JPS60261949A - Air-fuel ratio controller for internal-combustion engine - Google Patents

Abstract

PURPOSE:To improve the combustion stability and the exhaust purification effect of engine by making the combustion mixture gas thicker than the theoretical air- fuel ratio while feedback controlling the exhaust gas flowed to three element catalyst correctly to the theoretical air-fuel ratio. CONSTITUTION:When secondary air control means 6b is at the temperature lower than setting level, the block valve 13 of secondary air path 11 is opened by means of the output from a sensor 15 for detecting the engine temperature to lead secondary air into the exhaust gas. When feeding secondary air into the exhaust gas during or immediately after warming of engine, it is decided from the output of an exhaust sensor 5 that the mixture gas in the intake path 2 will be thinner in appearance than the theoretical air-fuel ratio to increment the fuel through air-fuel ratio control means 6a thus to make thick the combustion mixture gas. Since combustion gas composed of secondary air and thick mixture gas wil flow to the three element catalyst 4, similar effect with reaction of combustion exhaust having approximately theoretical air-fuel ratio is achieved. Consequently, combustion under said operating region is stabilized while the exhaust purification effect is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an air-fuel ratio control device for an internal combustion engine equipped with a three-way catalyst in an exhaust system.

(Prior art) In order to reduce NOx, HC, and Co emitted from internal combustion engines, exhaust purification systems that install a three-way catalyst in the exhaust passage and simultaneously reduce NOx and oxidize HC and GO are widely used. It has been adopted.

By the way, the three-way catalyst only converts NOx and HC to the exhaust gas that burns the mixture at the stoichiometric air-fuel ratio.

The oxidation of CO can be carried out efficiently, and for other air-fuel ratios, the reduction efficiency or oxidation efficiency will decrease if the ratio is biased towards the rich side or lean side, so it is necessary to oxidize the air-fuel ratio closely with the air-fuel ratio of combustion An oxygen sensor detects the oxygen concentration in the exhaust gas, which has a positive correlation, and feedback controls the fuel supply amount to accurately match the stoichiometric air-fuel ratio.

During normal operation of the engine, the air-fuel mixture at the stoichiometric air-fuel ratio provides stable combustion and good fuel efficiency, but during warm-up immediately after a cold start, fuel atomization is poor and combustion is unstable. Because this is likely to happen, the mixture is temporarily enriched to promote warming up.

Therefore, during this period, feedback control of the air-fuel ratio is discontinued and operation is performed with a mixture richer than the stoichiometric air-fuel ratio, but even if combustion is stabilized, the exhaust purification efficiency tends to decrease. .

Therefore, as stated in Tokukai No. 58-119950, when one engine is in operation with one mixture being supplied to the engine, secondary air in the Ut air on the upstream side of the three-way catalyst is introduced. By including an appropriate amount of oxygen in the exhaust gas, the three-way catalyst
In particular, it was considered to prevent a decrease in oxidation efficiency.

In this case, if the engine cooling water temperature rises and exceeds, for example, 50°C, the supply of secondary air is cut off, and at the same time feedback control is started so that the air-fuel mixture reaches the stoichiometric air-fuel ratio. is being reinstated.

(Problem that the invention attempts to solve) The air-fuel ratio does not reach the stoichiometric air-fuel ratio correctly, and the exhaust purification efficiency of the three-way catalyst cannot necessarily be said to be sufficient.

In addition, when the Ia cooling water temperature exceeds, for example, 50°C, feedback control is immediately started so that the mixture reaches the stoichiometric air-fuel ratio, so a step occurs in the air-fuel ratio immediately after this control is switched, and in this case, the operation Depending on the conditions, engine combustion may not be stable, which can lead to so-called "breathing" phenomenon when starting, or in severe cases, engine stalling.

The present invention occurs during or immediately after warm-up. The purpose is to solve such problems.

(Means for Solving the Problems) In the present invention, as shown in FIG. 1, an exhaust passage 3 is provided with a two-way catalyst 4 and an exhaust sensor 5 upstream thereof.

Based on the output of the exhaust sensor 5, the air-fuel ratio control means 6a adjusts the fuel supply amount @7 to the intake passage 2 so that the air-fuel ratio becomes almost the stoichiometric air-fuel ratio, 7<-1'/, 7, 11.
□6゜, 1 A secondary air passage 11 is connected to the exhaust gas upstream of the exhaust sensor 5, and the output from the sensor 15 detects the engine temperature.
When the temperature of the secondary air control means 6b is below a set temperature, the shutoff valve 13 of the secondary air passage 11 is opened to introduce secondary air into the exhaust gas.

(Function) Therefore, when secondary air is supplied to the exhaust gas during engine warm-up or immediately after engine warm-up, it appears from the output of exhaust sensor 5 that the air-fuel mixture in intake passage 2 is lower than the stoichiometric air-fuel ratio. It is determined that the mixture has become lean, and the air-fuel ratio control means 6a increases the amount of fuel to enrich the combustion mixture. However, since combustion gas with a rich mixture of secondary air flows into the three-way catalyst 4, the reaction is essentially the same as reacting combustion exhaust gas with a stoichiometric air-fuel ratio.

Therefore, combustion is stabilized in the above operating range, and
This increases exhaust purification efficiency.

(Example) FIG. 2 shows an embodiment of the present invention.

Reference numeral 1 designates an engine body, 2 an intake passage, and 3 an exhaust passage. The exhaust passage 3 is provided with a three-way catalyst 4 for reducing NOx and oxidizing -IC and CO.

An exhaust sensor (oxygen sensor) 5 is provided to measure the oxygen concentration in the exhaust upstream of the three-way catalyst 4, and this output is sent to a control circuit 6.
Enter. The carburetor 7, which serves as a fuel supply device provided in the intake passage 2, controls a fuel control solenoid valve 8 to perform feedback control of the fuel supply amount, and adjusts the air-fuel ratio of the generated air-fuel mixture according to the opening degree of the solenoid valve 8. It can be fine-tuned (however, these structures are well known, so details will be omitted).

In a part of the cleaner 10, there is a secondary air passage 11 connected upstream of the exhaust pipe 5 of the exhaust passage 3. communicate.

A cutoff valve 13 is interposed in the ten streams of the secondary air passage 11, and the cutoff valve 13 opens and closes according to the suction negative pressure from the negative pressure passage 13b selectively supplied via the three-way solenoid valve 13a. This three-way solenoid valve 13a and the solenoid valve 8 are connected to the control circuit 6.
The opening and closing degrees of the OFF valves are controlled by the signals from the OFF valves. Note that 18c represents an atmospheric passage, and 18d represents a diaphragm chamber.

The control circuit 6 includes a water jacket 14 of the engine body 1.
In addition to the output of the water temperature sensor 15 that detects the cooling water moisture level of
Various types of Shintan are input.

The control circuit 6 basically performs feedback control of the air-fuel ratio control solenoid valve 8 based on the output of the exhaust sensor 5 so that the air-fuel ratio of the mixture becomes the stoichiometric air-fuel ratio during normal operation. For example, when the exhaust gas contains oxygen, the amount of fuel is increased, and when there is no oxygen, the amount of fuel is decreased, while the engine temperature is set to the first set value based on the output of the water temperature sensor 15, such as when warming up the engine. (for example, 60°C) or below, the feedback control of the air-fuel ratio is stopped, and the solenoid valve 8 is fully opened to switch to open control so that the air-fuel mixture becomes a predetermined value richer than the stoichiometric air-fuel ratio, and at the same time, the engine temperature is When the temperature is below the second set value (for example, 70°C), the shutoff valve 13 of the secondary air passage 11 is opened regardless of the feedback control of the air-fuel ratio, and the Next, introduce air.

The control circuit 6 is composed of a micro-1 viewer or the like, and its operation is performed as shown in the flowchart of FIG.

Next, the operation will be explained with reference to FIG. 3.

Assuming that the engine is started from a cold state, the control circuit 6 reads the water temperature TW from the output of the water temperature sensor 15, determines the active state of the exhaust sensor (0, sensor), and if it is in the inactive state, the water temperature is 60. ℃ or below, the shutoff valve 13 of the secondary air passage 11 is opened, and at the same time, the solenoid valve 8 of the carburetor 7 is held fully open to make the air-fuel mixture richer than the stoichiometric air-fuel ratio.

Therefore, a rich air-fuel mixture is supplied to the engine body 1, which promotes warm-up of the engine, and improves the reaction efficiency at the three-way catalyst 4 due to the secondary air introduced into the exhaust gas.

When the detected water WTw is in the range of 60° C. to 70° C., the air-fuel ratio feedback control is performed while the shutoff valve 13 is kept open.

When secondary air is introduced upstream of the exhaust sensor 5, #)
% #, ″z'par:5y-i;n;bt=h・
tll: 'A t > +J-5.

Based on the output, the control circuit 6 determines that the air-fuel ratio is leaner than the stoichiometric air-fuel ratio, and performs control to enrich the air-fuel mixture produced by the carburetor 7.

Therefore, the exhaust gas that eventually flows into the three-way catalyst 4 is correctly controlled to the stoichiometric air-fuel ratio by combining rich combustion gas and secondary air, and the combustion mixture is slightly richer than the stoichiometric air-fuel ratio.
Immediately after warming up, the system is controlled to the optimum state, ensuring smooth operating performance while maintaining maximum exhaust purification efficiency. After that, when the engine temperature rises further and Tw becomes 70°C or higher, the control circuit 6
3 is closed to perform feedback control of the air-fuel ratio.

Since the supply of secondary air is cut off, the detected value of the exhaust sensor 5 directly corresponds to the air-fuel ratio of the combustion mixture. Therefore, the mixture gas at the stoichiometric air-fuel ratio flows completely into the two-way catalyst 4, and normally Achieves good fuel efficiency, output characteristics, and exhaust purification during operation.

Although the above embodiment shows a case in which a carburetor is provided as a fuel supply means, the present invention is also applicable to a case in which a fuel 1!3I injection valve is provided in an intake port or the like to inject fuel in synchronization with engine rotation. It is obvious that it can be done.

In addition, the secondary air may be introduced until the air-fuel ratio reaches a predetermined level during the air-fuel ratio feedback control after warming up, or for a predetermined period of time after the start of the feedback control. Idle stability can also be improved by introducing secondary air only when the engine is running.

(Effects of the Invention) According to the present invention, the combustion air-fuel mixture is made richer than the stoichiometric air-fuel ratio, and the three-way catalyst is Feedback control of the inflow exhaust gas to the stoichiometric air-fuel ratio is possible, which improves engine combustion stability and at the same time reduces υF atmospheric NOx and improves HC.
, Co can be oxidized efficiently.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of the present invention, FIG. 2 is a cross-sectional view showing an embodiment of the present invention, and FIG. 3 is a flow chart showing its control operation. DESCRIPTION OF SYMBOLS 1... Engine body, 2... Intake passage, 3... Exhaust passage, 4... Three-way catalyst, 5... Exhaust sensor, 6...
Control circuit, 7... Carburizer, 8... Solenoid valve, 11...
- Secondary air passage, 12... Reed valve, 13... Shutoff valve, 15... Water temperature sensor. Patent applicant Nissan Motor Co., Ltd. Figure 1

Claims (1)

[Claims] A fuel supply device is installed in the intake passage, and an exhaust sensor and a three-way catalyst are installed in the exhaust passage, and the fuel supply device is feedback-controlled based on the output of the exhaust sensor so that a mixture at approximately the stoichiometric air-fuel ratio is obtained. In an internal combustion engine equipped with means, a secondary air passage is connected to the exhaust passage upstream of the exhaust sensor, while means for detecting engine temperature are provided.
M! A control means is provided to open the secondary air passage and introduce secondary air when the engine temperature is below a set temperature, and the exhaust air-fuel ratio when the secondary air is introduced during or immediately after engine warm-up is approximately the stoichiometric air-fuel ratio. An air-fuel ratio control device for an internal combustion engine, characterized in that: