JPS6354127B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air-fuel ratio control device that controls the air-fuel ratio of an automobile engine using an oxygen concentration sensor (hereinafter referred to as an O ₂ sensor), and the present invention relates to an air-fuel ratio control device that uses an oxygen concentration sensor (hereinafter referred to as an O _{2 sensor) to accurately determine whether or not the O 2} sensor is activated. The present invention provides an air-fuel ratio control device with a simple configuration.

FIG. 1 schematically shows an example of an air-fuel ratio control device for an automobile engine. In Fig. 1, A is an engine, B is an air-fuel ratio control device that controls the weight ratio between the amount of air taken into the cylinder of engine A and the amount of fuel (hereinafter referred to as the air-fuel ratio), and C is an engine A.
This is an _O2 sensor that detects the oxygen concentration in exhaust gas and generates an electromotive force according to the oxygen concentration.In a rich state (state with a large proportion of fuel), the electromotive force of _O2 sensor C is large, and in a lean state (in a state where the proportion of fuel is small), the electromotive force of O ₂ sensor C becomes small. Figure 2 shows the relationship between the air-fuel ratio and the O ₂ sensor electromotive force. In Fig. 1, D is an analog-digital converter (hereinafter referred to as A/D converter) that converts the electromotive force of O ₂ sensor C into a digital signal;
E is a microcomputer that inputs a signal from A/D converter D and outputs a signal to bring the air-fuel ratio to the stoichiometric air-fuel ratio, and F is a digital-to-analog converter (hereinafter referred to as D/A converter). D/
The air-fuel ratio control device B is controlled by the output of the A converter F.

The relationship between the O ₂ sensor electromotive force and the air-fuel ratio shown in Figure 2 is after the O ₂ sensor C reaches the active state, and before the O ₂ sensor C becomes the active state, that is, the O ₂ sensor temperature is below a certain value, the third
As shown in the figure, the O ₂ sensor electromotive force is low and the response is also poor.

Therefore, in order to perform normal air-fuel ratio control, O ₂
It is configured to determine whether or not the sensor has reached a certain temperature, that is, whether or not it has been activated, and when it is determined that it has been activated, to start feedback control so that the stoichiometric air-fuel ratio is reached for the first time, Furthermore, when it is inactive, it is necessary to configure the device to perform different control than when it is activated.

Here, the internal resistance of the O ₂ sensor largely depends on the temperature as shown in FIG. 4, and when the O ₂ sensor temperature is low, the internal resistance is large.

Conventionally, determining whether or not the O ₂ sensor has been activated is as follows:
Utilizing the temperature dependence of the internal resistance of the above O ₂ sensor,
For example, this has been done using a circuit shown in FIG.
In Fig. 5, by turning on switch S using microcomputer 2, resistor _R1 and _O2 sensor 1
A current determined by the internal resistance R ₀ and the electromotive force V ₀ of the O ₂ sensor is passed through the O ₂ sensor, and the voltage V ₀₂ is the sum of the voltage generated by this current and the O ₂ sensor electromotive force V ₀ ,
When the _comparator 3 compares the reference voltage V _S obtained by dividing the constant voltage V B with the resistors R ₂ and R ₃ , and when V _S > V ₀₂ and the output of the comparator 3 changes from “L” to “H” The O ₂ sensor was determined to be activated. Furthermore, in the conventional example described above, a circuit for determining whether the air-fuel ratio is lean or rich must be separately connected.

This conventional method ignores the difference in _O2 sensor electromotive force when the air-fuel ratio is lean and rich, and makes a determination as to whether the O2 sensor is activated or not. When the fuel ratio is lean compared to when the fuel ratio is rich, when the internal resistance of the O ₂ sensor is higher, or in other words, when the O ₂ sensor temperature is lower, it is judged as activated.

The present invention eliminates the above-mentioned conventional drawbacks, and one embodiment of the present invention will be described below with reference to the drawings.

FIG. 6 shows an embodiment of the invention. 6th
In the figure, 1 is an O ₂ sensor made of a zirconia sintered body with a porous electrode, 2 is a microcomputer that forms the center of the air-fuel ratio control device, and 5 is a constant voltage V _B applied through resistors R ₄ and R ₅ . and divide the voltage into the reference voltage V _S
The O ₂ sensor 1 is connected in parallel to the reference voltage generating circuit ₅ . Reference numeral 4 denotes an analog-to-digital converter (hereinafter referred to as A/D converter) which digitally converts the O ₂ sensor output terminal voltage V _iN and inputs it to the microcomputer 2 .

FIG. 7 shows an equivalent circuit of the reference voltage generating circuit 5 and the O ₂ sensor 1 in FIG. However, the O ₂ sensor has an internal resistance R ₀ and an electromotive force V ₀ . Also resistance R ₄ , R ₅
The resistance value of R6 is practically negligible compared to the resistance _R6 , and the A/D converter input resistance is
Suppose that it is negligibly large compared to R ₆ and R ₀ .

In FIG. 7, the input voltage V _iN to the A/D converter 4 is V _iN = V ₀ + (V _S −V ₀ )×R ₀ /R ₀ +R ₆ =R ₆ V ₀ +R ₀ V _S /R ₀ +R
₆ ...(1) becomes.

Here, if R ₆ is a value near the O ₂ sensor internal resistance value when the O ₂ sensor reaches activation from inactivity, then in equation (1), if ΓR ₀ ≫ R ₆ (that is, the O ₂ sensor When temperature is low and inactive) V _iN ≒V _S ……(2) When ΓR ₀ ≒ R ₆ (when reaching active state from inactive state) V _iN ≒V ₀ +V _S /2 ……(3 ) ΓR ₀ <<R ₆ (when the O ₂ sensor is fully activated) V _iN ≒V ₀ ...(4).

Therefore, when the reference voltage V _S is set near the lean/rich judgment level (approximately 0.4V) after O ₂ sensor activation, the A/D converter 4 shown in equations (2), (3), and (4) above The relationship between the input voltage V _iN and the O ₂ sensor temperature is shown in FIG.

In Fig. 8, when the O ₂ sensor temperature reaches the activation temperature (TA in Fig. 8; the lowest temperature at which the O ₂ sensor can be considered active), V _iN , that is, in the rich state (V _S +ΔV ₂ ), is lean. Sometimes (V _S −
ΔV ₁ ) is exceeded (V _iN > V _S + ΔV ₂ or V _iN <
V _S −ΔV ₁ ...(5)) It is determined that the O ₂ sensor is activated, and the O ₂ sensor when (V _S −ΔV ₁ )<V _iN <(V _S +ΔV ₂ ) ...(6) It turns out that it is sufficient to judge that it is inactive. In order to prevent erroneous determination due to external noise or the like, it is better to perform the above determination only when the level of V _iN continues for a certain period or more and satisfies equations (5) and (6). The lean/rich judgment level after activation may be set to the above level (0.4V), or by selecting appropriate ΔV ₁ ′ and ΔV ₂ ′, V _iN =V _S
+ΔV ₂ ′ is the judgment level from lean to rich,
It is also possible to set V _iN =V _S −ΔV ₁ ' as the determination level from rich to lean. Also, ΔV ₁ = ΔV ₁ ′≠ΔV ₂ =
ΔV ₂ ′ or ΔV ₁ ′=ΔV ₁ ′=ΔV ₂ =ΔV ₂ ′. In the configuration example shown in FIG. 6, V _iN is input to the A/D converter 4, and V _iN >V _S +ΔV ₂ ,
The determination of V _iN <V _S −ΔV _1, etc. is performed by the microcomputer 2, but instead of this, (V _S +ΔV ₂ ),
It goes without saying that (V _S -ΔV ₁ ) may be input to two comparators each having a reference level for comparison, and the comparator output may be input to a microcomputer. In this case, the air-fuel ratio lean/rich determination level determined by the O ₂ sensor after activation of the O ₂ sensor is from lean to rich (V _S +ΔV ₂ ) and from rich to lean (V _S −ΔV ₁ ). The above-mentioned comparator output for determining activation/inactivation can be used as is for determining lean/rich, which is advantageous since there is no need to add a new comparator.

The present invention has the above-described configuration, and according to the present invention, a switch for determining activation as in the conventional example,
There is no need for a current source, the configuration is simple, and the presence or absence of activation can be easily determined by detecting whether the output voltage is at a predetermined level or within a predetermined range including the predetermined level.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of the air-fuel ratio control method, Figure 2 is a diagram showing the relationship between the air-fuel ratio and the O ₂ sensor electromotive force, and Figure 3 is a diagram showing the relationship between the air-fuel ratio and the O 2 sensor electromotive force.
Figure 4 shows the relationship between O ₂ sensor temperature, O ₂ sensor electromotive force, and O ₂ sensor response time, Figure 4 shows the relationship between O ₂ sensor temperature and O ₂ sensor internal resistance, and Figure 5 6 is an electrical circuit diagram of a main part of a conventional air-fuel ratio control system, FIG. 6 is an electrical circuit diagram of a main part of an air-fuel ratio control system according to an embodiment of the present invention, and FIG. 7 is a partial equivalent of FIG. 6. The circuit diagram, FIG. 8, is a diagram showing characteristics in the system of the present invention. 1...Oxygen concentration sensor ( _O2 sensor), 2...Microcomputer, 5...Reference voltage generation circuit.

Claims (1)

[Claims] 1. An oxygen concentration sensor that detects the oxygen concentration in exhaust gas of the engine and generates an electromotive force according to the oxygen concentration, and controls the air-fuel ratio of the engine based on the electromotive force of the oxygen concentration sensor. a control means, a reference voltage generation circuit connected in parallel to the oxygen concentration sensor and generating a reference voltage near a lean/rich determination level when the oxygen concentration sensor is activated; and the oxygen concentration sensor and the reference voltage generation circuit. an air-fuel ratio control device comprising determining means for detecting a voltage value at a connection point of and determining whether or not the oxygen concentration sensor is activated based on the voltage value. 2. The determining means determines whether or not the voltage value at the connection point between the reference voltage generation circuit and the oxygen concentration sensor is within a prescribed range that includes the reference voltage of the reference voltage generation circuit. The air-fuel ratio control device according to claim 1, which determines the presence or absence of the air-fuel ratio. 3. The determining means detects the oxygen concentration sensor when the voltage value at the connection point between the reference voltage generation circuit and the oxygen concentration sensor exceeds a specified range including the reference voltage of the reference voltage generation circuit for a certain period of time. The air-fuel ratio control device according to claim 1, which determines that the air-fuel ratio control device is activated. 4. When the oxygen concentration sensor is active, the lean/rich air-fuel ratio determination level by the oxygen concentration sensor is set to a voltage value that is a predetermined level higher than the reference voltage of the reference voltage generation circuit when going from lean to rich, and when from rich to lean, The air-fuel ratio control device according to claim 1, wherein the voltage value is set to be a predetermined level lower than the reference value of the reference voltage generation circuit.