JPH0355661B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an air-fuel ratio control device for an engine, and more particularly to an air-fuel ratio feedback control device using an oxygen sensor.

[Prior art]

Recently, in order to accurately control the air-fuel ratio of the engine intake air-fuel mixture to a target value, an oxygen sensor has been installed in the exhaust system, and the amount of fuel supplied is adjusted according to the oxygen concentration in the exhaust gas, which has a correlation with the air-fuel ratio. Feedback is controlled.

As such an air-fuel ratio control device, for example,
“Air-fuel ratio detection method” for which the applicant previously applied for a patent
(Japanese Unexamined Patent Publication No. 56-89051), and it can be shown as shown in FIG. In Fig. 1, 1 is an oxygen sensor, which applies the principle of a type of oxygen battery that generates an electromotive force according to the oxygen concentration, and is represented by a power source 2 representing the electromotive force and an internal resistance 3. It will be done. That is, the oxygen sensor 1 has a reference electrode on one side and an oxygen electrode on the other side with an oxygen ion conductive solid electrolyte in between. An inflow current Is is supplied to the reference electrode from the current supply means 4, and this inflow current Is generates a reference oxygen partial pressure Pa at the inner electrode. On the other hand, the oxygen partial pressure Pb at the oxygen electrode is the oxygen partial pressure of the gas to be measured, and based on these oxygen partial pressures Pa and Pb, E=(RT/4F)・1n(Pa/Pb ) However, an electromotive force E is generated, which is expressed by the Nernst equation, where R: gas constant, T: absolute temperature, and F: Faraday constant. When this electromotive force E switches from the lean side to the rich side with a predetermined air-fuel ratio as the boundary, it changes greatly and suddenly to the positive side, and the switching air-fuel ratio changes with the injected current Is.
It changes depending on the value of. Further, the oxygen sensor 1 has an internal resistance 3, and this internal resistance 3 changes depending on the activation state of the oxygen sensor 1. Therefore,
The oxygen sensor 1 is represented by a power source 2 and an internal resistor 3, and its output Vs is input to the positive terminal of a comparator 5. A comparison standard value SL, which is voltage-divided by resistors 6 and 7, is input to the negative terminal of the comparator 5, and the comparison standard value SL is normally a value at which the output Vs of the oxygen sensor 1 suddenly changes at the stoichiometric air-fuel ratio. The voltage value is set between the upper and lower limits of .
Therefore, when Vs>SL, comparator 5 outputs an over-concentrated signal.
When Vs< _SL , the feedback control circuit 8 outputs the lean signal S _L to the feedback control circuit 8, and the feedback control circuit 8 outputs the fuel supplied by a fuel supply means (for example, an injector) (not shown) based on the signal from the comparator 5. The air-fuel ratio is controlled to the target air-fuel ratio by controlling the injection amount. Then, the feedback control circuit 8 sets a target air-fuel ratio according to the operating state, and sends a signal S _I to the current supply means 4 to change the injected current Is so that the output Vs of the oxygen sensor 1 suddenly changes at this target air-fuel ratio. It is output to. Current supply means 4
controls the magnitude of the injected current Is based on the signal S _I from the feedback control circuit 8.

Therefore, by changing the injected current Is, the output Vs of the oxygen sensor 1 changes suddenly at the target air-fuel ratio, and the air-fuel ratio can be controlled to the target air-fuel ratio based on this sudden change in the output Vs.

However, with such conventional air-fuel ratio control devices, the output of the oxygen sensor, which changes rapidly at the target air-fuel ratio, is compared with a fixed comparison reference value to determine whether the air-fuel ratio is richer or leaner than the target air-fuel ratio. However, the air-fuel ratio was controlled to be the target air-fuel ratio, and the configuration was such that current was supplied to the oxygen sensor so that the output of the oxygen sensor suddenly changed at the target air-fuel ratio, so the output of the oxygen sensor is the voltage obtained by adding the internal resistance and the injected current to the pure electromotive force, and the output of the oxygen sensor changes depending on the magnitude of the injected current. Therefore, the air-fuel ratio judgment made by comparing the oxygen sensor output, which changes depending on the magnitude of the injected current, with a fixed comparison reference value becomes inaccurate, and there is a problem that the air-fuel ratio cannot be controlled with high precision. It was hot.

[Purpose of the invention]

Therefore, the present invention changes the comparison reference value according to the injected current, so that the comparison reference value is always adjusted to a value between the upper and lower limits of the oxygen sensor output, and the air-fuel ratio is accurately determined. The purpose is to improve control accuracy.

[Structure of the invention]

The air-fuel ratio control device of the present invention has a reference electrode on one side and an oxygen electrode that generates an oxygen partial pressure corresponding to the oxygen concentration in a gas to be measured, with an oxygen ion-conducting solid electrolyte in between. An oxygen sensor outputs a signal whose voltage value changes suddenly at a target air-fuel ratio according to the difference in oxygen partial pressure between electrodes, and a target air-fuel ratio generates a reference oxygen partial pressure at the reference electrode of the oxygen sensor, causing a sudden change in the oxygen sensor output. Current supply means for supplying an inflow current that determines the value of the fuel ratio, and comparing the output signal value of the oxygen sensor with a comparison reference value to determine whether the air-fuel ratio is leaner or richer than the target air-fuel ratio. Feedback control means that controls the amount of fuel supplied and determines the magnitude of the sinking current supplied by the current supply means according to the operating state; and a feedback control means that detects the magnitude of the sinking current and responds to the magnitude of the sinking current. and a comparison reference value determining means for changing the comparison reference value according to the injected current.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a diagram showing an embodiment of the present invention. In explaining this embodiment, the same components as those of the conventional example shown in FIG.

First, to explain the configuration, in FIG. 2, current is supplied to the oxygen sensor 1 from the current supply means 4.
Is is supplied, and the magnitude of the injected current Is is determined by the voltage across the resistor R ₁ and the buffer amplifier BA ₁ , BA ₂
The current value is detected by the current value detection circuit 11 inputted via the current value detection circuit 11. The current value detection circuit 11 includes resistors R ₂ , R ₃ ,
Consists of R ₄ and operational amplifier OP ₁ ,
A voltage Vi proportional to the voltage between the terminals of the resistor _R1 , that is, proportional to the magnitude of the injected current Is, is output to the comparison reference value determining circuit 12. The comparison reference value determination circuit 12 is composed of resistors R ₅ , R ₆ , R ₇ , R ₈ , R ₉ , R ₁₀ and operational amplifiers OP ₂ and OP ₃ .
A voltage obtained by multiplying the voltage Vi input from the current detection circuit 11 by K (K: constant) is added to the reference voltage Vo determined by dividing the voltage by R ₇ and R ₈ , and a comparison reference value SL is obtained at the negative terminal of the comparator 5. It is output to. That is, the comparison reference value SL is expressed by the following equation.

SL=Vo+KVi (K: constant) Therefore, this comparison reference value SL changes depending on the magnitude of the injected current Is, and the current detection circuit 11 and comparison reference value determination circuit 12 determine the comparison reference value. It constitutes means 13. and,
The output voltage Vs of the oxygen sensor 1 is inputted to the positive terminal of the comparator 5 via the buffer amplifier BA ₂ , and the comparator 5 outputs an overconcentration signal S _R when Vs>SL.
When Vs<SL, a lean signal S _L is output to the feedback control circuit 8. The feedback control circuit 8 outputs a control signal S _Q to a fuel supply means (for example, an injector) (not shown) based on the signals S _R and S _L from the comparator 5, thereby controlling the amount of fuel injection to be supplied to the engine. control so that the air-fuel ratio becomes the target air-fuel ratio. This feedback control circuit 8 sets a target air-fuel ratio that is optimal for the operating condition, and sends a signal S _I to the current supply means 4 to change the injected current Is so that the output Vs of the oxygen sensor 1 suddenly changes at this target air-fuel ratio. It is outputting. The current supply means 4 controls the magnitude of the injected current Is based on the signal S _I from the feedback control circuit 8. The comparator 5 and the feedback control circuit 8 are connected to the feedback control means 1.
4.

Next, the action will be explained.

The feedback control circuit 8 sets the optimal target air-fuel ratio for the operating condition and outputs a signal S _I to the current supply means 4, and the current supply means 4 injects a current Is corresponding to the signal S _I into the oxygen sensor 1. supplying.
When the injected current Is is changed, the output characteristics of the oxygen sensor 1 become as shown in Fig. 3, and the value of the air-fuel ratio at which the output Vs of the oxygen sensor 1 suddenly changes is as shown in Fig. 4. , shifts to the lean side as the inflow current Is increases. Furthermore, since the oxygen sensor 1 has an internal resistance 3, the oxygen sensor 1
The output Vs of is affected by the sink current Is, and as the sink current Is increases, as shown in Figure 3,
The output Vs also becomes higher. Therefore, oxygen sensor 1
The intermediate value between the upper and lower limits of the output Vs (hereinafter referred to as intermediate voltage) Vn is as the inflow current Is increases,
As shown in FIG. 5, the height increases. Therefore, based on the magnitude of this injected current Is, the comparison reference value determining means 13 adjusts the value of the comparison reference value SL to reliably detect a sudden change in the output Vs of the oxygen sensor 1. In other words, the current detection circuit 11
The voltage across _R1 is compared to detect the value of the sink current Is, and a voltage Vi proportional to the value of the sink current Is is output to the comparison reference value determining circuit 12. The comparison reference value determination circuit 12 outputs a voltage obtained by adding KVi to the voltage Vo divided by the resistors R ₇ and R ₈ to the comparator 5 as a comparison reference value SL,
is set so that KVi=IsRs. Therefore, if the voltage Vo is set to the intermediate voltage Vn of the oxygen sensor output Vs when the inflow current Is is zero, the comparison reference value SL will always be, even if the inflow current Is changes.
This becomes the intermediate voltage Vn of the oxygen sensor output Vs, and the comparator 5 can reliably determine a sudden change in the oxygen sensor output Vs at the target air-fuel ratio. As a result, it is possible to accurately judge whether the air-fuel ratio is leaner or richer than the target air-fuel ratio over a wide range, and it is possible to control the air-fuel ratio to the target air-fuel ratio with high precision and to adjust the operating conditions. Accordingly, the target air-fuel ratio can be set over a wide range.

(Effects) According to the present invention, the reference value for comparison with the output of the oxygen sensor is adjusted in accordance with the magnitude of the current flowing into the oxygen sensor that determines the target air-fuel ratio at which the output of the oxygen sensor suddenly changes. Therefore, a sudden change in the oxygen sensor output at the target air-fuel ratio can be reliably determined. Therefore, it is possible to accurately determine whether the air-fuel ratio is leaner or richer than the target air-fuel ratio, which changes by changing the injected current, and to precisely control the air-fuel ratio to the target air-fuel ratio. In addition, the target air-fuel ratio can be set over a wide range depending on the operating condition.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing a conventional air-fuel ratio control device.
Figures 2 to 5 are diagrams showing an embodiment of the air-fuel ratio control device of the present invention, Figure 2 is its circuit diagram, and Figure 3 shows the output characteristics of the oxygen sensor when the injected current is changed. FIG. 4 is a diagram showing the relationship between the air-fuel ratio, which suddenly changes the output of the oxygen sensor, and the flowing current, and FIG. 5 is a diagram showing the relationship between the intermediate voltage of the output of the oxygen sensor and the flowing current. 1... Oxygen sensor, 4... Current supply means, 13
. . . Comparison reference value determining means, 14 . . . Feedback control means.

Claims (1)

[Claims] 1 With an oxygen ion conductive solid electrolyte in between, it has a reference electrode on one side and an oxygen electrode that generates an oxygen partial pressure corresponding to the oxygen concentration in the gas to be measured on the other side, and the difference in oxygen partial pressure between the two electrodes is An oxygen sensor that outputs a signal whose voltage value changes suddenly at the target air-fuel ratio according to the target air-fuel ratio, and an injected current that generates a reference oxygen partial pressure at the reference electrode of the oxygen sensor and determines the value of the target air-fuel ratio at which the oxygen sensor output changes suddenly. the output signal value of the oxygen sensor is compared with a comparison reference value to determine whether the air-fuel ratio is leaner or richer than the target air-fuel ratio, and the amount of fuel supplied is controlled; , a feedback control means that determines the magnitude of the injected current supplied by the current supply means according to the operating state, and a feedback control means that detects the magnitude of the injected current and changes the comparison reference value in accordance with the magnitude of the injected current. An air-fuel ratio control device comprising: comparison reference value determining means for determining a comparison reference value.