JPH0412423B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a sensor that detects an air-fuel ratio by measuring oxygen concentration in exhaust gas from an internal combustion engine, etc. This invention relates to improvements to oxygen pump type air-fuel ratio sensors.

[Prior art]

Conventionally, for example, in order to control the operation of an automobile engine at a stoichiometric air-fuel ratio, an oxygen sensor made of an ion-conducting solid electrolyte (e.g. stabilized zirconia) has been used to detect the difference between the oxygen partial pressures of exhaust gas and air. It is well known that the combustion state at the stoichiometric air-fuel ratio can be detected based on the resulting change in electromotive force. Also, as is well known, depending on the operating condition of the engine, it is preferable to control the air-fuel ratio to the rich side (lower than the stoichiometric air-fuel ratio) where there is more fuel or to the lean side (larger than the stoichiometric air-fuel ratio) where there is more air. It is.

However, in the above oxygen sensor, the air-fuel ratio A/F, which is the weight ratio of air and fuel, is the stoichiometric air-fuel ratio of 14.7.
A large change in output can be obtained when the operating air-fuel ratio is , but there is almost no change in other operating air-fuel ratio ranges, and when the engine is operated at an air-fuel ratio other than the stoichiometric air-fuel ratio, it is not possible to use the output of the oxygen sensor mentioned above. Can not.

Furthermore, the solid electrolyte oxygen pump type oxygen concentration measuring device proposed in Japanese Patent Application Laid-Open No. 130649/1983 has a problem in that it is difficult to accurately detect the stoichiometric air-fuel ratio.

[Summary of the invention]

This invention uses a solid electrolyte oxygen pump type oxygen concentration measuring device, is provided with a means for switching the polarity of the oxygen pump and oxygen sensor during engine operation, and reverses the operation of the oxygen pump by switching the direction of the pump current. By making the partial pressure of oxygen in the minute gap between the parts higher or lower than the partial pressure of oxygen in the exhaust gas outside the gap, it is possible to not only accurately detect the stoichiometric air-fuel ratio but also detect other air-fuel ratios. It has been made possible.

[Embodiments of the invention]

An embodiment of the present invention will be described below.

FIG. 1 is a configuration diagram showing an embodiment of the present invention, and FIG. 2 is a sectional view taken along the line - in FIG. 1. In the figure, 1 is an exhaust pipe of the engine, and 2 is an air-fuel ratio sensor disposed within the exhaust pipe 1. The air-fuel ratio sensor 2 includes a solid electrolyte oxygen pump 6 configured by providing platinum electrodes 4 and 5 on both sides of a flat ion-conductive solid electrolyte (stabilized zirconia) 3 having a thickness of approximately 0.5 mm; A solid electrolyte oxygen sensor 10 is constructed by providing platinum electrodes 8 and 9 on both sides of a flat, ion-conducting solid electrolyte 7, like the oxygen pump 6, and the oxygen pump 6 and the oxygen sensor 10. It consists of support stands 11 that are placed opposite each other with a minute gap d of about 0.1 mm in between. 12 is an electronic control device, which controls the electromotive force e generated between the electrodes 8 and 9 by the oxygen sensor 10;
The oxygen pump oxygen sensor polarity changeover switch
SW, applied to the inverting input terminal of operational amplifier A via resistor R ₁ , and a reference voltage V _Ref that can be changed arbitrarily and applied to the non-inverting input terminal of operational amplifier A.
The operational amplifier A is proportional to the difference between the electromotive force e and the electromotive force e.
It has a function of controlling the pump current I _P flowing between the transistors 4 and 5 by the output of the transistor. That is, it functions to supply the pump current I _P necessary to maintain the electromotive force e at a constant value V _Ref . In addition, a resistor R _O for obtaining an output signal corresponding to the pump current I _P supplied from the DC power supply B is a desired resistance that corresponds to the DC power supply B and prevents the pump current I _P from flowing excessively. value is selected. C is a capacitor. The changeover switch SW is configured so that the polarity of the output of the oxygen sensor 10 and the direction of the pump current I _P of the oxygen pump 6 can be switched in conjunction.

FIGS. 3 and 4 show the results of a test in which the air-fuel ratio sensor of the present invention constructed as described above was installed in a 2000 c.c. gasoline engine for a domestic passenger car. In addition,
If an excessive pump current I _P flows, the oxygen pump 6
The pump current I _P was controlled by the DC power supply B so that it did not exceed 150 mA, as this would destroy the pump current I P . FIG. 3 shows that the changeover switch SW causes the pump current I _P to flow from the electrode 5 to the electrode 4 of the oxygen pump 6 so that the oxygen partial pressure within the minute gap d is higher than the oxygen partial pressure of the exhaust gas outside the gap. The experimental results are shown below. In this case, the oxygen sensor 10
When the electromotive force e generated by the electrode 8 is the ground electrode,
A positive voltage is generated at electrode 9. The above electromotive force e
When 20 mV is constant, the pump current I _P shows a V-shaped characteristic as the air-fuel ratio A/F changes, but when the above electric power e is constant 200 mV, the pump current I _P changes rapidly at the theoretical air-fuel ratio 14.7. However, in a range where the air-fuel ratio A/F was smaller than the stoichiometric air-fuel ratio, a characteristic was obtained in which the pump current I _P changed in proportion to the change in the air-fuel ratio. If the electromotive force e above is constant 200mV,
Since the pump current I _P changes greatly at the stoichiometric air-fuel ratio, the stoichiometric air-fuel ratio can be detected accurately, and an air-fuel ratio smaller than the stoichiometric air-fuel ratio can also be detected by the output signal corresponding to the pump current I _P . can. As mentioned above, in order to increase the change in the pump current I _P near the stoichiometric air-fuel ratio and to accurately detect the stoichiometric air-fuel ratio, the electromotive force e should be increased as shown in the characteristics shown in Figure 3.
It is sufficient to set the voltage to 200 mV, but since the change in the pump current I _P at the stoichiometric air-fuel ratio increases if the voltage exceeds 50 mV, it has been found that setting the voltage to 50 mV or more is practically sufficient. Figure 4 shows the above changeover switch SW.
The experimental results are shown when a pump current I _P is caused to flow from the electrode 4 to the electrode 5 of the oxygen pump 6 so that the oxygen partial pressure within the minute gap d is lower than the oxygen partial pressure of the exhaust gas outside the gap. In this case, the electromotive force e generated by the oxygen sensor 10 generates a positive voltage across the electrode 8 with the electrode 9 as the ground electrode. The above electromotive force e
When the pump current I P is constant at 50 mV, the pump current I _P exhibits a V-shaped characteristic as the air-fuel ratio A/F changes, but when the electromotive force e is constant at 200 mV, the theoretical air-fuel ratio is 14.7.
The pump current I _P changes rapidly, and in a range where the air-fuel ratio A/F is larger than the stoichiometric air-fuel ratio, a characteristic was obtained in which the pump current I _P changes in proportion to the change in the air-fuel ratio. In the characteristics when the above electromotive force e is kept constant at 200 mV, the pump current I _P changes greatly with the stoichiometric air-fuel ratio, so the stoichiometric air-fuel ratio can be detected, and at the same time, the pump current
It can be detected using an output signal compatible with _IP .

As mentioned above, in order to increase the change in the pump current I _P near the stoichiometric air-fuel ratio and to accurately detect the stoichiometric air-fuel ratio, the electromotive force e should be increased to 200 mV as shown in the characteristics of Figure 4.
I realized that it was necessary to do more than that.

From the above, in order to stably detect the air-fuel ratio under all operating conditions of the engine, when the air-fuel ratio is smaller than the stoichiometric air-fuel ratio, the partial pressure of oxygen in the minute gap d is lower than that of the oxygen in the exhaust gas outside the gap. The oxygen pump is operated with the direction of the pump current in a specific direction so that the partial pressure is higher than the partial pressure, and the air-fuel ratio is detected by the change in the pump current. The oxygen pump is operated with the pump current direction opposite to the specific direction so that the oxygen partial pressure inside the gap is lower than the oxygen partial pressure in the exhaust gas outside the gap, and the air-fuel ratio is detected by the change in the pump current. As shown in Figure 3, with the stoichiometric air-fuel ratio as the boundary,
This is very useful because the air-fuel ratio can be detected by arbitrarily selecting the characteristics shown in FIG.

It goes without saying that the changeover switch SW can be switched to the operating state while the engine is operating.

Further, the polarity switching means for the oxygen pump and the oxygen sensor is not limited to the above oxygen pump oxygen sensor polarity switching switch, but may also be a transistor switch or other means.

Furthermore, since an excessive pump current may flow depending on the value of the electromotive force, it is preferable to provide means for preventing the pump current from flowing beyond a desired value.

〔Effect of the invention〕

The present invention is configured to reverse the operation of the oxygen pump by switching the direction of the pump current so that the partial pressure of oxygen in the gap becomes higher or lower than the partial pressure of oxygen in the exhaust gas outside the gap. As a result, it has become easy to accurately detect the entire range of air-fuel ratios and the stoichiometric air-fuel ratio, which has been difficult until now.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram showing an embodiment of the present invention, Fig. 2 is a sectional view taken along the - line of Fig. 1, Fig. 3,
Figure 4 is a characteristic diagram obtained from a test using a 2000 c.c. gasoline engine. 1 is an exhaust pipe of the engine, 6 is a solid electrolyte oxygen pump, 10 is a solid electrolyte oxygen sensor, 12 is an electronic control unit, and SW is a changeover switch.

Claims (1)

[Scope of Claims] 1. An inner section for introducing engine exhaust gas; A solid electrolyte oxygen pump that controls the oxygen partial pressure inside the inner section; a solid electrolyte oxygen sensor that generates an electromotive force corresponding to the partial pressure of oxygen in exhaust gas, and a pump current of the solid electrolyte oxygen pump that is necessary to maintain the electromotive force generated by the solid electrolyte oxygen sensor at a predetermined value. In the air-fuel ratio sensor configured to detect the air-fuel ratio of the engine using an output signal corresponding to the engine, the air-fuel ratio sensor is provided with means for switching the polarity of the solid electrolyte oxygen pump and the solid electrolyte oxygen sensor depending on the operating state during the engine operation. An air-fuel ratio sensor for an engine, characterized in that it accurately detects a stoichiometric air-fuel ratio, an air-fuel ratio larger than the stoichiometric air-fuel ratio, and an air-fuel ratio smaller than the stoichiometric air-fuel ratio.