 1, wherein the selected purge time is optimized only upon operation of the engine at an operating point corresponding to a limited number of engine operating conditions.

6. A method for controlling a purge time cycle and a fill time cycle of an emission control device that receives exhaust gas generated by an internal combustion engine, wherein the device is filled with a constituent gas of the exhaust gas during a first engine operating condition and is purged of constituent gas during a second engine operating condition, the method comprising:

selecting, in a normal open-loop mode of operation, a fill time and a purge time from a set of predetermined values as a function of an engine operating condition;

cyclically filling and purging the device based on the selected fill and purge times;

after a predetermined number of fill and purge cycles, determining a first value representative of current total device capacity, and a second value representative of a quantity of oxygen stored in the device; and

updating at least one of the predetermined values as a function of the first and second values, wherein determining the first value representative of current total device capacity includes;

filling the device to a saturation levels;

generating a fourth value representative of an oxygen concentration present in the exhaust flowing through the device;

generating a first error value as a function of the fourth value and a predetermined reference value; and

determining an actual purge time necessary to purge the device when the device is filled to the saturation level using the first error value.

7. A method for controlling a purge time cycle and a fill time cycle of an emission control device that receives exhaust gas generated by an internal combustion engine, wherein the device is filled with a constituent gas of the exhaust gas during a first engine operating condition and is purged of constituent gas during a second engine operating condition, the method comprising:

selecting, in a normal open-loop mode of operation, a fill time and a purge time from a set of predetermined values as a function of an engine operating condition;

cyclically filling and purging the device based on the selected fill and purge times;

after a predetermined number of fill and purge cycles, determining a first value representative of current total device capacity, and a second value representative of a quantity of oxygen stored in the device; and

updating at least one of the predetermined values as a function of the first and second values, wherein determining the second value includes;

in sequence, partially filling and purging the device to a first sub-optimal level and a second sub-optimal level over different time periods; and

for the first sub-optimal filling and purging, generating a fifth value representative of the oxygen concentration in the exhaust passing through the device;

for the second sub-optimal filling and purging, generating a sixth value representative of the oxygen concentration in the exhaust passing through the device;

generating a second and third error value as a function of the fifth and sixth values, respectively, and a predetermined reference value;

determining an actual purge time necessary to purge the device for each sub-optimal fill time based on the second and third error values, respectively;

determining the second value as a function of the sub-optimal fill times and the actual purge times.

8. A system for controlling a purge time cycle and a fill time cycle of an emission control device that receives exhaust gas generated by an internal combustion engine, wherein the device is filled with a constituent gas of the exhaust gas during a first engine operating condition and is purged of constituent gas during a second engine operating condition, the system comprising;

an oxygen sensor positioned relative to the device to provide an output signal representative of a concentration of oxygen present in the exhaust flowing through the device during a sampling period; and

a control module including a microprocessor arranged to operate in a normal open-loop mode of operation by determining fill times and purge times based on engine operating conditions and corresponding values stored in a memory, wherein the control module is further arranged to periodically optimize a purge time associated with a selected fill time, determine that a predetermined number of fill and purge cycles have been performed, and in response, determining a first value representative of current total device capacity, and a second value representative of a quantity of oxygen stored in the device to update at least one purge time value as a function of the first and second values, wherein the processor is arranged to determine the first value by filling and purging the device to saturation, generate an error signal responsive to the sensor output signal as a function of the detected output signal and a predetermined reference value, and determine an actual purge time necessary to purge the saturated device of all NO_x.

9. The system of claim 8, wherein the processor is arranged to determine the second value by filling and purging the device to a first sub-optimal level of capacity and a second sub-optimal level of capacity over different time periods, and for each sub-optimal filling and purging, generate an error signal responsive to the sensor output signal as a function of the detected output signal and a predetermined reference value, and determine an actual purge time necessary to purge the device for the given sub-optimal fill time, wherein the second value is determined as a function of the fill times and corresponding actual purge times of the first and second sub-optimal capacity levels.

10. The system of claim 8, wherein the oxygen sensor comprises a HEGO type sensor.