JPS6115256B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for feedback controlling the amount of fuel supplied to an internal combustion engine based on a signal from an exhaust sensor.

Recently, as a method for purifying automobile exhaust gas, a fuel feedback control device has been put into practical use, which controls the air-fuel ratio of an air-fuel mixture by controlling the amount of fuel supplied in accordance with information regarding engine exhaust gas components.

FIG. 1 is a block diagram of an example of the above fuel feedback control device.

In Fig. 1, 1 is the engine, 2 is the exhaust pipe,
3 is an exhaust sensor installed in the exhaust pipe 2, 4 is an exhaust purification device, and 5 is a control device.

The control device 5 includes a fuel supply amount calculation section 6 and a feedback control section 7, and is configured by, for example, a microcomputer.

The exhaust sensor 3 outputs a signal _S2 depending on the oxygen concentration in the exhaust gas, for example.

The feedback control unit 7 determines whether the air-fuel ratio of the air-fuel mixture is larger or smaller than a set value (whether the air-fuel mixture is lean or rich) based on the signal _S2 , and performs a combination of both a proportional calculation and an integral calculation, for example. A control signal _S3 is output to increase the fuel supply amount when the fuel is lean, and to decrease it when the fuel is rich.

The fuel supply amount calculation unit 6 calculates the basic value of the fuel supply amount based on the operating status signal S ₁ (signal of intake air amount, rotation speed, engine temperature, etc.) given from various sensors installed in the engine 1. , corrects the basic value according to the control signal _S3 to calculate the actual fuel supply amount, and sends out the fuel supply amount signal _S4 . This fuel supply amount signal _S4 controls the fuel supply device (fuel injection valve or electronically controlled carburetor) in the engine 1, and by supplying the amount of fuel corresponding to the operating condition, the air-fuel ratio of the air-fuel mixture is adjusted. It is possible to maintain the desired value (hereinafter referred to as the set air-fuel ratio). Note that when a three-way catalyst device that simultaneously oxidizes CO and HC and reduces NOx is used as the exhaust purification device 4, the value of the set air-fuel ratio is set to a value near the stoichiometric air-fuel ratio (14.8).

Next, FIG. 2 is an output characteristic diagram of a zirconia oxygen meter (hereinafter referred to as an O ₂ sensor) which is generally used as the exhaust sensor 3.

As shown in the figure, the characteristics of the O ₂ sensor suddenly change step by step at a point near λ = 1 (the stoichiometric air-fuel ratio of 14.8 is set to λ = 1). It becomes a value signal. Therefore, it is very convenient to set the set air-fuel ratio to λ=1, but depending on the characteristics of the exhaust purification device 4, λ=1.
There are cases where it is desired to set the air-fuel ratio to an arbitrary point richer or leaner than 1.

As a method for setting the set air-fuel ratio to an arbitrary point, the applicant has already filed an application for two methods as shown in Figs.
52-81433), Japanese Patent Application No. 155768 (1982)
-81434))).

First, the method shown in Fig. 3 is to correct the deviation signal _S5 created by comparing the output of the _O2 sensor with a reference value using a comparator, and then adjust the center value of the control signal _S3 , that is, the set air-fuel ratio. It changes the value of .

In FIG. 3, the value of the set air-fuel ratio can be moved from a ₁ to a ₂ by modifying the time on the low level side (lean side) of the deviation signal S ₅ to be extended by T _D .

Next, in the method shown in FIG. 4, by changing the value of the integral constant in the integral calculation when increasing and decreasing, the slope β when the control signal S ₃ increases as shown in the figure.
The set air-fuel ratio value is moved from a ₁ to a ₂ by providing a difference between the gradient α and the gradient α during descent.

However, in the above method, the control signal
As the repetition period of S ₃ becomes longer (T ₁ < T ₂ , T ₃ < T ₄ ), the amplitude becomes larger (A ₁ < A ₂ , A ₃ < A ₄ ), so the fluctuation range of the air-fuel ratio becomes larger. Therefore, there is a risk that the purification function of the exhaust gas purification device will deteriorate.Also, if the control device as described above is configured with an analog circuit, the circuit configuration will be complicated, and even when controlled by a microcomputer, there is a risk that the calculations will be complicated. there were.

The present invention has been made in view of the above problem, and by configuring the proportional component in the control signal to have different values in the enriching direction and the diluting direction, the repetition period and the It is an object of the present invention to provide a fuel feedback control device that is easy to configure without increasing the amplitude.

The present invention will be explained in detail below based on the drawings.

FIG. 5 is a signal waveform diagram according to the method of the present invention.

In FIG. 5, τ is the delay time of the feedback control system, which is the time from when the fuel supply amount to the engine 1 is changed in the configuration shown in FIG. 1 until the result appears in the signal _S2 of the exhaust sensor 3. approximately corresponds to τ. Note that the value of τ changes depending on the operating condition of the engine (especially the rotational speed), but for the sake of explanation,
The figure illustrates the case where τ is constant.

Further, in the control signal S ₃ , the vertically increasing or decreasing portions, ie, P ₀ , P ₁ , and P ₂ are the proportional portions, and the portion having a predetermined slope is the integral portion.

In the present invention, the value of the set air-fuel ratio is changed by setting the above proportional value to different values in the enrichment direction (increase) and the dilution direction (decrease). .

That is, in Fig. 5, the set air-fuel ratio when the proportional component value is P ₀ (standard value, that is, the standard value when the air-fuel ratio is not deviated) in both the enrichment direction and the dilution direction is a ₁ In this case, P ₁ is the proportional value that changes the control signal to the lean side when the exhaust sensor signal changes from the lean side to the rich side, and the control signal when the signal changes from the rich side to the lean side. Let P ₂ be the proportional value that changes P to the over-concentrated side, and if P ₁ < P ₂ , then
The set air-fuel ratio becomes _a2 and moves in the direction of enrichment from _a1 . Note that if P ₁ <P ₂ , a ₂ moves in the direction of dilution compared to a ₁ .

Also, if you set 2P ₀ = P ₁ + P ₂ , the repetition period will not change (T ₅ = T ₆ ), and if you set 2P ₀ < P ₁ + P ₂ , the repetition period will become shorter (T ₅ > T ₆ ). You can also do that.
Furthermore, in either case, the amplitude of the control signal S ₃ does not become large (A ₅ =≧A ₆ ). Therefore, there is no fear that the fluctuation range of the air-fuel ratio will become large.

Next, FIG. 6 is an embodiment of a flowchart for calculating the above method using a computer, and FIG. 7 shows signal waveforms in the calculation of FIG. 6. Note that the control signal _S3 in FIG. 7 is a digital signal displayed in a stepped waveform.

The calculation in FIG. 6 is performed every fixed time period or every time the engine crankshaft rotates by a fixed angle. For example, _t1 to _t4 of _S3 in FIG. 7 each indicate the above-mentioned calculation start time.

In the flowchart of Figure 6, the block
The state of the air-fuel mixture is determined at L ₁ to L ₃ , and depending on the result, the integral 1 is added or subtracted from ALPHA (value of S ₃ ) for each calculation, and the air-fuel mixture is determined from lean to rich. When it changes from the rich side to the lean side, the proportional amount _P1 is subtracted, and when it changes from the rich side to the lean side, the proportional amount P1 is subtracted.
Add P ₂ .

The values of the above proportional portions P ₁ and P ₂ can be set to arbitrary values, and even if P ₁ < P ₂ , the configuration will not become particularly complicated. Therefore, if a microcomputer is used as the control device 5 in the device shown in FIG.
The present invention can be easily realized using the flowchart shown in FIG.

Next, FIG. 8 is a diagram showing an embodiment of the present invention when an analog circuit is used, and FIG. 9 is a signal waveform diagram of the circuit of FIG.

In FIG. 8, 8 is an operational amplifier, which together with a capacitor C ₁ and resistors R ₁ and R ₂ constitutes an integrating circuit. Further, V ₀ is a reference voltage.

9 is a switching signal generation circuit, which generates a deviation signal S ₅
It outputs a switching signal S ₆ which is triggered at the rising edge and falling edge of , and lasts for different lengths τ ₁ and τ ₂ , respectively.
This switching signal generating circuit 9 can be configured by combining, for example, a monostable multivibrator triggered by a rising edge, a monostable multivibrator triggered by a falling edge, and a circuit that outputs the sum of the outputs of both.

Further, 10 is a switching circuit, which is turned on while the switching signal _S6 is applied.

In the integration circuit described above, R ₁ << R ₂ and integration is performed extremely rapidly while the switching circuit 10 is on, so as shown in P ₁ and P ₂ in FIG. 9, it is almost the same as the proportional component. It becomes a waveform. Also P ₁
The magnitudes of and P ₂ are proportional to the time that the switching circuit 10 is on, that is, τ ₁ and τ ₂ . Therefore, if we change the values of τ ₁ and τ ₂ , we get
The values of P ₁ and P ₂ can be set arbitrarily.

As explained above, according to the present invention, the set air-fuel ratio can be set to an arbitrary value without increasing the repetition period or amplitude of the air-fuel ratio fluctuation, so that the exhaust purification device can be operated in an optimal state. This has the effect of improving exhaust purification performance.

[Brief explanation of the drawing]

FIG. 1 is an example of a fuel feedback control device to which the present invention is applied, FIG. 2 is an output characteristic diagram of an exhaust sensor, and FIG.
4 and 4 are signal waveform diagrams of the conventional method, FIG. 5 is a signal waveform diagram of the present invention, FIG. 6 is a flowchart of an embodiment of the present invention, and FIG. 7 is a signal according to the flowchart of FIG. 6. FIG. 8 is a circuit diagram of another embodiment of the present invention, and FIG. 9 is a signal waveform diagram of the circuit of FIG. 8. Explanation of symbols, 1...Engine, 2...Exhaust pipe,
3...Exhaust sensor, 4...Exhaust purification device, 5...
Control device, 6... Fuel supply amount calculation unit, 7... Feedback control unit, 8... Arithmetic amplifier, 9... Switching signal generation circuit, 10... Switching circuit.

Claims (1)

[Claims] 1. An exhaust sensor that detects the concentration of exhaust gas components of the engine, a control signal having at least a proportional control characteristic calculated based on the signal of the exhaust sensor, and a control signal that controls the engine by the control signal. In the fuel feedback control device, which includes a control means for correcting the fuel supply amount and controls the air-fuel ratio of the air-fuel mixture supplied to the engine to maintain the set air-fuel ratio, the signal from the exhaust sensor changes from the rich side to the lean side. The magnitude of the proportional component that changes the control signal in the direction of enrichment when it changes, and the magnitude of the proportional component that changes the control signal in the direction of dilution when it changes from the lean side to the over-concentrated side are set to different values. And if the standard value of the proportional component mentioned above is P ₀ , the value of the proportional component that changes in the direction of dilution is P ₁ , and the value of the proportional component that changes in the direction of enrichment is P ₂ , then P ₁ and P ₂ and
A fuel feedback control device characterized in that by setting a value that satisfies 2P ₀ ≦P ₁ +P ₂ , the value of a set air-fuel ratio is deviated without increasing the fluctuation width or repetition period of the air-fuel ratio. 2 A microcomputer is used as the control means, the signal of the exhaust sensor is sampled at a predetermined period, and a control signal is calculated according to the sample value, and when the signal of the exhaust sensor changes from the rich side to the lean side. The amount by which the control signal is changed in the direction of concentration when changing from the lean side to the rich side is set to different values, and the amount by which the control signal is changed in the direction of dilution when it changes from the lean side to the rich side are set to different values, and the above two amounts are added. 2. The fuel feedback control device according to claim 1, wherein the value is set to a value twice or more of a standard value.