Air/fuel ratio control device for an internal combustion engine

• US 4,355,615 A
• Filed: 05/02/1980
• Issued: 10/26/1982
• Est. Priority Date: 05/04/1979
• Status: Expired due to Term

• Current Assignee: Nissan Motor Co., Ltd.
• Original Assignee: Nissan Motor Co., Ltd.
• Inventors: Asano, Masaharu, Tamura, Hideyuki, Furuhashi, Shoji
• Primary Examiner(s): Nelli, Raymond A.
• Application Number:
  US06/145,987
• Time in Patent Office: 907 Days
• Field of Search: 123/440, 123/445, 123/437, 123/438, 123/489, 60/276, 60/285
• US Class Current: 123/688
• CPC Class Codes: F02D 41/149 Replacing of the control value by an other parameter
• CPC Class Codes: F02D 41/1495 Detection of abnormalities in the air/fuel ratio feedback system
• CPC Class Codes: F02D 41/1496 Measurement of the conductivity of a sensor F02D41/1455 takes precedence

Abstract

Disclosed herewith an air/fuel ratio control device for and internal combustion engine which is capable of carrying out either feedback control or open loop control. In feedback control, a signal indicating the concentration of exhaust gas components is generated and fed to a fuel supply control device. In open loop control, a fuel injection rate is determined corresponding to intake air flow rate. For switching between feedback control and open loop control, the air/fuel ratio control device is provided with a means for detecting an abnormal condition of signal, and a means operative in response to the abnormal signal to interrupt feedback control. The air/fuel ratio control device is further provided with a means for detecting stopping of the abnormal signal and for returning control operation to feedback control.

Claims

1. An air/fuel control device for an internal combustion engine having a fuel supply comprising:

an exhaust gas sensor provided in an exhaust gas passage of said internal combustion engine for determining an exhaust gas component concentration and for generating a sensor signal indicative of the determined concentration;

a discriminating circuit for comparing said sensor signal value with a first reference value and determining if said exhaust gas sensor temperature condition satisfies a feedback control condition, said discriminating circuit producing a switching signal when said feedback control condition is satisfied;

a control circuit, responsive to said switching signal, for effecting feedback control operation and open loop control operation selectively, said control circuit feedback controlling said fuel supply and producing a control signal indicative of a determined fuel rate, said control circuit resetting said first reference value to a minimum value when control operation mode is switched from feedback control to open loop control; and

an electric power supply control circuit for controlling an electric current supplied to said exhaust gas sensor, said power supply control circuit including a switching means for adjusting the electric current value, said switching means having first means for comparing said sensor signal value with a minimum value for determining the sensor condition, second means for measuring a period of time during which said first means determines said sensor signal value is lower than said minimum value and a third means for supplying a minimum value of electric current when said second means determining said sensor is not in a condition to effect feedback control.

6. A device as set forth in claim 1, wherein said exhaust gas sensor is a zirconia oxygen sensor having an internal resistance depending on sensor temperature.

7. A device as set forth in claim 1, wherein said switching means further includes means for detecting said sensor signal value and generating a switching signal when said signal value voltage exceeds said minimum value and a means for increasing the electric current supplied to said sensor in response to said switching signal.

8. A device as set forth in claim 1, wherein said control circuit includes a means for returning control operation from open loop control to feedback control if said sensor signal value exceeds said minimum value during open loop control operation.

9. A device as set forth in claim 1, wherein said reference voltage is increased by a given amount for a given amount of engine revolution.

10. A device as set forth in claim 1, wherein said reference voltage is increased at a fixed rate in read time.

11. A device as set forth in claim 1, wherein said timer means becomes inoperative under fuel shut off condition of fuel supply means.

2. A method for controlling the air/fuel ratio in an internal combustion engine having an air/fuel ratio control system and having fuel supply means for controlling the air/fuel ratio, said system including an exhaust gas sensor for determining the concentration of an exhaust gas component and generating an exhaust gas sensor signal corresponding to the sensed exhaust gas component concentration, said system being operable to control the air/fuel ratio by feedback control or by open loop control and having means for switching control operation between feedback control and open loop control corresponding to a condition of said sensor, the method comprising

supplying an electric current to said exhaust gas sensor;

changing said current value between predetermined maximum and minimum values;

generating a sensor signal indicative of the sensed exhaust gas component concentration while applying said electric current to said sensor;

comparing said sensor signal value with reference values, said reference values defining maximum and minimum values respectively to determine if the sensor is in a condition to carry out feedback control;

controlling said fuel supply means by feedback control;

measuring the period of time during which said sensor signal value remains below said minimum value;

switching control operation from feedback control to open loop control when said measured period of time is longer than a predetermined period; and

resetting the value of said reference values to be compared with said sensor signal value to the minimum value thereof and setting said electric current to be supplied to the exhaust gas sensor to the minimum value thereof when switching control operation from feedback control to open loop control.

12. A method as set forth in claim 2, wherein said reference value is set at said maximum value during feedback control operation.

13. A method as set forth in claim 12, wherein said reference value is gradually increased from said minimum value to said maximum value at a predetermined rate and a predetermined timing.

14. A method as set forth in claim 13, wherein said predetermined timing is determined as a function of engine revolution.

15. A method as set forth in claim 13, wherein said predetermined timing is defined by a clock timer.

16. A method as set forth in claim 2, including the step of interrupting said feedback control under a fuel cut off condition of said fuel supply means.

3. A feedback control system for an internal combustion engine, said control system operable as a feedback system or an open loop system comprising:

fuel supply means for supplying fuel to the engine at a controlled rate, said fuel being supplied as a gas mixture having an air/fuel ratio;

an exhaust system including an exhaust passage having an oxygen sensor for determining oxygen concentration in the exhaust gas and for producing a sensor signal indicative of the determined oxygen concentration;

a power circuit for supplying an electric current to said oxygen sensor, said power circuit varying the electric current value to be supplied to the oxygen sensor depending upon the sensor temperature;

control means for comparing said sensor signal value with a first reference value to discriminate whether the sensor temperature condition satisfies a feedback condition and for feedback controlling said fuel supply means based on a difference between said sensor signal value and a second reference value representative of a desired air/fuel ratio while said feedback condition is satisfied, said control means including means for incrementing said second reference value at a given rate and a given timing and for setting said second reference value at a minimum value when control operation is switched from feedback control to open loop control, said control means varying the current value supplied to the oxygen sensor to a predetermined minimum value during open loop operation.

17. A system as set forth in claim 3 or 4, wherein said control means includes means for measuring a period of time during which said sensor signal value remains less than said first reference value and for comparing said period with a predetermined period of time, wherein said control means switches control operation from feedback control to open loop control when the measured period exceeds said predetermined period.

18. A system as set forth in claim 17, wherein said power circuit includes a switch means for selectively changing between a first position supplying maximum value of current to said sensor, and a second position supplying minimum value of current and a third position disconnecting the sensor from a power source, said switch means being shifted to said second position in response to said control means switching the control operation from feedback control to open loop control.

4. A feedback control system for an internal combustion engine for controlling air/fuel ratio of a mixture to be supplied thereto, comprising:

fuel supply means for supplying fuel to the engine at a controlled rate;

an exhaust system including an exhaust passage having an oxygen sensor for determining an oxygen concentration in the exhaust gas and producing a sensor signal value indicative of said oxygen concentration;

a power circuit for supplying an electric current to said oxygen sensor, said power circuit varying the current value depending on the oxygen sensor temperature condition within a predetermined range;

discrimination means for discriminating if said mixture is rich or lean based on said sensor signal value, said discrimination means comprising said sensor signal value with a second reference value representative of a desired air/fuel ratio;

control means for feedback controlling said fuel supply means based on the difference between said second reference value and said sensor signal value, said control means having means for incrementing said second reference value at a given rate and a given timing during feedback control, said control means further comprising said sensor signal value with a first reference value indicative of the minimum value for feedback control operation and having means for switching control operation from feedback control to open loop control when the sensor signal value is smaller than said first reference value and setting said second reference value to a predetermined minimum value and said current value to be supplied to the sensor by said power circuit to a minimum value in said predetermined range.

5. A method for controlling air/fuel ratio in a mixture supplied to an internal combustion engine having a fuel supply comprising:

measuring an oxygen concentration in an exhaust gas and producing a sensor signal indicative of the measured oxygen concentration;

comparing said sensor signal value with a second reference value representative of a desired air/fuel ratio and obtaining any difference therebetween;

determining fuel supply to the engine based on said difference between the measured sensor signal value and said second reference value and feedback controlling said fuel supply so that the air/fuel ratio supplied to said engine approaches said desired value;

supplying electric current to said oxygen sensor,

varying said electric current to the sensor depending on the sensor temperature condition;

comparing said sensor signal value with a first reference value representative of the minimum value of the sensor signal for feedback control operation;

measuring a period of time during which the sensor signal value remains below said first reference value;

switching operational control of said fuel supply from feedback control to open loop control when the measured period exceeds a predetermined period;

setting said second reference value to a predetermined minimum value and said electric current to the sensor to a predetermined minimum value during open loop operation; and

returning the operational control from open loop to feedback control when the sensor signal value becomes larger than the minimum first reference value.

19. A method as set forth in claim 5, wherein said second reference value is incremented at a predetermined timing and a predetermined rate during feedback control operation.

20. A method as set forth in claim 5 or claim 19, wherein feedback control is disabled when the fuel supply is a state of cut-off.