JPS585446A - Air-fuel ratio controller of engine - Google Patents

Abstract

PURPOSE:To prevent abnormal combustion due to rapid explosion, by increasing a feed of fuel to a combustion chamber in an engine when intake air temperature reaches a high temperature range at least a prescribed level for a combustion speed to abnormally increase. CONSTITUTION:An injection quantity of fuel from a fuel injection valve 9, on the basis of the basic injection quantity in a basic injection quantity decision circuit 14 of a fuel feed controller 10, is corrected by a correction amount decision circuit 16 and adder subtractor circuit 15 in accordance with a detection value of an intake air temperature sensor 11. When intake air temperature is not higher than a prescribed value T, an injection quantity of fuel is decreased in accordance with a temperature rise to hold air-fuel ratio to a constant value, however, in a high temperature range at least the prescribed value T where a combustion speed tends to abnormally increase, the injection quantity of fuel is reversely increased in accordance with a temperature rise, and the air-fuel ratio is changed to the direction for a mixture to become rich. In this way, the speed of combustion is suppressed to prevent abnormal combustion.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air-fuel ratio control device for an engine that controls the air-fuel ratio according to intake air temperature.

Generally, the combustion state of an engine such as an automobile changes depending on the intake air temperature. Regarding the relationship between the intake air temperature and the combustion state, a widely known phenomenon is that when the intake air temperature increases, the charging efficiency in the combustion chamber decreases, and the air-fuel ratio of the mixture decreases due to the decrease in the density of the intake air. Due to the excessive enrichment, the combustibility of the air-fuel mixture within the combustion chamber deteriorates, resulting in a decrease in output.

Furthermore, fuel efficiency tends to deteriorate due to an overly rich mixture.

On the other hand, when the intake air temperature becomes low and the air-fuel mixture becomes lean, misfires tend to occur more easily. For this reason, conventionally, when controlling the fuel supplied to the combustion chamber of an engine according to the intake air temperature, as seen in Japanese Patent Laid-Open No. 10227/1982, the amount of fuel supplied is reduced as the intake air temperature increases, By increasing the amount of fuel supplied when the intake air temperature becomes low, the air-fuel ratio is controlled to be maintained near the stoichiometric air-fuel ratio in response to changes in the intake air temperature.

However, as mentioned above, the tendency that combustibility decreases as the intake air temperature rises is a phenomenon that can be seen within a certain range of intake air temperatures, and as the intake air temperature rises higher than this, the air-fuel mixture deteriorates. Abnormal combustion that causes sudden explosive combustion (
It has been newly discovered through experiments that detonation (detonation) is more likely to occur. Possible causes of this phenomenon are as follows. In other words, when the intake air temperature changes, if we consider only the temperature change, the increase in temperature will be a factor that accelerates the combustion rate, while the aforementioned decrease in charging efficiency accompanying the temperature increase will be a factor that slows down the combustion rate. Become. In the intake air temperature range up to a certain level, as the intake air temperature rises, the effect of the reduction in charging efficiency has a greater effect on the combustion state of the engine than the effect of the temperature rise itself, and the combustion speed tends to be delayed. However, when the intake air temperature and therefore the temperature inside the combustion chamber become extremely high, the effect of the temperature rise itself becomes more significant on the combustion state. As a result, it is thought that the combustion rate is abnormally accelerated in such a high temperature range.

Therefore, conventional control that reduces the amount of fuel supplied to keep the air-fuel ratio almost constant when the intake air temperature rises is more likely to cause the above-mentioned abnormal combustion, which can cause the piston to experience an excessively high temperature. There was a risk that the piston would melt or be destroyed due to high pressure. This tendency was particularly noticeable when intake supercharging was performed. According to the control means disclosed in the above-mentioned Japanese Unexamined Patent Publication No. 51-10227, the correction for reducing the fuel supply amount as the temperature rises does not work when the intake air temperature is 20° C. or higher. The above control means is mainly used to prevent misfires when the intake air temperature is low, and the intake air temperature is 2-6℃.
The above is based on the idea that there is no need for correction. However, simply keeping the amount of fuel supplied constant at an intake air temperature of 20° C. or higher does not prevent abnormal combustion when the intake air temperature becomes significantly high.

In view of these circumstances, the present invention actively increases the amount of fuel supplied to enrich the air-fuel ratio when the intake air temperature becomes significantly high, thereby preventing abnormal combustion in the high temperature range. It is an object of the present invention to provide an air-fuel ratio control device for an engine that can maintain proper and safe operating conditions by preventing damage to the engine due to excessive high temperature and pressure.

The present invention will be described below with reference to illustrative embodiments.

In Fig. 1, 1 is the engine body, 2 is the intake passage, and 6 is the engine body.
0 is an exhaust passage 0 Also, 4 is a turbo supercharger for increasing the output of the engine, which includes a blower 5 provided in the intake passage 2, a turbine 6 provided in the exhaust passage B, and the blower 5 and turbine 6. and a rotating shaft 7 that interlocks and connects the exhaust passage 6.
The turbine 6 is rotated by the exhaust gas flow within the
In conjunction with this, the blower 5 rotates to perform intake supercharging. The intake passage 2 downstream of the blower 5 is provided with a throttle valve 8 that is linked to an accelerator or the like.

In this embodiment, a fuel injection system is used as the fuel supply device, and a fuel injection valve 9 is installed in the intake passage 2 downstream of the throttle valve 8. This fuel supply control device 10 is provided with a fuel supply control device 10 that electrically controls the fuel injection amount of
The basic injection amount of fuel is determined according to the intake air amount and the engine speed, and the fuel injection amount is further corrected and controlled according to the intake air temperature detected by the intake air temperature sensor 11. In particular, in the present invention, the fuel supply control device 10 is configured to increase the amount of fuel supplied when the intake air temperature reaches a high temperature range equal to or higher than a predetermined value where the combustion rate becomes abnormally high. The intake air temperature sensor 11 converts the detected temperature into an electric signal and extracts it, and is designed to detect the intake air temperature at a predetermined point in the intake passage 2 that has a certain correspondence with the intake air temperature in the combustion chamber of the engine body 1. The detection signal from the intake air temperature sensor 11 is transmitted to the fuel supply control device 10.
is input. Further, 12 is an air flow meter for detecting an intake flow rate provided in the intake passage 2 upstream of the blower 5;
13 is a potentiometer that detects the amount of rotation of the air flow meter 12, and a detection signal from the potentiometer 16 and an engine rotation speed detection signal from an engine rotation speed detector (not shown) are also input to the fuel supply control device 10. .

FIG. 2 shows the circuit configuration of the fuel supply control device 10,
The fuel supply control device 10 includes a basic injection amount determining circuit 14 , an addition/subtraction circuit 15 , a correction amount determining circuit 16 , and an amplification circuit 17 . Based on the detected signal and the engine speed detection signal, an appropriate basic injection amount is set according to the intake air flow rate and the engine speed. The addition/subtraction circuit 15 also includes a correction amount determining circuit 16.
The basic injection amount set in the basic injection amount determining circuit 14 is increased or decreased in response to a correction signal sent from the basic injection amount determining circuit 14. The correction amount determining circuit 16 receives the output of the intake air temperature sensor 11, and sends a correction signal to the addition/subtraction circuit 15 to increase the fuel injection amount when the intake air temperature reaches a high temperature range equal to or higher than the predetermined value. ing. In the embodiment, as shown in the graph of FIG.
When the temperature is within the temperature range up to 1, the fuel supply amount is reduced to compensate for the natural mixture richness caused by the decrease in the density of the intake air as the temperature rises, and the intake air temperature exceeds the predetermined value T. The correction amount determination circuit 16 and the addition/subtraction circuit 15 are configured to increase the fuel supply amount as the temperature rises when the temperature reaches a high temperature range. As shown by solid line A, until the intake air temperature reaches a predetermined value T, the air-fuel ratio is kept at a constant value that approximately matches the stoichiometric air-fuel ratio (14,7), and when the intake air temperature exceeds the predetermined value T, the air-fuel ratio is gradually reduced. The fuel ratio is controlled in the direction of decreasing (the mixture becomes richer).The predetermined value T means the limit temperature at which the combustion speed begins to become abnormally high, and is considerably higher than the normal intake air temperature. When the rotational speed is 250 rpm, the temperature is about 85° C. The amplification circuit 17 amplifies the output of the addition/subtraction circuit 15 to a voltage level suitable for controlling the fuel injection valve 9.

Next, the operation of this air-fuel ratio control device will be explained.

The fuel supply amount, that is, the fuel injection amount from the fuel injection valve 9 is determined by the correction circuit 16 and the addition/subtraction circuit 15 based on the basic injection amount determined by the basic injection amount determination circuit 14 in the fuel supply control device 10. It is corrected according to the intake air temperature. As mentioned above, when the intake air temperature is below the predetermined value T, the air-fuel ratio is maintained at a constant value by decreasing the fuel injection amount as the temperature rises, but the combustion rate tends to become abnormally fast. In a high temperature range above a predetermined value T where . As a result, the combustion rate is suppressed in the high temperature range, and abnormal combustion (detonation) is prevented.

To explain this control action in comparison with the conventional technology, in the past, the air-fuel ratio was always kept around a constant stoichiometric air-fuel ratio (14,7) in response to changes in the intake air temperature, or fuel was supplied when the intake air temperature was 20°C or higher. This is just a matter of not making any amount corrections. However, if the air-fuel ratio is kept constant even in the high temperature range, as shown by the two-dot chain line B in Figure 4, the effect of the temperature increase itself becomes even more pronounced, and on the contrary, it encourages abnormal combustion. Put it away. In addition, if the amount of rice supplied is not corrected above a certain temperature, the air-fuel ratio will naturally become smaller due to the decrease in the density of the intake air as the intake air temperature increases, but even with this, the air-fuel ratio will naturally decrease. However, it is not possible to prevent the phenomenon that abnormal combustion is more likely to occur due to the influence of the temperature rise itself being greater in the high temperature range. In contrast, in the present invention, by actively increasing the amount of fuel supplied in the high temperature range, the air-fuel ratio is reduced to a sufficient degree to prevent the phenomenon of abnormally high combustion speed. .

However, in order to suppress the combustion speed, it is possible to change the air-fuel ratio to be larger than the stoichiometric air-fuel ratio (to make the air-fuel mixture leaner), but if the air-fuel mixture is made leaner, misfires are likely to occur. Compared to this, in order to enrich the air-fuel mixture, a large change in the air-fuel ratio is allowed in order to prevent misfires. Therefore, in the present invention, the air-fuel mixture is controlled to become richer in the high temperature range.

In particular, engines that perform intake supercharging using a supercharger are inherently prone to abnormal combustion in high temperature ranges.
The device of the present invention becomes more effective.

It should be noted that the specific structure of the device of the present invention is not limited to the above-mentioned embodiments, and can be modified in various ways without departing from the gist of the present invention. For example, a carburetor type fuel supply device may be used instead of the injection type shown in the figure, and in this case,
A valve capable of adjusting the flow rate may be provided in the fuel supply passage to the carburetor, and this valve may be controlled by a fuel supply control device according to the intake air temperature. Further, in the above embodiment, the intake air temperature is set to the predetermined value 1.
In the above case, the amount of fuel supplied is continuously increased in accordance with the temperature rise, but the required amount of supplied fuel may be increased in stages when the intake air temperature is equal to or higher than a predetermined value.

As explained above, according to the present invention, when the intake air temperature reaches a high temperature range above a predetermined value where the combustion rate becomes abnormally high, the fuel supply control device receives the output of the intake air temperature sensor.
Since the fuel supply amount is increased and the air-fuel ratio is actively controlled in the direction of decreasing, the combustion speed is suppressed in the above-mentioned high temperature range, and abnormal combustion due to sudden explosion of fuel can be prevented, and abnormal combustion due to abnormal combustion can be prevented. This prevents engine damage and greatly increases engine safety and durability.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing an embodiment of the present invention, Fig. 2 is a block diagram showing the circuit configuration of the fuel supply control device, and Fig. 6 shows the relationship between intake air temperature and fuel supply amount based on the control action of the device of the present invention. FIG. 4 is a graph showing the relationship between intake air temperature and air-fuel ratio based on the same control action. 1... Engine body, 9... Fuel injection valve, 10...
- Fuel supply control device, 11... intake temperature sensor. Patent applicant: Toyo Kogyo Co., Ltd. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1. An intake air temperature sensor that detects the intake air temperature, and upon receiving the output of the intake air temperature sensor, when the intake air temperature reaches a high temperature range above a predetermined value where the combustion rate is abnormally high, 1. An air-fuel ratio control device for an engine, comprising: a fuel supply control device that increases the amount of fuel supplied.