JPH0635956B2 - Air-fuel ratio detector for internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an air-fuel ratio detection device for an internal combustion engine, which detects the air-fuel ratio of a fuel mixture supplied to the internal combustion engine from the oxygen concentration in the exhaust gas. is there.

[Prior Art] Conventionally, as an air-fuel ratio sensor for detecting the air-fuel ratio of an internal combustion engine from the oxygen concentration in exhaust gas, for example, Japanese Patent Laid-Open No. 59-178.
As described in No. 354, each detection element such as an air-fuel ratio sensor in which two detection elements having porous electrodes formed on both surfaces of an oxygen ion conductive solid electrolyte are opposed to each other with a gap therebetween. There is known an air-fuel ratio sensor formed by disposing one of the porous electrodes in contact with a gas diffusion limiting chamber in which the diffusion of exhaust gas is limited.

In addition, in this type of air-fuel ratio sensor, one of the detection elements is operated as an oxygen concentration cell element and the other detection element is operated as an oxygen pump element so that the voltage generated at the electrodes at both ends of the oxygen concentration cell element becomes constant. Control the current flowing through
A detection circuit configured to detect the air-fuel ratio from the current value, or a detection circuit configured to apply a constant current to the oxygen pump element and detect the air-fuel ratio from the voltage generated across the electrodes of the oxygen concentration cell element. It is provided so that the air-fuel ratio can be detected. That is, the air-fuel ratio sensor and the detection circuit constitute an air-fuel ratio detecting device, and the air-fuel ratio can be detected by the operation of each part.

Then, this type of air-fuel ratio detection apparatus corrects the amount of fuel supplied to the internal combustion engine based on the detection result so that the air-fuel ratio becomes the target air-fuel ratio such as the theoretical air-fuel ratio. Used in equipment. Therefore, the air-fuel ratio detection device is operated in the exhaust gas in which the internal combustion engine is controlled to the target air-fuel ratio such as the theoretical air-fuel ratio, and during that operation, the exhaust gas in the gas diffusion limited chamber also corresponds to the target air-fuel ratio, HC, C
It becomes a small gas component such as O and O2.

[Problems to be Solved by the Invention] However, the above-described conventional air-fuel ratio detection device is operated because it is not necessary to detect the air-fuel ratio during so-called open-loop control in which air-fuel ratio control is not executed by the air-fuel ratio control device. However, there is a problem that the exhaust gas in the gas diffusion limiting chamber of the air-fuel ratio sensor becomes a gas component that does not correspond to the target air-fuel ratio, and the detection of the air-fuel ratio immediately after shifting to the air-fuel ratio control cannot be performed well.

That is, for example, when the internal combustion engine is started or during acceleration operation, the fuel amount increase control is executed, and the open-loop control is performed without executing the air-fuel ratio control. Since the exhaust gas in the room also becomes a rich gas with a large amount of CO and HC, rich gas such as CO and HC is adsorbed to the porous electrode inside the gas diffusion restriction chamber, and then the fuel increase control is stopped and the air-fuel ratio is targeted. Good control of air-fuel ratio by the air-fuel ratio detection device until the rich gas adsorbed on the electrode is removed even if the exhaust gas changes to the exhaust gas component near the target air-fuel ratio after shifting to normal control to control the air-fuel ratio. Therefore, the air-fuel ratio control could not be executed promptly. This problem is not limited to when the air-fuel ratio is rich due to fuel increase correction, etc.
The same occurs when the air-fuel ratio is controlled to the lean range by the fuel cut control executed during the principle operation of the internal combustion engine. This is because when the air-fuel ratio is lean, the amount of oxygen in the exhaust increases, and oxygen is adsorbed and oxidized by the porous electrode inside the gas diffusion limiting chamber.

Therefore, the present invention prevents the rich gas and oxygen from being adsorbed to the porous electrode in the gas diffusion limiting chamber during the open loop control in which the air-fuel ratio control is not executed, and promptly when the open-loop control is switched to the air-fuel ratio control. The present invention has been made for the purpose of providing an air-fuel ratio detection device for an internal combustion engine that can detect the air-fuel ratio satisfactorily, and has the following configuration.

[Means for Solving the Problems] That is, the constitution of the present invention as a means for solving the above problems is that two pairs of porous electrodes are laminated on both surfaces of an oxygen ion conductive solid electrolyte. One of the two detection elements, and an air-fuel ratio sensor having a detection element and a gas diffusion limiting chamber that is formed in contact with one porous electrode of each of the detection elements and in which diffusion of exhaust gas is limited. An air-fuel ratio signal output means for operating the detection element as an oxygen concentration cell element and the other detection element as an oxygen pump element to output an air-fuel ratio signal according to the oxygen concentration in the exhaust gas. In an air-fuel ratio detection device for an internal combustion engine, which detects an air-fuel ratio of a fuel mixture supplied to the internal combustion engine during control execution, a fuel mixture supplied to the internal combustion engine when the air-fuel ratio control of the internal combustion engine is stopped. Rich air-fuel ratio The internal combustion engine is characterized in that it is provided with a discrimination means for discriminating between the presence and the lean state, and a current supply means for supplying a predetermined current to the oxygen pump element according to the discrimination result of the discrimination means. The main point is an air-fuel ratio detector.

As the oxygen ion conductive solid electrolyte used in the detection element here, a solid solution of zirconia and yttria, or a solid solution of zirconia and calcia is typical, and other cerium dioxide, thorium dioxide, and hafnium dioxide A solid solution, a perovskite type oxide solid solution, a trivalent metal oxide solid solution and the like can also be used.

As the porous electrodes provided on both sides of the solid electrolyte, platinum or rhodium, which has a catalytic action for the oxidation reaction, may be used. Examples include a method in which powder of a ceramic material is mixed and made into a paste, which is printed by using a thick film technique and then sintered and formed, or a method in which a thin film technique such as flame spraying, chemical plating or vapor deposition is used. . Since the porous electrode is in direct contact with the measurement gas, that is, exhaust gas, the electrode layer is further provided with alumina,
It is preferable to form a porous protective layer of spinel, zirconia, mullite or the like using a thick film technique.

In the two detection elements thus formed, one porous electrode is provided in contact with the gas diffusion limiting chamber in which diffusion of exhaust gas is limited, and one detection element is an oxygen concentration cell element,
The other detection element is used as an oxygen pump element. As this type of air-fuel ratio sensor, an air-fuel ratio sensor in which two detection elements are arranged to face each other with a gap as a gas diffusion control chamber is known.

Further, as an air-fuel ratio sensor of this kind, in recent years, the obtained detection characteristics continuously change according to the oxygen concentration in the exhaust gas,
In order to detect the air-fuel ratio well in all areas, the air-fuel ratio sensor is formed by forming the atmosphere introduction chamber where the atmosphere is introduced on the porous electrode side that is not in contact with the gas diffusion limiting chamber of the detection element used as the oxygen concentration cell element. Or, similarly, on this electrode side, an air-fuel ratio sensor or the like formed by forming an internal reference oxygen source communicated with the outside or a gas diffusion limiting chamber through a leakage resistance portion for leaking oxygen is considered, The present invention can also be applied to this type of air-fuel ratio sensor. Incidentally, in the case of the latter air-fuel ratio sensor, by supplying a constant current to the oxygen concentration battery element to pump oxygen in the gas diffusion limiting chamber to the other electrode side, the oxygen of the internal reference oxygen source is kept constant, A voltage corresponding to the ratio of the partial pressure of oxygen gas in the gas diffusion limiting chamber to the partial pressure of oxygen gas in the internal reference oxygen source is generated between the electrodes at both ends of the oxygen concentration electronic device.

Next, the gas diffusion limiting chamber is a chamber into which exhaust gas is introduced in a diffusion limited manner, and as described in the section of the prior art, 2
When the individual detection element units are arranged to face each other with a gap therebetween, the gap serves as a gas diffusion limiting chamber. As the other gas diffusion limiting chamber, for example, Al ₂ O _{3 is provided} between the two detection element units. ,
It is also formed by sandwiching a hollow spacer made of spinel, forsterite, steatite, zirconia, or the like, and providing a hole for communicating the surrounding measurement gas atmosphere with the measurement gas chamber as a gas diffusion restriction part in a part of this spacer. be able to.

The current supply means, when the air-fuel ratio control of the internal combustion engine in which the determination means is operated is stopped, that is, when the operation of the air-fuel ratio sensor by the air-fuel ratio signal output means is stopped, the detection element used as the oxygen pump element is provided with the determination result A predetermined current is passed in the direction according to. This is to prevent the air-fuel ratio from becoming lean or rich by stopping the air-fuel ratio control, and to prevent oxygen, HC, CO, etc. from adsorbing to the porosity calculating electrode in the gas diffusion limiting chamber of the air-fuel ratio sensor. When the air-fuel ratio is lean, a current is passed in a direction to pump oxygen in the gas diffusion limiting chamber to the outside, and when the air-fuel ratio is rich, a current is passed in a direction to pump oxygen in the gas diffusion limiting chamber.

Further, a current may be applied to the oxygen pump element by applying a predetermined voltage between the porous electrodes on both ends of the oxygen pump element. For example, the oxygen pump element is controlled so that the voltage generated across the oxygen concentration cell element during air-fuel ratio control becomes constant. The lowest voltage applied to the oxygen pump element when the air-fuel ratio is detected by controlling the current flowing in the oxygen pump element may be applied to the oxygen pump element. It is also possible to apply a voltage above this value, but when the air-fuel ratio is rich, there is little oxygen in the exhaust gas, and if too much current is passed, the oxygen in the solid electrolyte itself decomposes and the detection element deteriorates, a so-called blackening phenomenon. Therefore, it is necessary to set the current flowing through the oxygen pump element to such a level that does not cause this phenomenon.

Next, the determination means is for determining whether the air-fuel ratio is lean or rich when the air-fuel ratio control of the internal combustion engine is stopped, and for determining the direction of the current flowing to the oxygen pump element by the current supply means. , For example, when the operation of the air-fuel ratio sensor is stopped by stopping the air-fuel ratio control, the voltage generated at the electrodes at both ends of the oxygen concentration battery element is detected, and it is determined whether this voltage is a predetermined value or more. do it. Further, as the determining means, it is sufficient to determine whether the air-fuel ratio becomes lean or rich when the air-fuel ratio control is stopped.Therefore, from the control device of the internal combustion engine, control states such as fuel increase control and fuel cut control are performed. It may be configured to output the signal representing.

[Operation] In the air-fuel ratio detection apparatus for an internal combustion engine of the present invention configured as described above, when the air-fuel ratio control of the internal combustion engine is stopped and the operation of the air-fuel ratio sensor by the air-fuel ratio signal output means is stopped, A predetermined current is supplied to the oxygen pump element according to the air-fuel ratio, and oxygen is pumped into the gas diffusion limiting chamber or oxygen is pumped into the gas diffusion limiting chamber.
Therefore, when the air-fuel ratio control is stopped, rich gas such as HC and CO and oxygen are not adsorbed on the electrodes in the gas diffusion limiting chamber.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

First, FIGS. 2 and 3 show the structure of the air-fuel ratio sensor of this embodiment. FIG. 2 is a partially cutaway perspective view thereof, and FIG. 3 is an exploded perspective view thereof.

As shown in FIG. 2 and FIG. 3, the air-fuel ratio sensor of this embodiment has an oxygen pump element 4 formed by laminating porous electrodes 2 and 3 on both sides of a solid electrolyte plate 1, and both sides of a solid electrolyte plate 5 as well. An oxygen concentration battery element 8 formed by stacking porous electrodes 6 and 7 on each side, and stacked between these detection elements 4 and 8,
A spacer 9 in which a hollow portion 9a is formed in the facing porous electrodes 3 and 6 of each of the detection elements 4 and 8 and a shield 10 laminated on the porous electrode 7 side of the oxygen concentration battery element 8. Has been done.

First, the spacer 9 is composed of the porous electrode 3 and the porous electrode 6.
Is to form a gas diffusion limiting chamber in which the diffusion of the measurement gas is limited, and the hollow portion 9a serves as a gas diffusion limiting chamber. The spacer 9 has a hollow portion 9a so that the surrounding measurement gas can be introduced into the hollow portion 9a.
Notches T are formed as gas diffusion limiting portions at three locations on the periphery.

Next, the shield 10 is used to shield the porous electrode 7 from the external measurement gas in order to use the porous electrode 7 of the oxygen concentration battery element 8 as an internal reference oxygen source. The porous electrode 7 covered with the shield 10 is made of, for example, alumina so that oxygen generated inside when it is used as an internal reference oxygen source can leak into the gas diffusion limiting chamber, that is, the hollow portion 9a. Porous insulator Z consisting of etc. and through hole H
And is connected to the lead portion 6l of the porous electrode 6 through. That is, the porous insulator Z, the through hole H, and the lead portion 6l of the porous electrode 6 are formed as a leakage resistance portion, and oxygen generated in the porous electrode 7 is allowed to pass through the leakage resistance portion and the hollow portion 9a. It is designed to leak inside.

Further, the electrode terminals of the porous electrodes 2, 3, 6, 7 of the oxygen pump element 4 and the oxygen concentration cell element 8 are formed on the outer wall surface of the air-fuel ratio sensor. That is, the oxygen pump element 4
Since the porous electrode 2 of is formed to be exposed to the outside,
In the porous electrode 3 of the oxygen pump element 4 or the porous electrodes 6 and 7 of the oxygen concentration cell element 8 which are laminated inside, the lead portion 2l is directly used as an electrode terminal, and the lead portion 3l or 6l and 7l , Solid electrolytic chamber plate 1
Alternatively, it is formed by electrically connecting the electrode terminals 3t or 6t and 7t respectively laminated on the outer wall surface of the shield 10 through the through holes 3h or 6h and 7h.

The air-fuel ratio sensor of this embodiment configured as described above has the first
As shown in the figure, the fixing portion 1 that seals the porous electrode layer 7 so that oxygen does not leak to the outside and fixes the air-fuel ratio sensor S.
5, and is attached to the exhaust pipe 17 of the internal combustion engine via the screw portion 16 and is operated by the sensor drive control circuit 20. In the figure, in order to facilitate understanding of the attachment state of the air-fuel ratio sensor S, the lead portion and electrode terminal of each porous electrode are omitted.

As shown in the figure, the sensor drive control circuit 20 drives the air-fuel ratio sensor S during execution of the air-fuel ratio control of the internal combustion engine, outputs an air-fuel ratio signal, and an air-fuel ratio control circuit 21 when the air-fuel ratio control of the internal combustion engine is stopped. It is determined whether the air-fuel ratio of the internal combustion engine is rich or lean, and the current supply circuit 22 that supplies a constant current to the oxygen pump element 4 of the air-fuel ratio sensor S according to the determination result, and the air-fuel ratio of the internal combustion engine. A changeover switch 23 or 24 for switching the connection with the air-fuel ratio sensor S from the air-fuel ratio detection circuit 21 to the current supply circuit 22 by an air-fuel ratio control stop signal output from an air-fuel ratio control device for an internal combustion engine (not shown) when the control is stopped. ,,.

Further, the current supply circuit 22 determines whether or not the voltage Vs generated between the porous electrodes 6 and 7 of the oxygen concentration battery element 8 is equal to or higher than a predetermined voltage E0, and outputs a high level signal when Vs ≧ E0. The operational amplifier O, which supplies a current by applying a predetermined voltage between the comparison circuit 31 configured using the operational amplifier OP1 and the porous electrodes 2 and 3 of the oxygen pump element 4.
It is composed of a constant voltage circuit 32 configured by using P2, and an integrator circuit or the like for inputting the air-fuel ratio control stop signal output from the air-fuel ratio control device of the internal combustion engine with a delay of a predetermined time (for example, 0.5 sec). Delay circuit 33 and this delay circuit 3
The holding circuit 34 holding the output signal from the comparison circuit 31 and the output signal from the holding circuit 34 are switched according to the output signal from the holding circuit 34, and the voltage is applied to the constant voltage circuit 32 to flow to the oxygen pump element 4. It is composed of a current direction changeover switch 35 that determines the current direction, and a current supply switch 36 that is turned on by an output signal from the delay circuit 33 and connects the constant voltage circuit 32 and the oxygen pump element 4.

Further, as shown in FIG. 4, the air-fuel ratio detection circuit 21 applies a predetermined voltage Vb (for example, 10 V) to the porous electrode 7 of the oxygen concentration battery element 8, and the other porous electrode to which the reference voltage Va is applied. A resistor R that limits the current flowing to the 6 side and an operational amplifier OP3 that detects the voltage generated at the electrodes on both sides of the oxygen concentration cell element 8 and raised by the reference voltage Va (for example, 5 V). Buffer circuit 41, a non-inverting amplifier circuit 42 configured by an operational amplifier OP4 for amplifying the detection voltage output from the buffer circuit 41, and the detection voltage amplified by the non-inverting amplifier circuit 42 as a predetermined reference. Compared with the voltage Vc, when the detected voltage is larger than the reference voltage Vc, it gradually decreases with a predetermined integration constant, and in the opposite case, it gradually increases with a predetermined integration constant. Like A comparison / integration circuit 43 configured by using an operational amplifier OP5 that outputs a control voltage, a buffer circuit 44 configured by an operational amplifier OP6 that outputs the reference voltage Va, and a reference voltage Va from the buffer circuit 44. Is applied to the porous electrode 3 on the hollow portion 9a side of the oxygen pump element 4, and a current flowing between this electrode 3 and the other porous electrode 2 to which the control voltage from the comparison / integration circuit 43 is applied is applied. A current detection resistor Ri for detecting,
The voltage generated in the resistor Ri is output as the air-fuel ratio signal Vλ. Output circuit 45 composed of operational amplifier OP7
It consists of and.

In the sensor drive control circuit 20 configured as described above, first, the changeover switch 2 is activated during the air-fuel ratio control of the internal combustion engine.
3 and 24 are respectively switched in the opposite direction to FIG. 1,
The air-fuel ratio sensor S and the air-fuel ratio detection circuit 21 are connected.
Then, in the air-fuel ratio detection circuit 21, a predetermined current is passed through the oxygen concentration battery element 8 of the air-fuel ratio sensor S to generate oxygen in the porous electrode 7, the generated oxygen gas partial pressure and the hollow portion 9a. An oxygen pump is used so that the voltage generated between the porous electrodes 6 and 7 of the oxygen concentration battery element 8 becomes constant according to the ratio with the oxygen gas partial pressure, that is, the oxygen gas partial pressure in the hollow portion 9a becomes constant. The air-fuel ratio sensor S is operated by bidirectionally controlling the current flowing through the element 4, and at that time, the voltage as shown in FIG. 6 generated in the current detecting resistor Ri in accordance with the current flowing through the oxygen pump element 4 is changed. The signal Vλ is output.

Next, when the air-fuel ratio control of the internal combustion engine is stopped, the changeover switches 23 and 24 are changed over to the directions shown in FIG.
The air-fuel ratio sensor S and the current supply circuit 22 are connected.

In the current supply circuit 22, first, the comparison circuit 31 determines whether the air-fuel ratio is lean or rich by the voltage Vs generated between the porous electrodes 6 and 7 of the oxygen concentration battery element 8, and the air-fuel ratio control is stopped. The holding circuit 34 outputs the determination result after a predetermined time has elapsed. That is, during execution of the air-fuel ratio control, when the oxygen sensor S is operated by the air-fuel ratio detection circuit 21 and the air-fuel ratio is also controlled to the target air-fuel ratio, the oxygen concentration in the hollow portion 9a becomes constant and the oxygen concentration battery The voltage generated between the porous electrodes 6 and 7 of the element 8 also has a constant value (for example, 5
However, when the air-fuel ratio control is stopped and the air-fuel ratio is controlled to be richer than usual by fuel increase control or the like, rich gas containing less oxygen enters the hollow portion 9a, and the oxygen concentration is reduced. Porous electrodes 6 and 7 of the battery element 8
If the air-fuel ratio is controlled to be leaner than usual by the fuel cut control or the like, the voltage generated between them becomes large, and exhaust gas (lean gas) containing a large amount of oxygen enters the hollow portion 9a, and the oxygen concentration cell element 8 is porous. Since the voltage generated between the quality electrodes 6 and 7 becomes small, it is possible to judge whether it is rich or lean by judging whether or not this voltage value Vs is the predetermined voltage E0 or more by the comparison circuit 31. . Therefore the voltage E
The value of 0 may be set to the voltage Vs between the porous electrodes 6 and 7 of the oxygen concentration battery element 8 which is controlled during execution of the air-fuel ratio control. Further, the holding circuit 34 stops the air-fuel ratio control, and holds and outputs the determination result after a predetermined time has elapsed. The output is that the operating state of the internal combustion engine changes and the exhaust gas according to the state is sent to the air-fuel ratio sensor S. This is because it takes a certain amount of time to reach it, so this time must be waited for.

The output signal from the holding circuit 34 is the current direction changeover switch 3
5 is input to the oxygen pump element 4, and the direction of the current flowing through the oxygen pump element 4 is determined. In FIG. 1, the current direction changeover switch 35 is
It shows a state when the output signal from the holding circuit 34 is at a high level, that is, a state when the air-fuel ratio is rich,
In this case, the current direction is determined so that the current flows from the porous electrode 3 on the hollow portion 9a side of the oxygen pump element 4 toward the external porous electrode 2. That is, when the air-fuel ratio at the time of stopping the air-fuel ratio control is rich, a current is caused to flow in the hollow portion 9a in the direction of pumping oxygen to bring the oxygen concentration inside the hollow portion 9a close to the oxygen concentration during air-fuel ratio control execution. , Hollow part 9
The rich gas is prevented from adsorbing to the porous electrodes 3 and 6 in the a (particularly the porous electrode 6 of the oxygen concentration battery element 8). On the other hand, when the air-fuel ratio is lean, the output signal from the holding circuit 34 becomes Low level, and the current direction changeover switch 35 is in the direction opposite to that in FIG. 1, that is, the porous electrode 2 outside the oxygen pump element 4 contacts the hollow portion 9a. The current can be switched to the direction in which a current is passed to the porous electrode 3 side. Then, the oxygen in the hollow portion 9a is pumped to the outside, the oxygen concentration inside the hollow portion 9a is brought close to the oxygen concentration during the execution of the air-fuel ratio control, and the adsorption of oxygen to the porous electrodes 3 and 6 in the hollow portion 9a is prevented. To be prevented.

Further, in the constant voltage circuit 32, after the air-fuel ratio control is stopped by the operation of the delay circuit 33 and a predetermined time elapses, that is, the holding circuit 34 outputs a signal indicating lean or rich of the air-fuel ratio, and the current direction changeover switch 35 is switched. At that time, either of the porous electrodes 2 or 3 of the oxygen pump element 4 is
And a constant voltage is applied between the porous electrodes 2 and 3 at both ends thereof. As a result, a current is supplied to the oxygen pump element 8, and as described above, the hollow portion 9 serving as the gas diffusion limiting chamber.
The oxygen concentration of a is brought close to the oxygen concentration at the time of executing the air-fuel ratio control. The applied voltage Ein is set to the lowest voltage applied to the oxygen pump element 8 by the operation of the air-fuel ratio detection circuit 21. That is, the voltage applied between the porous electrodes 2 and 3 when the air-fuel ratio detecting circuit 21 operates the air-fuel ratio sensor S as described above is expressed in correspondence with the detection characteristic of the air-fuel ratio signal Vλ shown in FIG. As shown in FIG. 7, the minimum voltage value at this time, that is, the voltage value in the vicinity of the excess air ratio λ = 1 (for example, 0.5 V) is set.

As described above, in the air-fuel ratio detection device of the present embodiment, when the air-fuel ratio control of the internal combustion engine is stopped, the oxygen pump element 4 of the air-fuel ratio sensor S is controlled according to the air-fuel ratio controlled according to its operating state. A predetermined voltage is applied to the electric current and a current flows, and the oxygen concentration in the hollow portion 9a of the air-fuel ratio sensor S is brought close to the oxygen concentration at the time of executing the air-fuel ratio control. Therefore, it is possible to prevent the rich gas and oxygen from adsorbing to the porous electrode in the hollow portion 9a when the air-fuel ratio control is stopped, and to quickly detect the air-fuel ratio when the internal combustion engine subsequently enters the air-fuel ratio control. Will be able to.

Such an effect is supported by the experiments described below. In carrying out the following experiment, two air-fuel ratio sensors each having the same configuration as that of the above-mentioned embodiment and having the dimensions shown in Table 1 were used.

(Experiment 1) First, FIG. 8 shows that, of the two air-fuel ratio sensors produced as described above, one of the air-fuel ratio sensors S1 has a predetermined oxygen pump element in which a current is passed in the direction of pumping oxygen into the hollow portion. Is applied to the oxygen pump element of the other air-fuel ratio sensor S2 without applying a voltage to the oxygen pump element of the other air-fuel ratio sensor S2.
1, S2 in rich gas atmosphere for 2 sec, 10 sec
It represents the change in voltage generated between the porous electrodes of each oxygen concentration battery element when the ambient atmosphere was changed to lean gas after being left for 10 minutes for 10 minutes.

As indicated by the broken line in the figure, in the air-fuel ratio sensor S2 that does not apply a voltage to the oxygen pump element, the voltage Vs generated in the oxygen concentration battery element increases as the time of exposure to the rich gas increases.
The time until the voltage becomes a voltage representing the lean air-fuel ratio, that is, the response time becomes longer. This is because when exposed to rich gas, the rich gas is adsorbed in the porous electrode on the hollow side of the oxygen concentration battery element, and then it takes time until the ambient atmosphere changes to lean gas and the rich gas is removed, and the detection of the air-fuel ratio is delayed. Is generated.

On the other hand, in the air-fuel ratio sensor S1 in which a predetermined voltage is applied to the oxygen pump element, the response time of the oxygen concentration cell element hardly changes even when the time of exposure to the rich gas becomes long as shown by the solid line in the figure. It can be seen that the detection delay of the air-fuel ratio does not occur. Therefore, when a predetermined voltage is applied to the oxygen pump element when the air-fuel ratio is rich as in the above embodiment, and a current is passed in the direction of pumping oxygen into the hollow portion, the porous electrode on the hollow portion side of the oxygen concentration battery element is formed. It can be seen that the rich gas can be prevented from being adsorbed inside, and the detection delay of the air-fuel ratio can be prevented.

In addition, in this experiment, it goes without saying that each detection element was sufficiently activated by the heater, and in order to generate the reference oxygen in the porous electrode on the side not in contact with the hollow portion of the oxygen concentration battery element, A constant current was applied to the concentration cell element.

(Experiment 2) The above Experiment 1 was related to the detection delay of the air-fuel ratio due to the rich gas, but this time, using the atmosphere as lean gas,
An experiment was conducted on the detection delay when the air-fuel ratio was lean.

In this experiment, first, 8.5 mA was applied in the direction of pumping out oxygen in the hollow portion of the oxygen pump element of each of the air-fuel ratio sensors S1 and S2.
Current is applied to measure the voltage Vs generated in each oxygen concentration battery element at that time, and then a predetermined voltage of 0.7 V is applied so that the oxygen pump element of one air-fuel ratio sensor S1 has a current flowing in the direction of pumping out the oxygen in the hollow portion. Is applied and no voltage is applied to the oxygen pump element of the other air-fuel ratio sensor S2, and the air-fuel ratio sensors S1 and S2 are respectively applied to the exhaust pipe through which air at room temperature (20 ° C.) flows at a flow velocity of 50 / min. A durability test when the air-fuel ratio was lean was carried out by leaving it for a while, and the voltage Vs generated in the oxygen concentration cell elements of the air-fuel ratio sensors S1 and S2 was measured in the same manner as above. Also in this experiment, as in Experiment 1, the sensors S1 and S
2 was heated to activate each detection element, and when detecting the voltage generated across the oxygen concentration cell element, a constant current was passed to generate reference oxygen at the electrode on the side opposite to the hollow portion. .

The measurement results of this experiment are shown in Table 2.

From the experiment, in the air-fuel ratio sensor S1 in which a current was passed through the oxygen pump element, the measurement results before and after the durability test showed almost no change, whereas no current was passed through the oxygen pump element. It can be seen that in the air-fuel ratio sensor S2, the measurement results before and after the endurance test greatly change and the air-fuel ratio sensor S2 deteriorates. This is because when an electric current is passed through the oxygen pump element and oxygen in the hollow portion is not pumped to the outside, oxygen is adsorbed by the porous electrode inside the hollow portion and the electrode is oxidized. Therefore, when the air-fuel ratio is lean as in the above-described embodiment, the air-fuel ratio sensor does not deteriorate if a current is passed through the oxygen pump element in the direction of pumping out oxygen in the hollow portion, and when detecting the air-fuel ratio thereafter, promptly It can be seen that good detection characteristics can be obtained.

[Effects of the Invention] As described in detail above, in the air-fuel ratio detection device for an internal combustion engine of the present invention, even when the air-fuel ratio control of the internal combustion engine is stopped and the air-fuel ratio is not detected, Since a predetermined current is supplied to the oxygen pump element of the fuel ratio sensor in accordance with lean or rich of the air-fuel ratio, the oxygen concentration in the gas diffusion limiting chamber can be brought close to the oxygen concentration during execution of the air-fuel ratio control. It is possible to prevent adsorption of rich gas such as HC and CO and oxygen to the internal porous electrode. Therefore, when the air-fuel ratio control is restarted after that, the air-fuel ratio can be detected quickly and accurately, and the delay in the response of the air-fuel ratio control can be prevented.

[Brief description of drawings]

1 to 8 show an embodiment of the present invention, FIG. 1 is a configuration diagram showing the configuration of an air-fuel ratio sensor and a sensor drive control circuit of this embodiment, and FIG. 2 is a partial fracture of the air-fuel ratio sensor. FIG. 3 is a perspective view, FIG. 3 is an exploded perspective view thereof, FIG. 4 is an electric circuit diagram showing an air-fuel ratio detection circuit, and FIG. 5 is a diagram showing control signals of an oxygen pump element generated in the air-fuel ratio detection circuit. Sixth
Fig. 7 is a diagram showing the air-fuel ratio signal obtained by the air-fuel ratio detection circuit, Fig. 7 is a diagram showing the voltage applied to the oxygen pump element of the air-fuel ratio sensor at the time of detecting the air-fuel ratio, and Fig. 8 is exhaust gas from rich gas. It is a diagram showing the experimental data by the experiment 1 which measured the response delay of the oxygen concentration battery element when changing to lean gas. 4 ... Oxygen pump element 8 ... Oxygen concentration battery element 9 ... Spacer 9a ... Hollow part (gas diffusion limiting chamber) 20 ... Sensor drive control circuit 21 ... Air-fuel ratio detection circuit 22 ... Current supply circuit 31 ... … Comparison circuit 32 …… Constant voltage circuit

Claims (1)

[Claims] 1. Diffusion of exhaust gas, which is formed by contacting with two detection elements formed by laminating a pair of porous electrodes on both surfaces of an oxygen ion conductive solid electrolyte and one porous electrode of each of the detection elements. An air-fuel ratio sensor having a limited gas diffusion limiting chamber, and one of the two detection elements is operated as an oxygen concentration cell element, and the other detection element is operated as an oxygen pump element. An air-fuel ratio signal output means for outputting an air-fuel ratio signal according to the oxygen concentration of the internal combustion engine, and detecting the air-fuel ratio of the fuel mixture supplied to the internal combustion engine during execution of the air-fuel ratio control of the internal combustion engine. In the air-fuel ratio detection device, the determination means for determining whether the air-fuel ratio of the fuel mixture supplied to the internal combustion engine is rich or lean when the air-fuel ratio control of the internal combustion engine is stopped; Depending on the discrimination result, the above An air-fuel ratio detection device for an internal combustion engine, comprising: a current supply means for supplying a predetermined current to an oxygen pump element.