Method and system for controlling a regeneration cycle of an emission control device

• US 6,615,577 B2
• Filed: 06/19/2001
• Issued: 09/09/2003
• 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:
  US09/884,248
• Publication Number:
  US 20020189235A1
• Time in Patent Office: 812 Days
• Field of Search: 602/74, 602/76, 602/77, 602/85, 602/86, 602/95, 602/97
• US Class Current: 60/276
• CPC Class Codes: F01N 2570/04 Sulfur or sulfur oxides
• CPC Class Codes: F01N 3/0842 Nitrogen oxides
• CPC Class Codes: F02D 2200/0806 NOx storage amount, i.e. amount of NOx stored on NOx trap
• 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 41/0275 the exhaust gas treating apparatus being a NOx trap or adsorbent
• CPC Class Codes: F02D 41/028 Desulfurisation of NOx traps or adsorbent
• CPC Class Codes: F02D 41/1454 the characteristics being an oxygen content or concentration or the air-fuel ratio

Abstract

A system and method for optimizing the regeneration cycle of an emission control device, such as a lean NO_x trap, is disclosed wherein the device is filled to a predetermined fraction of its existing capacity and is then completely emptied during a device purge. As device capacity is substantially reduced, as indicated by the actual fill time becoming equal to or less than a predetermined minimum fill time, a device desulfation event is performed to attempt to restore device capacity. A programmed computer controls the fill and purge times based on the amplitude of the voltage of a switching-type oxygen sensor and the time response of the sensor. The frequency of the purge, which ideally is directly related to the device capacity depletion rate, is controlled so that the device is not filled beyond the storage capacity limit.

Claims

1. A method of controlling the purging of a quantity of a constituent gas previously stored in an emission control device of an engine exhaust treatment system, wherein the engine exhaust treatment system includes a sensor operative to generate a signal representative of an oxygen concentration of engine exhaust gas passing through the device, the method comprising:

determining the quantity of constituent gas previously stored in the device based on a peak amplitude of the signal achieved during a first device purging;

purging the device of previously-stored constituent gas at a frequency that is inversely related to the quantity of the constituent gas determined to be stored in the device; and

performing a device regeneration operation to attempt to restore device capacity if a purge time is less than a predetermined minimum purge time.

2. The method of claim 1, further including indicating device deterioration if a predetermined number of device regeneration operations are performed without any increase in said purge time.

3. The method of claim 2, further including:

producing a purge adjustment multiplier related to device capacity;

adjusting a fill time as a function of the multiplier to achieve storage of enough constituent to fill the device to a predetermined fraction of the device capacity.

4. The method of claim 3, wherein an initial value for device fill time is determined from a lookup table as a function of an engine speed and load.

5. The method of claim 3, wherein an initial value for device fill time is determined from a lookup table as a function of an air mass flow rate.

6. The method of claim 3, wherein an initial value for device fill time is an inverse power of a product of an engine load and an engine speed.

7. A method of filling and purging an emission control device located in the exhaust passage of an engine upstream from an oxygen sensor, so that the device is substantially filled to capacity with one or more constituent gases of the engine-generated exhaust during a fill time and substantially emptied during a subsequent purge time, the method comprising:

inferring whether the device has been filled with the constituent gas to some predetermined fraction of the device capacity, by integrating the rate at which the device fills with respect to time, where the filling rate is determined from mapping data;

executing a purge event in which the strength of the purge event is just enough to purge the device of stored constituent gas, by monitoring the oxygen sensor signal using a time and voltage related oxygen sensor metric, and continuously adjusting the purge time to the optimum value so that the purge strength is just sufficient to purge the stored constituent gas from the device;

continuously comparing the purge time to a reference purge time that corresponds to that of a deteriorated device and if the reference purge time is exceeded, scheduling one or more desulfation events;

comparing the optimum purge time after desulfation to the reference purge time; and

if the purge time does not return to a value above the reference purge time, providing a deterioration indication.

8. A system for controlling purging of an emission control device located in the exhaust passage of an engine, the device operating to store a constituent gas of engine-generated exhaust gas flowing through the device during a first engine operating condition and releasing stored constituent gas during a second engine operating condition, the system comprising:

an oxygen sensor responsive to the exhaust flowing through the device;

a control module programmed to determine the quantity of constituent gas stored in the device based on the peak amplitude of the voltage of the oxygen sensor during device purging, the module being further programmed to purge the device of stored constituent gas at a frequency that is inversely related to the quantity of constituent gas stored in the device, and to perform a device desulfation operation to attempt to restore device capacity if a purge time is less than a predetermined minimum purge time.

9. The system of claim 8, wherein the module is further programmed to indicate device deterioration if a predetermined number of device desulfation operations are performed without any increase in said purge time.

10. The system of claim 9, wherein the module is further programmed to produce a purge adjustment multiplier related to device capacity and to adjust a fill time as a function of the multiplier to achieve storage of enough NOx to fill the device to a predetermined fraction of its capacity.