Method and system for controlling an emission control device based on depletion of device storage capacity

• US 6,553,754 B2
• Filed: 06/19/2001
• Issued: 04/29/2003
• 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:
  US09/884,703
• Publication Number:
  US 20030000201A1
• Time in Patent Office: 679 Days
• Field of Search: 602/74, 602/76, 602/77, 602/85, 602/95, 602/97, 603/01, 701/102, 701/103, 701/104, 701/105, 701/108, 701/109
• US Class Current: 60/277
• CPC Class Codes: B01D 53/9431 Processes characterised by a specific device
• CPC Class Codes: B01D 53/9495 Controlling the catalytic process
• 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 41/029 the exhaust gas treating apparatus being a particulate filter
• CPC Class Codes: F02D 41/1441 Plural sensors
• CPC Class Codes: F02D 41/1446 the characteristics being exhaust temperatures
• CPC Class Codes: F02D 41/1456 with sensor output signal being linear or quasi-linear with the concentration of oxygen
• CPC Class Codes: F02D 41/1462 with determination means using an estimation
• CPC Class Codes: F02D 41/1474 by detecting the commutation time of the sensor
• CPC Class Codes: F02D 41/1495 Detection of abnormalities in the air/fuel ratio feedback system
• CPC Class Codes: F02D 41/187 using a hot wire flow sensor
• CPC Class Codes: F02D 41/2454 Learning of the air-fuel ratio control

Abstract

A method of optimizing vehicle emissions during lean engine operation is disclosed wherein an emission control device receiving engine exhaust gases is filled with one or more constituent gases of the exhaust gas to a predetermined fraction of the device storage capacity, and is then completely emptied during a subsequent purge. As the device storage capacity is substantially reduced, as indicated by an actual fill time becoming equal to or less than a predetermined minimum fill time, a device regeneration cycle 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 its storage capacity limit.

Claims

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

calculating the depletion of device capacity of the device based on a calibrated device filling rate in engine speed load regions multiplied by the time spent in the region;

continuously summing the calculated depletion; and

scheduling a purge event when the summed calculated depletion exceeds a predetermined value for capacity depletion, wherein the predetermined value for capacity depletion is less than 100%, wherein the calibrated device filling rate is modified as a function of air-fuel ratio, EGR and spark advance, wherein the calculated depletion is modified as a function of device temperature, the method further including;

mapping the device filling rate over an engine speed and load operating range using a representative calibration for device temperature, air-fuel ratio, EGR and spark advance,

and wherein the depletion of device capacity is a time weighted sum based on the amount of time spent in a given speed-load region utilizing the mapped filling rates in each region modified to account for the difference between existing and calibrated operating conditions.

2. The method of claim 1, further including purging the device for a purge time t_P(k) and monitoring the output signal of an oxygen sensor to determine the purge time t_P(k+1) for the next purge cycle based on the output voltage of the sensor.

3. The method of claim 2, further including optimizing the fill time by adjusting the fill time by predetermined increments respectively greater than and less than an initial fill time until the change in the purge time with respect to the corresponding fill time equals a predetermined target value.

4. A system for filling and purging an emission control device so that the device is substantially filled to capacity with a constituent gas of the engine-generated exhaust gas during a fill time and is substantially emptied of previously-stored constituent gas during a subsequent purge time, the system comprising:

a sensor operative to generate a signal representative of an oxygen concentration in the exhaust flowing through the device;

a control module programmed to calculate the depletion of device capacity based on a calibrated device filling rate in engine speed load regions multiplied by the time spent in the region and further programmed to continuously sum the calculated capacity depletion and schedule a purge event when a predetermined percentage of capacity less than 100% is depleted, wherein the module is programmed to modify the calibrated device filling rate as a function of air-fuel ratio, EGR and spark advance, wherein the module is further programmed to modify the calculated depletion as a function of device temperature, wherein the module further includes;

a map of the device filling rate over an engine speed and load operating range using a representative calibration for device temperature, air-fuel ratio, EGR and spark advance;

and wherein the depletion of device capacity is a time weighted sum based on the amount of time spent in a given speed-load region utilizing the mapped filling rates in each region modified to account for the difference between existing and calibrated operating conditions.

5. A method of controlling the fill and purge time of an emission control device located upstream of a switching-type oxygen sensor in an exhaust treatment system for an internal combustion engine, wherein the emission control device stores a quantity of a constituent gas of the engine-generated exhaust gas during a first engine operating condition up to a device capacity, and releases stored constituent gas during a second engine operating, the method comprising:

calculating device capacity utilization in accordance with the following equation;

$\mathrm{RSM}=M_1<br><br>\left(t\right)<br><br>\underset{k=1}{\overset{k=P}{\sum <br><br>}}<br><br>M_2<br><br>\left(\mathrm{AFR}\right)<br><br>M_3<br><br>\left(\mathrm{EGR}\right)<br><br>M_4<br><br>\left({\mathrm{SPK}}_{\mathrm{ij}}\right)<br><br>R_{\mathrm{ij}}<br><br>\left(\%/s\right)<br><br>t_k$

terminating device filling and scheduling a device purge when the capacity of the device is substantially reached; and

determining an optimum purge time based on the amplitude of the voltage output of the sensor.

6. The method of claim 5, wherein determining the optimum purge time includes:

detecting, in a closed-loop process, whether the peak voltage of the sensor is above or below a reference voltage during a window following a purge cycle, the reference voltage representing an optimum purge time for the effective utilization of the device capacity on the preceding fill cycle, and

iteratively adjusting, in an open-loop process, a selected stored value for the purge time to force a measured characteristic of the sensor voltage to equal a reference characteristic of the sensor voltage.

7. The method of claim 6, wherein an optimum fill time is determined by dithering a selected stored value for the fill time about an initial value until the resulting change in purge time with respect to fill time equals a target value.

8. The method of claim 7, wherein a device desulfation event is scheduled if the adjusted selected stored value for the purge time is less than a predetermined purge time for a non-deteriorated device minus an offset.

9. The method of claim 8, including scheduling at least one subsequent desulfation event if the adjusted selected stored value for the purge time does not increase as a result of a previous desulfation event;

and

upon scheduling a predetermined number of subsequent desulfation events, triggering a warning indication.