JPS61251766A - Air fuel ratio detector - Google Patents

Abstract

PURPOSE:To detect an air fuel ratio accurately by acceleration the gas exchange in a diffusion chamber through the operation of a pump current control means and a current supply means when the air fuel ratio varies from a leak area to a rich area or vice versa. CONSTITUTION:When the air fuel ratio varies from the rich area to the leak area and an oxygen concentration electron element M2 generates electromotive force exceeding a set value, a reverse pump current flows to an oxygen pump element M3 and oxygen in exhaust gas is sucked in the diffusion chamber. At this time, the element M2 is operated as a pump element temporarily through the operation of a current supply means M7 to suck the oxygen in the exhaust gas in the chamber M1, thereby accelerating the gas exchange nearby the electrode of the element M2 facing the chamber M1. When the air fuel ratio varies from the leak area to the rich area, on the other hand, the element M2 is operated as a pump element temporarily through the operation of the means M7 and oxygen in the chamber M1 is discharged to the exhaust gas, thereby accelerating the gas exchange nearby the electrode of the element 2 facing the chamber M11. Thus, the gas exchange in the chamber M1 is performed smoothly.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an air-fuel ratio detection device, and more specifically, it uses an oxygen concentration cell element and an oxygen pump element arranged facing a diffusion chamber, and is used in internal combustion engines, etc. The present invention relates to an air-fuel ratio detection device that detects the air-fuel ratio of an air-fuel mixture supplied to various combustion devices based on exhaust composition.

[Prior Art] As an air-fuel ratio detection device that detects the air-fuel ratio of a mixture supplied to various combustion devices such as an internal combustion engine based on exhaust composition, especially oxygen concentration, a plate-shaped oxygen ion conductive solid electrolyte is used. Two sets of elements with porous electrodes on both sides are arranged facing each other with a diffusion chamber in between. One element is an oxygen pump element that pumps oxygen in the diffusion chamber to the surroundings, and the other element is an oxygen pump element that pumps oxygen from the diffusion chamber into the surrounding atmosphere. There is an oxygen concentration battery element that generates a voltage depending on the oxygen partial pressure ratio with respect to the chamber, and is constructed so as to be able to detect a signal corresponding to the air-fuel ratio at least in the lean range of the air-fuel ratio (Japanese Patent Laid-Open No. 59-178354).

Furthermore, in this type of air-fuel ratio detection device, as shown in FIG.
Go, CO2, and H in the exhaust gas not only in the lean range of the air-fuel ratio, that is, when residual oxygen exists in the exhaust gas, but also in the rich range of the air-fuel ratio, that is, when there is no residual oxygen in the exhaust gas.
20, etc., and generates a signal similar to that in the lean region.
As described in No. 4098, etc., in recent years, this characteristic has been utilized to reverse the output characteristic at the stoichiometric air-fuel ratio (excess air ratio λ-1), resulting in an air-fuel ratio that changes continuously from the rich region to the lean region. The idea is to detect signals.

[Problems to be Solved by the Invention] By the way, in the above-mentioned air-fuel ratio detection device, normally, the air-fuel ratio detection device detects an air-fuel ratio according to the ratio of the oxygen partial pressure in the diffusion chamber generated in the oxygen concentration cell element and the oxygen partial pressure in the exhaust gas. The pump current of the oxygen pump element is pumped out to the exhaust gas by turning the pump current of the oxygen pump element IIi1wJ to the set value, and the pump current is detected as an air-fuel ratio signal. When the fuel ratio changes from a lean range to a rich range or from a rich range to a lean range, the detected air-fuel ratio signal,
That is, there is a problem in that the pump current has a value that does not correspond to the air-fuel ratio, making it impossible to accurately detect the air-fuel ratio. In other words, as shown in Fig. 3 (A), when the air-fuel ratio changes, the pump current 1p changes in accordance with the air-fuel ratio as shown in Fig. 3 (A).
It is desirable that the value shown by the dotted line in b) is obtained.
In reality, the pump current ■p is shown by the solid line in Figure 3.
becomes a value that does not correspond to the air-fuel ratio.

This is due to the fact that gas exchange within the diffusion chamber is delayed in response to changes in exhaust gas.

In other words, at time t1 when the exhaust gas condition changes from the rich region to the lean region, the gas in the diffusion chamber is not exchanged and still
Since it corresponds to the rich region, the electromotive force generated in the oxygen concentration battery element will rise rapidly from the set value. At this time, the conventional detection device is configured to flow the pump current 1p only in the direction of pumping out the oxygen in the diffusion chamber into the exhaust gas, so the pump current Ip flows through the oxygen pump element until the gas exchange in the diffusion chamber is completed. does not flow, and the air-fuel ratio signal detected during this period has a value that does not correspond to the air-fuel ratio.

On the other hand, at time t2 when the exhaust gas condition changes from the lean region to the rich region, the interior of the diffusion chamber still corresponds to the lean region due to the delay in gas exchange as described above, and the electromotive force generated in the oxygen concentration cell element changes from the set value. It will decrease rapidly. At this time, in order to control the current to the set voltage, an excessive pump current 1p is passed through the oxygen pump element, and the air-fuel ratio signal detected in this case also becomes a value that does not correspond to the air-fuel ratio. be.

Therefore, the present invention improves the gas exchange delay in the diffusion chamber as described above, and even when the air-fuel ratio changes from a lean region to a rich region or from a rich region to a lean region, the air-fuel ratio corresponding to that air-fuel ratio is maintained. This device was designed to provide an air-fuel ratio detection device that can detect signals well, and has the following configuration.

[Means for solving the problem] In other words, the configuration as a means for solving the above problem is as follows.
As shown in FIG. 1, porous electrodes are formed on both sides of an oxygen ion conductive solid electrolyte, and one of the electrodes is connected to a diffusion chamber M1 in which the inflow of exhaust gas is restricted.
Two elements M2 and M3 are arranged facing each other, and one of the two elements M2 and M3 is used as an oxygen concentration battery element M2 and the other as an oxygen pump element M3, and the oxygen concentration battery element Pump current control means M4 performs feedback control of the pump current flowing through the oxygen pump element M3 according to the electromotive force generated by M2, and the pump current controlled by the cough pump current control means M4 corresponds to the air-fuel ratio. an air-fuel ratio signal output means M5 that outputs an air-fuel ratio signal based on the air-fuel ratio; means M6; and upon receiving a detection signal from the stoichiometric air-fuel ratio detection means M6, when the air-fuel ratio changes from a rich region to a lean region, a temporary voltage is applied to the oxygen concentration cell element M2 from the electrode side facing the diffusion chamber. A current supply means M7 is provided that supplies current and temporarily supplies current from the other electrode side to the oxygen concentration cell element M2 when the air-fuel ratio changes from a lean region to a rich region. The air-fuel ratio characterized in that the current control means M4 of the pump is configured to bidirectionally feedback control the pump current so that the electromotive force generated by the oxygen concentration cell element becomes a predetermined value. The gist is the detection device.

Here, the diffusion chamber M1 may be realized by a gap formed between two elements M3 and M4, or may be realized by a gap formed between two elements M3. It can also be configured as a room facing M4 and in which diffusion of oxygen molecules and the like is restricted by a diffusion resistor such as a hole or a porous material. In any case, the diffusion of the exhaust gas is limited so that oxygen molecules or other molecules that act to generate an electromotive force in the oxygen concentration cell element M3 in the rich region reach a predetermined concentration by being pumped out by the oxygen pump element M4. There is no problem as long as the room is raised as if it were a room. In addition, from the viewpoint of responsiveness, it is preferable that the above-mentioned molecules diffuse as freely as possible within the diffusion chamber.

Next, the oxygen concentration battery element M3 and the oxygen pump element M4
Representative examples of the oxygen ion conductive solid electrolyte that form the A kite type oxide solid solution, a 36I metal oxide solid solution, etc. can also be used. In addition, the porous electrodes provided on both sides of the solid electrolyte may be made of platinum, rhodium, etc., which have a catalytic effect on oxidation reactions, and the formation method is the same as that of the solid electrolyte, with these metal powders as the main components. There are two methods: mixing ceramic material powder into a paste, printing it using thick film technology, and then sintering it, or forming it using thin film technology such as flame spraying, chemical plating, and vapor deposition. It is preferable that the electrode layer is further formed with a porous protective layer of alumina, spinel, zirconia, mullite, etc. using thick film technology, and the porous layer on the electrode on the side of the diffusion chamber M1 is made of platinum,
It is preferable to disperse rhodium or the like to impart a catalytic effect to the oxidation reaction.

Among the 21I elements formed in this way, the element used as the oxygen concentration battery element M3 is made of an oxygen ion conductive solid electrolyte under suitable temperature conditions (for example, 400°C or higher when the solid electrolyte is zirconia). Oxygen ions move in the solid electrolyte from areas with high oxygen gas partial pressure on the surface to areas with low oxygen gas partial pressure, and by attaching oxygen gas permeable electrodes to the solid electrolyte, the oxygen gas partial pressure between the electrodes can be reduced. It takes advantage of the property that the difference can be extracted as an electromotive force (voltage between electrodes), and it generates a voltage according to the ratio of the oxygen partial pressure in the diffusion chamber and the oxygen partial pressure in the surrounding atmosphere, that is, the exhaust gas. It is something.

On the other hand, the element used as the oxygen bomb element M4 utilizes the property of an oxygen ion conductive solid electrolyte that oxygen ions move through the solid electrolyte by applying a voltage. The oxygen in the diffusion chamber is pumped out into the exhaust gas.

Next, the pump current control means M5 can be easily realized by a discrete circuit, but it converts the inter-electrode voltage of the oxygen concentration battery element M3 into a -H digital value and reads it, and uses a logic using a well-known microprocessor. It is also possible to adopt a configuration in which the pump current is controlled by an arithmetic circuit. In this case, it is also possible to configure the air-fuel ratio detection device integrally with an electronic fuel injection control device (EFI) of an internal combustion engine or the like.

Further, in the present invention, this pump current control means M5 is configured to control the pump current [in both directions], but this means that when the electromotive force generated in the oxygen concentration battery element M2 exceeds a set value, By pumping oxygen from the exhaust into M1, gas exchange within the diffusion chamber M1 is promoted when the air-fuel ratio changes from a rich range to a lean range.

Next, the stoichiometric air-fuel ratio detecting means M6 outputs a stoichiometric air-fuel ratio signal that can determine the air-fuel ratio slope region and rich region. physical semiconductors (e.g. T j 02 N G G O
etc.) can be used.

The current supply means M7 changes the air-fuel ratio from a lean range to a rich range based on the detection signal from the stoichiometric air-fuel ratio detection means M6.
Alternatively, by detecting a change from a rich region to a lean region and temporarily supplying current to the oxygen concentration battery element M2, the oxygen concentration battery element M2 is temporarily operated as a pump element, and the oxygen concentration battery element M2 is temporarily operated as a pump element. This is to promote gas exchange.

[Operation] In the air-fuel ratio detection device of the present invention configured as described above, the air-fuel ratio changes from a rich range to a lean range,
When an electromotive force exceeding a set value is generated by the oxygen concentration battery element, a pump current in the opposite direction is caused to flow through the oxygen pump element M3, and oxygen in the exhaust gas is pumped into the diffusion chamber M1. Further, at this time, the oxygen concentration battery element M2 is temporarily operated as a pump element by the operation of the current supply means M7, and the oxygen in the exhaust gas is pumped into the diffusion chamber M1, and the oxygen concentration battery element M2 is brought into the diffusion chamber M1 of the oxygen concentration battery element M2. gas exchange near the electrode is promoted. On the other hand, even when the air-fuel ratio changes from a lean range to a rich range, the oxygen concentration cell element M2 is temporarily operated as a pump element by the operation of the current supply means M7, and the oxygen in the diffusion chamber M1 is pumped out into the exhaust gas. As a result, gas exchange near the electrode facing the diffusion chamber M1 of the oxygen concentration battery element M2 is promoted.

Therefore, according to the air-fuel ratio detection device of the present invention, even when the air-fuel ratio changes from a lean range to a rich range or from a rich range to a lean range, gas exchange within the diffusion chamber M1 is performed smoothly, and gas exchange is delayed. Erroneous detection of the air-fuel ratio signal due to this can be prevented, and an air-fuel ratio signal corresponding to the actual air-fuel ratio can be obtained.

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

First, FIG. 4 shows how the detection element portion of the air-fuel ratio detection device of this embodiment, that is, the oxygen concentration cell element M2, the oxygen pump element M3, and the stoichiometric air-fuel ratio detection means M6 are attached to the exhaust pipe 10 of the internal combustion engine. It shows a state in which they are integrally attached via 11.

The figure represents an oxygen concentration battery element, and as shown in FIG. A porous platinum electrode layer 14a having a thickness of about 20μ is formed on both sides of the electrode 13 using thick film technology, respectively.
14b and a platinum electrode 15a115b for output extraction. Further, 16 is the oxygen concentration battery element 12
A porous platinum electrode layer 180118d and a platinum electrode 19 are provided on both sides of the ion conductive solid electrolyte 17.
c, 19d represents the oxygen pump element provided.

Next, 20 represents the above-mentioned stoichiometric air-fuel ratio detection element, which is made of, for example, alumina and has a thickness of 0.7R1, as shown in FIG.
A low heat generation pattern 22 and an electrode pattern 23e are formed using thick film technology on the side surface of the flat electrically insulating member 21 of 111.
123f, and electrodes 23e are formed on these pattern surfaces.
An electrically insulating member 24 having a thickness of 0.1111 mm and having an opening 24a provided to expose 123f is bonded and burned, and electrode patterns 23e1 and 23f are formed in the opening 24a.
A thickness of approximately 150μ made of titania, etc., bonded to
It is made by providing a metal oxide 25 of about 100 mL.

Each of the above-mentioned elements is integrally held by the member 11 via a heat-resistant and insulating spacer 27, and is attached to the exhaust pipe 10. Further, the spacer 27 connects the oxygen concentration battery element 12 and the oxygen pump element 16 with a 0.0-degree gap between them.
The diffusion chamber 28 is configured to be formed as a small gap of about 1 mm.

Next, FIG. 7 shows an air-fuel ratio signal detection circuit for operating the detection element section and detecting an air-fuel ratio signal.

This air-fuel ratio detection circuit detects 1gl of oxygen! A pump current control circuit 30 corresponding to the pump current control means M4 bidirectionally controls the pump current Ip so that the electromotive force of the battery element 12 is constant; and a pump current II controlled by the pump current control circuit 30) The air-fuel ratio signal output circuit 32 corresponding to the air-fuel ratio signal output means M5 detects the air-fuel ratio signal Vf, and receives the signal from the stoichiometric air-fuel ratio detection element 20 when the air-fuel ratio is in the lean range to the rich range. , or a current supply circuit 34 corresponding to the current supply means M7, which temporarily supplies current to the oxygen concentration battery element 12 when changing from a rich region to a lean region. Also,
Each terminal a, b, c, d, e.

t are the electrodes 15a and 15b of the detection element section, respectively.
, 18c, 18d, 23e, 23f,
An air-fuel ratio signal Vλ is generated between terminals g and h.

First, the pump current control circuit 30 is composed of an operational amplifier oP1, resistors R1 to R5, and a capacitor C1, and detects the electromotive force generated in the ms density battery element 12 as a voltage signal, amplifies it, and outputs a voltage S. Amplification circuit, operational amplifier OP2, resistor R6,
Compare the set voltage 0 determined by resistors R8 and R9 with the amplified voltage, and apply the difference voltage to one electrode 19d of the oxygen pump element 16. Integrating circuit and operational amplifier o
P3, resistor R10, and variable resistor VR1, amplifies the constant voltage VO determined by resistors R8 and R9, and supplies the constant voltage Vi to the oxygen pump element 16 via the resistor RO.
a non-inverting amplifier circuit that applies voltage to the other electrode 19C;
It consists of In the pump current 111111 circuit 30 configured in this way, the pump current Ip flowing through the oxygen pump element 16 is controlled so that the electromotive force generated in the oxygen concentration battery element 12 becomes constant, that is, so that the voltage VS becomes the set voltage VO. It operates to control the direction.

Next, the air-fuel ratio signal output circuit 32 detects the pump current Ip flowing through the oxygen pump element 16 via the resistor RO, and includes a buffer circuit configured using an operational amplifier OP4, resistors R11, R12, and capacitors C3, C4. The air-fuel ratio signal Vλ is output via the air-fuel ratio signal Vλ.

The current supply circuit 34 supplies a predetermined voltage E1 from one end of the stoichiometric air-fuel ratio detection element 20, and generates a stoichiometric air-fuel ratio signal having characteristics as shown in FIG. Vrl is detected via the operational amplifier OP5, and when the stoichiometric air-fuel ratio detection element Vrl changes from a lean range to a rich range or from a rich range to a lean range, the electrode 15a of the oxygen concentration battery element 12 on the opposite side from the diffusion chamber 28 The device is configured to temporarily supply a positive voltage or a negative voltage to the device. That is, the output terminal of the operational amplifier is connected to the electrode 15a of the oxygen concentration battery element 12 via a capacitor C5 and a resistor R15, and a diode D1 is connected in parallel with the resistor R15.
and a resistor R16 are provided in series, and a resistor R15
and capacitor C5, connect diode D2 and resistor R
By grounding using a series circuit of 17, when the air-fuel ratio changes from a lean range to a rich range, the potential of the electrode 15a is temporarily increased, and the oxygen concentration cell element 12 is used to increase the potential of the electrode 15a. While pumping oxygen into the exhaust gas, when the air-fuel ratio changes from a rich region to a lean region, the potential of the electrode 15a is temporarily lowered (negative potential), and the oxygen is pumped into the diffusion chamber 28 using the oxygen concentration cell element 12. It is designed to suck in oxygen from the exhaust gas.

In the air-fuel ratio detection device of this embodiment configured as described above, even when the air-fuel ratio changes from a lean range to a rich range, or from a rich range to a lean range, as shown in FIGS. 9(a) and 9(b), , pump current Ip (i.e., air-fuel ratio signal) corresponding to the air-fuel ratio without causing response delay or overshoot unlike the conventional air-fuel ratio detection device shown in FIG.
You will be able to obtain Incidentally, this is because the air-fuel ratio detection device of this embodiment detects the pump current ip of the oxygen pump element 16.
By flowing in both directions, gas exchange within the diffusion chamber 28 is promoted when the air-fuel ratio changes from a rich region to a lean region,
In addition to improving the responsiveness at that time, a voltage as shown in FIG. 9(c) is applied to the oxygen concentration battery element 12 by the operation of the current supply circuit 34, and the oxygen concentration battery element 12 temporarily operates as a pump element. This is because the structure is configured to further promote gas exchange within the diffusion chamber 28. Note that FIG. 10 simply shows the pump current I of the oxygen pump element 16.
This figure shows the change in the pump current It) when the current supply circuit 34 is not operated by only controlling p in both directions. It turns out that sex can be improved.

[Effects of the Invention] As detailed above, according to the air-fuel ratio detection device of the present invention,
When the air-fuel ratio changes from a lean range to a rich range or from a rich range to a lean range, gas exchange within the diffusion chamber is promoted by the operation of the pump current 11JII1 means and the current supply means.

Therefore, it becomes possible to accurately detect the air-fuel ratio without response delay, and it becomes possible to execute air-fuel ratio control with high precision.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the configuration of the present invention, and Fig. 2 shows an air-fuel ratio signal detected by a conventional air-fuel ratio detection device.
11 and 3 are diagrams explaining problems with the air-fuel ratio signal (pump current) obtained by a conventional air-fuel ratio detection device, and FIGS. 4 to 9 show an embodiment of the present invention. FIG. 4 is a sectional view showing the detection element section of the air-fuel ratio detection device of this embodiment, FIG. 5 is a perspective view showing the configuration of the oxygen concentration cell element, and FIG. 6 is an exploded perspective view showing the configuration of the stoichiometric air-fuel ratio detection element. figure,
FIG. 7 is a circuit diagram showing the air-fuel ratio signal detection circuit, and FIG. 8 is the stoichiometric air-fuel ratio signal Vr obtained by the stoichiometric air-fuel ratio detection element.
Figure 9 is a miniature diagram showing the characteristics of l, Figure 9 is a diagram m explaining the operation of the air-fuel ratio detection device of this embodiment and the air-fuel ratio signal (pump current) obtained thereby, and Figure 10 is a diagram showing the current supply circuit not operating. FIG. 3 is a diagram illustrating an air-fuel ratio signal (pump current) obtained in this case. 12... Oxygen concentration battery element 16... Oxygen pump element 20... Theoretical air-fuel ratio detection element 30... Pump current l11vA circuit 32... Air-fuel ratio signal output circuit 34... Current supply circuit

Claims (1)

[Claims] Two elements comprising porous electrodes formed on both sides of an oxygen ion conductive solid electrolyte, with one of the electrodes facing a diffusion chamber in which the inflow of exhaust gas is restricted. Of the two elements, one is used as an oxygen concentration battery element and the other as an oxygen pump element, and the pump current flowing through the oxygen pump element is feedback-controlled in accordance with the electromotive force generated by the oxygen concentration battery element. An air-fuel ratio detection device comprising: a pump current control means; and an air-fuel ratio signal output means for outputting an air-fuel ratio signal corresponding to an air-fuel ratio according to the pump current controlled by the pump current control means, comprising: a stoichiometric air-fuel ratio; a stoichiometric air-fuel ratio detection means that detects the air-fuel ratio and outputs different signals depending on the lean range and the rich range of the air-fuel ratio; , a current is temporarily supplied to the oxygen concentration battery element from the electrode side facing the diffusion chamber, and when the air-fuel ratio changes from a lean region to a rich region, the other electrode is supplied to the oxygen concentration battery element. current supply means for temporarily supplying current from the side; An air-fuel ratio detection device characterized by being configured to perform feedback control.