JPS63105262A - Control of air-fuel ratio in thin-combustion type internal combustion engine - Google Patents

Abstract

PURPOSE:To decrease the time delay at feedback control, so as to raise precision of control, by detecting combustion light in a combustion chamber by an optical sensor, and controlling air-fuel ratio as value of output of said optical sensor corresponds with the air-fuel ratio at the misfire limit. CONSTITUTION:An optical sensor 13 such as a phototransistor is set in an internal combustion engine 1, as this sensor 13 is isolated by a fused quartz 12 and confronts the inside of a combustion chamber 2, and the detected value of the optical sensor 13 is input in a control circuit 25. This control circuit 25 controls the quantity of fuel fed from a carburetor 5 through an air-fuel ratio control valve 24, as the detected value of the optical sensor 13 corresponds with the air-fuel ratio at the misfire limit.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention is directed to a lean-burn internal combustion engine in which the air-fuel ratio of the intake air-fuel mixture is leaner than the stoichiometric air-fuel ratio. The present invention relates to a method for controlling the fuel ratio to be lean.

[Conventional technology and its problems]

In recent internal combustion engines, in order to reduce harmful components in exhaust gas and improve fuel consumption, it is possible to make the air-fuel ratio of the intake air-fuel mixture leaner than the stoichiometric air-fuel ratio. It has been carried out, and JP-A-59-1989 is considered as prior art.
Publication No. 18253 discloses that a lean sensor is provided in the exhaust system of the internal combustion engine as a control for making the air-fuel ratio of the intake air-fuel mixture lean in such a lean-burn internal combustion engine, and the output of the lean sensor is adjusted to a target level. It is proposed that the air-fuel ratio in the intake system be feedback-controlled so that it becomes a value corresponding to a lean air-fuel ratio.

However, this feedback control is a control that adjusts the air-fuel ratio of the intake air-fuel mixture before combustion by looking at the result after the intake air-fuel mixture has been combusted. The time required to reach the lean air-fuel ratio becomes longer, in other words, the time during which the air-fuel ratio deviates from the target lean air-fuel ratio becomes longer, resulting in lower control accuracy.

Moreover, the lean sensor cannot determine the state of misfire in the combustion chamber, and the target lean air-fuel ratio is quite different from the air-fuel ratio at the misfire limit actually measured for a typical internal combustion engine. The actual situation is that the effect of diluting the intake air-fuel mixture cannot be sufficiently achieved because it must be set to a value that takes into account the safe value of .

An object of the present invention is to reduce the time delay during feedback control of the lean air-fuel ratio, thereby improving control accuracy and achieving more sufficient leanness.

[Means for solving problems]

The present invention is based on the fact that the combustion light emitted when the intake air-fuel mixture burns varies in strength depending on the value of the air-fuel ratio, and that this combustion light becomes weaker in proportion to the leaner air-fuel ratio.
The combustion light produced when the intake air-fuel mixture burns in the combustion chamber is directly detected by an optical sensor such as a phototransistor, and the intake system is The system is designed to adjust the air-fuel ratio at

[Action/effect of the invention]

In this way, the air-fuel ratio of the intake air-fuel mixture entering the combustion chamber can be adjusted by observing the state of combustion of the intake air-fuel mixture in the combustion chamber using an optical sensor, so the responsiveness to changes in the air-fuel ratio can be improved. , the air-fuel ratio of the intake air-fuel mixture can be much improved compared to the conventional feedback control using the lean sensor, which controls the air-fuel ratio of the intake air-fuel mixture based on the combustion result of the intake air-fuel mixture. Since the presence or absence of a misfire can be detected, it is possible to reliably reduce the air-fuel ratio of the intake air-fuel mixture to the misfire limit air-fuel ratio.

Therefore, according to the present invention, it is possible to reliably dilute the air-fuel ratio of the intake air-fuel mixture to the misfire limit air-fuel ratio, thereby further promoting the effect of diluting the intake air-fuel mixture and improving the accuracy of this control. have an effect.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. In the drawings, reference numeral 1 indicates a spark ignition type internal combustion engine. A carburetor 5 with a lean air-fuel ratio setting is connected to the carburetor 5 via an intake manifold 6, and an air cleaner 7 is connected to the upstream side of the carburetor 5. On the other hand, an exhaust port 9 communicating with the combustion chamber 2 of the internal combustion engine 1 via an exhaust valve 8 is connected to an exhaust purification device 10 via an exhaust manifold 11.
An optical sensor 13 such as a phototransistor is isolated from the combustion chamber 2 by a quartz glass 12 and is provided so as to look into the combustion chamber 2.

The carburetor 5 is provided with an air/lead bow) 19.20 in each of the main fuel passage 14 to the main nozzle 15 and the slow system fuel passage 18 to the idle boat 16 and slow boat 17, and each of these air bleeds. boat 1
An air-fuel ratio control valve 24 is provided in the air introduction passages 21, 22.23 that connect the air supply pipe 9.20 and the atmosphere communicating portion such as the air cleaner 7.

Reference numeral 25 in the figure compares the output from the optical sensor 13 with a value corresponding to the air-fuel ratio at the misfire limit.
When the output from the air-fuel ratio control valve 3 is leaner than the value corresponding to the misfire limit air-fuel ratio, the air-fuel ratio control valve 2
4, and when the output from the optical sensor 13 is richer than the value corresponding to the misfire limit air-fuel ratio, an open output is output to the air-fuel ratio control valve 24. It is a control circuit.

In this case, the output voltage of the optical sensor 13 that detects the combustion light of the intake air-fuel mixture in the combustion chamber 2 is a solid line curve A when the air-fuel ratio is the stoichiometric air-fuel ratio, as shown in FIG. However, when the air-fuel ratio is leaner than the stoichiometric air-fuel ratio, the curve B is a one-dot chain line, and when the air-fuel ratio is even leaner and the air-fuel ratio is at the misfire limit, the line is a two-dot chain curve C.

Therefore, the control circuit 25 controls the output voltage of the optical sensor 13 after the time to from when the ignition signal is issued.
and the voltage value Va after time to in the curve C of the dashed-dotted line of the air-fuel ratio at the misfire limit, and when vl is equal to Va, no output signal to open or close is output to the air-fuel ratio control valve 24. However, when Vl>Va, the air-fuel ratio of the intake air-fuel mixture is richer than the air-fuel ratio at the misfire limit. The fuel ratio control valve can be opened, and Vl<
When Va, a misfire has occurred in the combustion chamber 2, or there is a possibility that a misfire may occur. Therefore, by outputting a close output signal to the air-fuel ratio control valve 24, the air-fuel ratio is adjusted to the air-fuel ratio at the misfire limit. The goal is to bring it closer to .

In addition, in the curves A, B, and C of FIG. 2, the time from when the ignition signal is issued until reaching the constant voltage Vo is also tc in the curve C indicated by the chain double-dashed line at the air-fuel ratio at the misfire limit.
However, when the air-fuel ratio is richer than the air-fuel ratio at the misfire limit, it becomes shorter than tb in the dashed line curve B, and when the air-fuel ratio becomes leaner than the air-fuel ratio at the misfire limit, it becomes shorter than tc. Therefore, the control circuit 25 sets the time tc for the output voltage of the optical sensor 13 to reach the constant voltage Vo to the time tc for the output voltage at the optical sensor 13 to reach the constant voltage VO on the dashed-dotted curve C at the air-fuel ratio at the misfire limit.
When the output voltage of the optical sensor 13 reaches the constant voltage vO, an open output signal is sent to the air-fuel ratio control valve 24 when the time is shorter than tc, and the air-fuel ratio control valve is The air-fuel ratio may be controlled by outputting a closed output signal to each of the valves 24 and 24.

In the above embodiment, the air-fuel ratio was adjusted by the amount of air introduced into each air bleed 19, 20 in the carburetor 5, but the air-fuel ratio was adjusted by bypassing the intake manifold to the carburetor. It is also possible to use an air-fuel ratio adjustment means that adjusts the air-fuel ratio by increasing or decreasing the amount of air or other air-fuel ratio adjustment means. Needless to say, it can also be applied to a type internal combustion engine.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention, and FIG. 2 is a diagram showing the relationship between the output voltage of the optical sensor and the combustion time. ■... Internal combustion engine, 2... Combustion chamber, 6... Intake manifold, 5... Carburetor, 11... Exhaust manifold, 10... Three-way catalytic exhaust purification equipment,
13... Optical sensor, 14... May fuel passage,
18...Slow system fuel passage, 19.20...Air bleed boat, 21, 22.23...Air introduction passage, 24...Air-fuel ratio control valve, 25...Control circuit. Patent applicant Daihatsu Motor Co., Ltd. b tc

Claims (1)

[Claims] (1) A spark ignition internal combustion engine in which the air-fuel ratio of the intake air-fuel mixture is leaner than the stoichiometric air-fuel ratio is provided with an optical sensor for detecting combustion light in the combustion chamber,
A method for controlling an air-fuel ratio in a lean-burn internal combustion engine, characterized in that the air-fuel ratio in an intake system is adjusted so that the output of the optical sensor becomes a value corresponding to a misfire limit air-fuel ratio.