JPS63285241A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To avoid a stoichiometric air-fuel ratio so as to reduce the amount of emission of NOx until warm-up of an engine by maintaining a relatively rich air-fuel ratio during warm-up operation, and by changing over the air fuel ratio from the rich fuel ratio into a lean fuel ratio step by step during stable load operation when the warm-up operation is nearly completed. CONSTITUTION:A control unit 12 receives values detected by an air flowmeter 6, an idle switch 8, a crank angle sensor 9, a water temperature sensor 10, an oxygen sensor 11 and the like, and computes a basic fuel injection amount in accordance with an intake-air amount and a rotational speed while sets a ratio of increment of compensation in accordance with the temperature of cooling water during warm-up operation so as to enrich the air-fuel ratio. When the temperature of cooling water reaches at first, for example, 70 deg. C, it is judged that the time is just after completion of warm-up operation so that the air-fuel ratio is changed over step by step to the lean side with a ratio of increment of compensation of less than 1 during idle operation or stable running operation where the variation in basic fuel injection amount is below a predetermined value.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to an air-fuel ratio control device for an internal combustion engine such as an automobile.
Specifically, the present invention relates to a device that controls the air-fuel ratio to a rich air-fuel ratio during the warm-up process of the engine, and switches stepwise to a lean air-fuel ratio near the end of engine warm-up.

(Prior art) In recent years, the demands placed on automobile engines have become more sophisticated, and there is a tendency for contradictory issues such as reduction of harmful exhaust gases, high output, and low fuel consumption to be achieved at a high level. Air-fuel ratio control is also required during the process from when the engine is cold until the end of warm-up.

As a conventional air-fuel ratio control device for this type of internal combustion engine, for example, [Toyota Rikimuri New Car Manual: May 1980 Issue,
There is one described in N1161288.

This device detects the warm-up state from the engine cooling water temperature, and as shown in Figure 6, when the cooling water temperature is low, that is, immediately after the engine starts, the fuel increase ratio is increased to control the air-fuel ratio to the rich side. As the cooling water temperature rises, the air-fuel ratio gradually approaches the stoichiometric air-fuel ratio, and when warm-up is completed, the increase ratio is increased to 1.0.
In other words, the air-fuel ratio is controlled to the stoichiometric air-fuel ratio.

(Problem to be solved by the invention) However, in such a conventional air-fuel ratio control device for an internal combustion engine, the air-fuel ratio is gradually lowered from the rich side to the stoichiometric air-fuel ratio during the warm-up process of the engine. Because the configuration was such that exhaust emissions, especially N0x (nitrogen oxides)
There were the following problems regarding the engine displacement.

In other words, the amount of NOx generated with respect to the change in air-fuel ratio is
As shown in the figure, it is rare when the air-fuel ratio is in the Lynch region, but increases as it approaches the stoichiometric air-fuel ratio, reaches a maximum at a point slightly leaner than the stoichiometric air-fuel ratio, and then shifts from the stoichiometric air-fuel ratio to the lean side. decreases over time. therefore,
When the air-fuel ratio is gradually shifted from the rich side to the rich air-fuel ratio, the amount of NOx generated is small when the engine starts (point A in the diagram), but when warm-up is completed and the stoichiometric air-fuel ratio is reached, the amount of NOx generated is at point B in the diagram. )
When operating the vehicle, a large amount of NOx will be generated.

This means that if a vehicle is not equipped with a catalytic converter, or even if a catalytic converter is installed, the specifications do not take into account NOx countermeasures such as an oxidation catalyst, a large amount of generated NOx will be released into the atmosphere. means. In particular, as trains are often stopped during the warm-up period, they have a large impact on the surrounding environment, so it is desirable that they be used as government offices.

Note that the above-mentioned problem is the same even if the target air-fuel ratio is controlled to be leaner than the stoichiometric air-fuel ratio after warm-up.

(Purpose of the Invention) Therefore, the present invention maintains the air-fuel ratio at a relatively rich air-fuel ratio during the warm-up process, and switches stepwise from rich to lean near the end of warm-up. The purpose is to avoid operation in a region close to the fuel ratio, reduce the amount of NOx generated until the end of warm-up, and improve exhaust performance.

(Means for Solving the Problems) In order to achieve the above object, the air-fuel ratio control device for an internal combustion engine according to the present invention detects the operating state of the engine, as shown in FIG. The means a and the warm-up detection means for detecting the warm-up state of the engine set a target air-fuel ratio according to the operating state of the engine, and set the target air-fuel ratio to a richer side than the stoichiometric air-fuel ratio when the engine is cold. The target air-fuel ratio is set to be leaner than the stoichiometric air-fuel ratio near the end of warm-up, and the target air-fuel ratio is changed in steps when the engine is in a predetermined stable load state near the end of warm-up. a target setting means C for switching, a control means d for calculating a control value for controlling the fuel supply amount or intake air amount so as to achieve the target air-fuel ratio set by the target setting means C; and operating means e for controlling the amount of fuel supplied or the amount of intake air based on the fuel supply amount or intake air amount.

(Function) In the present invention, during warm-up, a relatively rich air-fuel ratio is actively used with priority, and near the end of warm-up, an instantaneous (
The air-fuel ratio switches from the rich side to the lean side in a stepwise manner. Therefore, NO close to the stoichiometric air-fuel ratio during the warm-up process
Operation in the region where the amount of x generation is the largest is avoided, and the amount of NOx generated from the time of cold engine operation to the end of warm-up is reduced.

(Example) Hereinafter, the present invention will be explained based on the drawings.

2 to 5 are diagrams showing an embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention.

First, the configuration will be explained. In FIG. 2, reference numeral 1 denotes an engine. Intake air is supplied from an air cleaner 2 to each cylinder through an intake pipe 3, and fuel is injected by an injector (operating means) 4 based on the new Si. Exhaust gas burned within the cylinder is exhausted through the exhaust pipe 5.

The intake air flow rate Qa is detected by an air flow meter 6 and controlled by a throttle valve 7 in the intake pipe 3. The idle state of the engine I is detected by the eye 1' switch 8, and the rotation ViN of the engine 1 is detected by the crank angle sensor 9. The temperature Tw of the cooling water flowing through the water jacket is detected by a water temperature sensor (warm-up detection means) 10, and the oxygen concentration in the exhaust gas is detected by an oxygen sensor 11. The oxygen sensor 11 used has a characteristic that its output Vs changes suddenly at the stoichiometric air-fuel ratio.

The signals of each sensor 6.8.9.10.11 are input to the control unit 12, and each sensor 6.8.9.1
1 constitutes an operating state detection means 13. The control unit 12 has functions as a target setting means and a control means, and includes a CPU 21, a ROM 22, a RAM 23, and an I
10 interface 24. The I10 interface 24 controls the input and output of signals, and
10 interface 24 has each of the sensors 6.8.9
．． 10.11 signal is input. CPU21 is ROM
It takes in necessary external data from the I10 interface 24 according to a program described later stored in the RAM 22, and calculates processing values necessary for air-fuel ratio control by exchanging data with the RAM 23 as necessary. , the result is I
10 interface 24. The I10 interface 24 outputs the injection signal Si based on the calculation result of the CPU 21.

Next, the effect will be explained.

FIG. 3 is a flowchart showing an air-fuel ratio control program. This program is started when the engine is started, and is repeatedly executed at predetermined intervals.

First, Pl looks up the corrected increase ratio (water temperature increase ratio) l< corresponding to the cooling water temperature Tw from the table map shown in FIG. 4, and P2 checks whether the corrected increase ratio K looked up is 1 or more. Determine. Here, the corrected increase ratio is Tw
= 70° C., the magnitude of which is around 1, and in this embodiment, 'T'w = 70° C. is the temperature immediately before the end of warm-up. When K≧1, it is determined that the engine is in the warm-up process, and in P3, the fuel injection time Ti is calculated based on the corrected increase ratio K that is greater than 1 according to the following equation (2).

Ti-<K+α)・Tp+Ts ・・・・・・■ However, α: Other correction coefficient Tp: Basic injection pulse width TS: Invalid pulse width Note that the basic injection pulse width 'rp is the intake air amount Qa and engine speed Calculate based on N using the following equation (2).

a Tp=k. Therefore, the air-fuel ratio (target air-fuel ratio) at this time is a predetermined rich air-fuel ratio according to the cooling water temperature Tw, and it is assumed that operation near the stoichiometric air-fuel ratio where a large amount of NOx is generated is intentionally avoided. Become. On the other hand, when the cooling water temperature TW reaches 70°C and K (lookup value) < 1, it is determined that the warm-up is about to end, and the correction increase ratio K actually used for calculation is set to 1 in P4 and P. It is determined whether the conditions are met to adopt the smaller value as is, that is, to switch the target value stepwise from a rich air-fuel ratio to an air-fuel ratio leaner than the stoichiometric air-fuel ratio. For example, when the idle switch 8 is ON at P4, it is determined that the vehicle is in an idling state, and when ΔTp/Δ[ is small (a value that is not in an acceleration state) at P, it is determined that the vehicle is in a steady running state. In either case, the lookup value is used as is for the corrected increase ratio K, and the process proceeds to P3 (according to the branch of YES). Therefore, the corrected increase ratio K is instantly switched from a value of 1 or more, and the air-fuel ratio is instantly switched from a rich air-fuel ratio to a lean air-fuel ratio. Therefore, the engine is operated while avoiding an air-fuel ratio near the stoichiometric air-fuel ratio, and an increase in the amount of NOx generated can be avoided as will be described later. The reason why the air-fuel ratio stepwise switching conditions are limited to idling or substantially constant driving conditions is to prevent sudden changes in engine output in areas where the vehicle driving force is relatively large, such as during gentle acceleration or more. This is to reduce the discomfort felt by the driver when operating the accelerator.

On the other hand, when following the No command at P4 and Pa, it is determined that there is no step-switching condition for the air-fuel ratio, and even if the lookup value for the corrected increase ratio is less than 1, it is fixed at 1 at P6. Then proceed to P. Therefore, at this time, the target air-fuel ratio becomes the stoichiometric air-fuel ratio, which is taken into account so that there is no problem with the accelerator operation feeling.

The effects of the air-fuel ratio control as described above will be compared with the conventional example with reference to FIG. Note that FIG. 5 shows changes in the air-fuel ratio during the engine warm-up process and the accompanying changes in the amount of NOx emissions.

In the case of this example, the movement mode is A-C-D in the figure, and when starting the engine, the air-fuel ratio is made rich at point A, and then at point C.
The engine operates in a rich range until the engine reaches this point, and although the air-fuel ratio becomes slightly leaner during this period, this is very slight. Therefore, when the water temperature is low, only a very small amount of NOx is emitted, and even if the air-fuel ratio becomes leaner as the water temperature rises, the number of NOx emissions will only increase slightly. Then, when the vehicle is in a stable running state just before the end of warm-up, the air-fuel ratio is switched from rich to rich in a stepwise manner, so that the state changes to solid in the figure.

When the air-fuel ratio becomes lean, the amount of NOx generated is approximately at the same level as the value in the rich air-fuel ratio region before switching. Therefore, unlike the conventional case in which the amount of NOx generated increases due to the A-C-B transition mode, in this embodiment, the amount of NOx generated increases.
The amount of Ox generated is suppressed to approximately half the level of the conventional Hon BiJT region (point B). be able to. In particular, the effects of this embodiment are extremely significant in exhaust systems that do not have a catalyst device or have an oxidation catalyst device that does not have a NOx reduction device. Furthermore, compared to the conventional example, since the engine is operated at a lean air-fuel ratio not only immediately before the end of warm-up, but also continuously after the end of warm-up, the fuel efficiency is greatly improved.

In this embodiment, the air-fuel ratio is controlled by changing the fuel injection amount, but the application of the present invention is not limited to this. For example, since the air-fuel ratio is the weight ratio of fuel and air, the air weight may be changed.

(Effects) According to the present invention, the air-fuel ratio is maintained at a relatively rich air-fuel ratio during the warm-up process, and the air-fuel ratio is switched from a rich to a lean air-fuel ratio stepwise near the end of the warm-up, so the amount of NOx generated increases the most. Operation in a region close to the stoichiometric air-fuel ratio can be avoided, and the amount of NOx generated until the end of warm-up can be reduced. As a result, exhaust performance can be improved.

[Brief explanation of the drawing]

FIG. 1 is a basic conceptual diagram of the present invention, FIGS. 2 to 5 are diagrams showing an embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention, FIG. 2 is an overall configuration diagram thereof, and FIG. 4 is a flowchart showing the air-fuel ratio control program, FIG. 4 is a diagram showing how the increase ratio is set with respect to the cooling water temperature, FIG. 5 is a diagram showing the amount of nitrogen oxide generated with respect to changes in the air-fuel ratio, and FIG.
This figure shows a conventional air-fuel ratio control device for an internal combustion engine, and shows how the increase ratio is set with respect to the cooling water temperature. 4... Injector (operating means), 10...
...Water temperature sensor (warm-up detection means), 12...
Control unit (target setting means, control means), 13... Operating state detection means.

Claims (1)

[Claims] a) Operating state detection means for detecting the operating state of the engine; b) Warm-up detection means for detecting the warm-up state of the engine; c) Setting a target air-fuel ratio according to the operating state of the engine. At the same time, the target air-fuel ratio is set richer than the stoichiometric air-fuel ratio when the engine is cold, and the target air-fuel ratio is set leaner than the stoichiometric air-fuel ratio near the end of warm-up. d) target setting means for changing the air-fuel ratio in steps when the engine is in a predetermined stable load state; and d) adjusting the amount of fuel supply or intake air to achieve the target air-fuel ratio set by the target setting means. An air-fuel ratio of an internal combustion engine, comprising: a control means for calculating a control value for controlling the amount; and e) an operation means for manipulating the amount of fuel supplied or the amount of intake air based on the output of the control means. Control device.