JPH0260143B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an air-fuel ratio control device for an automobile engine, and more particularly, to an air-fuel ratio control device for an automobile engine, and particularly for adjusting the operating air-fuel ratio of the engine to an arbitrary value within a wide range from a fuel-lean region to a fuel-rich region. The present invention relates to an air-fuel ratio control device for an engine that can perform feedback control.

[Prior art]

Conventionally, oxygen sensors composed of ion-conducting solid electrolytes (e.g. stabilized zirconia) are used to detect theoretical air pressure due to changes in electromotive force caused by the difference between the oxygen partial pressure in exhaust gas and the oxygen partial pressure in air. It is well known that, for example, an automobile engine can be controlled to operate at a stoichiometric air-fuel ratio by detecting a combustion state at a fuel ratio. By the way, the above oxygen sensor can obtain a large change output when the air-fuel ratio A/F, which is the weight ratio of air and fuel, is the stoichiometric air-fuel ratio, but there is almost no change in other operating air-fuel ratio ranges, and the air-fuel ratio is other than the stoichiometric air-fuel ratio. When operating the engine at an air-fuel ratio of , the output of the oxygen sensor cannot be used.

[Summary of the invention]

This invention has been made with the aim of improving such drawbacks.The present invention has been made to improve the operating air-fuel ratio based on the output signal of the air-fuel ratio sensor, not only when operating at the stoichiometric air-fuel ratio, but also when operating at a desired air-fuel ratio other than the stoichiometric air-fuel ratio. An object of the present invention is to provide an air-fuel ratio control device for an engine capable of feedback control of the fuel ratio.

[Embodiments of the invention]

An embodiment of the present invention shown in the drawings will be described below. FIG. 1 is a configuration diagram showing an embodiment of the present invention, in which 1 is an engine, 2 is an intake pipe of the engine 1, 3 is a throttle valve, and 4 is the amount of intake air taken into the engine 1. Intake air detection device for detecting, 5
is a fuel supply valve provided upstream of the throttle valve 3, 6 is an air cleaner provided upstream of the intake air detection device 4, 7 is an exhaust pipe of the engine 1, and 8 is the exhaust pipe 7. 9 is an air-fuel ratio detection electronic device; 10 is an air-fuel ratio sensor attached to the engine 1;
11 is a temperature detector for detecting the temperature of the engine 1; 12 is a temperature detector for each of the temperature detector 11, the intake air detection device 4, the air-fuel ratio detection electronic device 9, and the rotation speed detector 10; This is an electronic control device that receives output signals and drives the fuel supply valve 5 in accordance with the input information to control the amount of fuel supplied to the engine 1. This electronic control device 12
is the changeover switch SW of the air-fuel ratio detection electronic device 9.
It also has a function of driving the air-fuel ratio sensor 8 and switching the flow direction of the pump current I _P of the air-fuel ratio sensor 8 according to the input information.

FIG. 2 is a detailed configuration diagram of the air-fuel ratio sensor 8 and the air-fuel ratio detection electronic device 9, and FIG.
FIG. 3 is a sectional view taken along the - line in the figure. In the figure, the air-fuel ratio sensor 8 is a solid electrolyte oxygen pump 16 constructed by providing platinum electrodes 14 and 15 on both sides of a flat ion-conductive solid electrolyte (stabilized zirconia) 13 with a thickness of approximately 0.5 mm. And, like the oxygen pump 16, a solid electrolyte oxygen sensor 2 is constructed by providing platinum electrodes 18 and 19 on both sides of a flat ion-conducting solid electrolyte 17, respectively.
0, the oxygen pump 16 and the oxygen sensor 20
It is composed of a support stand 21 for arranging the two to face each other with a minute gap d of about 0.1 mm in between. Further, the air-fuel ratio detection electronic device 9 has the oxygen sensor 20 connected to the electrode 1.
The electromotive force e generated between 8 and 19 is applied to the inverting input terminal of the operational amplifier A through the resistor _R1 , and the reference voltage VR applied to the non-inverting input terminal of the operational amplifier _A and the electromotive force are It has a function of controlling the pump current I _P flowing between the electrodes 14 and 15 of the oxygen pump 16 by driving the transistor _TR by the output of the operational amplifier A which is proportional to the difference in e. That is, it functions to supply the pump current I _P necessary to maintain the electromotive force e at a constant value V _R . A resistor R ₀ is provided for obtaining an output signal corresponding to the pump current I _P supplied from the DC power supply B. This resistor R ₀ corresponds to the DC power supply B and has a desired resistance value selected so that the pump current I _P does not flow excessively. C is a capacitor. SW is a changeover switch, and the above pump current
At the same time as the direction in which I _P flows between the electrodes 14 and 15 of the oxygen pump 16 is changed, the oxygen sensor 20
The positive polarity of the electromotive force e generated between the electrodes 18 and 19 is switched so that it is applied to the inverting input terminal of the operational amplifier A.

FIGS. 4 and 5 are characteristic diagrams obtained by testing the air-fuel ratio sensor 8 shown in FIG. 2 above by installing it in a 2000 cc gasoline engine for a domestic passenger car. If an excessive pump current I _P flows, the oxygen pump 16 will be destroyed, so the pump current I _P is limited by the DC power supply B so that it does not flow more than 120 mA. FIG. 4 shows the pump current I _P and the operating air-fuel ratio A of the engine when the pump current I _P is made to flow from the electrode 15 to the electrode 14 with the electrode 15 on the microgap side of the oxygen pump 16 as the positive electrode. This is a characteristic diagram showing the correspondence of /F, and shows the test results when the reference voltage _VR was changed and the above electromotive force e was kept at 200mV, 100mV, and 50mV, respectively, and the air-fuel ratio A/F of the above engine was changed. There is. As mentioned above, the electrode 15 on the micro gap side
When a pump current I _P flows from the electrode 14 toward the electrode 14, the oxygen partial pressure within the minute gap d becomes higher than the oxygen partial pressure in the exhaust gas outside the gap due to the action of the oxygen pump 16. As is well known, as a result, the oxygen sensor 20 generates an electromotive force e that makes the electrode 19 on the small gap side positive. FIG. 5 shows that the pump current I _P is changed from the electrode 14 of the oxygen pump 16 to the electrode 1.
These are the test results when the flow was changed using the changeover switch SW so that the flow was in the direction of 5. In this case, contrary to the case shown in FIG. 4, the oxygen partial pressure within the minute gap d is lower than the oxygen partial pressure in the exhaust gas outside the gap, so the oxygen sensor 20 is activated to make the electrode 18 positive. Electric power e is generated. Therefore, the changeover switch SW simultaneously switches so that the positive polarity of the electrode 18 is applied to the inverting input terminal of the operational amplifier A. In FIGS. 4 and 5 obtained from the above test, the accurate _{stoichiometric} air-fuel ratio (A/F=
In order to detect 14.7), it is preferable that the change in the pump current I _P near the stoichiometric air-fuel ratio is large. This invention sets the electromotive force e to a predetermined value of 100 mV or more, for example, based on the characteristics shown in FIGS. 4 and 5.
200mV, and the pump current I _P changes rapidly near the stoichiometric air-fuel ratio to accurately detect the stoichiometric air-fuel ratio. When the engine is operated, the oxygen partial pressure in the minute gap d is adjusted to that outside the gap so that the characteristics shown in FIG. When the pump current is applied in a direction higher than the oxygen partial pressure in the exhaust gas and the engine is operated in an air-fuel ratio range (fuel lean range) larger than the stoichiometric air-fuel ratio, the above-mentioned pump current is proportional to the air-fuel ratio in the fuel lean range. The pump current is made to flow in a direction in which the partial pressure of oxygen in the minute gap d is lower than the partial pressure of oxygen in the exhaust gas outside the gap so that the characteristics shown in FIG. 5, which change the pump current, are obtained. The operating air-fuel ratio of the engine is feedback-controlled to an arbitrary air-fuel ratio in a wide range from a fuel rich region to a fuel lean region by an output signal corresponding to the pump current _IP .

The operation of this inventive device will be explained below.
When the engine 1 is started, the intake air taken into the engine 1 is introduced from the atmosphere into the air cleaner 6, the intake air amount is detected by the intake air detection device 4, and the intake air is introduced into the engine 1 through the intake pipe 2. . Electronic control device 1 into which the output signal of the intake air detection device 4 is input
2 drives the fuel supply valve 5 to inject and supply fuel corresponding to the intake air amount to the engine 1. When the electronic control unit 12 detects from the output signal of the temperature detector 11 that the temperature of the engine 1 is low, such as immediately after starting, the electronic control unit 12 changes the operating air-fuel ratio of the engine 1 to a desired air-fuel ratio on the fuel-rich side (for example, In order to operate at A/F=12), the changeover switch SW is driven so that the direction in which the pump current I _P of the air-fuel ratio sensor 8 flows is set in the direction in which the partial pressure of oxygen within the minute gap d becomes higher. Then, from the characteristics shown in FIG. 4, the desired air-fuel ratio in the fuel rich region is detected as an output signal corresponding to the pump current, and the electronic control device 1 receives the output signal.
2 controls the amount of fuel injected and supplied from the fuel supply valve 5 so that the output signal becomes a desired value. That is, the operating air-fuel ratio of the engine 1 is feedback-controlled to a desired value using the output signal. Next, the electronic control device 12 detects the operating state of the engine 1, which is usually used frequently such as when driving a car in the city, using the output signals of the intake air detection device 4 and the rotation speed detector 10. Drive the changeover switch SW of the air-fuel ratio detection electronic device 9 in order to set the operating air-fuel ratio to a desired air-fuel ratio on the side of the fuel lean region (for example, A/F = 17) so as to improve the fuel efficiency of the
The pump current is directed in a direction such that the oxygen partial pressure in the minute gap d is lower than the oxygen partial pressure in the exhaust gas outside the gap.
Switch so that _IP flows. Then, from the characteristics shown in FIG. 5, the desired air-fuel ratio in the fuel lean region is detected as an output signal corresponding to the pump current _IP , and the electronic control unit 12 receives the output signal.
controls the amount of fuel supplied from the fuel supply valve 5 so that the output signal becomes a desired value. That is, the operating air-fuel ratio of the engine 1 is feedback-controlled to a desired value on the fuel lean side using the output signal.
Next, the outputs of the intake air detection device 4, rotation speed detector 10, and temperature detector 11 determine the operating state in which the operating air-fuel ratio needs to be the stoichiometric air-fuel ratio in order to reduce harmful components in the exhaust gas of the engine 1. Detected by the signal, the electronic control device 12 adjusts the operating air-fuel ratio of the engine 1 in the same way as conventional devices by utilizing the characteristic shown in FIG. 4 or FIG. Feedback control to the stoichiometric air-fuel ratio.

〔Effect of the invention〕

As described above, the present invention arranges a solid electrolyte oxygen sensor, which has electrodes on both sides of a flat solid electrolyte, and a solid electrolyte oxygen pump, facing each other with a minute gap in between, and injects engine exhaust gas into the gap. At the same time, the electromotive force generated by the oxygen sensor is set to a predetermined value of 100 mV or more (for example,
The air-fuel ratio sensor is equipped with an air-fuel ratio sensor that detects the operating air-fuel ratio of the engine using an output signal corresponding to the pump current of the oxygen pump necessary to maintain the operating air-fuel ratio of the oxygen pump at 200 mV. When controlling the fuel lean side, the pump current flows in a direction such that the oxygen partial pressure within the gap is lower than the oxygen partial pressure in the exhaust gas outside the gap, and conversely, the operating air-fuel ratio is controlled to the fuel rich side. When this happens, the pump current is made to flow in a direction that increases the oxygen partial pressure in the gap, and the operating air-fuel ratio is feedback-controlled by an output signal corresponding to the pump current, so that the accurate stoichiometric air-fuel ratio can be maintained. To provide accurate feedback control to the optimum operating air-fuel ratio according to the operating condition of the engine over a wide air-fuel ratio range from a fuel-rich region to a fuel-lean region, which was a problem with conventional devices. An air-fuel ratio control device for an engine is obtained. In addition, in the above explanation, an example was explained in which the amount of fuel supplied to the engine is controlled in order to obtain a desired air-fuel ratio, but the invention is not limited to this, and the amount of air taken into the engine may also be controlled. There is no need to explain how good things are.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing an embodiment of the air-fuel ratio sensor used in the device of the present invention, and FIG.
4 and 5 are characteristic diagrams obtained by testing the air-fuel ratio sensor shown in FIG. 2 by installing it in a gasoline engine for a passenger car. 1... Engine, 4... Intake air detection device, 5...
Fuel supply valve, 7...Exhaust pipe, 8...Air-fuel ratio sensor, 12...Electronic control unit, 16...Solid electrolyte oxygen pump, 20...Solid electrolyte oxygen sensor.

Claims (1)

[Claims] 1. A solid electrolyte oxygen sensor and a solid electrolyte oxygen pump configured by providing electrodes on both sides of a flat solid electrolyte, the solid electrolyte oxygen sensor and the solid electrolyte oxygen pump being connected through a minute gap. The solid electrolyte oxygen pump is configured to face each other and introduce exhaust gas from the engine into the gap, and correspond to the pump current of the solid electrolyte oxygen pump necessary to maintain the electromotive force generated by the solid electrolyte oxygen sensor at a predetermined value. An air-fuel ratio sensor is provided to detect the air-fuel ratio of the engine using an output signal, and when the operating air-fuel ratio of the engine is controlled to be leaner than the stoichiometric air-fuel ratio, the oxygen partial pressure in the gap is outside the gap. When the pump current flows in a direction that makes the partial pressure of oxygen lower than the oxygen partial pressure in the exhaust gas, and conversely, when the operating air-fuel ratio is controlled to be richer in fuel than the stoichiometric air-fuel ratio, the oxygen partial pressure in the gap becomes higher. An engine comprising means for flowing the pump current in a direction, and means for controlling the amount of fuel or air supplied to the engine according to the direction in which the pump current flows and an output signal corresponding to the pump current. Air-fuel ratio control device. 2 The electromotive force generated by the solid electrolyte oxygen sensor is
The air-fuel ratio control for an engine according to claim 1, characterized in that it is equipped with an air-fuel ratio sensor that maintains the pump current of the solid electrolyte oxygen pump at a predetermined value of 100 mV or more and changes rapidly near the stoichiometric air-fuel ratio. Device.