JPS62162742A - Air-fuel ratio control device - Google Patents

Abstract

PURPOSE:To ensure operability and simultaneously reduce the exhaust amount of NOx, by setting up a ternary air-fuel ratio temporarily when a lean- combustion operation is shifted to a transitional condition. CONSTITUTION:In a control unit 20, a target air-fuel ratio is set up corresponding to the load of an engine 1, the supply of fuel is controlled in such a manner that the target air-fuel ratio can be achieved being based on the output of an oxygen sensor 17, and the fuel is injected from an injector 4. Here, the target air-fuel ratio is set for a leaner side than a theory air-fuel ratio during at least a part of a steady driving, however, it is set for a ternary air-fuel ratio when the load of the engine is detected to be in a prescribed transitional condition by signals from a load detecting means 18 comprising an air flow meter 8 and a crank angle sensor 15. Thus, air-fuel mixture in a cylinder becoming exhaust gas is conducted to a catalytic converter 7 through an exhaust pipe 6, and is exhausted being purified of its harmful ingredients by catalytic converter rhodium.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a device for controlling the air-fuel ratio of an engine such as an automobile.

(Prior art) In recent years, demands on automobile engines have become more sophisticated.
There is a tendency for mutually contradictory issues such as reduced exhaust gas, high output, and low fuel consumption to be achieved at a high level.

In order to address these issues, combustion control under ultra-lean air-fuel ratios has been attempted; for example, "Internal Combustion Engine, Vol. 23, No. 12 J, October 1984 issue.
There is a lean burn device described in pages 33-40 published by Sankaido. This device attempts to achieve the above requirements by performing feedback control of the air-fuel ratio up to the ultra-lean air-fuel ratio region based on the output of a lean sensor that can detect air-fuel ratios over a wide range from rich to lean.

In this case, unlike the characteristic where the stoichiometric air-fuel ratio is constant during steady driving, a moderate air-fuel ratio is set as the target value in a part of the acceleration region. For example, in the normal acceleration range, the air-fuel ratio is 22
．． 5. The air-fuel ratio is 21°5 in the steady running range, and 15.5 during idling. Further, in a full load state, an output air-fuel ratio of 12 to 13 is used to ensure vehicle power performance. As we move to such a lean air-fuel ratio, NO.
x tends to decrease significantly, which is in line with the recent reduction in NOx emissions. However, on the other hand, the adaptable air-fuel ratio range that satisfies both the NOx emission level to satisfy exhaust gas regulations and the allowable torque fluctuation level is narrow, and precise air-fuel ratio control is required.

(Problem to be solved by the invention) By the way, in order to clear NOx emissions within the regulation value while ensuring drivability during transient periods, it is necessary to change the constant air-fuel ratio, but current technology (i.e. With conventional devices, it is still difficult to perform precise control to maintain a constant air-fuel ratio during transient conditions.

Therefore, at present, the air-fuel ratio is enriched during transient periods so as not to impede drivability. However, if the engine is enriched halfway just to ensure drivability, the amount of NOx emissions will increase and it will not be possible to meet recent demands.

(Purpose of the Invention) Therefore, the present invention focuses on the original function of the three-way catalyst, and when transitioning to a transient state of acceleration that requires a large amount of torque, the target air-fuel ratio is changed to the three-way air-fuel ratio (for example, λ-1 ), the purpose is to provide an air-fuel ratio control device that meets recent demands by reducing NOx emissions while ensuring drivability.

(Structure of the Invention) The air-fuel ratio control device according to the present invention, as its basic conceptual diagram is shown in FIG. The means includes a transient state detection means C that detects that the engine is in a predetermined transient state, and sets a target air-fuel ratio according to the engine load, and sets the target air-fuel ratio to the stoichiometric air-fuel ratio during at least a part of steady running. a target setting means d that sets the target air-fuel ratio to a three-way air-fuel ratio when the engine shifts to a predetermined transient state; and an air-fuel ratio detecting means a.
a control means e for controlling the supply amount of intake air or fuel to reach a target air-fuel ratio based on the output of the control means e;
and an operating means f for controlling the amount of intake air or fuel supplied based on a signal from the engine, thereby reducing NOx emissions while ensuring drivability.

(Example) Hereinafter, the present invention will be explained based on the drawings.

2 to 7 are diagrams showing an embodiment of the present invention.

First, the configuration will be explained. In FIG. 2, reference numeral 1 denotes an engine, in which intake air is supplied from an air cleaner 2 to each cylinder through an intake pipe 3, and fuel is injected by an injector (operating means) 4 based on an injection signal Si. Then, the air-fuel mixture in the cylinder is ignited by the discharge action of the spark plug 5.
It explodes, becomes exhaust gas, and is introduced into the catalytic converter 7 through the exhaust pipe 6. In the catalytic converter 7, harmful components (Co, HC, NOx) in the exhaust gas are purified by a three-way catalyst and then discharged.

The intake air flow rate Qa is measured using a flap type air flow meter 8.
and is controlled by a throttle valve 9 in the intake pipe 3. The opening TVO of the throttle valve 9 is detected by a throttle valve opening sensor 10, and the pressure PB of intake air in the intake pipe 3 is detected by a pressure sensor 11. Further, a swirl valve 12 is provided in the intake pipe 3 near the intake port, and the swirl valve 12 opens and closes based on a control signal Sv input to a solenoid valve 14 that controls the negative pressure applied to the drive valve 13. This creates a so-called swirl from the intake boat into the cylinder to improve combustion.

The rotation speed N of the engine 1 is detected by the crank angle sensor 15, and the temperature Tw of the cooling water flowing through the water jacket is detected by the crank angle sensor 15.
is detected by the water temperature sensor 16.

Furthermore, the oxygen concentration in the exhaust gas is detected by an oxygen sensor (air-fuel ratio detection means) 17, which outputs V
A type in which i changes uniquely over a wide range of air-fuel ratios from rich to lean regions is used.

The air flow meter 8 and the crank angle sensor 15 constitute a load detection means 18, and signals from the load detection means 18 and each sensor 10, 11, 16, and 17 are input to the control unit 20. The control unit 20 controls the air-fuel ratio based on these sensor information.
Performs ignition timing control and swirl control.

That is, the control unit 20 has functions as a transient state detection means, a target setting means, and a control means,
It is composed of a CPU 21, a ROM 22, a RAM 23, and an I10 port 24. The CPU 21 executes the I10 boat 2 according to the program written in the ROM 22.
You can import the external data you need from 4, and also use RA.
It performs arithmetic processing on necessary processing values while exchanging data with the M23, and outputs the processed data to the I10 port 24 as necessary. Signals from the sensor group 10.11.15.16.17.18 are input to the I10 boat 24, and the injection signal Si and control signal SV (there are also other signals for ignition timing control, ) is output. ROM22
stores an arithmetic program for the CPU 21, and the RAM 23 stores data used in the arithmetic operations in the form of a map or the like.

Next, the action will be explained.

Figure 3.4 shows the air-fuel ratio side i written in the ROM22.
It is a flowchart which shows the program of IB.

FIG. 3 shows a program for determining a transient state, and this program is executed once every predetermined time (every 5 m5 ec).

First, the signal TVO from the throttle valve opening sensor lO is read at P and is A/D converted. Next, the difference value ΔTVO of the throttle valve opening degree TVO within a predetermined unit time is calculated at P, and this is set as a predetermined acceleration discrimination value A (Ago) at P3.
Compare with. Note that ΔT■0 may be calculated, for example, by calculating the difference (difference between the previous value and the current value) each time this program is executed.

When ΔTVO>A, it is judged as acceleration, and P is selected.

Set the acceleration flag KF and end this routine with Δ
When TVO<A, it is determined that there is no acceleration, the acceleration flag KF is lowered at P, and the routine is ended. This results in
Acceleration can be determined accurately and reliably. Note that the determination of acceleration is not limited to the above example; for example, the differential value dTV of the throttle valve opening TVO
Acceleration may be determined by determining o/dt and comparing it with a predetermined value.

FIG. 4 shows a program for controlling the injection amount, and this program is executed in synchronization with engine rotation.

First, the air flow rate (hereinafter referred to as cylinder flow rate) QACYL that is actually taken into each cylinder per cylinder is calculated using Pl+. The reason for performing such calculations is to obtain accurate air 2it amount information even during transient times.If the accuracy of this information is poor, the injection amount cannot be effectively manipulated in air-fuel ratio control. This is to support fuel ratio control.

Therefore, calculation of the cylinder airflow amount QACYL will be explained.

The calculation of QACYL is illustrated in the case of acceleration as shown in FIG. 5 as an example.

In FIG. 5, when the accelerator is started to be depressed at the timing t=Q and the throttle valve opening TVO starts to change, the waveform PBX obtained by signal processing the main waveform PB of the pressure sensor 11 has a period t2 due to the pulsation suppressing effect. It starts to change with a delay. In addition, the pressure correction flow rate value QACY predicted based on the PBX
Although L' has also been corrected considerably, it is still the same as period 1.
It starts to change with a delay of (1, < tz), and there is a difference between the hunting part (ΔQACYL) in the figure and the true air flow rate QACYL that is expected to be taken into the cylinder.

Therefore, the detection accuracy of the air flow rate decreases during such a transient period. This example corrects this problem.

First, QACYL' is calculated according to the following equation (2).

QACYL'-PBX+αΔPB ・・・・・・■■
2, PBX is a waveform obtained by signal processing the output of the pressure sensor 11 to suppress pulsation, and ΔPB is the intake pressure P
This is the difference value of B within a predetermined unit time. Also, α
is a function of the rotation speed N.

The reason for performing such a calculation is to predict the amount of air entering the cylinder when determining the injection amount, since air is drawn into the cylinder later than fuel. The prediction is made by adding ΔPB multiplied by α to the processed result.

On the other hand, in order to correct the deviation of the hunting part mentioned above,
Focusing on the throttle valve opening TVO that starts to move the earliest, a flow rate correction value ΔQACYL, which is a correction for the deviation, is calculated according to the following equation (2).

ΔQACYL= (ΔTVO/N)xlNTQA...
...■ In Equation 0, INTQA is the air flow 11Q at the initial stage of the transition.
A CY L, and uses, for example, a change in the throttle valve opening TVO. This equation 0 represents the air flow rate under operating conditions with ΔTVO/N, that is, the difference value ΔTVO per revolution (difference in throttle valve opening TVO per predetermined unit time).
This means that by multiplying this by INTQA, it is possible to sufficiently correct the deviation in the correlation between the actual air flow rate and the calculated flow rate amount based on sensor information. QA this ΔQACYL
Added to CYL' (QACYL=ΔQ A C'I
'L + QACYL') is the throttle valve opening T as shown in the figure.
It is correlated with the change in VO and corresponds accurately to the true flow rate of air expected to be drawn into the cylinder.

That is, by accurately calculating the amount of intake air during acceleration, the accuracy of detecting the flow rate of air taken into the cylinder can be dramatically improved. Note that, of course, the improvement in detection accuracy is achieved not only in the above-mentioned example of acceleration but also in the case of deceleration.

Then, when the correction by ΔQACYL is completed, QACY
The air flow rate is calculated by L', and QACYL
When ' becomes equal to F'BX, the air flow rate is thereafter calculated based on the output of the flap type air flow meter 8.

However, after reaching QACYL'-PBX, the air flow rate may be calculated directly from the output of the pressure sensor 11.

In this way, because it is based on accurate air flow information,
Injection amount control, which will be described later, will also be more precise.

Now, with the above in mind, let's return to the program again.

When pH is reached, the elapsed time Tc after the throttle valve 9 leaves the fully closed position at pHz is compared with a predetermined value t0.

This is because immediately after the throttle valve 9 opens from fully closed, the degree of acceleration required is greater than when the engine 1 accelerates from steady running.In response, the air-fuel ratio is enriched (λ-1). This is for the purpose of achieving this. When Tc<t, the acceleration flag KF is determined in Pl3, and when Tc≧1°, the process proceeds to Pl4. P.I.
When KF = 1 in 3, it is determined that the enrichment condition is present due to an acceleration request, and Pl sets the target air-fuel ratio KMR (set air-fuel ratio) to the three-way air-fuel ratio (hereinafter referred to as three-way KMR). Then proceed to Pl6. The three-way air-fuel ratio may be any air-fuel ratio at which the original function of the three-way catalyst is effectively exhibited, and in this embodiment, this is set as the stoichiometric air-fuel ratio of λ=1. On the other hand, when it is KF-0, the process proceeds to P14 in the same way as when following the No command at P1□. At Pl4, the target air-fuel ratio KMR is set according to the engine load at that time. For example, the optimum value is looked up from a table map using the basic injection amount Tp (Tp-K·Qa/N) determined by N and Qa and the rotation speed N as parameters.

Next, in Pl6, the fuel injection amount Ti is calculated according to the following formula 〇, and PI? Then set this in the I10 boat 24 and complete the routine.

Ti=QACYLXKMRXCOEFXALPHA+
Ts・・・・・・■ However, Ti: Represented by the pulse width of the injector ALPHA: Air-fuel ratio feedback correction coefficient TS: Invalid pulse width (voltage correction portion) In equation 0, QACYL is the air flow rate per cylinder This corresponds to , and also includes corrections based on intake air temperature. In this case, in this embodiment, QACYL is calculated based on the output of the air flow meter 8 in the steady state, and when the transition to the transient state occurs, correction is added based on the throttle valve opening TVO and the signal PB of the pressure sensor 1 as described above. Calculated by

C0EF is a fuel delay correction coefficient, and is used to correct the fuel amount during a transient period. The value is determined by the vaporization of the fuel and the wall flow rate, but specifically, it is calculated based on the magnitude of acceleration/deceleration, engine warm-up and operating conditions, and whether or not the engine has been started. ALPHA is a correction coefficient when the injection amount is feedback-controlled based on the air-fuel ratio detected by the oxygen sensor 17 so as to reach the target air-fuel ratio.

In this way, when the engine 1 shifts to a predetermined acceleration state, the air-fuel ratio changes to λ-
1. Therefore, the conventional problem of not achieving sufficient NOx reduction due to half-way enrichment is resolved, and by setting λ = 1, the effect of the three-way catalyst is fully demonstrated and NOx is significantly reduced. Drivability can also be ensured.

FIG. 6 shows the above-mentioned enrichment conditions in a time chart.

In FIG. 6, when the throttle valve 9 opens from the fully open position, when the elapsed time Tc is within the range of the predetermined value t0,
As shown in e), when the acceleration flag KF becomes KF=1, the target air-fuel ratio KMR is set to the three-way KMH. And T
At timing c=t0, KF=0 and the target air-fuel ratio is again given by the engine load from the ternary KMR, returning to the normal lean burn region.

Note that, as described above in which three-dimensional judgment is performed, the conversion conditions are not limited to those in this embodiment. There are the following cases where it is necessary to reduce NOx while achieving the acceleration request.

For example, a gear change may be determined and a three-way determination may be made within a predetermined time after the gear change.

This is because there is a request for acceleration after a gear change. It is convenient to process this determination simultaneously in step p+z of the program shown in FIG.

In addition, in the above embodiment, the throttle valve opening TVO is used to detect the transient state.
is used as a parameter, but it is not limited to this.

The point is that the intention of the driver can be detected as quickly as possible, so for example, an accelerator sensor may be used to detect the movement of the accelerator. If this is done, the effects of the present invention will be more effective than the throttle valve opening TVO.

Furthermore, detection of transient conditions is not limited to throttle or accelerator movements. For example, the cylinder airflow amount QACYL disclosed in the above embodiment may be used as a parameter.

(Effects) According to the present invention, when a transient state occurs during lean-burn operation, the air-fuel ratio is temporarily set to a ternary air-fuel ratio, thereby ensuring drivability while reducing N.

It is possible to reduce X emissions and provide a lean burn system that meets recent requirements.

[Brief Description of the Drawings] Fig. 1 is a basic conceptual diagram of the present invention, Figs. 2 to 6 are diagrams showing an embodiment of the present invention, Fig. 2 is an overall configuration diagram thereof, and Fig. 3 is a diagram showing an embodiment of the present invention.
Figure 4 is a flowchart showing the program for determining the transient state, Figure 4 is the flowchart showing the program for controlling the injection amount, Figure 5 is a waveform diagram to explain the effect of calculating the air flow rate, and Figure 6 is the rich flowchart. FIG. 1...Engine, 4...Injector (operating means), 18...
...Load detection means, 20...Control unit (transient state detection means, target setting means, control means).

Claims (1)

[Scope of Claims] a) air-fuel ratio detection means for detecting the air-fuel ratio of the intake air-fuel mixture; b) load detection means for detecting the load on the engine; and c) detecting that the engine is in a predetermined transient state. a transient state detection means; d) setting a target air-fuel ratio according to the engine load, setting the target air-fuel ratio leaner than the stoichiometric air-fuel ratio during at least a part of steady running, and causing the engine to enter a predetermined transient state; e) a control means for controlling the amount of intake air or fuel supplied so as to reach the target air-fuel ratio based on the output of the air-fuel ratio detection means; f) An air-fuel ratio control device comprising: an operating means for controlling the amount of intake air or fuel supplied based on a signal from the control means.