JPH0295744A - Air-fuel ratio controller for engine - Google Patents

Abstract

PURPOSE:To check any hunting at stationary time by measuring an elapsed time after reversal at each time a magnitude relationship between an air-fuel ratio detected and a desired air-fuel ratio is reversed, and according to this measured value, setting an integration constant so as to cause an integral portion to be varied at the stationary time and transient time. CONSTITUTION:In this controller, there is provided with a means 5 which measures a deviation EROR between an air-fuel ratio detected by an air-fuel ratio sensor 4 and a preset desired air-fuel ratio, and whether a magnitude relationship between both these air-fuel ratios is reversed or not is judging means 6. In addition, elapsed time after reversal is measured at each time the reversal is judged, or there is provided with a means 7 which integrates an intake air quantity after reversal, and such an integration constant K1 that is small till the specified time elapses or the specified intake air quantity is integrated and then grows larger is set up by a setting means 8. Then, a feedback compensation value alpha of the air-fuel ratio inclusive of at least an integral portion being calculated out of this integration constant K1 and the said deviation ERROR is calculated by a feedback compensation value calculating means 9, and a fundamental injection quantity Tp is compensated by this compensation value alpha, thereby determining a fuel injection quantity Ti by a fuel injection quantity decision means 10.

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 a target air-fuel ratio. The present invention relates to a device that performs feedback control to adjust the fuel ratio.

(Prior art) A fuel injection system controlled by a microcomputer is
It has been recognized that the performance is much higher than that of conventional carburetor systems, and the high precision with which this system controls the air-fuel ratio of the air-fuel mixture has resulted in exhaust gases that have come to be strictly regulated in Japan. This completely matches the needs for technology to suppress harmful components inside engines, and the use of electronics in important parts of engine control is remarkable.

Although the control content is multi-functional, it has fewer components and is smaller, and if you create and store programs according to the desired control function, you can freely use it. It is also possible to extend its functionality,
This can sometimes be done by changing only the program while leaving the computer as it is. In addition, since it is possible to store the necessary data for control, the optimal control obtained in advance in the laboratory can be executed as is without compromise, and this is especially true for the engine. Leading to higher performance (Automobile Engineering, published by Railway Japan Co., Ltd., October 1985 issue, pages 28-40, 19)
January 1986 issue, pages 108 to 114, and published by Taiga Publishing Co., Ltd. (see Car Electronics J, Hiroshi Hayashida, pages 47 to 56).

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, based on a reference position signal from a crank angle sensor (120° signal for a 6-cylinder engine). In other words, in a six-cylinder engine, a drive pulse is outputted to the injection valve at equal intervals once every three times the 120° 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 width (T i ) during normal operation is calculated by the following equation (1).

Ti=Tpx(i 10KTW+KAS+KA1+K
v+<) , the air-fuel ratio determined by this Tp is called the base air-fuel ratio.

1 (water temperature increase correction coefficient KTW + starting and post-start increase correction coefficient KAs, post-idling increase correction coefficient K
AI + mixture ratio correction coefficient KIJR) is adjusted according to various operating conditions input from sensors other than the air 70-7-ta.
l) is a coefficient for increasing correction (for example, KTW
is introduced to enrich the air-fuel mixture as the cooling water temperature (Tw) decreases, and works from below 60°C, and above 10°C, the increase correction amount is determined by the difference between ON and OFF of the idle contact) . The sum of these coefficients and 1 is the various correction amount 'P
It is expressed as i(CO). RFC is the phenyl cut coefficient.

α is a feedback correction coefficient for the air-fuel ratio, and is a value introduced to make the three-way catalyst function efficiently. A three-way catalyst generates three exhaust components (CO, HC, N).

In order to purify all This is because feed puncture control with high control accuracy is preferred.

Figure 12 shows a program for calculating this feedback correction coefficient α. This is a case where the following is satisfied. In the figure, the process is started when it is determined that 1'-F,/B control area is satisfied. If Sl is not in the feedback control area, S
At 15, α hits Franz. The program shown in the figure is executed, for example, at every predetermined crank angle.

The program in the same figure shows an example of proportional-integral operation in which the control center of α is 1.0 and parentheses a change periodically as shown in the lower part of Figure 13. According to this operation, one period is the next 4
(iv).

(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), (i
i) Thereafter, the integral (IR) is gradually changed to the lean side while the rich condition continues. On the other hand, (iii) when the air-fuel ratio reverses from rich to lean, it is changed stepwise to the rich side by the proportional amount (PL), and (iv) after that, the integral (IL) while the lean continues. ) to gradually change it to the rich side.

First, the above four cases (i) to (iv) are judged in S2, 3, and 9 using the output value of the air-fuel ratio sensor and the reference level (
This is done by combining the magnitude comparison with the sensor output value (corresponding to the stoichiometric air-fuel ratio) and the previous magnitude comparison. "RLJ" in S3 and 9 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.From this , S2, 3.4 occurs when rich is reversed to lean.Similarly, when rich continues, S2°9.7 proceeds.
If the transition from hari-n to rich progresses to 10, S
2, 9.13 is a continuation of the first line. In addition, immediately after the magnitude comparison is reversed, S
4 and 10, the 7 lag is changed to the value after inversion.

When the four cases are divided in this way, S5,7°11.
In step 13, the proportional components (PR and PL) and the integral components (IR and IL) are calculated according to the following equation according to each case.

PR=KPXERROR-(4) ΣI R= Σr R+ K +XERROR-(5)
P L= K PX ERROR... (6) Σ1. =
ΣI L+ K , x ERROR...(7) However, ERROR is the deviation from the stoichiometric air-fuel ratio, and KP is a feedback constant (KP is a proportional constant and tKI is an integral constant)
As shown in equations (4) to (7), the same value is often adopted as the feedback constant for the rich side and the lean side.

Then, in S6.8 and S12.14, a feedback correction coefficient (α) is calculated using these proportional and integral components. In terms of correspondence with (i) to (iv) above, in the case of (i), α=α-PR, in the case of (ii), α=α-IR, (ii
In the case of i), α=α0PL, in the case of (iv), α=α1■,
It is. Here, what these formulas mean is α
This means reading out the value stored as α, adding or subtracting the feed bank correction amount to it, and storing the added or subtracted value again as α.

(Problem to be solved by the invention) By the way, in such a device, the above-mentioned integral constant (K
+) is a constant value determined according to engine speed, engine load, cooling water temperature, etc., and different values are not adopted for steady operation and transient operation, so hunting may occur during steady operation, or transient Fluctuations in the air-fuel ratio cannot be fully absorbed during operation, and there may be a limit to the reduction of harmful exhaust components.

For example, Figure 13 shows how α changes when the base fuel-air ratio (reciprocal of the air-fuel ratio), which is the accumulation of system errors, changes almost stepwise from the rich side to the lean side (that is, during a transient period). , it is required that α also undergoes a stepwise change corresponding to the change in the base fuel-air ratio, as shown by the dashed line.

That is, the dashed line gives the required value of α.

However, since the actual α shown by the solid line changes depending on the integral constant, a response delay occurs in the section B with respect to the required value. This means that the constant of integration determines the slope of each line segment, upward and downward, so if you increase the constant of integration, α
It is possible to improve the response by rapidly changing the integral constant, but if the steady state control is performed using the same value of the integral constant as in the transient state, hunting will occur, so it is not necessary to change the integral constant unnecessarily. This is because it cannot be made larger.

In other words, air-fuel ratio control requires both steady-state stability and transient response at the same time, but in order to balance these requirements with one integral constant, a value that is not biased toward either must be selected. It cannot be said that a sufficient value is given for any driving time.

This invention has been made by focusing on such a conventional problem, and each time the magnitude relationship between the air-fuel ratio detected by the air-fuel ratio sensor and the target air-fuel ratio is reversed, the elapsed time after the reversal (or It is an object of the present invention to provide a device that measures the elapsed rotational speed) or integrates the amount of intake air after reversal (or the amount of fuel injection after reversal), and changes the integral constant according to the measured value or the integrated value. This is the goal.

(Means for Solving the Troubles) As shown in FIG. 2, a means 3 for calculating the basic injection amount Tp (=KXQa/Ne, where K is a constant) according to these detected values, a sensor 4 for detecting the actual air-fuel ratio, and a means 3 for calculating the basic injection amount Tp (=KXQa/Ne, where K is a constant); Predetermined target air-fuel ratio (
For example, means 5 for measuring the deviation (ERROR) from the stoichiometric air-fuel ratio; means 6 for determining whether the magnitude relationship between the two air-fuel ratios has been reversed; and each time this is determined, the elapsed time (T) after the reversal is determined. Or means 7 for measuring the elapsed rotational speed (N) or integrating the intake air amount or fuel injection amount after reversal, and a means 7 for measuring the elapsed rotational speed (N) or integrating the intake air amount or fuel injection amount after reversal, and based on this measured value or integrated value, until a predetermined time or rotational speed elapses or a predetermined rotational speed is elapsed. means 8 for setting an integral constant (K +) that is small until the intake air amount or fuel injection amount is integrated and then becomes large; and an integral that is calculated from this integral constant (K +) and the deviation (ERROR). (IR or IL) to calculate a feedback correction amount (α) of the air-fuel ratio; ).

(Function) During steady operation when the base air-fuel ratio determined by the basic injection amount (T p) is at a constant value, the feedback correction amount (α) is reversed within a time shorter than a predetermined time or within a rotation speed shorter than a predetermined rotation speed. However, since the inversion occurs when the intake air amount is smaller than the predetermined intake air amount integrated value or the fuel injection amount is smaller than the predetermined fuel injection amount integrated value, a small integral constant is set. Here, the integral calculated from a small integral constant is small, which suppresses hunting during steady state.

On the other hand, during a transient period in which the base air-fuel ratio changes in a stepwise manner, the air-fuel ratio does not reverse, so after a predetermined time or a predetermined number of revolutions,
Alternatively, when a predetermined intake air amount integrated value or fuel injection amount integrated value is exceeded, a larger integral constant is set.

Here, a large integral constant improves responsiveness, so it can better follow stepwise changes in the base air-fuel ratio, thereby preventing response delays during transient times.

(Embodiment) FIG. 2 shows a system diagram in which the present invention is applied to a fuel injection type engine. In the same figure, 24 is slotted.
The air meter 70 is provided in the intake passage upstream of the torque valve 23 and outputs a signal corresponding to the amount of air (Qa) taken in through the air cleaner, and functions as an engine load sensor. 25 is a sensor (crank angle sensor) that outputs a signal for each unit angle of crank angle and a signal for each reference position.
Then, from the signal for each unit angle, the engine rotation speed (
Ne) is calculated.

Reference numeral 26 denotes an oxygen concentration sensor which has a characteristic of rapidly changing after reaching the stoichiometric air-fuel ratio, and the signal from this sensor 26 is treated as a feedback control signal for the air-fuel ratio.

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.

Reference numeral 40 denotes a fuel control unit into which signals from these sensors (24 to 2) are input, and this unit 40 calculates the amount of fuel from the fuel injection valve 35 provided in the intake boat of each cylinder based on various operating variables. Control is performed so that a target air-fuel ratio (stoichiometric air-fuel ratio) is obtained by increasing or decreasing the air-fuel ratio. For example, basic pulse x width T p (= K
/ N, e, where K is a constant) and various coefficients (Co and Ts
) and the air-fuel ratio feedback correction coefficient (α), the injection pulse width during normal operation (T i
) is determined using the following formula.

Ti = TpXCoXα + Ts - (8) 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+L voltage correction (Ts)) are stored in the memory (ROM43).
They are each found by searching the table stored in .

The control unit 40 includes a valve 37 for α flame timing control and idle speed control (RSC).
Opening control is also performed at the same time.

FIG. 13 is a block configuration diagram when the control unit 40 is configured with a microcomputer, and includes input/output interfaces 7ace (Ilo) 41. CPU42, ROM4
3. RAM44. A RAM (BURAM) 45 that can retain stored information even when the ignition key is turned off, and an A/R that converts analog signals to digital signals among various signals.
It consists of a D converter (ADC) 4G and has the functions of each means 3.5 to 10 in FIG.

FIG. 4 shows a program for calculating the air-fuel ratio feedback correction coefficient (α), which is executed at every predetermined crank angle. This figure corresponds to Figure 12, and the first
The same parts as in Figure 2 are given the same step numbers. Note that the step numbers are assigned in the order of 'PJ' and then 'PJ', but in order to clarify the parts that are different from the f512 diagram, large numbers are assigned to those parts.

Therefore, I will mainly discuss the differences.

Proceeding to 322 in Figure 4 is because rich is continuing,
In S22, the integral (rR) during the rich period is calculated, and in this case, in addition to the engine speed, engine load, cooling water temperature, etc., in this example, the progress after the air-fuel ratio is reversed from lean to rich is calculated. Calculate by taking time (T) into account.

Figure f510 shows the relationship between the elapsed time after switching from lean to rich and the magnitude of the integral (IR) while rich continues. The predetermined time (T2) of
The predetermined time (T3) after l+T2 has elapsed is made small again. In other words, the elapsed time after reversal is divided into three categories: short, medium, and long, and when the time is short, the integral is made small, when it is medium, it is large, and when it is long, the integral is made small.

Here, in this example, the reason for reducing the IR during T1 is during a transient period, but we have not specifically determined whether or not.
This is because immediately after the air-fuel ratio is reversed, it is not known whether it is a steady state or a transient state, so an integral suitable for a steady state is used for the time being.

In other words, since the air-fuel ratio inverts at a nearly constant period during steady state, providing a small integral is suitable for steady state as long as this period is not exceeded, and with small integrals, hunting will not occur. In unison. From this, T1 is determined in accordance with the inversion period of α during steady state.

On the other hand, the reason why IR is increased during T2 is that since the air-fuel ratio does not reverse even after T2, it can be determined that this is a transient period. α during transition
is required to change with good response, and for this purpose a large integral is sufficient. From this, since T2 corresponds to the time from the start to the end of the transition, T2 is determined taking that time into consideration.

The reason why IR is made small again during T3 after TI+T2 is because it is determined that the transient influence ends after Tl+72 and the state returns to a steady state.

However, the integral in this case is made slightly larger than immediately after the inversion, so that the transition to the steady state is smooth.

Note that T1 to T3 are determined by taking into consideration the operating conditions.
For example, it should not be a constant value but a value that changes depending on the operating conditions)
In this case, the program shown in Fig. 5 can be used to adjust the value to small or large, taking into account the operating conditions.

Set each integral in

Returning to Figure 4, when calculating the integral (IL) during lean continuation at S24, which is during lean continuation, the elapsed time (T) after the air-fuel ratio reverses from rich to lean is also taken into account. Calculate. The content of 1 for the elapsed time (T) in this case is also given by the characteristics shown in FIG.

Here, since there is a relationship between each integral (IR and IL) and the integral constant of 1 as shown in equations (5) and (7') above, in order to increase the integral, increase the integral constant. (Set.) Conversely, to make the integral smaller, set the integral constant smaller.

A timer is used to measure the time elapsed since the air-fuel ratio reversal described above. For example, if you prepare a timer that counts time again when it is cleared, and clear this timer at 823 immediately after the lean-rich reversal,
The subsequent timer value represents the elapsed time after the lean-rich reversal, so it is calculated as the integral while the rich continues (
It is used in the step of calculating IR), that is, in S22. Similarly, 82 immediately after the rich-leaf reversal
Clear the timer with 1 and check the integral (IL) while lean continues.
In the step of calculating (S24), the timer value at that time is used.

Instead of measuring the elapsed time (T) after the air-fuel ratio reversal,
The elapsed rotational speed (N) of the engine after the rotation may be measured. The program in this case is shown in Figure 6.
The elapsed rotational speed (N) is counted in S31, and the S value is 334 immediately after the lean-rich reversal or the S immediately after the reversal to the reverse.
Cleared this power in 32 and continued rich 333
Alternatively, in step 335 while the rein continues, the integral (IR and IL) is calculated by taking this count value, that is, the elapsed rotational speed (N) into consideration. Also, the characteristics of the integral in this case are ! Elapsed rotational speed (N) after reversing the horizontal axis in Figure 510
This is the characteristic replaced by .

Similarly, instead of opening as time passes after reversal, the integrated value of intake air amount after reversal (M calculation intake air amount) Air or the integrated value of fuel injection amount after reversal (product W - fuel injection amount) S may also be used, and programs in this case are shown in FIGS. 7 and 9. The characteristics of the integral for each integrated value are also as shown in FIG.

However, regarding the intake air amount integrated value, since it is the air flow rate (Qa) that is measured at 24 with the air 70-meter, Qa is integrated in the program shown in Figure @8, which is executed every predetermined time. Memory for storing values (Air)
is prepared, and the values in this memory are used in the program shown in FIG. 7, which is executed at every predetermined crank angle.

In these other three embodiments as well, it is possible to determine the characteristics of the integral in consideration of the operating conditions.

The operation of the embodiment configured in this manner will be explained with reference to FIG. 11. This figure shows the feedbank according to this embodiment when the base fuel air ratio changes almost stepwise, as in FIG. 13. The change characteristics of the correction coefficient (α) are shown. The case shown in FIG. 4 is used as a representative example.

In the section D, which is constant f before the base fuel-air ratio changes, and in the section F after the transition ends, the air-fuel ratio reverses within a time shorter than T1, so according to the characteristics shown in Figure 10, the air-fuel ratio is small. The integrals (TR and IL) are given. Here, since each integral determines the slope of the upward-rightward or downward-rightward line segment shown in the figure, if the integral is small, the slope of the line segment will be gentler than before, and the value of α shown by the dashed-dotted line will be Hunting phenomenon does not occur much with respect to the required value.

When the base fuel-air ratio changes suddenly after passing the interval D, a small integral (ILI) is given during the period T1 from the start of the change, but in this case, even after the time T1 has passed, Since the air-fuel ratio does not reverse, it is determined that it is a transient period, and after passing T1 and during T2, P
According to the characteristics shown in diagram IIJ10, a large integral (IL2) is given. For this reason, the slope of the line segment rising to the right shown in the figure becomes steeper than before and rises during T2.

According to the integral (IL2) of this steep rise, 1
It follows well the required value of α shown by the point g4 line,
A response delay in the section E, which indicates a transient period, is prevented.

Then, after passing T2, it is determined that the transient has ended, and a small integral (IL3) similar to the steady state is given again, and the slope of the line segment is accelerated again.

In this way, in this example, we decided to set the integral constant so that the optimal integral is given for each of the steady state and transient state, and by doing so, it is possible to suppress hunting during steady state. Alternatively, response delays during transient periods can be prevented, and harmful exhaust gas components can be further reduced.

Furthermore, since a small integral is set again from the end of the transient to steady state, the air-fuel ratios have a smooth relationship.

In this example, we have explained an example of calculating α using proportional-integral operation, but Feedback IIJ, which includes integral operation,
If it is a control (for example, proportional-integral-derivative control), it can be similarly applied.

(Effects of the Invention) This invention measures the elapsed time (or elapsed rotational speed) after the reversal every time the magnitude relationship between the air-fuel ratio detected by the air-fuel ratio sensor and the target air-fuel ratio is reversed. The amount (or fuel injection amount) is integrated, and the integral constant is set so that the integral changes between steady state and transient states according to this measured value or integrated value, making it possible to suppress hunting during steady state. Alternatively, it is possible to prevent response delays during transient times and further reduce harmful exhaust gas components.

[Brief explanation of the drawing]

Fig. 1 is a claim correspondence diagram of this invention, Fig. 2 is a system diagram of an embodiment of this invention, Fig. 3 is a block diagram of a control system of this embodiment, and Figs. 4 and 5 are this embodiment. Figures 6 to 9 are flowcharts for explaining the calculation contents of the other three embodiments of this invention, and the Pt510 diagram is used in the four embodiments of the notation. A characteristic diagram of the integral, FIG. 11, is a waveform diagram for explaining the operation of the embodiment. FIG. 12 is a flowchart for explaining the calculation contents of the conventional example.
FIG. 13 is a waveform diagram for explaining the operation of the conventional example. DESCRIPTION OF SYMBOLS 1... Engine load sensor, 2... Engine speed sensor, 3... Basic injection IM, output means, 4... Air-fuel ratio sensor, 5... Deviation measuring means, 6... Reversal determination Means, 7... Measurement and integration means, 8... Integral constant setting means, 9... Feedback correction amount calculation means, 10.
...Fuel injection amount determining means, 24...Air 70-meter, 25...Crank angle sensor, 26...Oxygen concentration sensor (air-fuel ratio sensor), 35...Fuel injection valve, 40...
··control unit. Figure 3 Figure 10 Itoasa Moon T of the anti-shaft number. Counter support, number of rotations N. anti-j laramii ≦ mi, g) ftiL b skin enter a Eat = 13
-2 Father Bi's (accomplished by 9 yen,

Claims (1)

[Claims] A sensor that detects the engine load and the engine rotation speed, a means for calculating the basic injection amount according to these detected values, a sensor that detects the actual air-fuel ratio, and a means that detects the detected air-fuel ratio and a predetermined target air-fuel ratio. a means for measuring the deviation from the fuel ratio; a means for determining whether the magnitude relationship between the air-fuel ratios has reversed; and a means for measuring the elapsed time or the elapsed rotational speed after the reversal each time this is determined; means for integrating the amount of air or fuel injection; means for calculating an air-fuel ratio feedback correction amount including at least an integral calculated from the integral constant and the deviation; and means for calculating the basic injection amount using the feedback correction amount. 1. An air-fuel ratio control device for an engine, comprising: means for correcting and determining a fuel injection amount.