JPH08121213A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE: To improve fuel consumption ratio and suppress increase of exhaust temperature in the case that a rich air-fuel ratio is brought about by stopping feedback control when a high load condition of an engine succeeds for a specified time, by setting the specified time according to deviation between a fuel supply rate and a specified reference value. CONSTITUTION: An ECU 20 determines an operation condition as in a feedback control operation area or an open loop control operation area according to oxygen density in exhaust gas based on input of signals from a throttle valve opening sensor 18, an engine speed sensor 32 and an O2 sensor. A fuel injection time of a fuel injection valve 22 is computed according to the determination result. After a specified high load state of an engine succeeds for a specified time, the feedback control is stopped, for bringing about a rich air-fuel ratio. In such a control, the specified time which is a condition for stopping the feedback control is set according to deviation between a fuel supply rate and a specified reference value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control system for a high load operation of an internal combustion engine.

[0002]

2. Description of the Related Art Conventionally, when the engine load is relatively low, the air-fuel ratio of the air-fuel mixture supplied to the engine is controlled to be near the stoichiometric air-fuel ratio, and when the engine load becomes high, the air-fuel ratio of the air-fuel mixture becomes high. Although the air-fuel ratio is made richer and the temperature of the engine is prevented from rising excessively due to the so-called fuel cooling effect, the control is not appropriate, resulting in an increase in fuel consumption or deterioration of exhaust gas characteristics. Was occurring.

In order to improve such a problem, when the engine load becomes high, the air-fuel mixture is made leaner within a predetermined time than after a predetermined time has elapsed (Japanese Patent Laid-Open No. 59-59).
No. 128941) or a method of enriching the air-fuel mixture when a high load state continues for a predetermined time or longer (Japanese Patent Laid-Open No. 57-24435).

However, according to these methods, for example, as shown in (1) of FIG. 14, a predetermined operation parameter for determining the high load state of the engine is maintained for a predetermined time or more for a predetermined period. When the high load operation that is shorter than or equal to the time is intermittently performed, the air-fuel mixture is not enriched, so that a situation occurs in which the exhaust temperature continues to rise, as shown in (2) of FIG. As a result, there is a problem that the heat-resistant allowable time at the continuous exhaust allowable temperature or more is exceeded, and eventually the temperature limit is also exceeded, causing an excessive rise in the catalyst temperature of the exhaust purification device provided in the exhaust system in particular. there were.

Therefore, in order to avoid the above-mentioned situation, when a high load operation is performed, fuel is forcibly increased after a predetermined delay time elapses, and the delay time is set to a predetermined high load or more. There is one that avoids an excessive rise in exhaust gas temperature by adjusting the cumulative difference between the operating time and the operating time below the predetermined high load (JP-A-2-
No. 291442).

[0006]

However, in the above-mentioned method, the rate of increase or decrease of the exhaust temperature is not constant depending on the load region, and the operating time of a predetermined high load or more and the operating time of a predetermined high load or less are Since the delay time was set only by the cumulative difference, the rate of increase in the exhaust temperature tends to be significantly higher in the higher load region than the predetermined high load judgment value with high combustion energy. There was a problem that it could not be set large.

The present invention solves the above-mentioned problems, makes the exhaust gas favorable by adjusting the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine, and predicts the increase rate of the exhaust temperature more accurately. It is an object of the present invention to provide an air-fuel ratio control device for an internal combustion engine, which can improve fuel efficiency and suppress an increase in exhaust temperature.

[0008]

In order to achieve the above object, the present invention detects the exhaust gas component concentration based on the output of an exhaust gas concentration sensor provided in the exhaust system of an internal combustion engine,
Feedback control is performed so that the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine becomes a predetermined value according to the detected value, and the feedback control is stopped after the engine has been in a predetermined high load state for a predetermined period. In an air-fuel ratio control device for an internal combustion engine, which enriches an air-fuel ratio of an air-fuel mixture supplied to the internal combustion engine, a fuel supply amount calculation means for obtaining a fuel supply amount to the internal combustion engine, the fuel supply amount and a predetermined reference A deviation calculating means for obtaining a deviation from the value and a period setting means for setting the predetermined period according to the deviation are provided.

[0009]

In the present invention, the fuel consumption is reduced by setting the predetermined period for enriching the air-fuel ratio based on the deviation between the fuel supply amount to the internal combustion engine and the predetermined reference value in the high load state. It is possible to control the optimum exhaust temperature without the need.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an overall configuration diagram of a fuel supply control device to which the present invention is applied. Intake pipe 1 of internal combustion engine 10
A throttle body 14 is provided in the middle of 2, and a throttle valve 16 is arranged inside the throttle body 14. A throttle valve opening (θTH) sensor 18 is connected to the throttle valve 16 and outputs an electric signal according to the opening θTH of the throttle valve 16 and supplies it to an electronic control unit (hereinafter referred to as ECU) 20. .

The fuel injection valve 22 is provided for each cylinder between the engine 10 and the throttle valve 16 and slightly upstream of the intake valve (not shown) of the intake pipe 12, and each fuel injection valve 22 is not shown. The valve opening time of fuel injection is controlled by a signal from the ECU 20 as well as being connected to the fuel pump and electrically connected to the ECU 20.

On the other hand, an intake pipe absolute pressure (PBA) sensor 26 is provided immediately downstream of the throttle valve 16 via a pipe 24. The absolute pressure signal converted by the absolute pressure sensor 26 into an electric signal is the above-mentioned. It is supplied to the ECU 20.
An intake air temperature (TA) sensor 28 is attached downstream thereof, detects the intake air temperature TA, outputs a corresponding electric signal, and supplies it to the ECU 20.

The engine water temperature (TW) sensor 30 mounted on the main body of the internal combustion engine 10 comprises a thermistor or the like,
The engine water temperature (cooling water temperature) TW is detected and a corresponding temperature signal is output and supplied to the ECU 20. Engine speed (NE) sensor 32 and cylinder discrimination (CYL) sensor 3
Reference numeral 4 is attached around a cam shaft or a crank shaft (not shown) of the internal combustion engine 10. The engine speed sensor 32 outputs a signal pulse (hereinafter, T pulse) at a predetermined crank angle position every 180 ° rotation of the crankshaft of the internal combustion engine 10.
It outputs a DC signal pulse), and the cylinder discrimination sensor 34
Outputs a signal pulse at a predetermined crank angle position of a specific cylinder. Each of these signal pulses is output by the ECU 2
0 is supplied.

The three-way catalyst 36 is arranged in the exhaust pipe 38 of the internal combustion engine 10, and HC, CO, NO contained in the exhaust gas.
Purify components such as x. An O ₂ sensor 40 as an exhaust gas concentration detector is mounted on the exhaust pipe 38 upstream of the three-way catalyst 36, detects the oxygen concentration in the exhaust gas, and outputs a signal corresponding to the detected value to output the ECU 20. Supply to. E
An atmospheric pressure (PA) sensor 42 that detects the atmospheric pressure PA is connected to the CU 20, and a signal indicating the atmospheric pressure PA is supplied.

The ECU 20 shapes the input signal waveforms from various sensors, corrects the voltage level to a predetermined level, and converts the analog signal value into a digital signal value. , CPU) 44b, a storage means 44c for storing various calculation programs executed by the CPU 44b and calculation results, an output circuit 44d for supplying a drive signal to the fuel injection valve 22, and the like.

The CPU 44b discriminates various engine operating states such as a feedback control operating region and an open loop control operating region according to the oxygen concentration in the exhaust gas based on the various engine parameter signals which are the digital signals described above, and Depending on the operating state of
Based on the equation, the fuel injection time TOUT of the fuel injection valve 22 synchronized with the TDC signal pulse is calculated.

TOUT = TIM × K1 × KWOT × KTW × KO2 + K2 (1) Here, TIM is a reference value of the fuel injection time TOUT, and TIM is set according to the engine speed NE and the intake pipe absolute pressure PBA. Read from the map. KWOT
Is a high load increasing coefficient for enriching the air-fuel mixture when the throttle valve 16 is substantially fully opened, and is set by the method shown in FIG. 2 described later. KTW is a fuel increase coefficient that enriches the air-fuel mixture when the engine water temperature TW is equal to or lower than a predetermined value. KO2 is an air-fuel ratio feedback correction coefficient,
During feedback control, it is set according to the oxygen concentration in the exhaust gas. K1 and K2 are other correction coefficients and correction variables calculated according to various engine parameter signals, respectively, and have predetermined values for optimizing various characteristics such as fuel consumption characteristics and engine acceleration characteristics according to the engine operating state. Determined by the value.

The CPU 44b outputs a drive signal for opening the fuel injection valve 22 based on the fuel injection time TOUT obtained as described above via the output circuit 44d.
Supply to.

FIG. 2 shows a flowchart of a subroutine for calculating the high load increasing coefficient KWOT. This program is executed in synchronization with each generation of the TDC signal pulse.

In step S101, the engine speed N
The high load increase coefficient KWOT is calculated by applying the interpolation coefficient CWOT stored in the TIM map together with the reference value TIM of the fuel injection time TOUT according to E and the intake pipe absolute pressure PBA to the following equation (2).

KWOT = 1 + CWOT / 32 (2) Next, in step S102, the subroutine shown in FIG. 3 is executed. This subroutine determines a predetermined period determination flag FCRTWOT for determining a predetermined period (hereinafter referred to as WOT period) in which the high load should be increased.

Therefore, first, in step S201, it is confirmed whether or not the engine 10 is in the start mode, and if it is the start mode, the count value CRT and the predetermined period determination flag FCRTWOT which will be described later are initialized to "0" ( Steps S202 and S203).

On the other hand, when the starting mode of the engine 10 is released, the average fuel supply amount Q to the engine 10 is
The deviation DQFUEL is obtained from FUELAVE and the supply amount reference value QUELFG at which the exhaust system temperature does not exceed the allowable temperature (step S204). In addition, this step S204 functions as a deviation calculation means.

DQFUEL = | QFUELG−QFUELAVE | (3) Here, the average fuel supply amount QFUELAVE is shown in FIG.
It is obtained by the subroutine shown in. It should be noted that this subroutine functions as a fuel supply amount calculation means. In step S301, the fuel supply amount QFUE per minute
L is the engine speed NE and the reference value TIM of the fuel injection time TOUT obtained from the TIM map,
It is calculated by the following equation (4). Note that α is a predetermined coefficient.

QFUEL = TIM × NE × α (4) In step S302, the fuel supply amount QFUEL and the average fuel supply amount QFUELAVE (n obtained in the previous calculation are calculated.
−1) is used to calculate the current average fuel supply amount QFUELAVE by the following equation (5). Note that β is an averaging coefficient.

QFUELAVE = QFUEL × β + QFUELAVE (n−1) × (1−β) (5) The average fuel supply amount QFUELA obtained as described above.
After obtaining the deviation DQFUEL using VE, the average fuel supply amount QFUELAVE and the supply amount reference value QFUELG
Is compared with the size (step S205), and QFUELA
When VE <QFUELG, the subtraction amount CRTDOWN for subtracting the count value CRT is calculated (step S
206). In this case, the subtraction amount CRTDOWN is set to increase as the deviation DQFUEL increases, as shown in FIG. Then, step S20
In 7, the count value CRT is changed using the subtraction amount CRTDOWN as shown in the following expression (6), and the program is terminated. When the count value CRT becomes negative (step S208), the count value CR
This program is terminated by setting T to 0 (step S20).
9).

CRT = CRT−CRTDOWN (6) On the other hand, in step S205, QFUELAVE ≧
In the case of QFUELG, if the high load determination flag FWOT obtained by the subroutine described later is "1" (step S210), the current count value CRT is held (step S211), and the predetermined period determination is performed to perform the high load increase control. The flag FCRTWOT is set to "1" and the program ends (step S212).

Further, the high load discrimination flag FWOT is "0".
If so (step S210), it is confirmed whether or not the engine water temperature TW is higher than a predetermined water temperature TWCRT (for example, 65 ° C.) (step S213), and if it is higher, the addition amount CRTUP for adding the count value CRT. Is calculated (step S214). In this case, the addition amount CRTU
As shown in FIG. 6, P is set to increase as the deviation DQFUEL increases. Then, in step S215, the count value CRT is changed using the addition amount CRTUP as shown in the following expression (7).

CRT = CRT + CRTUP (7) When the engine water temperature TW is lower than the predetermined water temperature TWCRT, the count value CRT is changed to the predetermined count value CRTBAS.
After replacing with E (step S216), the count value CRT is changed based on the equation (7).

Count value CRT thus obtained
Is the count upper limit value CRTW in step S217.
Compared with OT, if CRT <CRTWOT, terminate this program, and if CRT ≧ CRTWOT,
The count value CRT is replaced with the count upper limit value CRTWOT (step S218), and the predetermined period determination flag F
CRTWOT is set to "1" and the program ends (step S212).

Here, based on FIG. 7, the count upper limit value C
The relationship between the average fuel supply amount QFUELAVE, the count value CRT, and the predetermined period determination flag FCRTWOT set in the above-described subroutine of FIG. 3 will be described by taking the case where RTWOT is set to “40” as an example. in this case,
When QFUELAVE ≧ QFUELG, the count value CRT increases to the count upper limit value CRTWOT = 40, and at the time when CRT = 40, the predetermined period determination flag F
CRTWOT is set to "1". The predetermined period determination flag FCRTWOT is the high load determination flag FW.
Even when OT is "1", it is set to "1" (step S
210, S212). In addition, QFUELAVE <QFU
In the case of ELG, the count value CRT is subtracted. The amount of addition or the amount of subtraction of the count value CRT depends on the magnitude of the deviation DQFUEL, and the timing at which the predetermined period determination flag FCRTWOT is set to "1" is adjusted accordingly.

The subroutine for adjusting the timing with the count value CRT functions as period setting means for setting a predetermined period for enriching the air-fuel ratio.

Next, step S103 of FIG. 2 is executed,
The high load determination flag FWOT is determined. The high load determination flag FWOT is a flag for determining whether or not the engine 10 is in the operating region where the high load should be increased, and is determined by the subroutine shown in FIG.

First, in step S401, the discriminant value PBW is determined from the PBWOT table according to the engine speed NE.
Search OT. The PBWOT table is, for example,
It is set as shown by the solid line in FIG. Further, in step S402, THWO is determined according to the engine speed NE.
The discriminant value THWOT is searched from the T table. This TH
The WOT table is set as shown by the solid line in FIG. 11, for example.

In step S403, the engine speed N
E is a predetermined rotation speed NWOTL (for example, 1000 rpm)
If NE ≦ NWOTL (low speed rotation), the discriminant value PBWOT is adopted (step S40).
4). If NE> NWOTL (high speed rotation),
In step S405, the engine water temperature TW is compared with a predetermined water temperature TWWOTE (for example, 110 ° C.), and TW ≧
If it is TWWOTE (high water temperature), the determination value PBWO
T is subtracted and corrected by a predetermined value DPBWOTE (step S
406, see FIG. 9 dash-dotted line). On the other hand, NE> NWOTL
If (high speed rotation) and TW <TWWOTE (low water temperature), the DPBWOTPA table shown in FIG. 10 is searched to calculate the predetermined value DPBWOTPA for the atmospheric pressure PA (step S407), and the determination value PBWOT is set to the predetermined value DPBWOTPA. Subtractive correction (step S408,
(See the dotted line in FIG. 9). As a result, when the engine speed NE is high speed and the engine water temperature TW is high, or when the atmospheric pressure PA is low, the discriminant value PBWOT is subtractively corrected, thereby enriching the air-fuel mixture (Fig. 9).

Next, at step S409, the throttle valve opening degree θTH depends on the engine speed NE set in the THWOT table shown in FIG.
If it is compared with T and θTH> THWOT (throttle fully open state), the predetermined period determination flag FCRTWOT is set to “1” (step S410) and the high load determination flag FWOT is set to “1” (step S4).
11) The program ends. In addition, θTH ≦ TH
If it is WOT, in step S412, the intake pipe absolute pressure PBA is compared with the determination value PBWOT set in step S404, S406 or S408,
If PBA <PBWOT, the predetermined period determination flag FC
While setting RTWOT to "0" (step S4
13), the high load determination flag FWOT is set to "0" (step S414), and this program ends. PB
If A ≧ PBWOT, the current predetermined period determination flag F
When CRTWOT is "1" (step S415), the high load determination flag FWOT is set to "1" (step S41).
1), the predetermined period determination flag FCRTWOT is "0"
In this case, the high load determination flag FWOT is set to "0", and this program ends (step S414).

As described above, when FWOT = 1, it is determined that the engine 10 is in the WOT region where the high load should be increased.

Next, step S104 in FIG. 2 is executed,
If the high load determination flag FWOT is "0", the engine 10 is not in the WOT region, and therefore the high load increase coefficient KWOT
Is set to 1.0 and the program is terminated (step S105). Further, the high load determination flag FWOT is "1".
If so (step S104), the engine 10 is the WOT.
Since it is in the region, the enrichment coefficient XWOT is determined based on the XWOT table shown in FIG. 12 in relation to the engine temperature TW (step S106), and the obtained enrichment coefficient XWOT is obtained.
Further increase correction is performed by multiplying WOT by the high load increase coefficient KWOT calculated in step S101 (step S107). Then, if the timer TMEXM down-counted from the previous value is not "0", this program is terminated (step S108).

The timer TMEXM is set by the subroutine shown in FIG. That is, in step S501, the engine speed NE and the predetermined value NEX
M (for example, 4500 rpm) is compared, and NE ≦ NE
If it is XM, the timer TMEXM is set to a predetermined value TMEXM0.
(For example, 5 minutes), NE> NEXM (engine 1
If the rotation speed is high (0), the timer TMEXM continues to count down.

In step S108, the timer T
If MEXM is "0", the high load increase coefficient KWOT is compared with a predetermined upper limit value KWOTE (for example, 1.375) (step S109). If KWOT≤KWOTE, this program is terminated, and KWOT> KWOTE In the case of, the high load increase coefficient KWOT is set to the upper limit value KWOTE and the program is terminated (step S110).

Here, the high load discrimination flag FWOT is a predetermined period discrimination flag F as shown in the subroutine of FIG.
When CRTWOT becomes “1”, or θTH
> THWOT, the predetermined period determination flag FCRTWOT is set to "1" when the count value CRT reaches the count upper limit value CRTWOT, as shown in the subroutine of FIG. Is set. Therefore, as shown in FIG.
Deviation DQ after entering the high load region where ≧ PBWOT
Period CRTWOT set according to the size of FUEL
After being delayed by a certain amount, it is determined to be in the WOT (high load) region, and the high load increasing coefficient KWOT is increased.

As a result, the predetermined period discrimination flag FCRTW
While OT is “0”, feedback control is performed by setting the air-fuel ratio feedback correction coefficient KO2 of the equation (1) according to the oxygen concentration in the exhaust gas, and PBA ≧ PB
After a lapse of a predetermined period after entering the WOT region after becoming the WOT, when the predetermined period determination flag FCRTWOT becomes "1", the fuel injection time TOUT calculated by the equation (1) based on the high load increase coefficient KWOT. The control is performed according to. The timing of increasing the fuel injection time TOUT depends on the fuel supply amount and the engine temperature TW.
Since the engine temperature TW is not excessively cooled when the fuel amount is increased, it is possible to maintain an optimum fuel supply amount and maintain a good exhaust gas state.

[0043]

As described above, according to the present invention, the air-fuel mixture is mixed in accordance with the deviation between the fuel supply amount to the engine and the predetermined reference value at which the exhaust system temperature does not exceed the allowable temperature, which correlates with the heat load of the exhaust system. Since the time to start the enrichment of the air-fuel ratio of is set,
By accurately predicting an early rise in the exhaust gas temperature in an operating state in which the combustion energy is large, that is, in an operating state in which the fuel supply amount is large, it is possible to achieve both improvement in fuel consumption and suppression of an increase in exhaust gas temperature.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of a fuel supply control device to which the present invention is applied.

FIG. 2 is a subroutine for calculating a high load increase coefficient.

FIG. 3 is a subroutine for calculating a predetermined period determination flag.

FIG. 4 is a subroutine for calculating an average fuel supply amount.

FIG. 5 is an explanatory diagram of a table for setting a count subtraction amount.

FIG. 6 is an explanatory diagram of a table for setting a count addition amount.

FIG. 7 is an explanatory diagram of an operation of the subroutine of FIG.

FIG. 8 is a subroutine for determining a high load determination flag.

FIG. 9 is an explanatory diagram of a table for setting a high load increase area.

FIG. 10 is an explanatory diagram of a table for setting a correction amount for atmospheric pressure.

FIG. 11 is an explanatory diagram of a table for setting a high load increase area.

FIG. 12 is an explanatory diagram of a table for setting the enrichment coefficient.

FIG. 13 is a subroutine for setting a timer.

FIG. 14 is an explanatory diagram of exhaust temperature in fuel control according to a conventional technique.

[Explanation of symbols]

10 ... Engine 16 ... Throttle valve 18 ... Throttle valve opening sensor 20 ... ECU 22 ... Fuel injection valve 26 ... Intake pipe absolute pressure sensor 28 ... Intake temperature sensor 30 ... Engine water temperature sensor 32 ... Engine speed sensor 34 ... Cylinder discrimination sensor 36 ... Three-way catalyst 40 ... O ₂ sensor

Claims (3)

[Claims] 1. An exhaust gas component concentration is detected based on an output of an exhaust gas concentration sensor provided in an exhaust system of an internal combustion engine, and an air-fuel ratio of an air-fuel mixture supplied to the internal combustion engine is set to a predetermined value according to the detected value. With the feedback control so that the engine is maintained in a predetermined high load state for a predetermined period of time, the feedback control is stopped, and the air-fuel ratio of the internal combustion engine that enriches the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine. In the control device, a fuel supply amount calculation means for obtaining a fuel supply amount to the internal combustion engine, a deviation calculation means for obtaining a deviation between the fuel supply amount and a predetermined reference value, and the predetermined period according to the deviation. And an air-fuel ratio control device for an internal combustion engine, comprising: 2. The apparatus according to claim 1, wherein the period setting means adjusts the count value so that the predetermined period is shortened when the fuel supply amount is larger than the reference value, and the fuel supply is performed. An air-fuel ratio control device for an internal combustion engine, comprising a timer counter that adjusts a count value such that the predetermined period becomes longer when the amount is smaller than the reference value. 3. The apparatus according to claim 2, wherein the timer counter comprises a counter whose speed for increasing or decreasing the count value is controlled according to a deviation between the fuel supply amount and the reference value. Air-fuel ratio control device for internal combustion engine.