JPH0715452B2 - Air-fuel ratio detector - Google Patents

Description

The present invention relates to an air-fuel ratio detector, and more particularly to an air-fuel ratio detector suitable for use in air-fuel ratio control of a meat-fuel engine.

[Conventional technology]

A conventional air-fuel ratio detector is, for example, Japanese Patent Laid-Open No. 51-4558.
As described in No. 7, there is one in which platinum electrodes are provided on the outside and inside of a bag-shaped solid electrolyte, the inner electrode is exposed to the atmosphere, and the outer electrode is brought into contact with exhaust gas of a meat combustion engine. The output of this detector changes stepwise at the stoichiometric air-fuel ratio (λ = 1.0). That is, a high output of about 800 mV is obtained in the rich region (λ <1.0) richer than the theoretical air-fuel ratio, and a low output of about 200 mV is obtained in the lean region (λ> 1.0) leaner than the theoretical air-fuel ratio. It is a thing. This air-fuel ratio detector is now popular and has been widely used for air-fuel ratio control of internal combustion engines.

However, this detector can only discriminate between rich and lean with respect to the theoretical air-fuel ratio, whereas in recent years, the necessity of lean burn control of the internal combustion engine has been taken up from the viewpoint of energy saving. In order to perform this control, an air-fuel ratio detector whose output changes linearly in the lean region is required.

Various types of such air-fuel ratio detectors have been researched and developed, and as one example, the one described in JP-A-55-62349 is known.

In this detector, platinum electrodes are provided on both sides of a solid electrolyte, one platinum electrode is covered with a porous diffusion resistor, an electric current is passed between both electrodes, and the electromotive force at that time is measured.
This electromotive force changes linearly in the lean region. The electromotive force can be linearly changed in the rich region by reversing the direction of current flow. That is, in this detector, the lean region and the rich region can be measured by changing the flowing direction of the current.

[Problems to be Solved by the Invention]

However, in the above-mentioned conventional technique, in order to be able to measure from the lean to the rich region, a means for switching the flowing direction of the current with the stoichiometric air-fuel ratio as a boundary is required, and there is a problem that the configuration becomes complicated.

An object of the present invention is to provide an air-fuel ratio detector capable of measuring the air-fuel ratio from the lean region to the rich region with a simple structure.

[Means for Solving the Problems]

The above object is to provide a first solid electrolyte having a first electrode provided on one surface and a second electrode provided on the other surface, and a third electrode provided on one surface and the other. A second solid electrolyte having a fourth electrode provided on the surface of the first solid electrolyte, and the second solid electrolyte provided between the first solid electrolyte and the second solid electrolyte, and the first solid electrolyte and the second solid electrolyte. An intermediate plate for independently arranging the solid electrolyte, the first solid electrolyte, the second solid electrolyte and the intermediate plate, and the inside of the first electrode and the third electrode.
And a diffusion chamber through which the exhaust gas passes by a diffusion resistor, and a current flows from the third electrode to the fourth electrode to send oxygen in the exhaust gas through the second solid electrolyte into the diffusion chamber. And a means for flowing a current from the first electrode to the second electrode, and the air-fuel ratio is detected by an electric signal obtained between the electrodes of the first electrode and the second electrode. It is achieved by

[Action]

A third electrode, a fourth electrode, and a second electrode which form the pump cell.
By providing means for sending oxygen in the exhaust gas into the diffusion chamber through the solid electrolyte of, even in the rich region,
Oxygen is present near the electrodes. Therefore, the characteristic of the lean region can be directly shifted to the rich side, and measurement from the rich region to the lean region can be performed.

〔Example〕

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

FIG. 1 is a block diagram showing an embodiment of a control system for an automobile engine equipped with an air-fuel ratio detector according to the present invention. In FIG. 1, 1 is a throttle chamber, 2 is a heat ray type intake air amount detector, 3 is an injection valve, 4 is a throttle actuator having a throttle angle sensor, 5 is a spark plug,
6 is a water temperature sensor, 7 is an air-fuel ratio detector according to the present invention, 8 is a crank angle sensor, 9 is an ignition coil, 10 is a microcomputer, 11 is a control circuit for the air-fuel ratio detector 7, 12 is a heater control circuit, and 13 is In the combustion chamber, in this system, the air-fuel ratio is detected by using the air-fuel ratio sensor 7 capable of detecting the air-fuel ratio in a wide range from the rich region (λ <1) to the lean region (λ> 1). Air-fuel ratio control is performed. That is, when the microcomputer 10 determines the air-fuel ratio to be controlled by the rotational speed, the load, the water temperature, etc., it is output to the injection valve 3 and the throttle actuator 4 for closed loop control. The intake air amount is detected by the intake air amount detector 2. The air-fuel mixture formed in the throttle chamber 1 enters the combustion chamber 13, is ignited by the spark plug 5, and then flows into the exhaust gas exhaust pipe 14. At this time, the actual air-fuel ratio is detected by the air-fuel ratio detector 7, and the signal is input to the microcomputer 10 to perform closed loop control.
Since the air-fuel ratio detector 7 must be heated to a high temperature due to the characteristics of the solid electrolyte used, the heater drive circuit 12 is provided.

FIG. 2 is a detailed block diagram of the microcomputer 10 of FIG. As the analog input signals, the air amount signal AF from the heat ray type intake air amount detector 2, the water temperature signal TW from the water temperature sensor 6, the throttle opening signal θ from the throttle actuator 4, the air-fuel ratio detector 7 from the air There is a fuel ratio signal O _2, etc., and these signals are input to the multiplexer 30 to select each signal in a time division manner, and the AD converter 31
To be converted into a digital signal. Also,
The information signal 15 input as an on-off signal is treated as a 1-bit digital signal. Further, pulse train signals CRP and CPP from the crank angle sensor 8 are also input. 32 is R
The OM and 33 are CPUs, the CPU 33 is a central processing unit that performs digital arithmetic processing, and the ROM 32 is a storage element that stores a control program and fixed data. The RAM 34 is a readable and writable storage element. The I / O circuit 35 sends signals from the AD converter 31 and each sensor to the CPU 33, and sends signals from the CPU 33 to the drive circuit 36 for the injection valve 3, the throttle actuator 4, the ignition coil 9, and the heater for driving the air-fuel ratio detector 7. It has a function of sending to the circuit 12 and sending a control signal 11a to the control circuit 11.

The air-fuel ratio detector 7 can detect the air-fuel ratio over a wide range from the rich region (λ <1) to the lean region (λ> 1). The principle will be described with reference to FIG.

The solid electrolyte 40, electrodes 41a and 41b are provided on both sides, further by a diffusion resistor 43 having an orifice 42,
A diffusion chamber 44 is formed so as to cover the electrode 41a. Further, a part of the diffusion resistor 43 is provided with a solid electrolyte 46 having electrodes 45a and 45b. Electrode 41 is measuring device 47, electrode 4
5 is connected to the power supply 48.

Here, the oxygen bias means consisting of the solid electrolyte 46, the electrodes 45a, 45b and the power supply 48 is the main part of the present invention, and first,
The operation of the configuration other than the oxygen bias means will be described.

There are two types of operation, and a constant current i ₁ from the measuring device 47
In the direction shown in FIG. 3 to measure the electromotive force at that time, or to apply a constant voltage V ₁ from the measuring device 47 and measure the current flowing at that time.

The solid line in FIG. 4 (a) shows the former example. That is, the electromotive force changes stepwise at the stoichiometric air-fuel ratio (λ = 1.0), and also changes in the lean region (λ> 1.0). Then, the point at which the electromotive force changes changes depending on the flowing currents i ₁₁ , i _{12, and the} like.
In FIG. 3, the orifice 45 restricts the diffusion of oxygen from the surroundings into the diffusion chamber 44. Then, oxygen corresponding to the ambient oxygen concentration diffuses. On the other hand, since a current is flowing from the device 47 in the direction shown in the figure, oxygen in the diffusion chamber 44 is reduced to oxygen ions at the interface of the electrolyte 40 of the electrode 41a. This oxygen ion conducts ion conduction in the electrolyte 40 and is oxidized to oxygen at the interface between the electrolyte 40 and the electrode 41b. That is, oxygen in the diffusion chamber 44 is pumped out by the oxygen pumping action of this solid electrolyte. here,
The pumping capacity of the oxygen pump differs depending on the value of the current flowing into it. When the air-fuel ratio is extremely large and the amount of oxygen in the surroundings is large, the amount of diffusion from the orifice 42 becomes larger than the pumping capacity of the pump. Therefore, since the surroundings and the inside of the expansion chamber 44 are filled with oxygen, the partial pressure difference of oxygen between the two is zero, but the electromotive force is close to zero because it is almost small. On the other hand, when the pumping capacity of the pump is sufficiently larger than the diffusion amount, the oxygen in the diffusion chamber is close to zero. Therefore,
Since there is a partial pressure difference in oxygen concentration between the surroundings and the diffusion chamber, electromotive force is generated. In the rich region, there is almost no oxygen in and around the diffusion chamber 44, so no electromotive force is generated. Therefore, in the method in which the current is applied between the electrodes, the characteristics are shown by the solid line in FIG.
The air-fuel ratio at which the electromotive force decreases in the lean region depends on the currents i ₁₁ and i ₁₂ flowing in, that is, the pumping capacity of the pump.

Further, in FIG. 3, electrodes 41a and 41b are measured by the measuring device 47.
A predetermined voltage V ₁ is applied between them, and the relationship between the limit current i ₁ flowing in the direction of the arrow in FIG. 3 at that time and the air-fuel ratio λ is as shown by the solid line in FIG. 4 (b). That is, the lean region (λ
> 1.0), an increasing current is obtained with increasing air-fuel ratio. The amount of oxygen diffused from the orifice 42 is proportional to the ambient oxygen partial pressure. On the other hand, a voltage V ₁ sufficient to pump out oxygen in the diffusion chamber 44 is applied between the electrodes 41a and 41b sandwiching the solid electrolyte 40. Therefore, this oxygen pump pumps out all the oxygen diffused in the diffusion chamber 44, and operates so that the oxygen partial pressure in the diffusion chamber 44 is maintained at zero. As a result, the oxygen diffused from the orifice 42 and the oxygen pumped out by the oxygen pump are balanced, so that the ionic current flowing through the oxygen pump is proportional to the ambient oxygen concentration. Further, the ionic current flowing through the oxygen pump is limited by the oxygen diffused from the orifice 42, and is called a limiting current. In the rich region (λ <1.0), even though a constant voltage is applied between the electrodes 41a and 41b, since there is no oxygen ion to be carried, the ion conduction region moves to the electron conduction region and the current value changes. Will increase.

In the example of the solid line in FIGS. 4 (a) and 4 (b), there are binary values in the lean region (λ> 1.0) and the rich region (λ <1.0). Therefore, measurement from the rich region to the lean region is impossible.

In the air-fuel ratio control of an internal combustion engine, the air-fuel ratio range to be controlled is such that the rich region is approximately 0.7 <λ <0.8, the theoretical air-fuel ratio is λ = 1.0 (± 0.05), and the lean region is ,
Almost 1.2 <λ <1.4. Therefore, as an air-fuel ratio detector, 2 in the rich to lean region where λ is 0.7 or more.
It is good if you do not take a value.

The oxygen bias means is provided to obtain such characteristics, and as shown in FIG.
It is composed of six electrodes 45a and 45b and a power supply 48. And
From the power supply 48, the voltage V ₁ is applied between the electrodes 45a and 45b, and the current i ₂ flows in the direction shown. This oxygen bias means
A constant amount of oxygen is constantly supplied from the surroundings into the diffusion chamber 44. By doing so, oxygen exists in the diffusion chamber 44 even in the rich region (λ <1.0), so that the electrode 41a
The oxygen partial pressure on the side is higher than the oxygen partial pressure on the electrode 41b side, and the electromotive force is maintained at a high level as indicated by the dotted line in FIG. 3 (a).

By biasing this constant oxygen amount, the decrease in electromotive force at λ = 1.0 at i ₂ = 0 is translated to the rich region as indicated by arrow A in FIG. 4 (a). Further, for the same reason, the point that the electromotive force decreases due to the balance between the amount of oxygen moved by the solid electrolyte 40 and the amount of oxygen diffused through the orifice 42 is parallel to the rich side as indicated by arrow B in FIG. 4 (a). Be moved.

That is, by controlling i ₂ and biasing an appropriate amount of oxygen in the diffusion chamber 44, the rich region can be detected.

Further, by biasing oxygen as described above, the limiting current characteristic can be moved in parallel as shown by an arrow C in FIG. 4 (b). As a result, even in a rich region where λ <1.0, it is possible to obtain a linear output (limit current value) as shown by a dotted line for λ equal to or larger than a predetermined λ (for example, λ = 0.7). Then, this parallel movement amount can be controlled by the magnitude of the current i ₂ .

In this way, the rich region can be detected without conversion of the supply current value and polarity as in the past, so even if the air-fuel ratio transiently enters the rich region during operation, the actual air-fuel ratio The change can be measured smoothly, and there is no need to enter the electron conduction region, so there is no dead zone and controllability is greatly improved.

FIG. 5 shows another embodiment of the thin plate type. The solid electrolyte 67a is for sensing the air-fuel ratio, and has electrodes 68a and 68b. Further, the solid electrolyte 67b is
To bias (pump) oxygen,
Electrodes 69a and 69b are attached, and an orifice 70 serving as a diffusion resistor is further provided. These two solid electrolytes 67a, 67
A diffusion chamber 72 communicating with the outside only by the orifice 70 is provided by b and the intermediate plate 71. In addition, solid electrolyte
A heater 73 is attached to 67a and 67b.

The operation of the sensor will be described with reference to FIG. Normally, the circuit 11a causes a current i ₁ to flow through the solid electrolyte 67a, causing oxygen ions to move in the direction of the arrow. When this moving amount and the moving amount of oxygen diffusing into the diffusion chamber 72 through the orifice 70 are balanced, the electromotive force changes stepwise at the air-fuel ratio corresponding to i ₁ . Further, here as well, a constant amount of oxygen is biased using the solid electrolyte 67b so that the air-fuel ratio can be detected even when λ <1.0. At this time, if the current i ₂ is made to flow in the direction of the arrow shown in the figure by the circuit 11b, the oxygen amount corresponding to this i ₂ is biased.

In the various sensor configurations described above, i ₁ and i ₂ are constantly supplied to simultaneously detect the oxygen bias and the air-fuel ratio.

Next, advantages of performing engine control by the air-fuel ratio detector according to the present invention will be described.

FIG. 6 shows a map of the air-fuel ratio with respect to the load for controlling the air-fuel ratio (A / F) to change depending on the operating state. The air-fuel ratio is a closed loop with the value of this (A / F) _MAP. Controlled. Here, in terms of power and fuel economy
The A / F is large under a partial load (lean region) and small under a full load (rich region). It is one of the features of the air-fuel ratio detector according to the present invention that the closed-loop control can be performed in such a wide range of air-fuel ratio.

Next, control of a transient operation state using the air-fuel ratio detector of the present invention will be described.

FIG. 7 (a) shows the state change when the accelerator pedal is pushed in.

(A) is the throttle opening, which changes so as to increase stepwise, and following this, the air amount shown in (b) also increases stepwise. However, the actual amount of fuel that enters the engine is increased with a delay as shown in (c), and the amount of air becomes insufficient by the shaded portion with respect to the amount of air. When the target air-fuel ratio of the map control in FIG. 6 changes from large to small with respect to this change in load, as shown in (d), the fuel amount delay shown in (c) causes The target air-fuel ratio will deviate by an amount corresponding to the shaded portion. Further, FIG. 7 (b) shows a state change when the load is reduced, and the meaning of the symbols is (a).
It corresponds to the case of. In this case as well, due to the delay in the fuel amount shown in (c), the air-fuel ratio deviation (hatched portion) shown in (e) occurs. In this case, the air-fuel ratio may suddenly jump to λ <1.0 at the point A, and even in such a case, if the air-fuel ratio detector of the present invention that can always detect the entire λ range, the A / F The trajectory can be detected without delay. Further, even if the change in A / F shown in (e) of FIGS. 7 (a) and (b) occurs in the region of λ <1.0, it can be detected by the air-fuel ratio detector according to the present invention.

A method of correcting the A / F shift in the shaded area shown in (e) of FIGS. 7 (a) and (b) based on the output of the air-fuel ratio detector according to the present invention will be described below.

As shown in FIG. 8, when the load state changes from →→→, the air-fuel ratio control target also changes correspondingly, but as explained in FIG. 7, the actual air-fuel ratio cannot follow. , As shown by the shaded area in FIG. Here, transient correction of the air-fuel ratio is performed based on these Δx ₁ , Δx ₂ , Δx ₃ and the changes ΔQa ₁ , ΔQa ₂ , ΔQa ₃ of the air amount Qa as a load.

First, the correction of the fuel amount is performed by the value obtained by multiplying the differential value dQa / dt of the change amount ΔQa of the air amount due to the load change shown in FIG. 8 by the time t by the correction coefficient K, that is, the correction amount is It becomes like the formula (1).

Correction amount = K · (dQa / dt) (1) Here, K is a map as shown in FIG. 9 with dQa / dt as the horizontal axis and stored in the computer 10.

A transient correction method will be described with reference to the flowchart of FIG. First, in step 80, the intake air amount Qa, ₀ before acceleration / deceleration as a load is read. At the same time, the air-fuel ratio (A / F) _MAP to be controlled for this load,
₀ is read from the map of FIG. 6 (step 82). Further, as the data after acceleration / deceleration, the intake air amount Qa, ₁ is read (step 84), and the air-fuel ratio (A / F) _MAP , ₁ to be controlled for this load is read (step 86). Step 8
Based on Qa, ₀ , Qa, ₁ read in ₀ , 84, dQa / dt is calculated in step 88. For this dQa / dt, in step 90, the correction coefficient K is read from the map of FIG. 9, and in step 92, K · dQa / dt is calculated. Based on this calculated value, in step 94, the correction of G = G + G '... (2) is added. After outputting this G, Δx proportional to the amount of the shaded portion in FIG. 8 is detected and read based on the signal of the air-fuel ratio sensor (step 96). Based on this Δx, K ′ is obtained from the equation Δx = K ′ · (dQa / dt) (3) (step 98). This K'is
When Δx occurs for some reason even after the correction is made by the equation (2), it is the correction amount of the correction coefficient for correcting it again. The correction coefficient K is rewritten as K = K + K ′ (4) (Step 100). This newly determined K is then rewritten with the K at the position corresponding to dQa / dt. Next, when a transient state is detected, K corresponding to dQa / dt is immediately read and correction is performed. In this way, Δx based on the sensor output is used to calculate the correction amount of the correction coefficient, the correction coefficient K is corrected, and it is constantly rewritten.

This eliminates fluctuations in the air-fuel ratio during the transition.

FIG. 11 (a) shows the fluctuation range of the CO concentration when fully opened, and the air-fuel ratio is in the rich region. Since the fluctuation of CO at the time of full closing is disadvantageous to the fuel economy, the closed loop control is performed by using the air-fuel ratio detector according to the present invention capable of measuring (A / F) even in the rich region. The CO fluctuation range ΔCO can be suppressed as shown in (b).

Next, advantages of using the air-fuel ratio detector according to the present invention at the time of starting and warming up will be described. Fig. 12 (a) is a diagram showing the relationship between the time immediately after start-up and the mixture concentration with the water temperature as a parameter. The curves n and o show the relationship when the initial water temperature is T ₁ and T ₂ , respectively. Show. Immediately after starting, the air-fuel mixture concentration is made thicker and becomes thinner as time passes, that is, as the water temperature rises. That is, in the warm-up operation state, if an appropriate A / F is given by the cooling water temperature, the operation can be performed without waste. By the way, since the air-fuel ratio detector according to the present invention can detect even in the rich region, it enables the rich air-fuel mixture control immediately after the start. Water temperature T shown in Fig. 12 (b)
_If the relationship between _W and A / F is stored in the computer 10, it can be operated by this function during warm-up.
FIG. 12 (c) is a control block diagram at this time. The signal of the water temperature sensor 6 is input to the computer 10, A / F is determined by the function showing the relationship of FIG. 12 (b), and output to the engine system 110. The air-fuel ratio detector 7 detects the actual air-fuel ratio, compares this output with the output indicating the A / F from the computer 10, and performs closed-loop control, thereby
A / F can be optimally controlled.

As described above, according to the embodiment of the present invention, the air-fuel ratio can be continuously detected even in the lean region where the excess air ratio λ is λ> 1.0 or in the rich region where λ <1.0. The air-fuel ratio can be controlled, the air-fuel ratio can be controlled accurately during transient operation, and the CO concentration fluctuation during full-open operation can be reduced by closed-loop control, greatly reducing fuel consumption. Further, there is an effect that it is useful for achieving appropriate air-fuel ratio control even in the warm-up operation immediately after start-up, and is useful for reducing fuel consumption.

〔The invention's effect〕

According to the present invention, the air-fuel ratio from the lean region to the rich region can be measured with a simple configuration.

[Brief description of drawings]

1 and 2 are engine control system diagrams using the present invention, FIGS. 3 and 4 are explanatory diagrams of the operating principle of the present invention, and FIG.
FIG. 6 is a view showing an embodiment of the present invention, FIG. 6, FIG. 7, and FIG.
FIG. 9, FIG. 10, FIG. 10, FIG. 11 and FIG. 12 are explanatory views of an engine control system using the present invention. 11,41,45,48,68,69 …… Electrode, 40,46,67 …… Solid electrolyte, 42,70 …… Oris, 47 …… Measuring device.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-55-30681 (JP, A) JP-A-56-70457 (JP, A) JP-A-57-97439 (JP, A) JP-A-56- 130649 (JP, A) JP 58-153155 (JP, A) Actual development 58-130261 (JP, U)

Claims (1)

[Claims] 1. A first solid electrolyte having a first electrode provided on one surface and a second electrode provided on the other surface, and a third electrode provided on one surface. A second solid electrolyte having a fourth electrode provided on the other surface, and a second solid electrolyte provided between the first solid electrolyte and the second solid electrolyte, the first solid electrolyte and the second solid electrolyte being provided between the first solid electrolyte and the second solid electrolyte. An intermediate plate for independently arranging the second solid electrolyte, the first solid electrolyte, the second solid electrolyte, and the intermediate plate, and the first plate inside the first solid electrolyte.
And a third electrode, the diffusion chamber passing the exhaust gas through a diffusion resistor, and the third electrode for feeding oxygen in the exhaust gas into the diffusion chamber through the second solid electrolyte. An electric current obtained between the first electrode and the second electrode, comprising means for supplying a current to the fourth electrode and means for supplying a current from the first electrode to the second electrode. An air-fuel ratio detector characterized by detecting an air-fuel ratio by a signal.