Feedback type air fuel ratio controlling system

• US 4,278,060 A
• Filed: 07/18/1980
• Issued: 07/14/1981
• Est. Priority Date: 05/02/1978
• Status: Expired due to Term

• Current Assignee: Toyota Jidosha Kogyo Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Toyota Jidosha Kogyo Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Isobe, Toshiaki, Yokoyama, Tatsuo
• Primary Examiner(s): Myhre, Charles J.
• Assistant Examiner(s): Nelli, R. A.
• Application Number:
  US06/169,986
• Time in Patent Office: 361 Days
• Field of Search: 123/437, 123/438, 123/440, 73/26, 73/27 R, 60/276, 60/285, 204/195 S, 204/15
• US Class Current: 123/696
• CPC Class Codes: F02D 41/1479 Using a comparator with variable reference

Abstract

A feedback type air fuel ratio controlling system for detecting and controlling an exhaust gas composition of an engine. A gas sensor provides a sensor signal related to an exhaust gas concentration. This sensor signal is coupled through an automatic gain control (AGC) DC level amplifier to a deviation detector. The deviation detector compares the signal to a reference signal V_p representing a stoichiometric air fuel mixture and provides a correction signal for adjusting the engine'"'"'s air fuel ratio. The AGC DC level amplifier provides automatic DC level compensation for a slowly deteriorating sensor and, working in combination with the deviation detector, an AC hysteresis response for judging rich to lean and lean to rich changes sensed by the exhaust gas sensor. When the output of the exhaust gas sensor varies slowly with respect to the time constant of the AGC DC amplifier, as with a deteriorating sensor, the DC level of the output voltage of the AGC DC amplifier is maintained substantially at a predetermined reference level Vs if the sensor signal coupled to the AGC DC amplifier is within a predetermined range. However, when the exhaust gas sensor output varies at a rate consistent with the time constant of the AGC DC level amplifier, a rich to lean change of the total air fuel ratio is detected at an earlier point in time than it would otherwise be detected in the absence of the AGC DC level amplifier by decreasing the gain of the AGC DC level amplifier and a lean to rich change of the total air fuel ratio is detected at an earlier point in time than it would otherwise be detected in the absence of the AGC DC level amplifier by increasing the gain of the AGC DC level amplifier.

Claims

1. A feedback type air fuel ratio controlling system comprising:

an exhaust gas sensor for supplying a sensor signal representative of an air fuel ratio,

an automatic gain control (AGC) DC level amplifier having a gain changeable at a predetermined time constant in response to said sensor signal of said sensor, including;

a variable gain DC amplifier having a signal input coupled to said sensor signal, an output, and a control input for controlling its gain,

said variable gain DC amplifier being responsive to said sensor signal so as to (a) decrease its gain in accordance with said predetermined time constant when the output of said variable gain DC amplifier is greater than a fixed predetermined reference signal Vs so that a rich to lean change of air fuel ratio is detected earlier than it would be in the absence of such a gain change, and (b) increase its gain in accordance with said predetermined time constant when the output of said variable gain DC amplifier is less than Vs so that a lean to rich change of air fuel ratio is detected earlier than it would be in the absence of such a gain change,

a comparator having a first input coupled to the output of said variable gain amplifier and a second input adapted to be coupled to a source of said reference signal Vs said comparator for producing a first signal whenever the output of said variable gain amplifier is greater than Vs and a second signal whenever the output of said variable gain amplifier is less than Vs, and

an integrator having an input coupled to the output of said comparator, for generating an output signal Vc, responsive to said first and second signals, said output signal Vc being coupled to said control input of said variable gain amplifier whereby the gain of said variable gain amplifier is controlled in accordance with the time constant of said integrator and the output signals of said comparator,

a deviation detector circuit for comparing the output of said automatic gain control DC level amplifier with a fixed reference signal Vp representing a stoichiometric air fuel ratio to produce a deviation signal, and

an actuator for controlling the air fuel ratio in response to the deviation signal.

2. In a feedback type air fuel ratio controlling system comprising an exhaust gas sensor for supplying a sensor signal representative of an air fuel ratio, a deviation detector circuit for comparing the output of the sensor with a first reference signal Vp, representing a stoichiometric air fuel ratio, to produce a correcting signal, and an air fuel ratio correcting circuit responsive to the correcting signal, the improvement comprising:

an automatic gain control DC level amplifier connected between the exhaust gas sensor and the deviation detector circuit and having a gain changeable at a predetermined time constant in response to the output signal of said sensor,

the output of said automatic gain control AGC DC level amplifier for being compared with said first reference voltage Vp,

said AGC DC level amplifier changing its gain at said predetermined time constant so as to (a) decrease when the output of said AGC DC level amplifier is greater than a second reference level Vs so that a rich to lean change of air fuel ratio is detected earlier than it would be in the absence of such a gain change, and (b) increase when the output of said AGC DC level amplifier is less than said second reference level Vs so that a lean to rich change of air fuel ratio is detected earlier than it would be in the absence of such a gain change.

3. An improvement according to claim 2, wherein said automatic gain control amplifier includes a reference voltage generator circuit for generating said second reference level Vs.

4. An improvement according to claim 3, wherein said automatic gain control amplifier includes a variable gain DC level amplifier for amplifying said sensor signals to provide an amplified signal, a comparator circuit for comparing the amplified signal with said second reference signal Vs to produce an error signal, and an integrating circuit responsive to the error signal for controlling the gain of said variable gain amplifier at said predetermined time constant.

5. An improvement according to either of claims 3 or 4, wherein said second reference voltage Vs is selected from a range of 0.8 Vs≦

Vp≦

0.9 Vs.

6. An improvement according to either of claims 3 or 4, wherein the parameters of said automatic gain are established such that when said exhaust gas sensor is deteriorated and its output is decreased thereby from a first range to a second image, said automatic gain control amplifier operates substantially at its maximum gain to compensate for the difference in magnitude between said ranges.

7. A feedback type air fuel ratio controlling system comprising an exhaust gas sensor for detecting gas composition concentrations, a controlling circuit receiving a detecting output signal of said exhaust gas sensor to produce an air fuel ratio controlling signal, and an actuator receiving the air fuel ratio controlling signal and responsive thereto to correct a total air fuel ratio to a target value, said controlling circuit comprising:

an automatic gain control DC level amplifier having a gain changeable at a predetermined time constant for receiving an output signal of said exhaust gas sensor and for providing an amplified signal responsive thereto, the gain of said automatic gain control DC level amplifier being responsive so as to (a) decrease in accordance with said predetermined time constant when the output of said variable gain DC amplifier is greater than a predetermined reference level so that a rich to lean change of air fuel ratio is detected earlier than it would be in the absence of such a gain change, and (b) increase in accordance with said predetermined time constant when the output of said variable gain DC amplifier is less than a predetermined reference level so that a lean to rich change of air fuel ratio is detected earlier than it would be in the absence of such gain change;

a reference value generator circuit for producing reference value of a fixed level, and

a deviation detector circuit for comparing and judging the output of said automatic gain control amplifier with the reference value.

8. A feedback type air fuel ratio controlling system comprising:

an exhaust gas sensor for supplying an output signal representative of an air fuel ratio;

an automatic gain control amplifier coupled to the output of said exhaust gas sensor and having an automatic hysteresis characteristic for automatically dynamically adjusting the gain of the automatic gain control amplifier so as to subject signals representing a rich to lean change of air fuel ratio to a greater gain than signals representing a lean to rich change of air fuel ratio and for automatically altering the range of the dynamic hysteresis characteristic to compensate for gas sensor deterioration;

a deviation detector for comparing the output of said automatic gain control amplifier with a fixed referenced voltage (Vp) to produce a deviation signal; and

an actuator for controlling the air fuel ratio in response to the deviation signal.

9. In a feedback air fuel ratio controlling system of the type including an exhaust gas sensor for providing a sensor signal indicative of a sensed air fuel ratio, a lean-rich detector for comparing the sensor signal with a first reference signal Vp representing a stoichiometric air fuel ratio and providing an air fuel ratio correcting signal responsive to the deviation of the sensor signal from the reference signal, and an air fuel ratio correcting circuit responsive to the correcting signal for controlling the air fuel ratio, an improvement comprising:

an automatic gain control (AGC) DC level amplifier coupling the output of said sensor to the input of said lean-rich detector, the gain of said AGC DC level amplifier being changeable at a predetermined time constant, said amplifier providing a variable gain changing at said predetermined time constant up to a maximum gain, to generate an amplified output of the sensor signal when the sensor signal is within a predetermined range, said AGC DC level amplifier responding to sensor signals varying slowly with respect to said time constant by changing its gain at said predetermined time constant so as to provide a predetermined nominal DC level output Vs, said AGC DC level amplifier also responding to said sensor signals on a cycle by cycle basis to decrease its gain when the amplified output is greater than Vs and to increase its gain when the amplified output is less than Vs,

said lean-rich detector being coupled to the output of said amplifier for comparing said first reference signal Vp and amplified output to generate the correcting signal;

whereby said AGC DC level amplifier by virtue of its gain change causes an earlier generation of said correcting signal to cause an earlier correction of air fuel ratio deviated from the stoichiometric air fuel ratio.

10. An improvement according to claim 9, wherein said AGC DC level amplifier comprises:

a variable gain DC level amplifier for amplifying said sensor signal,

a reference voltage generator for generating a second reference signal having a magnitude Vs;

a comparator for comparing the amplified output signal of said variable gain DC level amplifier with said reference signal to generate a first signal when said amplified output is higher than said voltage Vs and to generate a second signal when said amplified output is lower than said second voltage; and

an integrator responsive to said comparator for generating a third signal for decreasing the gain of said amplifier circuit in response to said first signal and for generating a fourth signal for increasing the gain of said amplifier circuit in response to said second signal said increasing or decreasing gain occurring at said predetermined time constant.

11. A feedback type air fuel ratio controlling system comprising:

an exhaust gas sensor for supplying a sensor signal representative of an air fuel ratio;

an automatic gain control DC level amplifier having a gain which changes at a predetermined time constant in response to the output signal of said sensor, said amplifier including

a variable gain DC level amplifier circuit having a signal input, an output, and a control input for controlling its gain, the signal input coupled to the output of said exhaust gas sensor,

a comparator having a first input coupled to the output of said variable gain amplifier circuit and a second input being adapted to be coupled to a first predetermined reference voltage Vs and producing a first signal whenever the output of said variable gain amplifier is greater than Vs and a second signal whenever the output of said variable gain amplifier is less than Vs, and

an integrator coupling the output of said comparator to said control input of said amplifier circuit for decreasing or increasing the gain of said amplifier circuit in response to said first or second signal, respectively, of said comparator at said predetermined time constant;

a lean-rich detector circuit for comparing the decreased or increased output of said amplifier circuit with a second predetermined reference voltage Vp to produce a detection signal representing a lean or rich state of air fuel ratio; and

an actuator for controlling the air fuel ratio to stoichiometric ratio in response to the detection signal;

whereby when the sensor signal changes in accordance with said predetermined time constant, said decreased or increased output of said amplifier provides a hysteresis characteristic to said lean-rich detector between increase or decrease of the sensor output signal in order to cause an earlier detection of a lean to rich change and a rich to lean change of the air fuel ratio in order to cause a corresponding earlier control of the air fuel ratio by said actuator.

12. An air fuel ratio controlling system comprising:

an exhaust gas sensor for supplying a sensor signal representative of an air fuel ratio;

a deviation detector for comparing a signal representative of said sensor signal with a fixed reference level Vp representing a desired air fuel ratio to produce a deviation signal indicating a difference between an air fuel ratio sensed by said sensor and said desired air fuel ratio;

an actuator for controlling the air fuel ratio in response to the deviation signal; and

an automatic gain control (AGC) DC level amplifier, coupled between said exhaust gas sensor and said deviation detector, for receiving said sensor signal and providing an amplified signal to said deviation detector, said AGC DC level amplifier having a DC response to the sensor signal for maintaining said amplified signal at a predetermined nominal DC level, and having an AC response to the output signal of said sensor so as to (a) change its gain in a first direction when said amplified signal is greater than a second predetermined reference level Vs and change its gain in a second direction when said amplified signal is less than Vs, whereby both rich to lean and lean to rich changes of air fuel ratio are detected earlier than they would be in the absence of such gain changes.

13. An air fuel ratio controlling system according to claim 12, wherein said AGC DC level amplifier comprises,

a variable gain DC amplifier having a signal input coupled to said sensor signal, an output, and a control input for controlling its gain;

a comparator having a first input coupled to the output of said variable gain DC amplifier and a second input coupled to said second reference level Vs, said comparator for comparing said amplified signal to said second reference level, Vs and providing a comparator signal indicative thereof; and

an integrator coupling the output of said comparator to said control input of said variable gain DC amplifier.

14. An air fuel ratio controlling system according to either of claims 12 or 13 wherein said fixed reference level Vp represents a stoichiometric air fuel ratio.

15. An air fuel ratio controlling system according to either of claims 12 or 13, wherein said first direction represents a decrease in gain and wherein said second direction represents an increase in gain.

16. An air fuel ratio controlling system according to either of claims 12 or 13, wherein said second predetermined reference level is selected from a range of 0.8 Vs≦

Vp≦

0.9 Vs.

17. In a feedback type air fuel ratio controlling system comprising an exhaust gas sensor for supplying a sensor signal representative of air fuel ratio, a deviation detector circuit for comparing the sensor signal with a fixed reference signal Vp, representing a stoichiometric air fuel ratio, to produce a correcting signal, and an air fuel ratio correcting circuit responsive to the correcting signal, the improvement comprising:

an automatic gain control (AGC) DC level amplifier, coupled between said exhaust gas sensor and said deviation detector circuit, for receiving said sensor signal and providing an amplified signal to said deviation detector circuit, said AGC DC level amplifier having a DC response to the sensor signal for maintaining said amplified signal at a predetermined nominal DC level, and having an AC response to the output signal of said sensor so as to (a) change its gain in a first direction when said amplified signal is greater than a second predetermined reference level Vs and change its gain in a second direction when said amplified signal is less than Vs, whereby both rich to lean and lean to rich changes of air fuel ratio are detected earlier than they would be in the absence of such gain changes.

18. An improvement according to claim 17, wherein said AGC DC level amplifier comprises:

a variable gain DC amplifier having a signal input coupled to said sensor signal, an output, and a control input for controlling its gain;

a comparator having a first input coupled to the output of said variable gain DC amplifier and a second input adapted to be coupled to a second fixed reference signal Vs, said comparator for comparing said amplified signal to said second reference signal Vs and providing a comparator signal indicative thereof; and

an integrator coupling the output of said comparator to said control input of said variable gain DC amplifier.

19. An improvement according to either of claims 17 or 18 wherein said fixed reference level Vp represents a stoichiometric air fuel ratio.

20. An improvement according to either of claims 17 or 18, wherein said first direction represents a decrease in gain and wherein said second direction represents an increase in gain.

21. An improvement according to either of claims 17 or 18, wherein said second predetermined reference level is selected from a range of 0.8 Vs Vp 0.9 Vs.