JPH02211345A - Air-fuel ratio controller for engine - Google Patents

Abstract

PURPOSE:To always secure the high control precision of air-fuel ratio by installing a differentiation values calculating means for calculating the differentiation value of the output signal of an air-fuel ratio sensor and a standard value correcting means for correcting the standard value according to the differentiation value. CONSTITUTION:When air-fuel ratio is reversed from lean to rich at the point (a), the output value O2 of an air-fuel ratio sensor 1 starts up in correspondence, and in this case, the differentiation value of the output value O2 is switched to the positive value, and the standard value SL changes to the value SLL1 slightly larger than the output value O21 in the case when lean state is detected, and the reversal to the rich state of air-fuel ratio in the initial stage of the starting-up of the output value O2 is detected at the point (b) by the comparison with the SLL1. Further, though the output value O2 of the sensor 1 starts down when the air-fuel ratio is reversed from rich to lean at the point (c), the differentiation value of the output value O2 is switched to the negative value, and the standard value SL is changed to the value SLH1 which is slighty smaller than the output value O22 in the case when rich state is detected, and the reversal to the lean state of the air-fuel ratio is detected at the initial stage of the starting-down of the output value O2 through the comparison with the value SLH1.

Description

Detailed Description of the Invention (Field of Industrial Application) This invention detects the air-fuel ratio from the exhaust gas components of an automobile engine, etc., and uses this detection signal to adjust the air-fuel ratio of the air-fuel mixture supplied to the engine to the target air-fuel ratio. This invention relates to a device that performs feedback control so that

(Prior art) There is a fuel injection system controlled by a microcomputer ("Automotive Engineering" published by Railway Former Headquarters, October 1985 issue, pages 28 to 40, January 1986 issue, No. 1)
(See pages 08 to 114, and pages 47 to 56 of ``Car Electronics'' by Hiroshi Hayashida, published by Taiga Publishing Co., Ltd.). Here, we will specifically explain fuel injection control. Based on input signals from various sensors, the microcomputer calculates the optimal injection amount according to the program stored in its memory, and adjusts the injection valve's deflection/idle coil according to the injection amount. The optimal injection amount is injected into the intake manifold by determining the energization time. In this case, the normal injection timing is, for example, once per engine revolution in the case of simultaneous injection in all cylinders, and the reference position signal from the crank angle sensor (120° signal for a 6-cylinder engine).
It is carried out based on. In other words, for a 6-cylinder engine, 12
A drive pulse is output to the injection valve at equal intervals once every three times the 0° signal is input.

The composition of the fuel injection amount is "basic injection amount + various increase correction amounts." However, by keeping the fuel pressure acting on the injection valve constant, the injection amount corresponds to the valve opening pulse width of the injection valve. Therefore, the injection pulse @(Ti) during normal operation is
It is calculated by the following formula (1).

"ri="l'9x (to t+: TW +KA 5 +
KA i+K MR)×a+T5
... (1) Here, the basic pulse width (Tp) is a value (equivalent to the basic injection amount) determined from the intake air amount (Q a) and the engine speed (Ne), and the air pressure determined by this Tp The fuel ratio is called the base air-fuel ratio.

1 (water temperature increase correction coefficient KTW, starting and post-start increase correction coefficient KA5 + post-idle increase correction coefficient K
AI + mixture ratio correction coefficient KMR) is a coefficient for increasing and correcting Tp according to various operating conditions input from sensors other than the air 70-meter (for example, K t W is a coefficient for increasing the amount of Tp due to a decrease in cooling water temperature (Tw) (introduced to enrich the mixture). The sum of these coefficients and 1 is expressed as various correction coefficients (Co).

a is an air-fuel ratio feedback correction coefficient, which is a value introduced in order to make the three-way catalyst function efficiently. Three-way catalyst generates three exhaust components (Co, HC, N).

In order to purify X), the air-fuel ratio of the mixture must be kept within a certain narrow range (this range is called a window) around the stoichiometric air-fuel ratio. This is because high feedback control is good.

Figure 8 shows a program for calculating this air-fuel ratio feedback correction coefficient α. (In the figure, it is abbreviated as "F/B control range."). Sl
If a is not in the feedback control range, a is clamped in S15. The program shown in the figure is executed, for example, at every predetermined crank angle.

The program shown in the figure shows an example of proportional-integral operation in which the control center of α is 1.0 and α changes periodically as shown in Figure 9. According to this operation, one cycle is equal to the following 4 It consists of two cases (i) to (iv).

That is, (i) When the air-fuel ratio is reversed from lean to rich, it is changed stepwise to the lean side by a proportional amount (PR).

(ii) Thereafter, it is gradually changed to the lean side by the integral (IR) while the rich continues.

On the other hand, (iii) when the air-fuel ratio is reversed from rich to lean, it is changed stepwise to the rich side by a proportional amount (PL).

(iv) Thereafter, it is gradually changed to the rich side in the integral (IL) while the lean continues.

That is what it is.

First, the above four cases (i) to (1v) are judged by comparing the output value of the air-fuel ratio sensor with the reference level (corresponding to the sensor output value for the stoichiometric air-fuel ratio) in S2, S3, and S9. This is done in combination with the size comparison done last time. "RLJ" in S3 and S9 is a flag that stores the result of the previous size comparison, and RL=R means that it was rich last time, and RL=L means that it was lean last time. , S2, S3, and S4 are the case when lean is reversed to rich.Similarly, when the rich continuation is to proceed to S2, S3, and S7, the process is to proceed to S2, S9, and SIO. If rich is reversed to lean, proceeding to S2, S9, and S13 is a case of lean continuation.Incidentally, immediately after the above-mentioned magnitude comparison is reversed, 7 lags after the reversal are in S4 and S10, respectively. value has been changed.

When the four cases are divided in this way, S5, S7, S1
1. In S13, calculate the proportional amount (PR and PL) according to each case.
and the integral (IR and IL) are calculated, S6, S8.81
2. In S14, the feedback correction coefficient (l) is calculated using these proportional and integral components. (i) to (iv) above
In terms of correspondence with (i), a=a-PRs (i
i>) if a=a −IR, if (iii) then α=α+PI, if (iv) then α=C1+I.

It is. Here, what these formulas mean is α
This means reading out the value stored as a, adding or subtracting the feelback correction amount to it, and storing the added or subtracted value again as a.

(Problem 8 to be Solved by the Invention) However, even if the air-fuel ratio is feedback-controlled in this way, if the air-fuel ratio sensor deteriorates due to changes over time, etc., errors will occur in the control.

In other words, when the air-fuel ratio sensor deteriorates, its output waveform will have a steeper falling slope when changing from rich to lean, as shown in Figure @10, compared to the output waveform that has not deteriorated.
When switching from lean to rich, the slope of the rise becomes gentler, so the timing at which the output of the air-fuel ratio sensor crosses a certain reference level (C8/L) is when the actual air-fuel ratio is too rich compared to before deterioration over time. It will be at the point when

As a result, with conventional control, it is inevitable that the air-fuel ratio becomes richer, and there is a problem in that Co and HC in the exhaust gas increase.

An object of the present invention is to provide an air-fuel ratio control device that solves the control error caused by the deterioration of the air-fuel ratio sensor.

(Means for Solving the Problems) As shown in the vJi diagram, the present invention includes an air-fuel ratio sensor 1 that detects an air-fuel ratio based on engine exhaust gas components, and compares the output signal of this air-fuel ratio sensor 1 with a reference value. Comparison method 2
, a correction calculation means 3 for calculating a feedback control amount according to the comparison result, and an air-fuel ratio control means 4 for controlling the air-fuel ratio to a target air-fuel ratio according to the feedback control amount, and the air-fuel ratio sensor A differential value calculating means 5 for calculating a differential value of the output signal of one output signal, and a reference value correcting means 6 for correcting the reference value according to this differential value are provided.

(Function) When the air-fuel ratio is reversed from rich to lean, the differential value of the output signal of the air-fuel ratio sensor 1 switches from positive to negative. Therefore, by increasing the reference value with which the output signal is compared at this time,
The lean air-fuel ratio is detected at the beginning of the fall of the output signal, which is not affected by deterioration, and when the air-fuel ratio is reversed from lean to rich, the reference value is detected when the differential value of the output signal changes from negative to positive. By lowering the value, the richness of the air-fuel ratio is detected at the beginning of the rise of the output signal, which is also not affected by deterioration, and thereby error-free air-fuel ratio control can be obtained.

(Embodiment) FIG. 2 shows a system diagram in which the present invention is applied to a fuel injection type engine 21. In the same figure, 24 is an air meter that outputs a signal according to the amount of air (Qa) taken in through the air cleaner, and the throttle valve 23
It is provided in the intake passage 22 upstream of the engine and functions as an engine load sensor.

25 is a sensor (crank angle sensor) that outputs a signal for each unit angle of the crank angle and a signal for each reference position, and the signal for each unit angle is sent to the control unit 40.
The engine rotational speed (Ne) is determined by counting at .

Reference numeral 26 denotes an air-fuel ratio sensor (oxygen concentration sensor) having a characteristic of rapidly changing the stoichiometric air-fuel ratio, and a signal from this sensor 26 is treated as an air-fuel ratio feedback control signal.

27 is a water temperature sensor, 28 is an idle switch, 29 is a knock sensor, 30 is a battery, 31 is a vehicle speed sensor, 32
is a key switch.

40 is a control unit into which signals from these sensors (24 to 30) are input, and this unit 40 increases or decreases the amount of fuel from the fuel injection valve 35 provided in the intake boat of each cylinder based on various operating variables. As a result, control is performed so that the target air-fuel ratio (theoretical air-fuel ratio) is obtained. For example, the basic pulse width T p (= K
/N e (K is a constant) and various coefficients (Co and Ts
) and the air-fuel ratio feedback correction coefficient α, the injection pulse 1lliii(
T i) is determined by the following formula.

Ti=TpXCoXQ+Ts...-(2
) However, α is the basic pulse width (
Tp), each coefficient in the various correction coefficients (Co) (for example, the water temperature increase correction coefficient KTW and the post-idle increase correction coefficient KA)
+), voltage correction amount (Ts), etc. are stored in the memory (R
Each is obtained by searching a table stored in the OM43).

Note that the control unit 40 simultaneously controls the ignition timing and the opening degree of the valve 37 for idle speed control (RSC).

Figure 3 1! This is a block configuration diagram when the control unit 40 is configured with a microcomputer, and the input/output interface 7. -x (Ilo) 41, CPU 42, ROM 4
3. RAM44, Ikuniy shi! I7 Consists of a RAM (BURAM) 45 that can retain stored information even when the key is turned off, and an A/D converter (ADC) 46 that converts analog signals t into digital signals among various signals, and each means 2 in FIG. It has ~6 functions.

FIG. 4 shows a program for calculating the air-fuel ratio feedback correction coefficient α, which is executed at every predetermined crank angle.

In FIG. 4, if the air-fuel ratio is in the feedback control range, the output value 02 of the air-fuel ratio sensor 26 is compared with a predetermined reference value SL at 5102, and if it is equal to or greater than the reference value SL, the output value 02 of the air-fuel ratio sensor 26 is compared with a predetermined reference value SL.
At 103, the process proceeds to 5104-5IO7, 5108-5111 according to the 7 lag RL (representing the previous comparison result),
If it is smaller than the reference value SL, 7 lag RL at 5112
The process advances to 5113-5116 and 8117-5120 accordingly.

That is, when the output value 02 of the air-fuel ratio sensor 26 becomes equal to or higher than the reference value SL (5LLI, which will be described later), the flag RL1.
: Set R (represents rich) and set SLL to standard value SL.
Instead of 1, a predetermined value 5LL2 is set.

This 5LL2 is set to approximately the same value as the sensor output value 02 at the time of lean detection (S104, 5105).

In this case, it is determined that the air-fuel ratio has reversed from lean to rich, so the proportional amount PR at the time of rich reversal is calculated, and the feedback correction coefficient α is determined by subtracting this proportional amount PR (810G, 5107).

After this reversal, the sensor output value 02 is compared with the previous output value 02G, and when it becomes lower than the previous output value 02G, that is, when the differential value of the sensor output value 02 becomes negative, the reference value SL is A predetermined value 5LHI is set in place of 5LL2. This 5LHI is set to a value somewhat smaller than the sensor output value 02 at the time of rich detection (S108,
5109).

Also, in this case, since the rich is continuing, the integral IR during the rich is being calculated, and the feedback correction coefficient a is obtained by subtracting this integral yR (S110.
5111).

Next, when the output value o2 of the air-fuel ratio sensor 26 becomes smaller than the reference value SL (the above-mentioned 5LHI), L (representing lean) is set in the 7 lag RL, and the predetermined value 5LH2 is set in the reference value SL instead of 5LHI. be done.

This 5LH2 is set to approximately the same value as the sensor output value 02 at the time of rich detection (Sl 13, 8114).

In this case, it is determined that the air-fuel ratio has reversed from rich to lean, so the proportional amount PL at the time of lean reversal is calculated, and the feedback correction coefficient α is determined by adding this proportional amount PL (S115.8116 ).

After this reversal, when the sensor output value o2 rises above the previous output value 02G, that is, when the differential value of the sensor output value 02 becomes positive, the predetermined value 5LLI is set to the reference value SL in place of the above-mentioned 5LH2. Ru. This 5LLI is set to a value somewhat larger than the sensor output value o2 at the time of lean detection (S117.8118). Further, in this case, since the lean engine is continuing, the integral IL during the lean engine is calculated, and the feedback correction coefficient α is determined by adding this integral ■L (S119, 5120).

Note that the proportional portion PR+PL and the integral portion IR, I- are calculated according to the engine speed, load, cooling water temperature, etc.

With this configuration, when the air-fuel ratio is reversed from lean to rich as shown in FIG. 5 (point a in the figure), the output value 02 of the air-fuel ratio sensor 26 rises in response.
In this case, the differential value of the output value 02 switches to positive, and the reference value SL
is 5L, which is somewhat larger than the output value 021 during lean detection.
Since the change is made to LI, a reversal of the air-fuel ratio to rich is detected at the beginning of the rise of the output value 02 by comparing it with 5LLI (the dot in the figure). In other words, a reversal to rich is detected in a region where the error due to deterioration of the air-fuel ratio sensor 26 is small (see FIG. 10), and this detection allows the proportional amount PR to be
Further, the air-fuel ratio is controlled to be lean in accordance with the integral IR.

Then, when the air-fuel ratio reverses from rich to rich (
(point C in the figure), the output value o2 of the air-fuel ratio sensor 26 falls, but in this case, the differential value of the output value 02 switches to negative, and the reference value S
L is somewhat smaller than the output value 022 when rich is detected 5
By comparing S L H1, a reversal of the air-fuel ratio to lean is detected at the beginning of the fall of the output value 02 (point d in the figure). As a result, a reversal to lean is detected in a region where the error due to deterioration of the air-fuel ratio sensor 26 is small during lean reversal, and by this detection, the air-fuel ratio is controlled to be rich in accordance with the proportional component PL and the integral component ■L. There is a possibility.

Therefore, even if the air-fuel ratio sensor 26 deteriorates, the air-fuel ratio will not become rich as in the conventional example, and the detected value 02 can quickly and accurately detect whether or not the air-fuel ratio is reversed. This makes it possible to maintain high air-fuel ratio control accuracy at all times, and ensure optimal exhaust emissions.

In addition, after detecting the reversal of the air-fuel ratio, change the reference value 5LLI to C in the diagram.
There is no need to change 5LHI to point a in the figure, but
As in this embodiment, after reversal detection, 5LL1 is set to S L L 2, which is smaller than this, and 5LHI is set to 5LH, which is larger than this.
By changing to 2, erroneous control due to noise can be prevented.

Furthermore, if there are variations in the air-fuel ratio between each cylinder of the engine, the output value of the air-fuel ratio sensor 26 will be 0 due to the exhaust from each cylinder.
2 has a waveform as shown in FIG. 7, which may cause an error in detecting the reversal of the air-fuel ratio. To prevent this, it is preferable to provide a low-pass filter 50 as shown in FIG. 6. 51~ in the figure
53 is a resistor for applying a predetermined bias voltage to the air-fuel ratio sensor 26, 54 is an amplifier, 55 is a normal band filter, and the low-pass filter 50 has a time constant of 200 +l1s.
It is set to pass signals below ec.

According to this, the output 02A of the air-fuel ratio sensor 26 that has passed through the low-pass filter 50 has a smoothed waveform as shown by the broken line in FIG. These average values can be detected from the average value, and a reversal of the air-fuel ratio can be accurately detected from the average value.

In this case, the control is as follows: The S117-02 chisel may be set as 02 A and used only for determining whether the air-fuel ratio is reversed.

(Effects of the Invention) As described above, according to the present invention, there is provided an air-fuel ratio sensor that detects the air-fuel ratio based on engine exhaust gas components, a comparison means that compares the output signal of the air-fuel ratio sensor with a reference value, and a comparison unit that compares the output signal of the air-fuel ratio sensor with a reference value. a correction calculation means for calculating a feedback control amount according to the result; 1. an air-fuel ratio control means for controlling the air-fuel ratio to a target air-fuel ratio according to the second feedback control amount, and a differential value calculation means for calculating a differential value of the output signal of the air-fuel ratio sensor; Since the reference value correction means for correcting the reference value is provided, the air-fuel ratio can be accurately detected regardless of the deterioration of the air-fuel ratio sensor.
Therefore, high control accuracy of the normal air-fuel ratio can be ensured, and optimum exhaust emissions can be ensured.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the present invention, Figs. 2 and 3 are cross-sectional views of the structure of an embodiment of the present invention and a block diagram of the control system, Fig. 4 is a flowchart showing control details, and Fig. 5 is a block diagram of the control system. Figures 6 and 7 are circuit diagrams of the low-pass filter and graphs showing their output waveforms. Figures 8 to 10 are conventional 70-charts, control characteristic diagrams, and output waveforms. This is a graph showing. 24... Air flow meter, 25... Crank angle sensor, 26... Air-fuel ratio sensor, 27... Water temperature sensor, 35... Fuel injection Jit valve, 40... Control unit, 50... low pass filter. Figure 5 Figure 6 Figure 7

Claims (1)

[Claims] an air-fuel ratio sensor that detects an air-fuel ratio based on engine exhaust gas components; a comparison unit that compares the output signal of the air-fuel ratio sensor with a reference value; and a correction calculation unit that calculates a feedback control amount according to the comparison result. an air-fuel ratio control means for controlling the air-fuel ratio to a target air-fuel ratio according to the feedback control amount; a differential value calculation means for calculating a differential value of the output signal of the air-fuel ratio sensor; An air-fuel ratio control device for an engine, comprising a reference value correction means for correcting the reference value.