Reducing emissions using transport delay to adjust biased air-fuel ratio

• US 5,220,905 A
• Filed: 07/17/1992
• Issued: 06/22/1993
• Est. Priority Date: 07/17/1992
• Status: Expired due to Fees

• Current Assignee: Brad Lundahl
• Original Assignee: Brad Lundahl
• Inventors: Lundahl, Brad
• Primary Examiner(s): ARGENBRIGHT, TONY MICHAEL
• Application Number:
  US07/916,167
• Time in Patent Office: 340 Days
• Field of Search: 123/492, 123/493, 123/672, 123/681, 123/682, 123/683, 123/684, 123/693, 123/694, 123/696
• US Class Current: 123/681
• CPC Class Codes: F02B 1/04 with fuel-air mixture admission into cylinder
• CPC Class Codes: F02D 19/023 to adjust the fuel mass or volume flow
• CPC Class Codes: F02D 41/0027 the fuel being gaseous non-electrical control F02D19/02
• CPC Class Codes: F02D 41/1474 by detecting the commutation time of the sensor
• CPC Class Codes: F02D 41/18 by measuring intake air flow
• CPC Class Codes: Y02T 10/30 Use of alternative fuels, e.g. biofuels

Abstract

A method for controlling the air-fuel ratio in an internal combustion engine equipped to operate from a gaseous alternative fuel. The output signal of the engine'"'"'s exhaust gas oxygen sensor is used to measure the variable engine transport delay. The variable is used to approximate a reciprocal of the delay. The reciprocal is used as a representation of the variable engine mass air-flow. A limit cycle operating in a transport-delay-oscillator mode is modified by extending the duration of the enrichment phase in proportion to the mass air-flow. The resulting exhaust gas concentrations are biased rich and thus shifted within an optimum operating window of the engine'"'"'s gasoline catalytic converter. A significant reduction of unwanted exhaust emissions is observed.

Claims

1. A method for reducing unwanted exhaust emissions for use with an internal combustion engine equipped with an air-fuel ratio limit-cycle controller and a fuel metering actuator responsive to a controller generated signal, the controller having an operating cycle including complementary fuel phases each having a duration, the engine having operating variables which include an air-fuel ratio, a stoichiometric level and a mass air-flow, the method comprising the steps of:

cyclically adjusting the level of the actuator control signal to center the operating cycle about the stoichiometric level;

determining a value of the mass air-flow;

comparing the air-fuel ratio with the stoichiometric level, and if these engine operating variables differ by more than a predetermined amount, adjusting the air-fuel ratio by extending the duration of a fuel phase in proportion to the value of the mass air-flow;

maintaining the level of the actuator control signal approximately constant during the step of extending the duration of a fuel phase; and

continuously repeating these steps,

whereby a change in engine air-flow produces a change in the air-fuel ratio which decreases the difference between the air-fuel ratio and the stoichiometric level with a consequent reduction in unwanted exhaust emissions.

2. The method of claim 1 wherein the controller complementary fuel phases include a fuel enrichment and a fuel reduction phase, and wherein a fuel enrichment phase is extended.

3. The method of claim 2 further including the steps of equipping the internal combustion engine to operate from a gaseous alternative fuel and operating the engine from such fuel.

4. The method of claim 1 further including the steps of equipping the internal combustion engine to operate selectively from gasoline or an alternative gaseous fuel, selecting a fuel and operating the engine from the selected fuel, and wherein the controller complementary fuel phases include a fuel enrichment and fuel reduction phase and wherein if the alternative gaseous fuel is selected the step of adjusting the duration of a fuel phase is accomplished by extending the duration of a fuel enrichment phase in proportion to the value of the mass air-flow.

5. A method for reducing unwanted exhaust emissions for use with an internal combustion engine equipped with an air-fuel ratio limit-cycle controller and a fuel metering actuator responsive to a controller generated signal, the controller having an operating cycle including complementary fuel phases each having a duration, the engine having operating variables which include an air-fuel ratio, a stoichiometric level, a mass air-flow, and a variable transport delay, the method comprising the steps of:

cyclically adjusting the level of the actuator control signal to center the operating cycle about the stoichiometric level;

determining a value of the mass air-flow by determining a value of the transport delay, forming the reciprocal of the value, and using the reciprocal of the value of the mass air-flow;

comparing the air-fuel ratio with the stoichiometric level, and if these engine operating variables differ by more than a predetermined amount, adjusting the air-fuel ratio by adjusting the duration of a fuel phase in proportion to the value of the mass air-flow; and

continuously repeating these steps,

whereby a change in engine air-flow produces a change in the air-fuel ratio which decreases the difference between the air-fuel ratio and the stoichiometric level with a consequent reduction in unwanted exhaust emissions.

6. The method of claim 5 wherein the controller complementary fuel phase include a fuel enrichment and fuel reduction phase, and wherein a fuel reduction phase is extended.

7. The method of claim 5 wherein the step of determining a value of the transport delay is accomplished by equipping the engine with an exhaust gas oxygen sensor producing an output signal having a pair of voltage levels and transitions therebetween, measuring the time between a predetermined pair of the transitions, and using the result as the value of the transport delay.

8. The method of claim 5 wherein the step of forming a reciprocal is accomplished by forming an approximation of the reciprocal.

9. The method of claim 8 wherein the step of forming an approximation of the reciprocal is accomplished by forming a product of a first constant and a value of the transport delay, forming a difference between a second constant and the product, and using the difference as the approximation of the reciprocal.

10. The method of claim 9 wherein the incorporated step of adjusting the duration of a fuel phase is accomplished by extending the duration in proportion to the approximation of the reciprocal.

11. The method of claim 10 further including the step of equipping the internal combustion engine to operate from a gaseous alternative fuel and operating the engine from such fuel.

12. The method of claim 5 further including the step of using a fuel wavefront to effect operation of the controller in a transport-delay-oscillator mode.

13. The method of claim 5 further including the step of forming a sum of an offset and the air-fuel ratio and comparing the sum with the stoichiometric level, whereby the operating cycle will be centered about the sum of the stoichiometric level and the offset.

14. The method of claim 13 further including the steps of equipping the internal combustion engine to operate selectively from gasoline or an alternative gaseous fuel, selecting a fuel and operating the engine from the selected fuel, and using a zero offset if the selected fuel is gasoline, else using a rich offset.

15. A method for reducing unwanted exhaust emissions for use with an internal combustion engine equipped with an air-fuel ratio limit-cycle controller and a fuel metering actuator responsive to a controller generated signal, the controller having an operating cycle including complementary fuel phases each having a duration, the engine having operating variables which include an air-fuel ratio, a stoichiometric level and a mass air-flow, the method comprising the steps of:

cyclically adjusting the level of the actuator control signal to center the operating cycle about the stoichiometric level;

determining a value of the mass air-flow;

forming a sum of an offset and the air-fuel ratio;

comprising the sum with the stoichiometric level, and if these engine operating variables differ by more than a predetermined amount, adjusting the air-fuel ratio by adjusting the duration of a fuel phase in proportion to the value of the mass air-flow, whereby the operating cycle will be centered about the sum of the stoichiometric level and the offset; and

continuously repeating these steps,

whereby a change in engine air-flow produces a change in the air-fuel ratio which decreases the difference between the air-fuel ratio and the stoichiometric level with a consequent reduction in unwanted exhaust emissions.

16. The method of claim 15 wherein the offset is selected to produce a rich air-fuel ratio.

17. The method of claim 15 wherein the offset is selected to produce a lean air-fuel ratio.

18. A method for reducing unwanted exhaust emissions by controlling an air-fuel ratio in an internal combustion engine operating on a gaseous alternative fuel and having an exhaust gas oxygen sensor, comprising the steps of:

(a) examining an output signal of the exhaust gas oxygen sensor to determine whether the air-fuel ratio is rich or lean;

(b) detecting a transition of the sensor output from a rich level to a lean level;

(c) rapidly increasing the output voltage of a first integrator by a first fuel wavefront step;

(d) setting an output voltage of a second integrator to an initial value;

(e) while the sensor output signal remains at the lean level, continuously repeating substeps (1)-(3),

(1) increasing the output voltage of the first integrator at a first rate,

(2) increasing the output voltage of a second integrator at a second rate,

(3) adjusting the air-fuel ratio in proportion to the first integrator output voltage; and

(f) detecting a transition of the sensor output signal from the lean level to the rich level;

(g) while the second integrator output voltage remains less than a predetermined threshold voltage, continuously repeating substeps (4)-(6),

(4) maintaining the approximate level of the first integrator output voltage,

(5) adjusting the air-fuel ratio in proportion to the first integrator output voltage,

(6) increasing the output voltage of the second integrator at the second rate; and

(h) detecting that the second integrator voltage equals the threshold voltage;

(i) rapidly decreasing the output voltage of the first integrator by a second fuel wavefront step;

(j) while the sensor output signal remains at the rich level, continuously repeating substeps (7) and (8),

(7) decreasing the first integrator output voltage at a third rate,

(8) adjusting the air-fuel ratio in proportion to the first integrator output voltage; and

(k) continuously repeating steps (b) through (k).

19. A method for reducing unwanted exhaust emissions by controlling an air-fuel ratio in an internal combustion engine operating on a gaseous alternative fuel and having an exhaust gas oxygen sensor, comprising the steps of:

(a) examining an output signal of the exhaust gas oxygen sensor to determine whether the air-fuel ratio is rich or lean;

(b) detecting a transition of the sensor output signal from the rich level to the lean level;

(c) adding a first fuel wavefront constant to a first count;

(d) initializing a second count to zero;

(e) while the sensor output signal remains at the lean level, continuously repeating substeps (1)-(4),

(b) incrementing the second count at a second rate,

(2) incrementing the second count at a second rate,

(3) converting the first count to an analog voltage level, and

(4) adjusting the air-fuel ratio in proportion to the analog voltage level;

(f) detecting a transition of the sensor output signal from the lean level to the rich level;

(g) until the second count equals a predetermined maximum value, continuously repeating substeps (5) and (6),

(5) maintaining the approximate level of the analog voltage, and

(6) incrementing the second count at the second rate;

(h) detecting that the second count equals the maximum value;

(i) subtracting a second fuel wavefront constant from the first count;

(j) while the sensor output signal remains at the rich level, continuously repeating substeps (7)-(9),

(7) decrementing the first count at a third rate,

(8) converting the contents of the first count to the analog voltage level, and

(9) adjusting the air-fuel ratio in proportion to the analog voltage level; and

(k) continuously repeating steps (b) through (k).