JPH032655A - Air/fuel ratio sensor of internal combustion engine - Google Patents

Abstract

PURPOSE:To perform feedback control for the different air/fuel ratios in correspondence with the operating conditions by providing a plurality of detecting elements having the different characteristics, and connecting electrodes in series. CONSTITUTION:The characteristic of electromotive voltage which is generated between a first inner electrode 15A and a first outer electrode 15B of a first detecting element 1 becomes the characteristic as follows: the oxygen component of NOx is excellently detected by the NOx reduction action of the reducing catalyst particles in the NOx in a first electrode protecting layer 17; and the characteristic is suddenly changed at a point close to a theoretical air/fuel ratio when NOx is increased. On the contrary, the characteristic of the electromotive voltage generated between an inner electrode 16A and an outer electrode 16B in a second detecting element 13 becomes the characteristic as follows: the oxygen component of NOx is not detected as the concentration of oxygen is exhaust gas; and a point where the electromotive voltage is suddenly changed in correspondence with the increase in concentration of NOx is shifted to the lean side. Therefore the output voltage characteristic between the electrodes 15A and 16B at both ends of the part wherein the electrodes of the elements 12 and 13 are connected in series becomes the characteristic obtained by adding the individual electromotive voltage characteristics. Thus, the feedback control can be performed for the different air/fuel ratios in correspondence with the operating conditions at a low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an air-fuel ratio sensor for use in feedback control of an air-fuel ratio in an internal combustion engine.

<Prior Art> In internal combustion engines, as an exhaust purification measure, it has become common to have a three-way catalyst installed in the exhaust system that oxidizes Co and HC in the exhaust and reduces and purifies NOX.

The conversion efficiency (purification efficiency) of the three-way catalyst is set so that it functions effectively in the exhaust state during stoichiometric air-fuel ratio combustion.

Therefore, during normal operation other than during high-load operation where particularly high output is required, an air-fuel ratio sensor installed in the exhaust system detects the air-fuel ratio based on the exhaust characteristics, and controls the air-fuel ratio to near the stoichiometric air-fuel ratio. It is common practice to do so.

As a conventional example of the air-fuel ratio sensor for the internal combustion engine mentioned above,
There are some such as those shown in Publication No. 8-204365.

This tube has a platinum catalyst layer that promotes the oxidation reaction of Co and HC in the exhaust gas on the outer surface of a zirconia tube having oxygen ion conductivity that comes into contact with the exhaust gas. Then, when combustion is performed with a mixture richer than the stoichiometric air-fuel ratio, the low concentration of O2 remaining near the platinum catalyst layer is reacted favorably with Co and HC to bring the concentration close to zero, and the inner surface of the zirconia tube is A large electromotive force is generated between the inner and outer surfaces of the zirconia tube by increasing the concentration ratio to the 0□ concentration of the atmosphere with which it is in contact.

On the other hand, when combustion is performed with a mixture leaner than the stoichiometric air-fuel ratio, a high concentration of 0□ and a low concentration of Co and HC are present in the exhaust gas, so even if Co and HC react with 0□, there is still no 0□. □
The remainder is 0 on the inner and outer surfaces of the zirconia tube! The concentration ratio is small and almost no power is generated.

In this way, the electromotive force (output voltage) generated by the air-fuel ratio sensor has the characteristic of rapidly changing near the stoichiometric air-fuel ratio, and this output voltage VO2 is compared with the reference voltage (slice level) to determine the air-fuel ratio. Determines whether the fuel ratio is rich or lean relative to the stoichiometric air-fuel ratio.

For example, when the air-fuel ratio is lean (rich),
The feedback correction coefficient α, which is multiplied by the basic fuel injection amount T, which is set based on the engine's intake airflow itQ and engine speed N, corrected based on the engine temperature, etc., is gradually increased (decreased) by a predetermined integral constant of 1 minute. ), the fuel injection amount T
By increasing (decreasing) , the air-fuel ratio is controlled to be close to the stoichiometric air-fuel ratio.

<Problem to be solved by the invention> However, in such a conventional air-fuel ratio sensor,
The following problems occurred.

That is, the oxygen content in NO,l should originally be detected as the oxygen concentration in the exhaust gas, but since the air-fuel ratio sensor cannot detect this, the NOx concentration is high (
Indeed, the electromotive force is reversed on the lean side of the true stoichiometric air-fuel ratio, thereby controlling the air-fuel ratio to the lean side.

In addition, when using methanol etc., H2
Since a large amount of is present, the control point of the air-fuel ratio may shift to the lean side in this case as well.

In this way, if the control point is shifted to the lean side and the air-fuel ratio is controlled to be lean, fuel efficiency can be improved to a certain extent, which is actually a convenient control, but if the control point is shifted significantly to the lean side, the The NOx reduction function of the base catalyst is impaired and the amount of NOx generated increases significantly.

The present invention was developed in view of these conventional problems, and has the characteristic that the output characteristics change suddenly with different air-fuel ratios, thereby making it possible to perform feedback control to different air-fuel ratios depending on operating conditions. An object of the present invention is to provide an air-fuel ratio sensor for an internal combustion engine that can solve the above problems.

Means for Solving the Problems> Therefore, the present invention provides an air-fuel ratio sensor that detects an air-fuel ratio by a change in an electromotive force generated between electrodes of a detection element having a concentration battery function in response to the properties of exhaust gas. A plurality of detection elements having the characteristic that the electromotive force changes suddenly depending on the exhaust properties corresponding to different air-fuel ratios are integrally arranged in the sensor body, and the electrodes of each detection element are connected in series. The configuration is such that output is taken out from the electrodes at both ends.

<Operation> The output voltage characteristics from the electrodes of each detection element are such that the electromotive voltage changes suddenly depending on the exhaust gas characteristics corresponding to different air-fuel ratios.

Therefore, the output characteristic taken out from the electrodes at both ends of the electrodes of each detection element connected in series is such that the electromotive force changes suddenly in multiple stages in response to a change in the air-fuel ratio.

A plurality of air-fuel ratios can be detected by comparing the sudden change portions of the plurality of stages with the respective slice levels.

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

1 to 3 show a first embodiment of the present invention.

In the figure, first and second detection elements 12 and 13 are attached to the air-fuel ratio sensor 11 with a predetermined gap between them by an insulating member 14 made of alumina or the like. Each detection element 12.1
3, hollow air introduction chambers 12B and 13B are respectively formed by solid electrolyte members 12A and i3A mainly composed of, for example, zirconium oxide (ZrO□). 2 inner electrode 15
A, 16A, and first and second outer electrodes 15B which face these inner electrodes 15A, 16A via solid electrolyte members 12A, 13A and are in contact with the exhaust gas.

16B is formed. These electrodes are platinum (pt
) is formed. The first and second outer electrodes 15B
, 16B are covered with first and second electrode protection layers 17.18.

Here, the first outer electrode 15B on the first detection element 12 side
The first electrode protective layer 17 covering the electrode is made of, for example, gamma alumina (γ-Alz Ox), titanium oxide (TiO
Pt (platinum), Rh (rhodium), R
It is formed to have a NOx reduction function by mixing particles of at least one kind of catalyst that promotes the NOx reduction reaction, such as u (ruthenium) and Pd (palladium).

On the other hand, the second electrode protective layer 18 covering the second outer electrode 16B on the second detection element 13 side is formed of a magnesium spinel layer, similar to the conventional air-fuel ratio sensor.

And the first inner electrode 15A on the first detection element 12 side.

The first outer electrode 15B, the second inner electrode 16A on the second detection element 13 side, and the second outer electrode 16B are connected in series, and the electrodes at both ends of the series connection, that is, the first inner electrode 15A
Output is taken out from the second outer electrode 16B.

In the air-fuel ratio sensor 11 having such a structure, the first inner electrode 15A and the first outer electrode 15B of the first detection element 12
As shown by the solid line in Fig. 4, the electromotive force characteristic between the It is well detected and has a characteristic that changes suddenly at a point close to the stoichiometric air-fuel ratio even when NOx increases.

On the other hand, the electromotive force characteristic generated between the second inner electrode 16A and the second outer electrode 16B of the second detection element 13 is as shown by the dotted line in FIG. Since it has the protective layer 18, NOx
The oxygen content in the exhaust gas is not detected as the oxygen concentration in the exhaust gas, and NO
The point where the electromotive force suddenly changes as the x concentration increases is a characteristic that shifts to the lean side.

Therefore, the first detection element 12 and the second detection element 13
The first inner electrode 1 at both ends of the electrodes connected in series.
The output voltage characteristics between 5A and the second outer electrode 16B are the characteristics obtained by adding the above-mentioned individual electromotive voltage characteristics, and as shown in FIG. 5, when the air-fuel ratio is close to the stoichiometric air-fuel ratio and the NOx concentration is high, As the air-fuel ratio becomes leaner, the output voltage suddenly changes.

FIG. 6 shows the configuration of an air-fuel ratio control device for an internal combustion engine using the air-fuel ratio sensor 11 having such a configuration.

The intake passage 22 of the internal combustion engine 21 is provided with an air flow meter 23 that detects the intake air flow ilQ and a throttle valve 24 that controls the intake air flow rate Q in conjunction with the accelerator pedal. An electromagnetic fuel injection valve 25 is provided. The fuel injection valve 25 is driven to open by an injection pulse signal from a control unit 26 having a built-in microcomputer, and injects fuel that is pressure-fed from a fuel pump (not shown) and controlled to a predetermined pressure by a pressure regulator. Furthermore, a water temperature sensor 27 for detecting the temperature Tw of the cooling water in the cooling jacket of the engine 21 is provided, and the air-fuel ratio sensor 11 is provided in the exhaust passage 28, further downstream to detect CO in the exhaust gas.

A three-way catalyst 29 is provided that performs purification by oxidizing HC and reducing NOx. Further, the distributor (not shown) has a built-in crank angle sensor 30, and the crank angle unit angle signal outputted from the crank angle sensor 30 in synchronization with engine rotation is counted for a certain period of time, or the crank angle reference angle The engine rotation speed N is detected by measuring the period of the signal.

Next, the air-fuel ratio control routine by the control unit 26 will be explained according to the flowchart shown in FIG.

In step 1 (denoted as S in the figure), the amount of intake air per unit rotation is calculated based on the intake air flow IQ detected by the air flow meter 23 and the engine rotation speed N calculated from the signal from the crank angle sensor 30. The basic fuel injection amount T is calculated using the following equation.

f'P = K - Q/N (K is a constant) In step 2, various correction coefficients C0EF are set based on the water temperature Tw etc. detected by the water temperature sensor 27.

In step 3, an invalid injection pulse numerator is set based on the battery voltage value.

In step 4, it is determined whether the engine operating conditions are such that air-fuel ratio feedback control is performed.

If the above determination is YES, the process proceeds to step 5, where the engine speed N is set to a high predetermined value N (for example, 300 rpm).
Compare with m). Here, when the load is high, which is equal to or higher than the predetermined value N0, the exhaust gas temperature is high and the NOx concentration increases accordingly.

Then, when the Step 50 determination is N≧No,
That is, when the operating condition is such that the NOx'lA degree increases, the process proceeds to step 6, and the reference voltage SL, which is compared with the output voltage of the air-fuel ratio sensor 11, is detected at the air-fuel ratio at which the electromotive force of the first detection element 12 suddenly changes. Therefore, the relatively high value■. z
+ ('t1500mV).

In addition, if the Step 50 determination is N<No, that is,
Under operating conditions where the NOx concentration is at a level below the reference level, the process proceeds to step 7, where the reference voltage SL, which is compared with the output voltage of the air-fuel ratio sensor 11, is used to detect the air-fuel ratio at which the electromotive force of the second detection element 13 suddenly changes. Therefore, the relatively low value v02□(
#1500mV).

After passing through step 6 or step 7, the process proceeds to step 8, where the air-fuel ratio feedback correction is performed by increasing or decreasing the output voltage of the air-fuel ratio sensor 11 while comparing it with the reference voltage SL, which is set by changing the output voltage for each operating condition as described above. Set the coefficient α.

After passing through step 8, or if the determination in step 4 is NO
In this case, the process proceeds to step 9, and the final fuel injection amount T1 is calculated according to the following equation.

T+ = Tp -C0EF -a ten Ts Step 10
Now, the calculated fuel injection amount T is set in the output register.

As a result, when the predetermined fuel injection timing is synchronized with the engine rotation, a drive pulse signal having a pulse width of the calculated fuel injection amount T is applied to the fuel injection valve 25 to perform fuel injection.

During such control, during air-fuel ratio feedback control, NOx
Under operating conditions where the R degree is high, the air-fuel ratio is controlled to a value near the true stoichiometric air-fuel ratio by the air-fuel ratio feedback correction coefficient α, which is set by comparing the output voltage of the air-fuel ratio sensor 11 with the reference voltage VO2□. Therefore, the increase in NOx concentration can be suppressed.

Further, under conditions where the NOx concentration can be kept relatively low, the output voltage of the air-fuel ratio sensor 11 is set to the reference voltage ■. The air-fuel ratio is controlled by the air-fuel ratio feedback [coefficient α] which is set in comparison with 2°, so that the air-fuel ratio is shifted to a certain degree in accordance with the NOx concentration, thereby achieving air-fuel ratio control with good fuel efficiency.

In addition, since multiple air-fuel ratio control points can be switched with - number of air-fuel ratio sensors 11, the sensor installation space and wiring are the same as before, making it possible to implement at low cost and controlling only by switching the reference voltage. It's simple and easy.

FIG. 8 shows the configuration of an air-fuel ratio sensor according to a second embodiment of the present invention. However, the same elements as those in the first embodiment shown in FIGS. 1 to 3 are given the same reference numerals. omitted.

That is, the first and second inner electrodes 15A of the first and second detection elements 12.13 are placed at opposing positions in the single atmosphere introduction chamber 19.
, 16A are provided, and the atmosphere introduction chamber 19 is shared by the first and second detection elements 12.13. The electrode connection method is the same as in the first embodiment.

Even in this configuration, the same functions as those in the first embodiment can be obtained, and the sensor can be further miniaturized.

<Effects of the invention> As explained above, according to the invention, the air-fuel ratio sensor has a configuration in which a plurality of detection elements with different characteristics are provided in the sensor body and each electrode is connected in series. This allows for feedback control to different air-fuel ratios depending on operating conditions.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an air-fuel ratio sensor according to a first embodiment of the present invention, FIG. 2 is a cross-sectional view taken along the arrow ■-■ of the same, FIG. 3 is a left side view of the same, and FIG. A diagram showing the electromotive force characteristics of each detection element of the air-fuel ratio sensor as above, Fig. 5 is a diagram showing the output characteristics of the air-fuel ratio sensor as above, and Fig. 6 shows an air-fuel ratio control device using the air-fuel ratio sensor as above. As an example, FIG. 7 is a flowchart showing an air-fuel ratio control routine by the above device, and FIG. 8 is a diagram showing the configuration of an air-fuel ratio sensor according to a second embodiment. 11... Air-fuel ratio sensor 12... First detection element
12A, 13A... solid electrolyte member 12B,
13B, 19...Air introduction chamber 13...Second detection element 15A...First inner electrode 15B...
Second outer electrode 16A...first outer electrode 16B
...Second outer electrode patent applicant Fujio Sasashima, agent of Japan Electronics Co., Ltd., patent attorney

Claims (1)

[Claims] In an air-fuel ratio sensor that detects the air-fuel ratio by changes in the electromotive force generated between the electrodes of a detection element that has a concentration battery function in response to the characteristics of exhaust gas, a characteristic in which the electromotive force changes suddenly depending on the characteristics of the exhaust that corresponds to different air-fuel ratios. A plurality of detection elements having
In addition to being integrated into the sensor body, the electrodes of each detection element are connected in series, and the output is taken from the electrodes at both ends of the series connection, which allows the electromotive force to suddenly change in multiple stages in response to changes in the air-fuel ratio. An air-fuel ratio sensor for an internal combustion engine, characterized in that: