JPS59211737A - Air-fuel ratio control device - Google Patents

Abstract

PURPOSE:To improve a fuel cost by providing a means to increase or decrease a fuel volume temporarily when a control target air-fuel ratio is changed for controlling a fuel supply volume of an internal combustion engine precisely. CONSTITUTION:An acute output changing point of an oxygen sensor 23 is moved to a lean air-fuel ratio side according to an electric current sent to the sensor. An air-fuel ratio judging unit 35 judges whether the detected air-fuel ratio is richer or leaner than a control target air-fuel ratio. A means 2 to increase a fuel volume temporarily when the control target air-fuel ratio is switched to the rich side and a means 43 to decrease the fuel volume temporarily when it is switched to the lean side are provided. This construction permits to control the supply volume of the fuel efficiently according to the various air-fuel ratios required.

Description

[Detailed description of the invention]

The present invention detects the oxygen concentration in the exhaust gas while controlling the internal combustion engine.
The present invention relates to an air-fuel ratio control device that performs feedback control of fuel supply amount. It is already well known that fuel efficiency and exhaust composition can be improved by precisely controlling the fuel efficiency supplied to an internal combustion engine, in other words, the air-fuel ratio of the air-fuel mixture. Therefore, a device that detects oxygen 111M in the exhaust gas, which has a close correlation with the air-fuel ratio of the supplied air-fuel mixture, and feedback-controls the fuel supply m based on this detection result has already been put into practical use. However, the output characteristics of the oxygen sensor vary greatly depending on whether or not there is oxygen in the exhaust gas, that is, whether the exhaust gas is richer or thinner than the stoichiometric air-fuel ratio; Since the rate of change is extremely small and difficult to judge, the air-fuel ratio that becomes the control target value usually has to be the stoichiometric air-fuel ratio. On the other hand, for example, Japanese Patent Application Laid-Open No. 56-2548, Special IJ
IIn! (As seen in Publication No. 56-105634, the oxygen concentration detection characteristic is expressed in correspondence to the value of oxygen contained in the exhaust gas on the lean side of the stoichiometric air-fuel ratio.) A device has been proposed that uses a tilted oxygen sensor that fluctuates widely to feedback control the air-fuel ratio to a predetermined value on the lean side. However, in this case, the absolute value of the acid IT sensor output may change over time, and the output value for the same target air-fuel ratio will differ, so even if various corrections are made, stable control over a long period of time cannot be achieved. The disadvantage was that it was difficult to maintain. However, recently, even with ordinary membrane oxygen sensors, by flowing a current between the electrodes, and depending on the current value, the point of sudden change in the output of the oxygen sensor can change on the lean side of the stoichiometric air-fuel ratio. Focusing on this, a device capable of detecting a lean air-fuel ratio was proposed in Japanese Patent Application No. 164822/1983. This is shown in FIGS. 1 and 2. FIG. 1 is a vertical cross-sectional schematic wiring diagram of the oxygen sensor element 1, and FIG. 2 is a schematic exploded perspective view of the oxygen sensor element 1 of FIG. , the diaphragm layer 2 is made of an insulating material such as alumina, mullite, spinel, etc., and a heating element 3 is installed inside it.

[It also maintains its strength as a structural base.] On the surface of this diaphragm layer 2, a two-part reference electrode electron conductive layer 4.5 is laminated, and an oxygen ion conductive solid electrolyte layer 6 is further laminated thereon. The material of this solid electrolyte layer 6 is Y. ZrO2 stabilized with O8 or CaO or other known materials can be used. A measurement electrode electron conduction layer 7 is laminated on the surface of this solid electrolyte layer 6.
A voltage measuring means 8 is connected between the reference electrode electron conducting layer 7 and the one reference electrode electron conducting layer 4 to enable the measurement of the electromotive force F, and the measuring electrode electron conducting layer 7 and the other reference electrode electron conducting layer 5 A current supply circuit 9 is connected between them. At this time, it is desirable to use catalytically active platinum for the reference electrode electron conductive layers 4, 5 and the measurement electrode electron conductive layer 7, and in addition, alloys of platinum and platinum group elements and other materials are appropriately selected and used. It's good to read. Further, when laminating each of the electron conductive layers 4.5.7 and the solid electrolyte layer 6, it is possible to use a method in which, for example, these powders are formed into pastes 1 to 1, screen printed, and then fired, etc. It is also possible to take the following measures. In addition, the heating element 3 is provided with a heating power source 10.
Connect the oxygen sensor element 8i! I try to control the amount of water. Furthermore, a diffusion layer 11 is provided on the measurement electrode electron conduction layer 7 to control 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. As the material of this diffusion layer 11, for example, mullite, spinel, forsterite, calcium zirconate, etc. can be used, and it is laminated by a screen printing method using powder or a customer side method. Therefore, when using the above-mentioned oxygen sensory element 1 and connecting the positive electrode side of the current supply circuit 9 to the other reference electrode electron conductor #B5 to supply a current, from the measurement electrode electron conductive layer 7 to the reference electrode electron conductive layer 5. (Forcibly causes the movement of oxygen ions. At this time, the presence of the diffusion layer 11 controls the inflow and diffusion of oxygen molecules from the sample gas, so the oxygen content at the measurement pole is The pressure also decreases due to the partial pressure of oxygen in the test gas.On the other hand,
13 The reference oxygen partial pressure is increased by the flow of oxygen ions toward the quasi-electrode electron-conducting layer 5. When the diaphragm layer 2 is porous, the oxygen molecules present in the reference-electrode electron-conducting layer 5 The influx of oxygen ions and the oxygen A reference polar oxygen partial pressure is maintained in equilibrium with molecular diffusion. Therefore, what is the measured polar oxygen partial pressure that is lower than the oxygen partial pressure in the test gas and the above group? #If the electromotive force E generated in response to the difference with the polar oxygen partial pressure is measured by the voltage measuring means 8, the relationship that the measured polar oxygen partial pressure is lower than the oxygen partial pressure in the test gas is maintained. At the same time, since the measured polar oxygen partial pressure also changes in accordance with changes in the oxygen partial pressure in the test gas, it becomes possible to detect an air-fuel ratio leaner than the stoichiometric air-fuel ratio. 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 I, 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 on the lean side than the stoichiometric air-fuel ratio J, it is possible to accurately determine the air-fuel ratio. The fuel efficiency rate of internal combustion engines is J! It is already well known that the best air-fuel ratio is slightly leaner than the stoichiometric air-fuel ratio, but in order to increase engine output, a mixture that is at or slightly richer than the stoichiometric air-fuel ratio is required. In this way, the air-fuel mixture required by the engine changes in various ways depending on the operating conditions at the time, and it is desirable to control the air-fuel ratio accurately to the target value. For example, even if the fuel supply ■ is feedback-controlled using the oxygen sensor mentioned above so that a predetermined air-fuel ratio can be obtained in a part-load region with high driving performance,
At full load 1, the feedback control was temporarily stopped and the air-fuel ratio was enriched using A-pun loop control, so the control accuracy in such a region was not necessarily high, and the fuel was consumed unnecessarily. There was a tendency to The present invention has been made with attention to this problem, and it is possible to accurately respond to various required air-fuel ratios that vary depending on the operating state of the internal combustion engine by constantly feedback controlling the fuel supply amount, and to switch the air-fuel ratio. The aim is to improve fuel efficiency in all driving ranges, and improve driving power performance. Therefore, the present invention provides an oxygen sensor in which the sudden change point of the sensor output shifts to the lean air-fuel ratio side according to the sensor current;
means for detecting the operating state of the engine; means for determining the optimum control target air-fuel ratio according to the operating state; and means for calculating the fuel injection amount so as to obtain the control target air-fuel ratio;
Similarly, means for flowing a current corresponding to the control target air-fuel ratio into the oxygen sensor, means for determining whether the detected air-fuel ratio is richer or leaner than the control target air-fuel ratio based on the output of the oxygen sensor, and based on the determination result. A feedback control means that corrects the fuel supply amount to match the control target air-fuel ratio when the control target air-fuel ratio switches to the rich side; and means for temporarily reducing the amount of fuel when the fuel ratio is switched to the lean side. - Therefore, when the control target air-fuel ratio changes, in addition to the basic relative increase/decrease in the fuel supply amount, there is a temporary increase or decrease in fuel consumption at the moment of the change. Since the increase or decrease of +1 m or ■ is added, the target air-fuel ratio can be quickly approached after switching, and the same air-fuel ratio can be accurately set to the target air-fuel ratio by normal feedback control. can be maintained. 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. The oxygen sensor element 1 is housed inside a holder 17, and exhaust gas flows into the louver section 12 having a small hole 11 formed at its tip. Is oxygen sensor element 1 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 19 is provided inside the insulating tube 18. be stopped. Reference numeral 16 denotes a connector for wiring, and the part 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 20, which is composed of a microcomputer, etc., and controls various elements necessary for the engine, including the amount of fuel supplied to the engine. In the embodiment, engine load detection means (for example, suction negative pressure sensor,
The operating state is determined from the detection signal of the intake air (intake air length, etc.) 21, and the control target value of the air-fuel ratio is determined and the fuel supply m is controlled in accordance with the operating state, as will be described later. 25 is a circuit that increases or decreases the current flowing into the oxygen sensor 23 according to the control target value;
A transistor 26 is conductive when the signal S from 0 is at a high level "T1", a transistor 27 is conductive when the signal S is at a low level "1-", and these transistors 26 and 27 are connected in series, and the sensor It is composed of resistors 28 and 29 that change the magnitude of the flowing current. 30 is an amplifier for amplifying and extracting 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 output of the oxygen sensor suddenly changes due to the sensor current, and the air-fuel ratio shifts to the lean side.
At the same time, the sensor output voltage also changes relatively (the output voltage increases as the air-fuel ratio shifts to the leaner side), so it is necessary to switch the comparison voltage (slice level) of the comparator 35 in conjunction with switching the target air-fuel ratio. There is. 36 is a switching circuit for this purpose, which is connected to the control circuit 20.
The transistor 31 is conductive when the signal S from is ``I'' and applies the voltage from the comparison voltage setting section 33 to the comparator; The voltage from the comparison voltage setting section 34 is transferred to the comparator 35.
It is composed of a transistor 32 that applies an voltage to the voltage. 22 is a feedback control unit for fuel supply amount, and comparator 3
The supply amount is corrected to increase or decrease based on the signal S output from the control circuit 20 based on the output of the control circuit 20. 24 is a heating element (heater) built into the sensor. By the way, as shown in FIG. 6, the control circuit 20 includes the following components in addition to the circuit 40 that determines the optimum control target air-fuel ratio according to the operating state as described above. 41, when the control target air-fuel ratio is determined, basic fuel injection is performed based on detection signals such as intake air amount and engine speed so that this air-fuel ratio is waited for! )111. 42 is a circuit that temporarily increases the fuel supply amount m-t when the control target air-fuel ratio switches to the rich side due to a change in the operating condition, and 43 is a circuit that temporarily increases the fuel supply amount when the control target air-fuel ratio switches to the lean side. It is a circuit that reduces the amount of air, and specifically, it is a circuit that reduces the amount of
In integral) control, the proportional control component is made larger when switching the air-fuel ratio compared to when controlling at the same air-fuel ratio. When switching the air-fuel ratio, the basic fuel injection amount also changes, but since this is detected as the oxygen concentration in the exhaust gas and then corrected, the response delay inevitably increases immediately after switching. Therefore, at the moment when the air-fuel ratio is switched, the amount of fuel is increased or decreased by a predetermined amount in advance, so that the air-fuel ratio can be brought close to the target air-fuel ratio as quickly as possible. 44 is a correction circuit, which converts the basic fuel supply m signal into
Based on the signal from the comparator 35, it is corrected so that the control target air-fuel ratio is obtained as described above, and when (g) is input from the fuel increase or decrease time 2842.43, these are added immediately. and outputs a fuel supply amount correction signal to the fuel feedback control section 22.Next, the operation will be explained with reference to FIG. Oxygen ions move toward the conductive layer 5, the oxygen partial pressure on the outside measurement electrode side decreases, and as a result, the sudden change point of the sensor output with respect to the air-fuel ratio changes as shown in Figure 3. As mentioned above, specifically, as the above-mentioned injected current increases, the sharp change point of the sensor output shifts to the leaner air-fuel ratio side, and therefore, the air-fuel ratio corresponding to the current 10 is the boundary - (, Since the sensor output changes significantly depending on whether the air-fuel ratio is higher or lower than the stoichiometric air-fuel ratio, it is possible to detect air-fuel ratios other than the stoichiometric air-fuel ratio. The driving status is determined based on the signal from the
rHJ is output as the signal S to enrich the control I II 4ff air-fuel ratio during high load, and rLl is output to make the target air-fuel ratio S<t during idle and low load. Now, when the accelerating operation state is entered and the signal S becomes r I-I J, the transistor 26 of the current supply circuit 25 is turned on, and the current 1. is oxygen senna 2
As a result, in this embodiment, the oxygen senna 23 has a characteristic in which the output suddenly changes after reaching the stoichiometric air-fuel ratio. In addition, the comparison voltage switching circuit 3
6, as the transistor 31 turns on, the voltage setting section 33
The output of the comparator 35 is inputted as a comparison reference voltage. Therefore, during such acceleration, if the fuel supply amount is insufficient and the air-fuel ratio is leaner than the stoichiometric air-fuel ratio, the output of the oxygen sensor 23 is low and the comparator 35 outputs a signal of 1 core level to the control circuit 2o. , a command is sent to the fuel supply feedback control unit 22 to increase the amount of fuel,
On the other hand, if the air-fuel ratio is rich, the output of the oxygen sensor 23 rises and the comparator 3
The output of No. 5 switches to high level, and control to reduce the fuel is also carried out. In reality, these operations are repeated in an extremely short period of time, so the air-fuel mixture is reduced to the stoichiometric air-fuel ratio, which is the target value. can be converged with high accuracy. By the way, when the operating state shifts to accelerated operation and the control target air-fuel ratio is switched to the low side, the fuel injection amount is temporarily increased by a predetermined value by the increase circuit 42 at the moment of switching. Therefore, the air-fuel ratio quickly shifts toward the stoichiometric air-fuel ratio during switching, improving acceleration response. This increase is only instantaneous at the time of switching, but
At the same time, the fuel calculation circuit 41 calculates the fuel injection amount necessary to obtain the -C stoichiometric air-fuel ratio based on the intake air amount, engine speed signal, etc., and compares the fuel with the previous lean air-fuel ratio. In order to increase this, fuel will be added on top of this, so to speak. Feedback control based on the basic fuel injection calculation by the fuel calculation circuit 41 and the output of the oxygen sensor 23 inevitably causes a response delay at the moment the air-fuel ratio is switched.
In this way, by temporarily increasing the amount of fuel regardless of feedback control, this control delay can be eliminated. Next, if the operating state changes and, for example, shifts to low-load operation, the control target air-fuel ratio determining circuit 40 of the control circuit 20
The signal S, from , is switched to r L J, and accordingly, the transistor 27 of the current supply circuit 25 is turned on, and the current I2 corresponding to, for example, the air-fuel ratio Δ, -' F = 20 is supplied to oxygen via the resistor 29. Pour into sensor 23. For this reason, the oxygen sensor 23 switches to a characteristic in which the output changes abruptly at Δ/F=20, which is leaner than the stoichiometric air-fuel ratio. At the same time, the set reference voltage of the comparator 35 is also set by the transistor 32.
As the voltage setting unit 34 turns on, the output is switched to Δ, /F as the control target air-fuel ratio.
==20, it is determined whether the air-fuel ratio is richer or leaner than that, and feedback control of the fuel supply amount is performed so that the air-fuel ratio of A/F=20 is obtained. When switching the control target air-fuel ratio, the fuel is temporarily reduced by a predetermined value in response to a signal from the reduction circuit 43 in the same manner as described above, and the air-fuel ratio quickly approaches the lean target air-fuel ratio. . In addition, in FIG. 7, the control target air-fuel ratio is switched between two types, and during steady running, the air-fuel ratio is A7・'F=20.
During acceleration, the air-fuel ratio is controlled to be at the stoichiometric air-fuel ratio. When switching the air-fuel ratio, the proportional control component of the fuel injection m correction signal changes significantly, so even though the oxygen (02) sensor output changes with a slight delay, the controlled air-fuel ratio responds well to the target value. converge towards. By the way, FIG. 8 shows a flowchart when a microcomputer is used to perform a series of controls in the control circuit 20, and the control target air-fuel ratio is the stoichiometric air-fuel ratio (A/
F=14.7) and A/F=20, it is determined whether the same state is maintained or when the control target air-fuel ratio is to be switched, and when the air-fuel ratio is switched, Only in that case, the proportional control portion is set larger than in normal times. When switching from Δ/F=14.7 to A/F=20,
In order to control the fuel in the direction without reducing it, the downhill [) (proportional) control is normally set at 1 fl J, and the limit is increased, and vice versa △/
When switching from F=20 to A/F=14.7, the upstream P control is made larger than the normal value by α in order to increase the amount of fuel. In addition, in the ° flow chart, the first stage and second stage are determined whether the control target air-fuel ratio is Δ/F = 20 or A/
It is determined whether F=14.7, and from then on, a determination is made as to whether the target air-fuel ratio should be rich (1) or thin (1). Downward l control refers to integral control in the direction of fuel depletion, and upward l control refers to integral control in the direction of increase. As explained above, according to the present invention, it is possible to control the fuel supply m with high precision for different required air-fuel ratios depending on the operating conditions, especially in the operating range with a lean mixture. This greatly contributes to improving combustion stability and further improves fuel efficiency. Also, when switching the control target air-fuel ratio, the fuel l! Since I is increased or decreased instantaneously, the convergence response of the air-fuel ratio immediately after switching is affected, and the acceleration performance of the engine is improved.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a conventional oxygen sensor, Figure 2 is an exploded perspective view of the same, and Figure 3 is a characteristic diagram showing the relationship between sensor output and air-fuel ratio when the sensor current is varied. be. FIG. 4 is a cross-sectional view of the structure of the oxygen tank V of the present invention, FIG. 5 is a circuit diagram of the air-fuel ratio control circuit, FIG. 6 is a block circuit diagram, and FIG. FIG. 8 is a flowchart of air-fuel ratio control. 20...Air-fuel ratio control circuit, 21...Operating state detection means, 22...Fuel supply amount feedback control unit, 2
3...Oxygen sensor, 25...Oxygen sensor inflow current control circuit, 35...Comparator (air-fuel ratio judgment means), 3
6... Comparison voltage switching circuit, 40... Control target air-fuel ratio determining circuit, 41... Fuel injection! )1! Arithmetic circuit, 42・
...Fuel increase circuit, 43...Fuel reduction m circuit. Patent applicant Nissan Motor Co., Ltd.

Claims (1)

[Claims] An oxygen L sensor whose sensor output suddenly shifts to a leaner air-fuel ratio depending on the sensor current, a means for detecting the operating state of the engine, and a means for determining the optimum control target air-fuel ratio according to the operating state. and a means for calculating the fuel supply amount so as to obtain the control target air-fuel ratio, a means for flowing a current corresponding to the control target air-fuel ratio into the oxygen sensor, and a means for calculating the detected air-fuel ratio based on the output of the oxygen sensor. A means for determining whether the air-fuel ratio is at the edge or thinner than the control target air-fuel ratio; and a feedback control means for correcting the fuel supply (4) so as to match the control target air-fuel ratio based on the determination result;
A means for temporarily increasing the amount of fuel (m-t) when the control target air-fuel ratio switches to the rich side, and a means for temporarily decreasing the fuel (m-t) when the control target air-fuel ratio also switches to the lean side. An air-fuel ratio control device characterized by comprising: