Inter-cylinder air-fuel ratio imbalance determination apparatus for internal combustion engine

• US 8,560,208 B2
• Filed: 11/05/2009
• Issued: 10/15/2013
• Est. Priority Date: 11/05/2009
• Status: Active Grant

• Current Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Miyamoto, Hiroshi, Iwazaki, Yasushi, Sawada, Hiroshi
• Primary Examiner(s): Kwon, John
• Application Number:
  US13/505,849
• Publication Number:
  US 20120215427A1
• Time in Patent Office: 1,440 Days
• Field of Search: 701103-105, 701/114, 701/115, 123/434, 123/672, 123/674, 123/679, 123/690
• US Class Current: 701/103
• CPC Class Codes: F02D 41/0065 Specific aspects of external EGR control constructional details of EGR system F02M26/00
• CPC Class Codes: F02D 41/0085 Balancing of cylinder outputs, e.g. speed, torque or air-fuel ratio
• CPC Class Codes: F02D 41/1454 the characteristics being an oxygen content or concentration or the air-fuel ratio
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

An inter-cylinder air-fuel ratio imbalance determination apparatus (determination apparatus) according to the present invention obtains, as an “EGR supplying state imbalance determination parameter”, a value corresponding to a differential value d(abyfs)dt of a detected air-fuel ratio abyfs represented by an output value of an air-fuel ratio sensor when an EGR gas is being supplied, and obtains, as an “EGR stop state imbalance determination parameter”, a value corresponding to a differential value d(abyfs)dt when an EGR gas supply is being stopped. The determination apparatus obtains an “EGR-causing imbalance determination parameter Pegr” by subtracting the EGR stop state imbalance determination parameter Poff from the EGR supplying state imbalance determination parameter Pon, and determines that an inter-cylinder air-fuel ratio imbalance state has occurred due to the supply of the EGR gas when the parameter Pegr is larger than a threshold Pegrth.

Claims

1. An inter-cylinder air-fuel ratio imbalance determination apparatus, which is applied to a multi-cylinder internal combustion engine having a plurality of cylinders, and which determines whether or not an inter-cylinder air-fuel ratio imbalance state in which a cylinder-by-cylinder air-fuel ratio difference is larger than or equal to a predetermined value has been occurring, said cylinder-by-cylinder air-fuel ratio difference being a difference between air-fuel ratios of mixtures supplied to at least two or more of a plurality of said cylinders, said at least two or more of a plurality of said cylinders being configured to discharge exhaust gases to an exhaust merging portion of an exhaust passage of said engine, comprising:

a plurality of fuel injection valves, disposed in such a manner that each of said injection valves corresponds to each of said at least two or more of said cylinders, each of said fuel injection valves injecting fuel contained in an air-fuel mixture supplied to each of combustion chambers of said at least two or more of said cylinders;

an EGR gas supply unit which includes a plurality of EGR gas supply openings, each of said EGR gas supply openings being disposed for each of said at least two or more of said cylinders and supplying an external EGR gas to each of said combustion chambers of said at least two or more of said cylinders;

an EGR gas supply control unit, which is configured to realize an EGR supplying state in which said external EGR gas is supplied through a plurality of said EGR gas supply openings when an operating condition of said engine satisfies a predetermined EGR execution condition, and to realize an EGR stop state in which said external EGR gas supply is stopped when said operating condition of said engine does not satisfy said EGR execution condition;

an air-fuel ratio sensor, which is disposed at said exhaust merging portion or at a portion downstream of said exhaust merging portion in said exhaust passage, and which outputs an output value corresponding to an air-fuel ratio of an exhaust gas at a position where said air-fuel ratio sensor is disposed;

an imbalance determination parameter obtaining unit,

that obtains, based on said output value of said air-fuel ratio sensor, an EGR stop state imbalance determination parameter whose absolute value becomes larger as said cylinder-by-cylinder air-fuel ratio difference becomes larger when said EGR stop state is being realized,

that obtains, based on said output value of said air-fuel ratio sensor, an EGR supplying state imbalance determination parameter whose absolute value becomes larger as said cylinder-by-cylinder air-fuel ratio difference becomes larger when said EGR supplying state is being realized, and

that obtains an EGR-causing imbalance determination parameter varying depending on a degree of a difference between said EGR supplying state imbalance determination parameter and said EGR stop state imbalance determination parameter; and

an imbalance determination unit, which is configured to compare said EGR-causing imbalance determination parameter with a predetermined EGR-causing imbalance determination threshold, and to determine whether or not said inter-cylinder air-fuel ratio imbalance state has occurred based on said result of said comparison.

2. The inter-cylinder air-fuel ratio imbalance determination apparatus according to claim 1, wherein said imbalance determination parameter obtaining unit is configured to obtain, as said EGR-causing imbalance determination parameter, a value corresponding to said difference between said EGR supplying state imbalance determination parameter and said EGR stop state imbalance determination parameter.

3. The inter-cylinder air-fuel ratio imbalance determination apparatus according to claim 1, wherein said imbalance determination parameter obtaining unit is configured to obtain, as said EGR-causing imbalance determination parameter, a value corresponding to a ratio of said EGR supplying state imbalance determination parameter to said EGR stop state imbalance determination parameter.

4. The inter-cylinder air-fuel ratio imbalance determination apparatus according to claim 1, wherein,

said EGR execution condition is a condition which is satisfied when an actual rotational speed of said engine and an actual load of said engine is in an EGR execution region, and

said EGR gas supply control unit is configured to

set said EGR execution region to a predetermined usual EGR execution region, when neither said EGR supplying state imbalance determination parameter nor said EGR stop state imbalance determination parameter has been obtained, or when both of said EGR supplying state imbalance determination parameter and said EGR stop state imbalance determination parameter have been obtained;

and

set said EGR execution region to a narrowed EGR execution region which is within said usual EGR execution region and is narrower than said usual EGR execution region, when said EGR supplying state imbalance determination parameter has been obtained and said EGR stop state imbalance determination parameter has not been obtained.

5. The inter-cylinder air-fuel ratio imbalance determination apparatus according to claim 4, wherein,

said imbalance determination parameter obtaining unit is configured to

obtain said EGR supplying state imbalance determination parameter when said actual rotational speed of said engine and said actual load of said engine is in a predetermined parameter obtaining region in which said imbalance determination parameters are allowed to be obtained and said EGR supplying state is being realized, and

obtain said EGR stop state imbalance determination parameter when said actual rotational speed of said engine and said actual load of said engine is in said parameter obtaining region and said EGR stop state is being realized;

and

said EGR gas supply control unit is configured to

set said narrowed EGR execution region to a region which is within said usual EGR execution region but is not within said parameter obtaining region.

6. The inter-cylinder air-fuel ratio imbalance determination apparatus according to claim 1, wherein,

said EGR execution condition is a condition which is satisfied when an actual rotational speed of said engine and an actual load of said engine is in an EGR execution region, and

said EGR gas supply control unit is configured to

set said EGR execution region to a predetermined usual EGR execution region, when neither said EGR supplying state imbalance determination parameter nor said EGR stop state imbalance determination parameter has been obtained, or when both of said EGR supplying state imbalance determination parameter and said EGR stop state imbalance determination parameter have been obtained;

and

set said EGR execution region to an enlarged EGR execution region which includes said usual EGR execution region and is wider than said usual EGR execution region, when said EGR stop state imbalance determination parameter has been obtained and said EGR supplying state imbalance determination parameter has not been obtained.

7. The inter-cylinder air-fuel ratio imbalance determination apparatus according to claim 6, wherein,

said imbalance determination parameter obtaining unit is configured to

obtain said EGR supplying state imbalance determination parameter when said actual rotational speed of said engine and said actual load of said engine is in a predetermined parameter obtaining region in which said imbalance determination parameters are allowed to be obtained and said EGR supplying state is being realized, and

obtain said EGR stop state imbalance determination parameter when said actual rotational speed of said engine and said actual load of said engine is in said parameter obtaining region and said EGR stop state is being realized,

said EGR gas supply control unit is configured to

set said enlarged EGR execution region to a region which is included within at least one of said usual EGR execution region and said parameter obtaining region.

8. The inter-cylinder air-fuel ratio imbalance determination apparatus according to claim 1, wherein,

said EGR gas supply control unit is configured, in a case in which said EGR supplying state imbalance determination parameter has been obtained and said EGR stop state imbalance determination parameter has not been obtained, to realize said EGR supplying state when a state in which said EGR execution condition is satisfied continues for a time period equal to or longer than a predetermined start delay time, and to realize said EGR stop state when said EGR execution condition becomes unsatisfied.

9. The inter-cylinder air-fuel ratio imbalance determination apparatus according to claim 8, wherein,

said imbalance determination parameter obtaining unit is configured to

obtain said EGR stop state imbalance determination parameter when a predetermined parameter obtaining condition for obtaining said imbalance determination parameters is being satisfied and said EGR stop state is being realized, and

obtain said EGR supplying state imbalance determination parameter when said parameter obtaining condition is being satisfied and said EGR supplying state is being realized, and

said EGR gas supply control unit is configured to realize said EGR supplying state when said parameter obtaining condition becomes unsatisfied even before said state in which said EGR execution condition is satisfied continues for said time period equal to or longer than said start delay time, in said case in which said EGR supplying state imbalance determination parameter has been obtained and said EGR stop state imbalance determination parameter has not been obtained.

10. The inter-cylinder air-fuel ratio imbalance determination apparatus according to claim 1, wherein,

said EGR gas supply control unit is configured, in a case in which said EGR stop state imbalance determination parameter has been obtained and said EGR supplying state imbalance determination parameter has not been obtained, to realize said EGR supplying state when said EGR execution condition is satisfied, and to realize said EGR stop state when a state in which said EGR execution condition is unsatisfied continues for a time period equal to or longer than a predetermined stop delay time.

11. The inter-cylinder air-fuel ratio imbalance determination apparatus according to claim 10, wherein,

said imbalance determination parameter obtaining unit is configured to

obtain said EGR stop state imbalance determination parameter when a predetermined parameter obtaining condition for obtaining said imbalance determination parameters is being satisfied and said EGR stop state is being realized, and

obtain said EGR supplying state imbalance determination parameter when said parameter obtaining condition is being satisfied and said EGR supplying state is being realized, and

said EGR gas supply control unit is configured to realize said EGR stop state when said parameter obtaining condition becomes unsatisfied even before said state in which said EGR execution condition is unsatisfied continues for said time period equal to or longer than said stop delay time, in said case in which said EGR stop state imbalance determination parameter has been obtained and said EGR supplying state imbalance determination parameter has not been obtained.

12. The inter-cylinder air-fuel ratio imbalance determination apparatus according to claim 1, wherein,

said imbalance determination unit is configured to compare said EGR supplying state imbalance determination parameter with a predetermined EGR supplying state imbalance determination threshold, and to determine whether or not said inter-cylinder air-fuel ratio imbalance state has occurred also based on said result of said comparison.

13. The inter-cylinder air-fuel ratio imbalance determination apparatus according to claim 1, wherein,

said imbalance determination unit is configured to compare said EGR stop state imbalance determination parameter with a predetermined EGR stop state imbalance determination threshold, and to determine whether or not said inter-cylinder air-fuel ratio imbalance state has occurred also based on said result of said comparison.

14. The inter-cylinder air-fuel ratio imbalance determination apparatus according to claim 1, wherein,

said EGR supplying state imbalance determination parameter is a value corresponding to a change amount of said output value of said air-fuel ratio sensor per unit time, and

said EGR stop state imbalance determination parameter is a value corresponding to said change amount of said output value of said air-fuel ratio sensor per unit time.

15. The inter-cylinder air-fuel ratio imbalance determination apparatus according to claim 1, wherein,

said EGR supplying state imbalance determination parameter is a value corresponding to a change amount of a change amount of said output value of said air-fuel ratio sensor per unit time, and

said EGR stop state imbalance determination parameter is a value corresponding to said change amount of a change amount of said output value of said air-fuel ratio sensor per unit time.

16. The inter-cylinder air-fuel ratio imbalance determination apparatus according to claim 1, wherein,

said EGR supplying state imbalance determination parameter is a value corresponding to a trace length of said output value of said air-fuel ratio sensor, and

said EGR stop state imbalance determination parameter is a value corresponding to said trace length of said output value of said air-fuel ratio sensor.