JPH0311139A - Air-fuel ratio control for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent the deterioration of a catalytic converter by determining the selection timing from feedback control to opened loop control according to the ratio between the number of times of combustion in the high load state over the standard value of an engine and the number of times of combustion less than a standard value. CONSTITUTION:A control circuit 20 determines the fuel injection timing of an injector 15 on the basis of the throttle opening degree detected by sensors 10-14, 16, absolute intake pressure, cooling water temperature, crank angular speed, O2 concentration, and atmospheric pressure. In this case, feedback control is performed so that a prescribed air-fuel ratio is maintained on the basis of the O2 concentration, and opened loop control for obtaining the rich air-fuel ratio is performed in a prescribed high load state. In this case, a prescribed high load standard value is set, and the selection timing from feedback control to opened loop control is determined according to the ratio between the number of times of combustion related to the temperature of a catalytic converter 9 in the case when an engine 4 is over the above-described standard value and the number of times of combustion less than a standard value. Therefore, the deterioration of the catalytic converter can be prevented, maintaining the high purifying action.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the air-fuel ratio in an internal combustion engine.

In the internal combustion engine installed in a vehicle, a three-way catalytic converter is installed in the exhaust system to purify the exhaust gas. Works most effectively.

Therefore, an oxygen concentration sensor is installed in the exhaust system to detect the oxygen concentration in the exhaust, and based on this detected value, feedback control is performed to maintain the air-fuel ratio of the mixture near the stoichiometric air-fuel ratio, thereby keeping the exhaust gas within the regulation value. things are done.

However, when the engine load increases, if the air-fuel ratio is controlled near the stoichiometric air-fuel ratio, the temperature of the exhaust system will rise more than necessary and exceed the allowable temperature of the three-way catalytic converter.
The catalyst no longer works effectively and the exhaust gas is no longer purified.

Therefore, when the load is high, the air-fuel ratio is enriched in order to obtain an output commensurate with the load and to suppress the temperature of the exhaust system within an allowable limit, thereby suppressing the temperature rise by the fuel cooling effect.

However, if the air-fuel ratio is enriched from around the stoichiometric air-fuel ratio immediately after a certain high load has been reached, the exhaust gas may become worse.

In other words, even though it is not necessary to enrich the air-fuel ratio when the car slowly starts or when there is a temporary high load when changing gears, the air-fuel ratio is enriched, which worsens exhaust gas and wastes fuel. becomes.

Therefore, in the conventional example (Japanese Unexamined Patent Application Publication No. 57-24435), the air-fuel ratio is not enriched immediately after a high load, but the air-fuel ratio is enriched when a high load state continues for a predetermined time or more. This prevents operation under high loads.

In addition, in the case of the same side, in order to avoid a decrease in output torque due to a delay in enrichment, the air-fuel ratio is slightly enriched immediately after high load to maintain engine output, and after a certain period of time, the exhaust system temperature is reduced to a certain extent. An example (Japanese Unexamined Patent Publication No. 128941/1983) has been proposed in which the air-fuel ratio is further enriched.

In any case, in both of the conventional examples mentioned above, when the high load state continues for a predetermined period of time from a certain high load point, the air-fuel ratio is enriched and the exhaust system temperature is kept within a certain allowable range. It is something that is tried to be suppressed.

Therefore, the air-fuel ratio will not be enriched unless the high load condition continues.

By the way, the temperature of the exhaust system, especially the temperature of the three-way catalytic converter, depends on the number of combustions in the engine, and increases according to the number of combustions under high load conditions due to the calorific value of combustion, and increases due to the presence of unburned fuel under low load conditions. descend.

When this high load state and low load state are repeated,
When the total number of combustions under high load conditions is larger than the number of combustions under low load conditions, the temperature of the three-way catalytic converter will increase.

Therefore, when high load states and low load states are repeated, if the control method is to enrich the air-fuel ratio after a certain period of time as described above, even though the temperature of the three-way catalytic converter is rising, Since the load condition does not continue,
No matter how long the air-fuel ratio is not enriched, the temperature of the catalytic converter increases and exceeds a permissible range, and the exhaust gas may not be effectively purified.

The present invention has been made in view of the above, and its purpose is to always keep the temperature of the catalytic converter within an allowable range by controlling the timing of enriching the air-fuel ratio based on the number of combustions of the engine. The object of the present invention is to provide an air-fuel ratio control method that can maintain an exhaust gas purification effect.

That is, the present invention provides an internal combustion engine that performs open-loop control that performs feedback control to maintain a predetermined air-fuel ratio based on exhaust component concentration, and stops the feedback control in a predetermined state of high load to enrich the air-fuel ratio. In the air-fuel ratio control method, a predetermined high load reference value is set, and the ratio of the number of combustions when the engine is in a high load state above the reference value to the number of combustions when the engine is in a load state below the reference value. This is an air-fuel ratio control method for an internal combustion engine, which determines when to switch from the feedback control to the open loop control according to the above.

The ratio between the number of combustions in a high load state and the number of combustions in a load state below a predetermined high load reference value corresponds to the temperature of the catalytic converter. By determining the timing for enriching the air-fuel ratio based on this, the temperature of the catalytic converter can always be kept within the allowable range, and it is possible to prevent a decrease in the purification effect and deterioration of the catalytic converter due to an excessive rise in temperature.

Further, the second invention sets the high load reference value and a second high load reference value that is higher than the same reference value, and when the engine is operated at a high load equal to or higher than the second reference value, This is an air-fuel ratio control method for an internal combustion engine that immediately enriches the air-fuel ratio and further enriches the air-fuel ratio when the time for switching from feedback control to open loop control has passed.

When the load exceeds the second reference value, which is higher than the first high load reference value, it is possible to prevent the output from decreasing by immediately enriching the air-fuel ratio, and enriching the air-fuel ratio determined from the number of combustions. When the switching timing has elapsed, the air-fuel ratio is further enriched to prevent the temperature of the catalytic converter from rising excessively.

Embodiments of the present invention will be described below with reference to FIGS. 1 to 5.

In the electronically controlled fuel injection supply system for an on-vehicle internal combustion engine using the air-fuel ratio control method according to the present invention shown in FIG. An injector 15 is provided downstream of the throttle valve 5 in the intake pipe 3 and near an intake valve (not shown) of the engine 4 .

The exhaust pipe 8 of the engine 4 has harmful components (Co,
A three-way catalytic converter 9 is provided to facilitate the reduction of HC and NOx.

On the other hand, the reference numeral 10 is a throttle opening sensor which is composed of, for example, a potentiometer and generates an output voltage at a level corresponding to the opening degree of the throttle valve 5. The reference numeral 11 is a throttle opening sensor provided downstream of the throttle valve 5 and outputs an output voltage at a level corresponding to the magnitude of the pressure. 12 is a cooling water temperature sensor that generates an output voltage at a level corresponding to the cooling water temperature of engine 4; 13 is a sensor that generates a pulse signal in response to the rotation of the crankshaft (not shown) of engine 4; The crank angle sensor 14 is an oxygen concentration sensor that generates an output voltage at a level corresponding to the oxygen concentration in the exhaust gas, and the three-way catalytic converter 9 of the exhaust pipe 8
It is installed upstream from the installation position of.

The output terminals of the throttle opening sensor 10, the absolute pressure sensor 11, the coolant temperature sensor 12, the crank angle sensor 13, and the oxygen concentration sensor 14 and the input terminal of the injector 150 are connected to the control circuit 20.

The control circuit 20 is further connected to an atmospheric pressure sensor 16 that detects atmospheric pressure.

As shown in FIG. 2, the control circuit 20 includes a level conversion circuit 21 that converts the output levels of the throttle opening sensor 10S, absolute pressure sensor 11, water temperature sensor 12, oxygen concentration sensor 14, and atmospheric pressure sensor 16, and a level conversion circuit. 21, and an A/D converter 2 that converts the analog signal output from the input signal switching circuit 22 into a digital signal.
3, a waveform shaping circuit 24 that transforms the waveform of the output of the crank angle sensor 13, and a clock pulse outputted from a clock pulse generation circuit (not shown) to determine the generation interval of the TDC signal outputted as a pulse from the waveform shaping circuit 24. It consists of a counter 25 that measures numbers, a drive circuit 2B that drives the injector 15, a CPU (central processing unit) 29 that performs digital calculation operations according to programs, a ROM 30 that stores various processing programs, and a RAM 31. There is.

Input signal switching circuit 22, A/D converter 23, counter 2
5. Drive circuit 28, CPU 29, ROM 30 and RA
M31 is connected by an input/output bus 32.

Further, a TDC signal is supplied from the waveform shaping circuit 24 to the CPU 29.

In this configuration, the A/D converter 23 selectively outputs information on the throttle valve opening, intake absolute pressure, cooling water temperature, exhaust oxygen concentration, and atmospheric pressure, and the counter 25 outputs information representing the engine rotation speed. is input/output bus 32 to CPtJ29.
are respectively supplied via.

A processing program and various data for the CPU 29 are stored in advance in the ROM 30, and the CPU 29 reads each of the above information according to this processing program, and based on the information, generates a clock pulse of a predetermined period or T.
The fuel injection time T of the injector 15 corresponding to the amount of fuel supplied to the engine 4 is calculated from the calculation formula described later in synchronization with the DC signal.
Calculate out.

Then, the drive circuit 28 drives the injector 15 to supply fuel to the engine 4 in synchronization with the TDC signal for the fuel injection time Tout.

For example, in the basic mode after the engine starting period, the fuel injection time Tout is calculated from the following equation.

Tout = Ti ・(Ktw ・Kast l(afc-ffw
ot-Ko2 ・K15) Here, Ti is the basic injection time corresponding to the basic supply amount determined from the engine speed and intake absolute pressure, Kt- is the cooling water temperature increase coefficient, and Kas
t is the increase coefficient after starting, Kafc is the increase coefficient after fuel cut, Kwot is the enrichment coefficient when the throttle valve 5 is fully opened,
Ko2 is a feed pump/punk correction coefficient for the air-fuel ratio, and Xis is a lean grandchild number.

Correction coefficients such as the cooling water amount increase coefficient Xtw and the enrichment coefficient Kwo are each calculated in a subroutine of the basic mode calculation routine for the fuel injection time Tout.

Next, the procedure of the air-fuel ratio control method according to the present invention executed by the CPU 29 will be explained according to the flowcharts of FIGS. 3 and 4.

Figure 3 shows a subroutine for setting the air-fuel ratio enrichment coefficient Kwot.
The contents of the hsfe subroutine are shown in the flowchart shown in FIG.

First, the Fhsfe subroutine shown in FIG. 4 will be explained.

Fhsfe is a flag for switching between air-fuel ratio feedback control based on the oxygen concentration of exhaust gas and open-loop control that enriches the air-fuel ratio.
-0, the feedback control is B, and Fhsfe
When = 1, open loop control is performed.

In this embodiment, the engine load condition is checked based on the fuel injection time Tout t, and a constant fuel injection reference time Tout t2, which is the boundary between the state in which the temperature of the three-way catalytic converter 9 rises and falls according to the number of combustions, is determined in advance. When the load is high (Tvo t > Two t2), the count value NCX of the number of combustion times is incremented, and the T
When the load is low (wo t < Two t2), the count value NCX is decremented.

Therefore, the addition count value NCX almost faithfully represents the temperature of the three-way catalytic converter 9, and this count value NCX corresponds to the predetermined limit value GNC (for example, 3000 times).
If the temperature exceeds , the temperature of the three-way catalytic converter 9 may deviate from the permissible range.

Therefore, in the Fhsfe subroutine, the fuel injection time Tout is first compared with the reference time Two t2 (Step [phase]), and when it is determined that the load is high (Tout>Tt4ot2), the process proceeds to Step 0, and the count value NCX exceeds the limit value GNC. It is determined whether the value is exceeded, and if it is not exceeded (NCX<GNC), NCX is incremented (step @) and the flag Fhsfe is set to 0 (step @l).

When count value NCX exceeds limit value GNC,
Proceeding from step 0 to step @, the flag Fhsfe is set to 1.

On the other hand, if step [phase] determines that the load is low (Twot<Twot2), proceed to step [phase] and count value N.
It is determined whether CX is O or not, and if it is not 0, the count value NCX is decremented in step @), and if it is 0, it is skipped over step @ and proceeds to step [phase], and the flag Fbsfe is set to O.

Therefore, until the count value NCX corresponding to the temperature of the three-way catalytic converter 9 exceeds the limit value GNC, the flag Fh
sfe is O, and when exceeded, Fhsfe becomes 1.

The relationship between the load condition (corresponding to the fuel injection time Tout) and the count value NCX is illustrated in FIG.

The upper diagram shows changes in the load state, and the lower diagram shows changes in count value NCX.

When the load condition Tout is below the reference value Two L2, the count value NCX decreases, and when it is above it, it increases, and this count 4MNCX corresponds to the temperature of the catalytic converter.

Such a change in the count value NCX is performed when NCX is below the limit value GNC, and at this time the flag Fhs
fe is 0.

On the other hand, when NCX exceeds GNC, NCX does not change,
At this time, Fhsfe is 1.

The subroutine for determining the flag Ph5fe as described above is carried out in step (2) of the enrichment coefficient Kwot subroutine shown in FIG. 3, and the Kwot subroutine will be explained below.

In this subroutine, when Kwot is 1, feedback control is performed without affecting Tout, and when Kwot>1, open loop control is performed to enrich the air-fuel ratio.

First, in step (2), the enrichment coefficient Kwot is derived by calculation or from a map, then the fuel injection reference time Twot is calculated in the same way (step (2)), and then the flag Fhsfe is determined by the Fhsfe subroutine (step (2)). ).

Then, in step ■, the engine speed Ne is determined, and when the engine speed Ne is smaller than the low-speed reference speed Nwoto (for example, 600 rpa+), step [
phase] and always performs feedback control to avoid enriching the air-fuel ratio.

When Ne≧Nwoto, proceed to the next step ■, and this time set the high standard rotation speed Nhsfe (for example, 2000r
pm), and when the engine speed Ne is smaller than the reference speed Nhsfe, the process jumps to step @ and determines the valve opening θth of the throttle valve. When Ne≧Nhsfe, the process goes to step ■ and determines the fuel injection time. Determine Tout.

In other words, the engine rotation speed Ne is a high reference rotation speed Nhs.
If it is larger than fe, compare the fuel injection time Tout with the fuel injection reference time Twot2 and step (■)
, when it is determined that the load is low (Tout<Twot2), the process jumps to step (2), sets Kwot=1, and performs feedback control.

At high speed rotation and low load (Dou t < Two t2), the temperature of the three-way catalytic converter 9 does not rise and the engine operates near the stoichiometric air-fuel ratio, so the air-fuel ratio is always enriched as feedback control based on the oxygen concentration. do not have.

However, when the load is high (Tout ≧ Two t2), in the next step ■, the second
Tout
When the load is high such that Toutn is larger than the second reference time Twotn, the process jumps to step ■, and Tout < Twotn.
If it is tn, the process proceeds to the next step (2), in which case it is determined whether the flag Fhsfe is 0 or 1.

Even if Tso t2≦Tout<Twotn, if the flag Fhsfe is O, the three-way catalytic converter 9
The temperature is within the permissible range, so we jump to step (3) and set Kwot=1 to perform feedbank control.

On the other hand, if Fhsfe = 1 in step ■, the count value NCX will reach the limit value GNC, and the temperature of the three-way catalytic converter 9 may exceed the allowable range. and the enrichment coefficient -ot, and when Ktw > Kwo t, proceed to step [phase], ■, set Kwot = 1, and enrich the air-fuel ratio by the water temperature increase coefficient Kt-, while When Ktw≦Kwo t, enrichment coefficient Kw
The air-fuel ratio is enriched by ot, and in any case, the air-fuel ratio is enriched using the larger coefficient to lower the temperature of the three-way catalytic converter 9 and keep it within an allowable range.

Note that in step [phase], the time t of the timer described below is set to O when the water temperature increase coefficient Kt- is adopted.

Next, if the engine rotation speed Ne is smaller than the reference rotation speed Nhsfe in step ①, proceed to step @, and set the throttle valve opening θth to a constant reference valve opening θ−ot.
(For example, 50@), when the throttle valve opening is small (θth < θ-0t), proceed to step (2), check the fuel injection time Tout, and if Tout is smaller than the second reference time Toutn, the timer Set the time t in step o), proceed to step 0, and set wot=1.
shall be.

In other words, θth<θ−ot and Tout t is Tout tn
When it is smaller, the setting of time t on the timer is repeated, and feedback control is performed.

Here, when the load becomes high (Tout≧Twotn),
Proceed from step @ to step ■, wait until the time t set in step ■ becomes O, then proceed to step ■ for feedback control, and when time t reaches O, jump to step ■. Tout≧Tw again
After checking o tn, proceed to step (3) and enrich the air-fuel ratio.

That is, enrichment of the air-fuel ratio due to a temporal increase in load is avoided by the timer, and when the high load continues for a certain period of time, the air-fuel ratio is enriched to prevent a decrease in output.

In addition, if the throttle valve opening θth is larger than the reference valve opening θ−ot in step @, proceed to step
Looking at the load condition by t, if the load is higher than Twotn, proceed to step ③ to enrich the air-fuel ratio to increase the output, and if it is smaller than Twotn, Fhsfe is set to 1.
The air-fuel ratio should be enriched after waiting for this to occur.

Note that when proceeding from step ■ to step [phase] under a high load in which Tout is greater than the second reference value Twotn, the state of the flag Fhsfe is checked and the count value N is
CX has not reached the limit value GNC and Fhsfe = 0
In this case, proceed to step @, and add the correction value Xwot (approximately 0.9) to the enrichment coefficient Kwot calculated in step ■.
The air-fuel ratio is immediately enriched with a slightly lower value to prevent a drop in output, and when the count value NCX reaches GNC and becomes Fhsfe = 1, it passes step @ and proceeds to step ■, and the correction value Xwo The air-fuel ratio is further enriched without applying t to lower the temperature of the three-way catalytic converter 9.

In this embodiment, as described above, the count value N is based on the engine combustion speed corresponding to the temperature of the three-way catalytic converter 9.
Since the enrichment timing of the air-fuel ratio is determined by CX and the flag Fhsfe, the temperature of the three-way catalytic converter 9 will not rise more than necessary when the load changes above and below the reference value as in conventional control based on the passage of a certain period of time. There is no problem that the air-fuel ratio is not enriched even though the air-fuel ratio is not enriched, and the temperature can be controlled appropriately according to the temperature of the three-way catalytic converter 9, and the purification effect of the three-way catalytic converter 9 is always maintained at a high level. Deterioration can be prevented.

In addition, when the load becomes so high that Tout exceeds the second reference value Twotn, the air-fuel ratio is immediately enriched to prevent the output from decreasing, and the count value NCX is set to the limit value G.
When the temperature reaches NC, the air-fuel ratio is further enriched to prevent the temperature of the three-way catalytic converter 9 from rising excessively, and to maintain the purifying effect within the allowable range.

The present invention controls the timing of switching from feedback control to open-loop control that enriches the air-fuel ratio based on the number of engine combustions corresponding to the temperature of the catalytic converter, so the temperature of the catalytic converter is always maintained. Keep it within acceptable limits;
The purification effect can be maintained at a high level, and deterioration of the catalytic converter can be prevented.

In addition, when the engine exceeds the second high load reference value, the air-fuel ratio is immediately enriched to a certain extent to prevent a drop in output, thereby maintaining good drivability, and enriching the air-fuel ratio based on the number of combustions. When the time comes, the air-fuel ratio is further enriched to prevent the temperature of the catalytic converter from rising excessively, maintain the purifying action, and prevent deterioration of the catalytic converter.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an electronically controlled fuel injection supply system to which the air-fuel ratio control method according to the present invention is applied, FIG. 2 is a block diagram showing a control circuit of the same embodiment, and FIG. 3 is a block diagram showing the control circuit of the same embodiment. A flowchart showing the fuel ratio control method, FIG. 4 shows the flag Ph
A flowchart showing a subroutine for determining 5fe,
FIG. 5 is a diagram showing the relationship between the load state and the count value NCX. 1...Atmospheric intake port, 2...Air cleaner, 3...
Intake pipe, 4... Engine, 5... Throttle valve, 8
...Exhaust pipe, 9...Three-way catalytic converter, 10...
・Potentiometer, 11...Absolute pressure sensor, 12・
...Cooling water temperature sensor, 13...Crank angle sensor, 1
4...Oxygen concentration sensor, 15...Injector, 1
6... Atmospheric pressure sensor, 20... Control circuit, 21...
-Level conversion circuit, 22...Input signal switching circuit, 23
... A/D converter, 24... Waveform shaping circuit, 25.
...Counter, 28...Drive circuit, 29...CPU
, 30...ROM, 31...RAM, 32...I/O bus.

Claims (1)

[Claims] 1. Feedback control is performed to maintain a predetermined air-fuel ratio based on the concentration of exhaust components, and open-loop control is performed in which the feedback control is stopped in a predetermined state of high load to enrich the air-fuel ratio. In the air-fuel ratio control method for an internal combustion engine, a predetermined high load reference value is set, and the number of combustions when the engine is in a high load state above the reference value and the number of combustions when the engine is in a load state below the reference value are determined. 1. An air-fuel ratio control method for an internal combustion engine, characterized in that a switching timing from the feedback control to the open-loop control is determined according to a ratio of the feedback control to the open-loop control. 2. The high load reference value and the second higher load reference value
A high load reference value is set, and when the engine is operated at a high load higher than the second reference value, the air-fuel ratio is immediately enriched, and when the time for switching from feedback control to open loop control has passed. 2. The air-fuel ratio control method for an internal combustion engine according to claim 1, further comprising enriching the air-fuel ratio.