JPH0788794B2 - Air-fuel ratio controller for engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an engine air-fuel ratio control device for controlling the air-fuel ratio of an air-fuel mixture supplied to an engine based on the oxygen concentration in exhaust gas. is there.

(Prior Art) Engines, particularly automobile engines, are often controlled to control the air-fuel ratio (primary air-fuel ratio) of the air-fuel mixture supplied to the engine based on the oxygen concentration in the exhaust gas. That is, it is common practice to arrange a three-way catalyst in the exhaust passage of the engine in order to remove harmful components in the exhaust gas. The air-fuel ratio (secondary air-fuel ratio) in the air needs to be the theoretical air-fuel ratio (air surplus ratio λ = 1). Therefore, the primary air-fuel ratio can be feedback-controlled based on the oxygen concentration in the exhaust gas. Has been done.

Further, recently, even when performing lean operation with an air-fuel ratio higher than the theoretical air-fuel ratio or rich operation with an air-fuel ratio less than the stoichiometric air-fuel ratio, the exhaust gas should be kept at this predetermined lean or rich. It is also strongly desired to perform feedback control of the primary air-fuel ratio based on the oxygen concentration of.

As described above, in order to perform feedback control of the air-fuel ratio based on the oxygen concentration in exhaust gas, it is first necessary to detect the oxygen concentration itself in this exhaust gas. As an oxygen sensor that detects the oxygen concentration in such exhaust gas, there is a sensor known as a so-called lean sensor that can detect over a relatively wide range of air-fuel ratio, but this is mainly composed of zirconia. Since platinum is used for the electrodes, the cost is extremely high, and a considerably large circuit is also required as a circuit for extracting the output.

Therefore, it has been proposed to use a semiconductor (metal oxide semiconductor) as an oxygen sensor (Japanese Patent Publication No. 57-37824).
(See Japanese Patent Publication). That is, since the resistance value of the metal oxide semiconductor changes according to the change of the oxygen concentration, the change of the resistance value can be grasped as a voltage with a very simple circuit, and the cost is extremely low and the size is very small. Therefore, there are great expectations for oxygen sensors in the future.

(Problems to be Solved by the Invention) By the way, when the oxygen sensor is composed of a metal oxide semiconductor, due to the characteristics of the metal oxide semiconductor, only one metal oxide semiconductor has a wide range of required space. It becomes difficult to effectively detect the oxygen concentration with respect to the fuel ratio, and some measure is desired in this respect.

Explaining this point in detail, a p-type metal oxide semiconductor,
The n-type is well known, but if the p-type is appropriate in a certain air-fuel ratio range, the p-type cannot be optimally handled in other air-fuel ratio ranges. (Same for n type), over a wide range of air-fuel ratio,
It becomes difficult to perform feedback control of the air-fuel ratio of the air-fuel mixture supplied to the engine due to the output of the oxygen sensor using the metal oxide semiconductor. That is, as the output characteristics of the oxygen sensor, therefore, the object of the present invention is to provide the oxygen concentration in the exhaust gas over a wide range of the air-fuel ratio even when the oxygen sensor is configured by using a metal oxide semiconductor. It is an object of the present invention to provide an engine air-fuel ratio control device capable of accurately controlling the air-fuel ratio of the air-fuel mixture supplied to the engine in accordance with the engine operating state.

(Means and Actions for Solving Problems) In order to achieve the above-mentioned object, in the present invention, an oxygen sensor is constituted by using both n-type and p-type metal oxide semiconductors, By using both of these metal oxide semiconductors, the first value that is the output value from the n-type metal oxide semiconductor, the second value that is the output value from the p-type metal oxide semiconductor, and the The optimum value according to the operating condition of the engine, that is, the required air-fuel ratio, is selected from among at least two values out of the three values of the combined value obtained by combining both the first and second values, that is, the third value. The air-fuel ratio of the air-fuel mixture supplied to the engine is controlled based on the selected value.

With such a configuration, it becomes possible to accurately detect the oxygen concentration even in an inappropriate air-fuel ratio range when the n-type or p-type metal oxide semiconductor is used alone, and the oxygen concentration is supplied to the engine. It is possible to accurately control the air-fuel ratio of the air-fuel mixture that operates.

Further, in the present invention, the p-type metal oxide semiconductor is compared with the n-type metal oxygen semiconductor in consideration of the fact that the control of the air-fuel ratio is desired to be performed with good response during the transient state when the engine operating state changes. And its responsiveness is extremely good,
In consideration of the fact that the output characteristics change in all regions of lean, rich, and stoichiometric air-fuel ratio, the output value from this p-type metal-oxygen semiconductor is preferentially set to the air-fuel ratio during this transition time. It is used for control.

Specifically, as shown in FIG. 8, it is composed of a first detection piece made of an n-type metal oxide semiconductor and a second detection piece made of a p-type metal oxide semiconductor, and determines the oxygen concentration in the exhaust gas. An oxygen sensor for detecting, a fuel supply means for supplying fuel to the engine, a transient time detecting means for detecting whether or not the engine operating state is changing, and an oxygen sensor and a transient time detecting means. Of the output value of the first detection piece, the output value of the second detection piece, and the combined value of the output values of the both detection pieces, and outputs one value from the engine. The fuel supply means based on the value selected by the selecting means and the selecting means for giving priority to the output value of the second detection piece when the engine is in transition, and controlling the fuel supply means based on the value selected by the selecting means. The air-fuel mixture supplied to the engine It is constituted with the air-fuel ratio control means for controlling the ratio of.

(Example) Hereinafter, an example of the present invention will be described with reference to the accompanying drawings.

In FIG. 1, reference numeral 1 designates an engine body, which is an intake port 4 opening to a combustion chamber 3 defined by a piston 2 by an intake valve 5 and an exhaust port 6 opening to the combustion chamber 3 an exhaust valve 7. Thus, the reciprocating type is opened and closed at a known timing.

In the intake passage 8 connected to the intake port 4, an air cleaner 9, an intake temperature sensor 10 for detecting the temperature of intake air, a flap type air flow sensor 11 for detecting the intake air amount, a throttle valve 12, in order from the upstream side thereof. An intake negative pressure sensor 13 for detecting an intake negative pressure as an engine load and a fuel injection valve 14 as a fuel supply device are provided. Also,
In the exhaust passage 15 connected to the exhaust port 6, an oxygen sensor 16 and a three-way catalyst 17 are sequentially arranged from the upstream side.

In FIG. 1, reference numeral 18 denotes a control unit composed of a microcomputer. The control unit 18 receives the signals from the sensors 10, 11, 13 and 16 described above, and an engine from an igniter 19. A pulse signal corresponding to the rotation speed and a signal from the throttle sensor 26 that detects the throttle opening are input. The control unit 18 also outputs a signal corresponding to the fuel injection amount to the fuel injection valve 14 and an ignition timing signal to the igniter 19 as is well known.

The oxygen sensor 16 includes a first detection piece 21 made of an n-type metal oxide semiconductor and a second detection piece made of a p-type metal oxide semiconductor.
22 and the three output values from the two detection pieces 21 and 22 and the combined value of the both output values are input to the control unit 18, and the two detection pieces 21 and 22 are connected to each other. A heater 20 for maintaining a predetermined activation temperature is additionally provided.

The resistance values of the two detection pieces 21 and 22 change according to the change of oxygen concentration, and the change of the resistance value is shown in FIG. 3 together with the combined value (“difference” in the embodiment). Is used to extract the voltage value. That is, with respect to the constant voltage source 23 (constant voltage Vc), the first detection piece 21
And the resistor 24 are connected in series, the second detection piece 21 and the resistor 24 are also connected in series to form a bridge circuit, and the change in the resistance value of the first detection piece 21 is set to Vsen, Further, the change in the resistance value of the second detection piece 22 is set as Vref, and the combined value Vout of the two is set as Vref−Vsen, that is, “difference”, and each is converted into a voltage and taken out.

FIG. 2 shows how the output values (voltage values) Vsen, Vref, and Vout described above change in response to changes in the air surplus ratio λ in the exhaust gas. As is clear from Fig. 2, Vs
As shown by the broken line in FIG. 2, en shows a large drooping characteristic when the air surplus ratio λ = 1 (at the stoichiometric air-fuel ratio), and λ is 1
It becomes smaller as it becomes larger (becomes leaner), and when λ becomes smaller than 1 (becomes richer), it shows a constant output value + Vc. Further, Vref shows a small drooping characteristic at λ = 1 as shown by the alternate long and short dash line in FIG.
Becomes larger as becomes larger than 1, and becomes larger as λ becomes smaller than 1. Furthermore, the composite value Vout is
As shown by the solid line in FIG. As is apparent from FIG. 2, the air-fuel ratio control by the air surplus ratio λ = 1, that is, the precise control for exhaust gas purification using the three-way catalyst 18 is performed by the first n-type metal oxide semiconductor. It is advantageous to use the output value (Vsen) of the detection piece 21 because the output greatly changes at the boundary of λ = 1. In addition, the air surplus ratio λ
In the lean region where is larger than 1, the output values Vsen and Vref of both the detection pieces 21 and 22 themselves made of a p-type or n-type metal oxide semiconductor have a small change rate with respect to the change of the air surplus rate λ, but Since the combined value Vout of the two has a large change rate with respect to the change of λ, it is advantageous to use the combined value Vout in this lean region. Furthermore, the air surplus rate λ
In the rich region where is less than 1, both Vref and Vout have a large change ratio with respect to the change of the air surplus ratio λ, so either can be used, but since the output voltage of Vout changes to the “−” side, In order to avoid the processing for this, it is advantageous to use the output value (Vref) of the second detection piece 22. As is apparent from FIG. 2, the output characteristic of the second sensing piece 22 made of the p-type metal oxygen semiconductor changes over the entire range of the air surplus ratio, so that the preferable value described above is used. Apart from this, it is also understood that it is possible to detect the entire range of the air surplus ratio λ by the second detection piece 22.

The metal oxide semiconductor forming the both sensing pieces 21 and 22 as described above is, for example, BaSnO ₃ as an n-type.
-Δ (δ = non-stoichiometric parameter) as the main component, and p-type as TiSrO ₃ -δ as the main component, and SiO ₂ or Al ₂ O ₃ additive to these main components What added is sufficient.

Various other materials can be used as the metal oxide semiconductor. For example, n-type semiconductors include TiO ₂ and Nb ₂ O ₅ ,
Examples of p-type semiconductors include C ₀ O, LaC ₀ O ₃ , and FrFeO ₃ . However, among these, BaSnO ₃ and TiSrO ₃ are materials having high oxygen sensitivity and excellent resistance stability over time. Furthermore, the characteristic that the output increases when the air-fuel ratio is rich and decreases, is also generated in p-type semiconductors other than TiSrO ₃ ,
O ₃ is the most prominent.

Now, next, an example in the case of performing feedback control of the air-fuel ratio of the air-fuel mixture supplied to the engine by the control unit 18 using the oxygen sensor 16, will be described based on FIG. 4A, FIG. 4B, the above description. As is clear from the above, in the embodiment, the output value Vsen of the first detection piece 21 is used when the air surplus ratio λ = 1, and the combined value is used in the lean region where λ is larger than 1.
While using Vout and assuming that the output value Vref of the second detection piece 22 is used in the rich region where λ is smaller than 1, Vref is preferentially used during the transient time when the operating state of the engine changes, and intake is performed. The amount of fuel is adjusted with respect to the amount of air. Further, whether or not it is a transitional time during which the operating state of the engine changes is determined depending on whether or not the change in the throttle opening is a predetermined value or more.

Assuming the above, in step S0, each flag Fz, Fr, Fl is set to O, and the feedback coefficient Cfb is set to 1.
To initialize. In addition, the calculation of the basic fuel amount is performed using a timer (basic timer) that is commonly used.
Due to the fact that the process is performed before the loop is rotated, the basic timer is reset in step S1, that is, the basic timer starts counting, and then in step S2, the throttle opening θ ₀ is read in order to detect the transient state of the engine. Then, in step S3, after confirming that the set time by the basic timer has elapsed, the basic timer is reset again in step S4.

After step S4, in step S5, the value measured by the air flow sensor 11 is temperature-corrected to calculate the intake air amount Ue, and then in step S6, the engine speed Ne is calculated from the pulse signal from the igniter 19. . Then, in step S7, a target air-fuel ratio TAF according to the engine operating state is obtained from a predetermined map (table) created in advance from the intake air amount Ue and the engine speed Ne. That is, in the embodiment, the air-fuel ratio at which the engine is operated is determined in advance according to the engine operating state with the intake air amount Ue and the engine speed Ne as parameters.

Then, in step S8, the throttle opening θ ₁ is read again, and in step S9, the difference θ ₁ between the throttle opening θ ₁ read this time and the throttle opening θ ₀ read last time (step S2). It is determined whether −θ ₀ is greater than or equal to a predetermined value θm set in advance. If it is determined that the change in the throttle opening is less than or equal to the predetermined value θm, it is not during the engine transient, but in step S10.
At, it is determined whether the target air-fuel ratio TAF is rich (less than λ = 1), and when TAF is in the second rich region, as the output value Vs from the oxygen sensor 16,
The output value Vref of the second detection piece 22 is input (step S1
0, 11). In step S10, the target air-fuel ratio T
If it is determined that the AF is not in the rich region, step S1
In step 2, it is determined whether or not the current rich region is present. If the current rich region is not present, the process proceeds to step S13. In this step S13, it is determined whether or not the target air-fuel ratio TAF is in the lean region, and when it is in the lean region, the combined value Vout is input as the output value Vs from the oxygen sensor 16 (step S14). . Further, when the target air-fuel ratio TAF is λ = 1, that is, the stoichiometric air-fuel ratio, the output value Vs from the oxygen sensor 16 is the first n-type metal oxide semiconductor.
The output value Vsen of the detection piece 21 is input (step S15).

On the other hand, when it is determined in step S9 that the amount of change in the throttle opening is equal to or greater than the predetermined value θm, it is determined that it is a transient time, the process proceeds to step S17, and the output value of the oxygen sensor 16 is p-type. Second detection piece 22 made of metal oxygen semiconductor
The output value Vref of is set. Similarly, step S12
When it is determined that the current region is the rich region, λ
= 1 or the time of transition to the lean region, the process also proceeds to step S17 at this time and Vref is set as Vs.

FIG. 7 shows the difference in response speed between the detection pieces 21 and 22 including the relationship with temperature. In FIG. 7, the response of the first detection piece 21 made of an n-type metal oxygen semiconductor is shown. Speed,
The time from rich to lean is indicated by Y1, the time from lean to rich is indicated by Y2, and the response speed of the second detection piece 22 made of a p-type metal oxygen semiconductor is indicated by X1 from rich to lean. The time from lean to rich is indicated by X2. As is apparent from FIG. 7, the response speed of the second detection piece 22 made of the p-type metal oxygen semiconductor is significantly faster than that of the first detection piece 21 made of the n-type metal oxygen semiconductor. To be understood.

After each of steps S11, 14, and 15 described above, in step S16, and in step S18 after step S17, the slice level median value VSL with respect to the target air-fuel ratio TAF is respectively determined by a predetermined map (
Or) and the target air-fuel ratio T
Various control gains for AF (constant for feedback) Vh
l, Vhr, tdl, tdr, Csl, Csr, Cl, Cr are required.
The meaning of each of the above control gains is schematically shown in the fifth
The fuel injection interval τ shown in FIGS. 5A and 5B and shown in FIG. 5 corresponds to the fuel injection amount. In addition, step
The maps used in S16 and step S17 are different because one (step S16) is during steady operation and the other (step S17) is during transition (when the air-fuel ratio region changes). To deal with.

After this, the selected output value (composite value) Vsen, Vref, Vout
Based on either of the above, the fuel injection (time τ) is corrected in a known manner, and this corrected amount of fuel is injected from the fuel injection valve 14 at a predetermined timing. The control example will be described with reference to FIG. 4B showing the common processing after steps S16 and 18 in FIG. 4A, focusing on the lean region where the air surplus ratio λ is larger than 1.

First, in step S41, the flag Fz is determined. This flag Fz indicates whether the present is leaner or richer than the target air-fuel ratio TAF, and when Fz = "0" is leaner, , "1" is rich. When this flag Fz is "0", that is, leaner than the target air-fuel ratio TAF, at step S42, the feedback of VSL-Vhl obtained by subtracting the control gain Vhl from the slice level median value VSL is changed from lean to rich. After setting as the target value V'SL, in step S43, Vs-V'SL
It is determined whether or not ≧ O. Of course, Vs at this time is
In the description, since the combined value Vout is input as the output of the oxygen sensor 16 on the premise of a lean region where the air surplus ratio λ is larger than 1, it means that the larger Vs is, the leaner the fuel is.
Therefore, when it is determined that Vs−V′SL ≧ O, it is assumed that the target value is lean at present, and the control for correcting the air-fuel ratio toward the smaller value (the air-fuel mixture becomes richer). Is done. That is, the flag Fz is once determined in step S44, but since it is initially 0, the process moves to step S45 and the flag Fz is determined. This flag F
r is for distinguishing whether or not the delay for delaying the transition processing from the lean to the rich for the predetermined time (tdr) in FIG. 5 (b) is being performed, and "1" is during the delay and "0" is during the delay. It means when it's not inside. And initially Fr
Is not 1, so this flag Fr is set to 1 in step S46.
After that, the delay timer is reset in step S48, that is, the delay timer starts counting. After that, in step S48, it is determined whether or not the delay is being performed, that is, the set time by the delay timer.
If it is determined whether tdr has elapsed, and if the delay time tdr has not elapsed, the feedback coefficient Cfb is newly set in step S49 as a value obtained by adding a predetermined control gain Cl to the previous feedback coefficient Cfb. To do. Then, after this, the newly set feedback coefficient Cfb
Based on, the fuel injection time τ is calculated in step S51.
The expression K shown in step S51 is a constant. In this way, the route of step S49 (Fig. 5 (b))
Is also a process of enrichment in which the air-fuel ratio of the air-fuel mixture supplied to the engine is gradually reduced.

In this way, the air-fuel ratio of the air-fuel mixture supplied to the engine is gradually reduced (gradually enriched), but if it comes to step S45 again in this process, the flag Fr is converted to 1 through step S46 before. Therefore, after step S45 to step S48 and the delay time tdr elapses, that is, when Vs becomes smaller than V'SL (VSL-Vhl) (enriched sufficiently), Go from step S48 to step S50, where flag Fz is set to 1 and F
After setting r to O, the feedback coefficient Cfb is set as a new feedback coefficient Cfb by subtracting a predetermined control gain Csr from the previous feedback coefficient Cfb,
After this, the process of step S51 described above is performed. Route of going through this step S51 (see also Fig. 5 (b))
Is an initial process when the enrichment is completed and the lean enrichment is performed in the future.

As described above, when the leaner than the target air-fuel ratio TAF, the enrichment process for the target air-fuel ratio TAF is performed.

On the other hand, the process for leaning when the air-fuel ratio is richer than the target air-fuel ratio TAF is the route from step S41 to step S51, but instead of performing lean-to-leach as described above, the process from lean-to-lean is performed. Since it is only performed, the step corresponding to the description of each step described above is denoted by “′” and the description thereof is omitted. In addition,
In the process from rich to lean, the route through step S49 ′ corresponding to step S49 and step S51
The route of passing through step S51 'corresponding to is shown in FIG. 5 (b).

FIG. 6 shows another embodiment of the present invention.
(Vsen) and 22 (Vref) as a composite value of the two "ratio"
That is, Vsen / Vref is used as the combined value Vou. In this case, the combined value Vout of the “ratio” is Vs
A characteristic similar to the above-described embodiment, which is the “difference” between en and Vref, is obtained. Then, the composite value Vout by this "ratio" is
Since the circuit configuration becomes complicated when calculated in terms of electric circuits,
As shown in FIG. 6, it is calculated. That is, in this embodiment, the steps in FIG.
The route from S13 to step S14 has been changed due to the above calculation. Explaining such an arithmetic processing part, when it is determined in step S13 that the target air-fuel ratio TAF is in the lean region larger than the air surplus ratio λ = 1, the output values Vsen of both the detection pieces 21 and 22, Vref is sequentially read (steps S31 and 32), and the combined value Vout as the "ratio" is calculated based on the read values (step S33). And finally, the composite value Vout calculated above
Is set as the output Vs of the oxygen sensor 16. The control in the other parts is the same as in the case of the above-mentioned embodiment, and the explanation thereof is omitted.

Although the embodiment has been described above, the present invention is not limited to this, and includes the following cases, for example.

Output value Vse of both detection pieces 21 and 22 that make up the oxygen sensor 16
Instead of using all three values of n, Vref and their combined value Vout, two of these three values may be used separately. For example, when the air-fuel ratio feedback control is not performed in the rich region where the air surplus ratio λ is smaller than 1, it is sufficient to use these two values properly.

When the control unit 18 is composed of a microcomputer, it may be digital type or analog type.

As the fuel supply device, a carburetor may be used instead of the fuel injection valve 14, and in this case, the air-fuel ratio may be adjusted by adjusting the jet (including the air jet).

After all, in the determination of step S9, the degree of acceleration is to be seen, but it is also possible to see the time of deceleration by comparing the absolute value of θ ₁ −θ ₀ with θm.

The engine transient can be detected by observing an appropriate behavior change such as a change in intake pressure.

(Effects of the Invention) As is apparent from the above description, the present invention makes use of this oxygen sensor over a wide range of changes in the air-fuel ratio in the exhaust gas while the oxygen sensor is made of a metal oxide semiconductor. It is possible to accurately detect the oxygen concentration of, and as a result, it is possible to accurately control the air-fuel ratio of the air-fuel mixture supplied to the engine.

Further, according to the present invention, based on the output value of the second detection piece made of a p-type metal-oxygen semiconductor having an extremely excellent responsiveness, in a transient time when the operating state of the engine is required to be highly responsive, the transient state is changed. So that the air-fuel ratio control is performed.
The air-fuel ratio control during this transition can be performed more accurately than when the open-loop control is simply performed.

[Brief description of drawings]

FIG. 1 is an overall system diagram showing an embodiment of the present invention. FIG. 2 is a characteristic diagram showing output characteristics of both detection pieces constituting the oxygen sensor and their combined characteristics. FIG. 3 is an electric circuit diagram showing an example of a circuit for extracting an output from the oxygen sensor. 4A and 4B are flowcharts showing an example of air-fuel ratio control according to the present invention. FIG. 5 is a diagram schematically showing an example of feedback control so that a target air-fuel ratio is achieved. FIG. 6 is a flowchart showing the main part of another control example according to the present invention. FIG. 7 is a graph showing the relationship of the response speed with respect to the temperature of each of the n-type and p-type metal oxygen semiconductors. FIG. 8 is an overall configuration diagram of the present invention. 8: Intake passage 14: Fuel injection valve 15: Exhaust passage 16: Oxygen sensor 17: Three-way catalyst 18: Control unit 21: First detection piece 22: Second detection piece 26: Throttle sensor (for transient detection)

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kazufumi Hirata 3-1, Shinchi Fuchu-cho, Aki-gun, Hiroshima Prefecture Mazda Co., Ltd. Giken Co., Ltd. (56) References Japanese Patent Publication Sho 57-37824 (JP, B2)

Claims (1)

[Claims] 1. An oxygen sensor for detecting the oxygen concentration in exhaust gas, comprising an first detection piece made of an n-type metal oxide semiconductor and a second detection piece made of a p-type metal oxide semiconductor, and an engine. The fuel supply means for supplying fuel, the transient time detection means for detecting whether or not it is a transient time when the operating state of the engine changes, and the outputs from the oxygen sensor and the transient time detection means, One of the output values of the detection piece, the output value of the second detection piece, and the combined value of the output values of both detection pieces is selected according to the operating state of the engine. On the other hand, when the engine is in transition, the selection means for preferentially selecting the output value of the second detection piece, and the fuel supply means based on the value selected by the selection means are controlled so as to control the air-fuel mixture to be supplied to the engine. Air-fuel ratio control that controls the air-fuel ratio An air-fuel ratio control device for an engine, comprising: