Air-fuel ratio feedback control system including at least downstreamside air-fuel ratio sensor

• US 4,964,272 A
• Filed: 07/18/1988
• Issued: 10/23/1990
• Est. Priority Date: 07/20/1987
• Status: Expired due to Term

• Current Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Kayanuma, Nobuaki
• Primary Examiner(s): Dolinar, Andrew M.
• Application Number:
  US07/220,790
• Time in Patent Office: 827 Days
• Field of Search: 123/440, 123/489, 123/589, 60/274, 60/276, 60/285
• US Class Current: 60/274
• CPC Class Codes: F02D 41/1441 Plural sensors
• CPC Class Codes: F02D 41/1481 Using a delaying circuit
• CPC Class Codes: F02D 41/1488 Inhibiting the regulation

Abstract

In an air-fuel ratio feedback control system including at least one air-fuel ratio sensor downstream of a catalyst converter provided in an exhaust gas passage, an actual air-fuel ratio is controlled in accordance with the output of the downstream-side air-fuel ratio sensor. When the engine is transferred from an open loop control state such as a fuel cut-off state or an OTP incremental state to an air-fuel ratio feedback control state for a stoichiometric air-fuel ratio by the downstream-side air-fuel ratio sensor, the speed of changing an air-fuel ratio correction amount in accordance with the output of the downstream-side air-fuel ratio sensor is at a conventional speed before the switching of the output of the downstream-side air-fuel ratio sensor, but thereafter (only immediately after the switching of the output of the downstream-side air-fuel ratio sensor or for a predetermined time period), this speed is increased.

Claims

1. A method for controlling an air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in the exhaust gas thereof, and upstream-side and downstream-side air-fuel ratio sensors disposed upstream and downstream, respectively, of said catalyst converter, for detecting a concentration of a specific component in the exhaust gas, comprising the steps of:

determining whether said engine is in an air-fuel ratio feedback control state for a stoichiometric air-fuel ratio by said downstream-side air-fuel ratio sensor or in an open loop control state for said upstream-side and downstream-side air-fuel ratio sensors;

calculating an air-fuel ratio correction amount in accordance with outputs of said upstream-side and downstream-side air-fuel ratio sensors when said engine is in said air-fuel ratio feedback control state;

determining whether or not a switching from the rich side to the lean side and a switching from the lean side occurs at an output of said downstream-side air-fuel ratio sensor;

changing the air-fuel ratio correction amount in accordance with the output of said upstream-side and said downstream-side air-fuel ratio sensors;

increasing the speed of change of said air-fuel ratio correction amount in accordance with the output of said downstream-side air-fuel ratio sensor for a predetermined time after a switching occurs in the output of said downstream-side air-fuel ratio sensor only the first time after said engine is switched from said open loop control state to said air-fuel ratio feedback control state; and

adjusting an actual air-fuel ratio in accordance with said air-fuel ratio correction amount.

2. A method as set forth in claim 1, wherein said open loop control state is a lean air-fuel ratio driving state,

said speed increasing step increasing the speed of change of said air-fuel ratio correction amount to the lean side.

3. A method as set forth in claim 1, wherein said open loop control state is a rich air-fuel ratio driving state,

said speed increasing step increasing the speed of change of said air-fuel ratio correction amount to the rich side.

4. A method as set forth in claim 1, wherein said speed increasing step increases the speed of change of said air-fuel ratio correction amount only immediately after a first occurrence of said switching after said engine is switched from said open loop control state to said air-fuel ratio feedback control state.

5. A method as set forth in claim 1, wherein said speed increasing step increases the speed of change of said air-fuel ratio correction amount from a first occurrence of said switching to a second occurrence of said switching after said engine is switched from said open loop control state to said air-fuel ratio feedback control state.

6. A method as set forth in claim 1, wherein said air-fuel ratio correction amount calculating step comprises the steps of:

calculating a first air-fuel ratio correction amount in accordance with the output of said upstream-side air-fuel ratio sensor;

calculating a second air-fuel ratio correction amount in accordance with the output of said downstream-side air-fuel ratio sensor; and

calculating said air-fuel ratio correction amount in accordance with said first and second air-fuel ratio correction amounts,

said speed increasing step increasing the speed of change of said second air-fuel ratio correction amount.

7. A method as set forth in claim 1, wherein said air-fuel ratio correction amount calculating step comprises the steps of:

calculating an air-fuel ratio feedback control parameter in accordance with the output of said downstream-side air-fuel ratio sensor;

calculating said air-fuel ratio correction amount in accordance with the output of said upstream-side air-fuel ratio sensor and said air-fuel ratio feedback control parameter,

said speed increasing step increasing the speed of change of said air-fuel ratio feedback control parameter.

8. A method as set forth in claim 7, wherein said air-fuel ratio feedback control parameter is defined by a lean skip amount by which said air-fuel ratio correction amount is skipped down when the output of said upstream-side air-fuel ratio sensor is switched from the lean side to the rich side and a rich skip amount by which said air-fuel ratio correction amount is skipped up when the output of said downstream-side air-fuel ratio sensor is switched from the rich side to the lean side.

9. A method as set forth in claim 7, wherein said air-fuel ratio feedback control parameter is defined by a lean integration amount by which said air-fuel ratio correction amount is gradually decreased when the output of said upstream-side air-fuel ratio sensor is on the rich side and a rich integration amount by which said air-fuel ratio correction amount is gradually increased when the output of said upstream-side air-fuel ratio sensor is on the lean side.

10. A method as set forth in claim 7, wherein said air-fuel ratio feedback control parameter is determined by a rich delay time period for delaying the output of said upstream-side air-fuel ratio sensor switched from the lean side to the rich side and a lean delay time period for delaying the output of said upstream-side air-fuel ratio sensor switched from the rich side to the lean side.

11. A method as set forth in claim 7, Wherein said air-fuel ratio feedback control parameter is determined by a reference voltage with which the output of said upstream-side air-fuel ratio sensor is compared, thereby determining whether the air-fuel ratio is on the rich side or on the lean side.

12. A method for controlling an air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in the exhaust gas thereof, and a downstream-side air-fuel ratio sensor disposed downstream of said catalyst converter, for detecting a concentration of a specific component in the exhaust gas, comprising the steps of:

determining whether said engine is in an air-fuel ratio feedback control state for a stoichiometric air-fuel ratio by said downstream-side air-fuel ratio sensor or in an open loop control state for said downstream-side air-fuel ratio sensor;

calculating an air-fuel ratio correction amount in accordance with the output of said air-fuel ratio sensor when said engine is in said air-fuel ratio feedback control state;

determining whether or not a switching from the rich side to the lean side and a switching from the lean side occurs in the output of said downstream-side air-fuel ratio sensor;

changing the air-fuel ratio correction amount in accordance with the output of said upstream-side and said downstream-side air-fuel ratio sensors;

increasing the speed of change of said air-fuel ratio correction amount in accordance with the output of said downstream-side air-fuel ratio sensor for a predetermined time after a switching occurs in the output of said downstream-side air-fuel ratio sensor only the first time after said engine is switched from said open loop control state to said air-fuel ratio feedback control state; and

adjusting an actual air-fuel ratio in accordance with said air-fuel ratio correction amount.

13. A method as set forth in claim 12, wherein said open loop control state is a lean air-fuel ratio driving state,

said speed increasing step increasing the speed of change of said air-fuel ratio correction amount to the lean side.

14. A method as set forth in claim 12, wherein said open loop control state is a rich air-fuel ratio driving state,

said speed increasing step increasing the speed of change of said air-fuel ratio correction amount to the rich side.

15. A method as set forth in claim 12, wherein said speed increasing step increases the speed of change of said air-fuel ratio correction amount only immediately after a first occurrence of said switching after said engine is switched from said open loop control state to said air-fuel ratio feedback control state.

16. A method as set forth in claim 12, wherein said speed increasing step increases the speed of change of said air-fuel ratio correction amount from a first occurrence of said switching to a second occurrence of said switching after said engine is switched from said open loop control state to said air-fuel ratio feedback control state.

17. An apparatus for controlling an air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in the exhaust gas thereof, and upstream-side and downstream-side air-fuel ratio sensors disposed upstream and downstream, respectively, of said catalyst converter, for detecting a concentration of a specific component in the exhaust gas, comprising:

means for determining whether said engine is in an air-fuel ratio feedback control state for a stoichiometric air-fuel ratio by said downstream-side air-fuel ratio sensor or in an open loop control state for said upstream-side and downstream-side air-fuel ratio sensors;

means for calculating an air-fuel ratio correlation amount in accordance with the outputs of said upstream-side and downstream-side air-fuel ratio sensors when said engine is in said air-fuel ratio feedback control state;

means for determining whether or not a switching from the rich side to the lean side and switching from the lean side occurs in the output of said downstream-side air-fuel ratio sensor ;

means for changing the air-fuel ratio correction amount in accordance with the output of said upstream-side and said downstream-side air-fuel ratio sensors;

means for increasing the speed of changing said air-fuel ratio correction amount in accordance with the output of said downstream-side air-fuel ratio sensor for a predetermined time after a switching occurs in the output of said downstream-side air-fuel ratio sensor only the first time after said engine is switched from said open loop control state to said air-fuel ratio feedback control state; and

means for adjusting an actual air-fuel ratio in accordance with said air-fuel ratio correction amount.

18. An apparatus as set forth in claim 17, wherein said loop control state is a lean air-fuel ratio driving state,

said speed increasing means increasing the speed of change of said air-fuel ratio correction amount to the lean side.

19. An apparatus as set forth in claim 17 wherein said open loop control state is a rich air-fuel ratio driving state,

said speed increasing means increasing the speed of change of said air-fuel ratio correction amount to the rich side.

20. An apparatus as set forth in claim 17, wherein said speed increasing means increases the speed of change of said air-fuel ratio correction amount only immediately after a first occurrence of said switching after said engine is switched from said open loop control state to said air-fuel ratio feedback control state.

21. An apparatus as set forth in claim 17, wherein said speed increasing means increases the speed of change of said air-fuel ratio correction amount from a first occurrence of said switching to a second occurrence of said switching after said engine is switched from said open loop control state to said air-fuel ratio feedback control state.

22. An apparatus as set forth in claim 17, wherein said air-fuel ratio correction amount calculating means comprises:

means for calculating a first air-fuel ratio correction amount in accordance with the output of said upstream-side air-fuel ratio sensor;

means for calculating a second air-fuel ratio correction amount in accordance with the output of said downstream-side air-fuel ratio sensor; and

means for calculating said air-fuel ratio correction amount in accordance with said first and second air-fuel ratio correction amounts;

said speed increasing means increasing the speed of change of said second air-fuel ratio correction amount.

23. An apparatus as set forth in claim 17, wherein said air-fuel ratio correction amount calculating means comprises:

means for calculating an air-fuel ratio feedback control parameter in accordance with the output of said downstream-side air-fuel ratio sensor;

means for calculating said air-fuel ratio correction amount in accordance with the output of said upstream-side and air-fuel ratio sensor and said air-fuel ratio feedback control parameter,

means for said speed increasing step increasing the speed of change of said air-fuel ratio feedback control parameter.

24. An apparatus as set forth in claim 23, wherein said air-fuel ratio feedback control parameter is defined by a lean skip amount by which said air-fuel ratio correction amount is skipped down when the output of said upstream-side air-fuel ratio sensor is switched from the lean side to the rich side and a rich skip amount by which said air-fuel ratio correction amount is skipped up when the output of said downstream-side air-fuel ratio sensor is switched from the rich side to the lean side.

25. An apparatus as set forth in claim 23, wherein said air-fuel ratio feedback control parameter is defined by a lean integration amount by which said air-fuel ratio correction amount is gradually decreased when the output of said upstream-side air-fuel ratio sensor is on the rich side and a rich integration amount by which said air-fuel ratio correction amount is gradually increased when the output of said upstream-side air-fuel ratio sensor is on the lean side.

26. An apparatus as set forth in claim 23, wherein said air-fuel ratio feedback control parameter is determined by a rich delay time period for delaying the output of said upstream-side air-fuel ratio sensor switched from the lean side to the rich side and a lean delay time period for delaying the output of said upstream-side air-fuel ratio sensor switched from the rich side to the lean side.

27. An apparatus as set forth in claim 23, wherein said air-fuel ratio feedback control parameter is determined by a reference voltage with which the output of said upstream-side air-fuel ratio sensor is compared, thereby determining whether the air-fuel ratio is on the rich side or on the lean side.

28. An apparatus for controlling an air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in the exhaust gas thereof, and a downstream-side air-fuel ratio sensor disposed downstream of said catalyst converter, for detecting a concentration of a specific component in the exhaust gas, comprising:

means for determining whether said engine is in an air-fuel ratio feedback control state for a stoichiometric air-fuel ratio by said downstream-side air-fuel ratio sensor or in an open loop control state for said downstream-side air-fuel ratio sensor;

means for calculating an air-fuel ratio correction amount in accordance with the output of said air-fuel ratio sensor when said engine is in said air-fuel ratio feedback control state;

means for determining whether or not a switching from the rich side to the lean side and a switching from the lean side occurs in the output of said downstream-side air-fuel ratio sensor;

means for changing the air-fuel ratio correction amount in accordance with the output of said upstream-side and said downstream-side air-fuel ratio sensors;

means for increasing the speed of change of said air-fuel ratio correction amount in accordance with the output of said downstream-side air-fuel ratio sensor for a predetermined time after a switching occurs in the output of said downstream-side air-fuel ratio sensor only the first time after said engine is switched from said open loop control state to said air-fuel ratio feedback control state; and

means for adjusting an actual air-fuel ratio in accordance with said air-fuel ratio correction amount.

29. An apparatus as set forth in claim 28, wherein said open loop control state is a lean air-fuel ratio driving state,

said speed increasing means increasing the speed of change of said air-fuel ratio correction amount to the lean side.

30. An apparatus as set forth in claim 28, wherein said open loop control state is a rich air-fuel ratio driving state,

said speed increasing means increasing the speed of change of said air-fuel ratio correction amount to the rich side.

31. An apparatus as set forth in claim 28, wherein said speed increasing means increases the speed of change of said air-fuel ratio correction amount only immediately after a first occurrence of said switching after said engine is switched from said open loop control state to said air-fuel ratio feedback control state.

32. An apparatus as set forth in claim 28, wherein said speed increasing means increases the speed of change of said air-fuel ratio correction amount from a first occurrence of said switching to a second occurrence of said switching after said engine is switched from said open loop control state to said air-fuel ratio feedback control state.