JPS61171850A - Air-fuel ratio control device - Google Patents

Abstract

PURPOSE:To keep an accurate air-fuel ratio at all times and thereby purify exhaust gas by operating a means for fixing a reference value to a prescribed one when concentration of a specific component in the exhaust gas of an engine is under specific conditions. CONSTITUTION:An exhaust gas sensor 2 detects concentration of a specific component involved in exhaust gas of an engine 1 as a binary signal comprising a maximum value on the rich side and a minimum value on the lean side. A reference value determination circuit 7 investigates the maximum value of a sensor output O input from a maximum value detecting circuit 5 and an amplitude B indicating a difference between the maximum and minimum values of the sensor output O input from an amplitude detecting circuit 6. Provided the amplitude B lines in a region less than a prescribed value, a reference value S fixed to a prescribed value is generated. Thus, an air-fuel ratio accurate at all times can be kept for purifying exhaust gas.

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention relates to air-fuel ratio feedback control of an internal combustion engine using an exhaust gas sensor, and in particular to air-fuel ratio feedback control using an exhaust gas sensor whose detection characteristics are temperature dependent. Regarding a control device.

[Background of the invention]

In internal combustion engines such as automobile gasoline engines,
A method is used in which the output air-fuel ratio of the engine, that is, the actual air-fuel ratio, is determined by detecting a specific component in the exhaust gas, and the air-fuel ratio is controlled based on the feedback. This can be found in Japanese Patent Publication No. 5G-9262.

Incidentally, an exhaust gas sensor used in such a method is, for example, the 03 sensor, which measures the concentration of a specific component in the exhaust gas between the maximum value on the rich side (a region darker than a predetermined value) and the maximum value on the lean side (a region darker than a predetermined value). 2 with the local minimum value in the thin region)
A sensor that outputs a value signal has conventionally been used, but as shown in Figure 3, the sensor that outputs the binary signal outputs the local maximum or minimum value. It changes depending on the temperature of the
A method in which a reference value necessary for signal identification is changed in accordance with the maximum value of an output signal is widely adopted as an effective method.

However, as a result, in the conventional air-fuel ratio control device,
In the inactive region where the temperature of the exhaust gas sensor is low, as shown by the large region in Figure 3, the level of the reference value is lower than the minimum value of the sensor output. It ends up.

Therefore, conventionally, as shown in the above-mentioned publication, feedback control has been stopped in the large area of FIG. 3.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and its purpose is to perform correct feedback control even in a region where the temperature of the exhaust gas sensor does not reach a predetermined value and the sensor is not sufficiently activated. An object of the present invention is to provide an air-fuel ratio control device that can maintain good air-fuel ratio characteristics.

[Summary of the invention]

To achieve this objective, the present invention changes a reference value for binary signal identification, which is the output of an exhaust gas sensor, in accordance with the maximum value of the binary signal in a region where the sensor is sufficiently activated. However, in regions where activation is insufficient, this reference value is fixed to a predetermined constant value.

[Embodiments of the invention]

Hereinafter, the air-fuel ratio control device according to the present invention will be described in detail with reference to the illustrated embodiment. FIG. 1 shows an embodiment of the present invention, in which 1 is an engine, 2 is an exhaust gas sensor, 3 is a comparison circuit, and 5 is a fuel amount control device, 5 is a maximum value detection circuit, 6 is an amplitude detection circuit, 7 is a reference value determination circuit, and 8 is an exhaust pipe.

When the engine 1 is operating, exhaust gas flows into the exhaust pipe 8, and its components are the amount of air taken in by the engine 1,
It is determined by the ratio to the amount of fuel supplied and mixed into the air, the so-called air-fuel ratio.For example, the 03 component in the exhaust gas is leaner than the stoichiometric air-fuel ratio of 14.7 (air-fuel ratio>14. 7), it becomes zero, rich (air-fuel ratio > 1)
4.7), it becomes a finite value.

The exhaust gas sensor 2 is an Ox sensor installed so as to be exposed to the exhaust gas in the exhaust pipe 8. Therefore, its detection output of 0 indicates that K is a minimum value when the air-fuel ratio of the engine 1 is in a lean state. , when the signal is in a rich state, it becomes a binary signal indicating a local maximum value.

The comparison circuit 3 compares the detection output 0 from the sensor 2 with the reference value S given from the reference value determination circuit 7, and outputs a weight loss signal when 0>8 (rich state!), and 0>S (lean state). When , an increase signal is output respectively.

The fuel amount control device t4 functions to gradually increase K when a reduction signal is applied from the comparator circuit 3.

The maximum value detection circuit 5 checks the output 0 of the exhaust gas sensor 2,
It functions to detect the maximum value on the rich side shown in FIG.

The amplitude detection circuit 6 similarly checks the output 0 of the exhaust gas sensor 2, and functions to detect an amplitude B consisting of the difference between the maximum value on the rich side and the minimum value on the lean side, as shown in FIG.

The reference value determination circuit 7 determines a swing amplitude B representing the difference between the maximum value of the senna output 0 input from the maximum value detection circuit 5 and the maximum value and minimum value of the senna output 0 input from the vibration amplitude detection circuit 6. As shown in Fig. 2, when there is a region YK where the amplitude B reaches a predetermined value or more, a reference value S is generated that follows and changes in a predetermined relationship with the maximum value, and the amplitude B is When in the region N where the predetermined value has not been reached, K operates to generate a reference value S fixed to a predetermined constant value.

Next, the operation of this embodiment as a whole will be explained.

When the engine 1 starts operating, the temperature of the exhaust gas sensor 2 reaches a predetermined value or higher, the sensor is activated, and there is a region YK shown in FIG. 2, the reference value changes to follow the rich side maximum value of the sensor output 0 Operates under S, sensor output 0
While K is <O>S > with respect to the reference value S, the amount of fuel supplied to the engine 1 is gradually decreased, and the sensor output O becomes (0 (S )) with respect to the reference value S. When the state is reached, the fuel supply amount is increased sequentially, and this causes the sensor output O to become (0) again with respect to the reference value.
> 3), and by repeating this, the well-known air-fuel ratio feedback control is performed so that the air-fuel ratio converges to a predetermined value (the stoichiometric air-fuel ratio). Note that so-called proportional-integral control is generally applied to such control.

Incidentally, the above operation is the same as that of the conventional feedback type air-fuel ratio control device, but in this embodiment, the operation in region N of FIG. 2 is different from the conventional example. Region N1: When a short period of time has not elapsed since the engine 1 started operating, the temperature of the exhaust gas sensor 2 is low and the senna is not activated sufficiently, so that the amplitude of the output 0 is a predetermined value. When B has not been reached, the reference value S is set to a constant value that is unrelated to the rich side maximum value of sensor output 0, and the reference value S is kept at this constant value.
Based on this, it is judged whether the sensor output 0 is too large or small, and whether it is 0<8), and whether the fuel supply amount is gradually increased or decreased. feedback control of the air-fuel ratio is to be carried out.

Therefore, according to this embodiment, the problem with the method using a reference value S that changes following the maximum value of the sensor output O, that is, the problem that the area becomes inoperable in the area shown in FIG. 3, can be solved. However, feedback control can be performed in almost all areas.

As is clear from FIG. 2, the predetermined constant value of the reference value S in the region NK of FIG. 2 may be set to a value when the swing @B of the senna output O is almost zero.

By the way, although it was not explained in detail in the embodiment shown in FIG. 1, in order to perform overall control including the proportional and integral operation of the fuel supply amount described above, the "Iku°" 1 viewer is used.
All you have to do is make the combined program perform multiple actions.

〔Effect of the invention〕

As explained above, according to the present invention, even in an air-fuel ratio control device that changes the reference value for identifying the output of the exhaust gas sensor in accordance with the maximum value of the sensor output, it is possible to change the reference value for identifying the output of the exhaust gas sensor even immediately after starting the engine. Since feedback control can be performed in almost all operating ranges,
By eliminating the shortcomings of the prior art, it is possible to easily provide an air-fuel ratio control device that enables an engine to be operated while maintaining an accurate air-fuel ratio at all times and is highly effective in purifying exhaust gas.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the air-fuel ratio control device according to the present invention, Fig. 2 is a characteristic curve diagram for explaining its operation, and Fig. 3 is a characteristic curve diagram for explaining problems in the conventional example. It is. 1... Engine, 2... Exhaust gas sensor, 3...
Comparison circuit, 4...Fuel amount control device, 5...Other value detection circuit, 6...Wave amplitude detection circuit, 7...Reference value determination circuit, 8...Kabuto l illusion

Claims (1)

[Claims] 1. Equipped with an exhaust gas sensor that detects the concentration of a specific component in engine exhaust gas as a binary signal consisting of a local maximum value on the rich side and a local minimum value on the lean side, and the level identification of the binary signal is performed based on the local maximum value. In this air-fuel ratio control device, the output air-fuel ratio is determined by using a reference value that changes in accordance with a change in the level of the signal. An air-fuel ratio control device characterized in that the above means is operated only when the difference between the minimum value and the minimum value is equal to or less than a predetermined value.