Air-fuel ratio control apparatus and method of internal combustion engine

Abstract

An air-fuel ratio feedback control range is enlarged to improve exhaust purification performance and output stability. In one aspect, an air-fuel ratio control apparatus of an internal combustion engine comprises an air-fuel ratio sensor capable of detecting an air-fuel ratio across both lean and rich ranges with a theoretical air-fuel ratio interposed therebetween. Feedback control is performed so as to bring an actual air-fuel into a target air-fuel ratio at least in a predetermined operational range on the basis of a detected value of the air-fuel ratio sensor. Even in a range where the air-fuel ratio is made richer than the theoretical air-fuel ratio, the target air-fuel ratio is set to be richer, and the air-fuel ratio feedback control may still be executed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

While the claims are not limited to the illustrated embodiments, an appreciation of various aspects of the apparatus and methods is best gained through a discussion of various examples thereof. Referring now to the drawings, illustrative embodiments are shown in detail. Although the drawings represent the embodiments, the drawings are not necessarily to scale and certain features may be exaggerated to better illustrate and explain an innovative aspect of an embodiment. Further, the embodiments described herein are not intended to be exhaustive or otherwise limiting or restricting to the precise form and configuration shown in the drawings and disclosed in the following detailed description. Exemplary embodiments of the present invention are described in detail by referring to the drawings as follows.

FIG. 1 is a system diagram of an air-fuel ratio control apparatus of an internal combustion engine;

FIG. 2 is a block diagram in the case where feedback control is performed by using a sliding mode control;

FIG. 3 is a flowchart of the sliding mode control;

FIG. 4 is a showing motions of the sliding mode control on a phase plane;

FIGS. 5A and 5B are timing charts for explaining a first effect of the control;

FIG. 6 is a timing chart for explaining a second effect of the control;

FIGS. 7A and 7B are timing charts for explaining a third effect of the control;

FIG. 8 is a block diagram in the case where the feedback control is performed by using PID control; and

FIG. 9 is flowchart in which a feedback gain of the PID control is calculated.

Claims

1. An air-fuel ratio control apparatus of an internal combustion engine, comprising: an air-fuel ratio sensor capable of detecting a stoichiometric air-fuel ratio and provided in an exhaust gas passage of an engine; anda controller selectively performing an air-fuel ratio feedback control to bring an air-fuel ratio of the engine toward a target air-fuel ratio on the basis of an output from the air-fuel ratio sensor, in which the target air-fuel ratio is a rich air-fuel ratio when the engine is operated in a rich operational region where fuel supply to the engine is increased.

2. The air-fuel ratio control apparatus of an internal combustion engine according to claim 1, wherein the air-fuel ratio feedback control is performed with a feedback coefficient for selectively bringing the air-fuel ratio toward the target air-fuel ratio and a selectively limiting the feedback coefficient at a limit value, in which the limit value used in the rich operational region is determined such that the feedback coefficient is generally limited as compared to the limit value used in an operational region other than the rich operational region.

3. The air-fuel ratio control apparatus of an internal combustion engine according to claim 2, wherein the air-fuel ratio control is performed with a sliding mode control, an inclination of a transfer function for the sliding mode control used in the rich operational region is smaller as compared to that used in the operational region other than the rich operational region.

4. The air-fuel ratio control apparatus of an internal combustion engine according to claim 2, wherein the air-fuel ratio control is performed with at least one of a Proportional Integral (PI) control and a Proportional Integral Derivative (PID) control, a proportional portion used in the rich operational region being smaller as compared to that used in the operational region other than the rich operational region.

5. The air-fuel ratio control apparatus of an internal combustion engine according to claim 2, wherein the air-fuel ratio control is performed with at least one of a Proportional Integral (PI) control and a Proportional Integral Derivative (PID) control, an integral portion used in the rich operational region being smaller as compared to that used in the operational region other than the rich operational region.

6. An air-fuel ratio control method of an internal combustion engine having an air-fuel ratio sensor capable of detecting a stoichiometric air-fuel ratio in an exhaust gas of the engine, comprising: determining whether an engine is operated in a rich operational region where fuel supply to the engine is increased, andperforming an air-fuel ratio feedback control for bringing an air-fuel ratio of the engine toward a target air-fuel ratio on the basis of an output from the air-fuel ratio sensor, in which the target air-fuel ratio is a rich air-fuel ratio when the engine is in the rich operational region.

7. An air-fuel ratio control method of an internal combustion engine according to claim 6, including the step of performing the air-fuel ratio feedback control with a feedback coefficient selectively bringing the air-fuel ratio toward the target air-fuel ratio and a limiter selectively limiting the feedback coefficient at a limit value, and determining the limit value used in the rich operational region such that the feedback coefficient is generally limited as compared to the limit value used in an operational region other than the rich operational region.