JPS59200040A - Air-fuel ratio controller - Google Patents

Abstract

PURPOSE:To secure an accurate air-fuel ratio in all driving range, by controlling a fuel feed quantity to feed back to a control-desired air-fuel ratio varying according to a driving state on the basis of the output of an oxygen sensor at all times. CONSTITUTION:In time of acceleration and so on, if it is rarer than a theoretical air-fuel ratio as a fuel feed quantity runs short, the output of an oxygen sensor 23 comes to low, and a compartor 35 outputs a low level signal to a control circuit 20 whereby a command for fuel increment is transmitted to a feedback control part 22, and in contrast with this, if the air-fuel ratio is denser than it, the output of the oxygen sensor 23 rises and at the point that exceeds comparative reference voltage of the comparator 35, the output of the comparator 35 is changed over to a high level so that the control circuit 20 makes the control part 22 so as to reduce the fuel quantity to some extent. These operations are repeated but in an extemely short period of time, therefore the air-fuel ratio of mixture in time of acceleration is accurately controlled to converge on the desired value.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air-fuel ratio control device that performs feedback control on fuel supply m to an internal combustion engine while detecting oxygen concentration in exhaust gas.

By accurately controlling the amount of fuel supplied to the internal combustion engine, in other words, the air-fuel ratio of the air-fuel mixture, to the target value, fuel efficiency and Dl-
It is already well known that the gas composition can be improved.

Therefore, a device that detects 81 degrees of oxygen in the exhaust gas, which is closely correlated with the air-fuel ratio of the supplied air-fuel mixture, and controls the fuel supply amount based on this detection result has already been put into practical use. .

However, the output characteristic of an oxygen sensor is that the output changes greatly depending on whether or not there is oxygen in the exhaust gas, that is, whether the air-fuel mixture is richer or leaner than the stoichiometric air-fuel ratio; otherwise, the output changes. Since the air-fuel ratio is extremely small and difficult to judge, the air-fuel ratio that is normally the control target value must be the stoichiometric air-fuel ratio. ! There wasn't.

On the other hand, as seen in, for example, JP-A-56-254.8 and JP-A-56-105634, the detection characteristics of oxygen concentration in the exhaust gas are A device has been proposed that uses a tilted oxygen sensor whose output fluctuates relatively largely in accordance with the oxygen concentration value, and performs feedback control of the air-fuel ratio to a predetermined value on the lean side. However, in this case, the absolute value of the output of the oxygen sensor may change over time, resulting in different output values for the same target air-fuel ratio. b) It had the disadvantage that it was difficult to maintain stable control over a long period of time.

However, recently, researchers have noticed that even with regular molded oxygen sensors, when a current is passed between the electrodes, the point at which the output suddenly changes depending on the current value changes on the lean side of the stoichiometric air-fuel ratio. A device capable of detecting a lean air-fuel ratio was published in a patent application published in 1973, January 1, 1983. -164' 822
It was proposed as @.

This is shown in Fig. 1 and Fig. 2. Fig. 1 is a longitudinal section 7 of the oxygen sensor element 1, and Fig. 2 is an exploded diagram of the oxygen sensor element 1 shown in Fig. 1. This is a perspective view, and the diaphragm layer 2 is made of an insulating material such as alumina, mullite, spinel, etc. A heating element 3 is provided inside the diaphragm layer 2, and it maintains the strength as an MA base. On the surface of this diaphragm m2, a two-part reference electrode electron conductor HH'J4.5 is laminated, and an oxygen ion conductive solid electrolyte layer 6 is further laminated thereon. The cumulative period of this solid electrolyte layer 6 is Y2
ZrO2 stabilized with O, or CaO, which is well known in the art, can be used. A measurement electrode electron conduction layer 7 is laminated on the surface of this solid electrolyte layer 6.
and the one reference electrode electron conductive layer 4, a voltage J (q constant means 8 is connected to enable measurement of the electromotive force E, and
A current supply circuit 9 is connected between the measurement electrode electron conduction layer 7 and the other reference electrode electron conduction layer 5. At this time, it is desirable to use catalytically active platinum for the reference electrode electron conductive layers 4 and 5 and the measurement electrode electron conductive layer 7, and other materials such as an alloy of platinum and a platinum group element may be selected and used as appropriate. is good. Further, when laminating the electron conductive layers 4.5.7 and the solid electrolyte layer 6, for example, a method may be used in which powders thereof are made into a paste, screen printed, and then fired, or other methods may be used. It is also possible to do so. In addition, a heating power source 1o is connected to the heating element 3.
The temperature of the oxygen sensor element can be controlled by connecting the oxygen sensor element. Further, on the measurement electrode electron conduction layer 7, there is provided a diffusion layer 11 capable of controlling the diffusion of oxygen molecules flowing from the test gas, and this diffusion layer 11 is made to be in contact with the test gas. The material of this diffusion layer 11 can be made of, for example, Murai 1~, spinel, )A Lusterai (~), calcium zirconate, etc., and can be formed by a screen printing method using powder or a custom-made method. Laminated vines.

Therefore, using the oxygen sensor υ element 1, the current supply circuit 9
When the positive electrode side of the electrode is connected to the other reference electrode electron conductive layer 5 and a current is supplied, oxygen ions are forcibly moved from the measurement electrode electron conductive layer 7 to the base Q electrode electron conductive layer 5. .

At this point, the inflow and diffusion of oxygen molecules from the sample gas is controlled by the presence of 1'lk 1m 11.
The measured polar oxygen partial pressure is lower than the oxygen partial pressure in the test gas. On the other hand, the reference electrode oxygen partial pressure is increased by the flow of oxygen ions toward the base L$ electrode electron conductive layer 5, but the oxygen molecules present in the reference electrode electron conductor layer 5 are When the diaphragm layer 2 is dense and the solid electrolyte layer 6 is porous, the oxygen ions are diffused through the solid electrolyte layer 6, or both. A reference polar oxygen partial pressure is maintained in which the inflow of oxygen and the diffusion of oxygen molecules are balanced. Therefore, if the voltage measuring means 8 measures the electromotive force E generated in response to the difference between the measured polar oxygen partial pressure, which is lower than the oxygen partial pressure in the test gas, and the reference polar oxygen partial pressure, While maintaining a relationship in which the measured polar oxygen partial pressure is lower than the oxygen partial pressure in the test gas, the measured polar oxygen partial pressure changes according to changes in the oxygen partial pressure in the test gas, so the theoretical air-fuel ratio This makes it possible to detect air-fuel ratios that are rarer than those described above.

FIG. 3 shows the relationship between the sensor output V and the air-fuel ratio when the current flowing from the reference electrode electron conductive layer 5 to the measurement electrode electron conductive layer 7 is changed from I to 1, respectively.

It can be seen that when the injected current is small, the air-fuel ratio at which the sensor output suddenly changes approaches the stoichiometric air-fuel ratio, and as the injected current increases, the air-fuel ratio that suddenly changes the output shifts to the lean side.

Therefore, according to such a device, even if the air-fuel mixture is leaner than the stoichiometric air-fuel ratio, it is possible to accurately determine the air-fuel ratio.

It is already well known that the fuel efficiency of internal combustion engines is best when the air-fuel ratio is slightly leaner than the stoichiometric air-fuel ratio. The air-fuel mixture required for the engine changes in various ways depending on the operating conditions at the time, and the air-fuel ratio must be controlled accurately to the target value in any case. However, conventionally, for example, a predetermined air-fuel ratio can be obtained in a part load region where operation is frequently performed, but even if the fuel supply amount is feedback-controlled using the oxygen sensor described above,
In the full load range, feedback control was temporarily stopped and open-loop control was used to enrich the air-fuel ratio, so control accuracy in this range was not necessarily high and there was a tendency for fuel to be wasted. .

The present invention has been made with attention to such problems, and it accurately responds to various required air-fuel ratios that vary depending on the operating state of the internal combustion engine by feedback-controlling the fuel supply amount. The aim is to further improve fuel efficiency in all driving ranges.

Therefore, the present invention provides an oxygen sensor in which the sudden change point of the sensor output voltage with respect to the air-fuel ratio (oxygen concentration) changes according to the sensor current value, and an oxygen sensor that detects the engine operating state and determines the optimum control target air-fuel ratio at that moment. The device is equipped with a means for determining the optimum control target air-fuel ratio and a means for flowing a current into the oxygen sensor according to the optimum control target air-fuel ratio, and constantly supplies fuel based on the output of the oxygen sensor in response to the control target air-fuel ratio that changes depending on the operating state. Feedback control is applied to the air-fuel ratio to ensure a highly accurate air-fuel ratio throughout the entire operating range.

Embodiments of the present invention will be described below based on the drawings.

FIG. 4 shows the specific structure of the demolded oxygen sensor used in the present invention.・1
The oxygen sensor element 1'' is housed inside a holder 17, and exhaust gas flows into it through a louver section 12 having a small hole 11 formed at its tip.

The oxygen sensor element 1 is exposed to this exhaust gas and generates an output depending on the oxygen concentration in the exhaust gas.

Reference numerals 13 to 15 indicate a sensor output lead wire, a heater lead wire, and a common ground lead wire, respectively.In order to prevent exhaust gas from leaking, a gas leakage prevention filler is provided inside the insulating tube 18. sealed.

16 indicates a connector for wiring.

Note that the portion to the left of line A-A in the figure is inserted into the exhaust pipe (not shown) of the internal combustion engine.

Figure 5 shows the control circuit, and 2o is a control circuit composed of a microcomputer, etc., which controls various elements necessary for the engine, including the amount of fuel supplied to the engine. In the embodiment, engine load detection means (e.g. suction negative pressure sensor,
The operating state is determined from the detection signal of the intake air amount sensor, etc.) 21, and a control target value for the air-fuel ratio is determined in accordance with this operating state.

Reference numeral 25 denotes a circuit that increases or decreases the current flowing into the oxygen sensor 23 according to the control target value, and the control circuit 20
The transistor 26 conducts when the signal S from J is at high level j'-1-IJ, and the transistor 26 is conductive when the signal S is at high level rLJ
It consists of a transistor 27 that is conductive when , and resistors 28 and 29 connected in series with these transistors 26 and 27 to change the magnitude of the current flowing into the sensor.

30 is an amplifier that amplifies and extracts the output of the oxygen sensor 23;
Reference numeral 35 is a comparator that determines whether the target air-fuel ratio J: is rich or lean based on changes in the oxygen sensor output.

As shown in Figure 3, the air-fuel ratio at which the output of the oxygen sensor suddenly changes due to the current flowing into the sensor shifts toward the lean side, but at the same time, the sensor output voltage also changes relatively (as the air-fuel ratio shifts toward the lean side, the output voltage increases). ), the comparator 3 above
It is necessary to switch the comparison voltage (slice level) of No. 5 along with the switching of the target air-fuel ratio.

36 is a switching circuit for this purpose, which is connected to the control circuit 20.
When the signal S, from .

22 is a feedback control unit for fuel supply m, and comparator 3
The supply m is increased or decreased by a signal $2 outputted from the control circuit 2o based on the output of the control circuit 2o. 24 is a heating element (heater) built into the sensor.

Next, the operation will be explained with reference to FIG.

By flowing a current into the oxygen sensor 23, oxygen ions move from the measurement electrode electron conduction layer 7 to the reference electrode electron conduction layer 5, and the oxygen partial pressure on the outside measurement electrode side decreases. As mentioned above, the sudden change point of the sensor output with respect to the air-fuel ratio changes as shown in FIG.

Specifically, as the above-mentioned injected current is increased, the abrupt change point of the sensor output shifts to the lean air-fuel ratio side, and therefore, the air-fuel ratio becomes richer than the air-fuel ratio corresponding to the current value. Since the sensor output changes significantly depending on whether the temperature is high or low, air-fuel ratios other than the stoichiometric air-fuel ratio can also be detected.

The control circuit 20 determines the operating state based on the signal from the load detecting means 21 as the operating state detecting means, and accelerates,
rHJ is output as a signal S for increasing the control target air-fuel ratio during high load, and rLJ is output for reducing the target air-fuel ratio during idle and low load.

Assuming that the acceleration operation state has now started and the signal S becomes "T1", the transistor 26 of the current supply circuit 25 is turned on, and the current I is supplied to the oxygen sensor 23 via the resistor 28, which causes the oxygen In this embodiment, the sensor 23 has a characteristic that the output j suddenly changes after reaching the stoichiometric air-fuel ratio.

Also, due to f[J of signal @$1, comparison voltage switching circuit 36
Then, when the transistor 31 is turned on, the output of the voltage setting section 33 is inputted as the comparison reference voltage of the comparator 35.

Therefore, during such acceleration, if the amount of fuel supplied is insufficient and the fuel is leaner than the stoichiometric air-fuel ratio, the output of the oxygen sensor 23 is low and the comparator 35 outputs a low level signal to the control circuit 20. Therefore, a command to increase the amount of fuel is sent to the feedback control unit 22 of the fuel supply M, and conversely, when the air-fuel ratio rises, the output of the oxygen sensor 3 rises, and the comparison reference voltage of the comparator 35 increases. Comparator 35 when exceeds
The output of JI is cut to a high level, and the control circuit 2o operates the control unit 22 to reduce the fuel consumption.Actually, these operations are repeated at extremely short intervals, so that during acceleration The air-fuel ratio of the air-fuel mixture is precisely controlled to converge to the stoichiometric air-fuel ratio, which is the target value.

On the other hand, if the operating state changes and, for example, shifts to low-load operation, the signal S from the control circuit 2o will be rLJ
Accordingly, the transistor 27 of the current supply circuit 25 is turned on, and the air-fuel ratio A is changed via the resistor 29.
A current I2 corresponding to /F=20 is applied to the oxygen sensor 23.

For this reason, the oxygen sensor 23 switches to a characteristic in which the output changes suddenly at A/F=20, which is leaner than the stoichiometric air-fuel ratio.

At the same time, the comparison base I#- voltage of the comparator 35 is also switched to the 1 output of the voltage setting section 34 as the transistor 32 is turned on.
Therefore, this time, the control target air-fuel ratio is A/F=20.
A decision is made as to whether the air-fuel ratio is richer or leaner than that.

As a result, the control circuit 20 outputs a correction signal to the fuel supply amount control section 22 so that the air-fuel ratio A/F=20.

In this way, since the fuel supply amount is feedback-controlled in response to the target air-fuel ratio that changes depending on the operating state, accurate and highly accurate air-fuel ratio control can be realized.

In addition, in FIG. 6, changes in vehicle speed over time are shown under the assumption that the driving state is poor, and the case where fuel is supplied through a fuel injection valve provided at an intake port is illustrated.

By the way, the amount of fuel injected and supplied from the fuel injection valve basically corresponds to the color of the engine intake air and the engine speed, and is set at a predetermined air-fuel ratio depending on the above-mentioned operating conditions. /F = 20, and when this J and the fuel supply m determined in this way are corrected and controlled based on the output of the oxygen sensor 1 as described above, an emergency Accurately matches the target value
As a result, it becomes possible to

It is clear that the control target value of the air-fuel ratio is not limited to each value mentioned above, and can be freely set according to the characteristics and specification conditions of the internal combustion engine, and can also be set at low idle, medium, high load, etc. The air-fuel ratio may be switched to the optimum air-fuel ratio depending on various operating conditions.

As described above, according to the present invention, fuel supply can be accurately feedback-controlled for different required air-fuel ratios depending on operating conditions, and combustion can be stabilized especially when operating with a lean mixture. performance, and fuel efficiency is further improved.

In addition, since the oxygen sensor shown in A-1 detects various air-fuel ratios and controls the air-fuel ratio to an arbitrary value, the number of components is small and the cost can be reduced by 1.

[Brief explanation of drawings]

Figure 1 shows a longitudinal cross-sectional membrane wall connection diagram of a conventional oxygen sensor, Figure 2 shows an exploded perspective view of the same, and Figure 3 shows the relationship between the sensor output and air-fuel ratio when the current flowing into the sensor is changed. It is a characteristic diagram. FIG. 4 is a sectional view showing the structure of the oxygen sensor of the present invention, FIG. 5 is an air-fuel ratio control circuit diagram,
FIG. 6 is a time chill rate showing the air-fuel ratio control state. 20... Control target value determination circuit, 21... Operating state (load) detection means, 22... Feedback control unit for fuel supply m, 23... Oxygen sensor, 25... Oxygen sensor inflow Current supply circuit, 35... Comparator (air-fuel ratio judgment means), 36... Comparison voltage switching circuit. Patent applicant Nissan Motor Co., Ltd.

Claims (1)

[Claims] an oxygen sensor in which a sudden change point of a sensor output with respect to an air-fuel ratio changes according to a sensor current; a means for detecting an engine operating state; and a means for determining an optimal control target air-fuel ratio according to the operating state; A means for flowing a current corresponding to the control target air-fuel ratio into the oxygen sensor, a means for determining the air-fuel ratio based on a change in the output of the oxygen sensor, and a GM-means for determining the air-fuel ratio to match the control target air-fuel ratio based on the determination result. 1. An air-fuel ratio control device comprising: a means for feedback controlling a fuel supply amount;