JP3324640B2 - Air-fuel ratio control device for internal combustion engine using natural gas - Google Patents

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 apparatus for an internal combustion engine using natural gas, and more particularly, to an air-fuel ratio control for an internal combustion engine using natural gas which appropriately controls the air-fuel ratio of an air-fuel mixture with respect to changes in fuel composition. Related to the device.

[0002]

2. Description of the Related Art Conventionally, there has been known an air-fuel ratio control device for an internal combustion engine in which a learned value of an air-fuel ratio correction amount is stored in a nonvolatile memory and is used for calculating a supplied fuel amount.

For example, a conventional method (Japanese Patent Publication No. 63-3640)
No. 8), a plurality of values are stored in a non-volatile memory in association with the operating state of the engine, and the plurality of values are stored in accordance with a deviation between an air-fuel ratio correction amount as integration processing information and a predetermined value. A plurality of values are corrected, that is, learned, and the basic fuel amount given to the internal combustion engine is corrected based on the learned values.

[0004] This makes it possible to absorb the effects of aging and deterioration of the engine and sensors.

[0005]

However, in an internal combustion engine using natural gas as a fuel, the composition of the natural gas, which is the fuel, differs for each sampling area. Therefore, when the learning value of the air-fuel ratio correction amount is calculated on the assumption that the composition of the fuel used in the engine is constant as in the above-described conventional method, the center of the air-fuel ratio feedback control is shifted, and the exhaust emission characteristics are reduced. There was a problem that it might worsen. In order to solve such a situation, it is necessary to re-learn the entire operating region of the engine every time the fuel composition changes, and it is difficult to avoid deterioration of the exhaust emission characteristics in the unlearned region.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide a natural gas system capable of appropriately controlling the air-fuel ratio of an air-fuel mixture regardless of fuel composition variations. An object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine to be used.

[0007]

According to a first aspect of the present invention, there is provided an air-fuel ratio control apparatus for an internal combustion engine using natural gas, the basic fuel being supplied to the internal combustion engine in accordance with the operating state of the engine. Basic fuel amount determining means for determining an amount, air-fuel ratio detecting means for detecting an air-fuel ratio of the air-fuel mixture supplied to the engine, and air-fuel ratio correction for calculating an air-fuel ratio correction amount according to the detected air-fuel ratio An internal combustion engine using natural gas, comprising: an amount calculation unit; and a supply fuel amount calculation unit that calculates an amount of supply fuel to be supplied to the engine based on the determined basic fuel amount and the calculated air-fuel ratio correction amount. In the air-fuel ratio control device, cruise state detection means for detecting a cruise state of a vehicle equipped with the engine, and an average value for calculating an average value of the calculated air-fuel ratio correction amount when the vehicle is in a cruise state. Calculator When, a fuel variation correction coefficient calculating means averages issued the calculated is to calculate the fuel variation correction coefficient based on the average value when exceeding the predetermined range,
The supply fuel amount calculation means calculates the supply fuel amount based on the calculated fuel variation correction coefficient.

With this configuration, the basic fuel amount to be supplied to the internal combustion engine is determined according to the operating state of the engine, the air-fuel ratio of the air-fuel mixture supplied to the engine is detected, and the air-fuel ratio is determined according to the detected air-fuel ratio. An air-fuel ratio correction amount is calculated, a cruise state of the vehicle equipped with the engine is detected, and when the vehicle is in a cruise state, an average value of the calculated air-fuel ratio correction amounts is calculated and the calculated value is calculated. When the average value exceeds a predetermined range, a fuel variation correction coefficient is calculated based on the average value. The amount of fuel supplied to the engine is calculated based not only on the determined basic fuel amount and the calculated air-fuel ratio correction amount, but also on the calculated fuel variation correction coefficient.

In general, the average value of the air-fuel ratio correction amount reflects the influence of variations in fuel composition. In particular, the average value of the air-fuel ratio correction amount calculated during a cruise state of a vehicle whose engine operation state is relatively stable reflects such an effect more accurately. Therefore, when the calculated average value exceeds a predetermined range, a fuel variation correction coefficient is calculated based on the average value, and the supplied fuel amount is corrected based on the calculated fuel variation correction coefficient. In addition, it is possible to absorb the deviation of the air-fuel ratio from the target value due to the variation of the fuel composition, and to reduce the deviation of the center of the air-fuel ratio feedback control. Therefore, the air-fuel ratio of the air-fuel mixture can be appropriately controlled irrespective of the variation in the composition of the fuel.

Further, as a result, the air-fuel ratio correction amount moves so as to converge to the center value, so that a sufficient margin from the limit value in the limit processing for the air-fuel ratio correction amount can be secured.

Further, the fuel variation correction coefficient calculating means is provided when the average value of the air-fuel ratio correction amount calculated by the average value calculating means exceeds a predetermined range and the cruise state of the vehicle continues for a predetermined time. Preferably, the fuel variation correction coefficient is calculated based on the calculated average value.

With this configuration, the fuel variation correction coefficient is calculated in a more stable state, so that the air-fuel ratio of the air-fuel mixture can be controlled more stably without causing hunting or the like.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing an overall configuration of an internal combustion engine (hereinafter referred to as an “engine”) and an air-fuel ratio control device thereof according to an embodiment of the present invention. The engine 1 uses natural gas as fuel. A throttle valve 3 is arranged in the intake pipe 2 of the engine 1. A throttle valve opening (θTH) sensor 4 is connected to the throttle valve 3, outputs an electric signal corresponding to the opening of the throttle valve 3, and supplies it to an electronic control unit (hereinafter referred to as “ECU”) 5. .

A fuel injection valve 6 is provided for each cylinder between the engine 1 and the throttle valve 3 and slightly upstream of the intake valve (not shown) of the intake pipe 2, and each injection valve is connected to a fuel pump (not shown). The ECU 5 is electrically connected to the ECU 5 and controls a valve opening time of the fuel injection valve 6 based on a signal from the ECU 5.

On the other hand, immediately downstream of the throttle valve 3, a pipe 7
An absolute pressure signal (PBA) sensor 8 is provided through the intake pipe, and an absolute pressure signal converted into an electric signal by the absolute pressure sensor 8 is supplied to the ECU 5. Further, an intake air temperature (TA) sensor 9 is attached downstream thereof.
Detects intake air temperature TA and outputs the corresponding electrical signal for EC
Supply to U5.

An engine water temperature (TW) sensor 10 such as a thermistor is mounted on the main body of the engine 1. The sensor 10 detects an engine water temperature (cooling water temperature) TW, outputs a corresponding temperature signal, and supplies the signal to the ECU 5. I do. The engine speed (NE) sensor 11 and the cylinder discrimination (CYL) sensor 12 are mounted around a camshaft or a crankshaft (not shown) of the engine 1. Engine speed sensor 1
Reference numeral 1 denotes a pulse at a predetermined crank angle position every time the crankshaft of the engine 1 rotates 180 degrees (hereinafter referred to as a “TDC signal pulse”
), And the cylinder discrimination sensor 12 outputs a signal pulse at a predetermined crank angle position of a specific cylinder. These signal pulses are supplied to the ECU 5.

A three-way catalyst (catalytic converter) 14 is disposed in an exhaust pipe 13 of the engine 1 and purifies components such as HC, CO, and NOx in the exhaust gas. On the upstream side of the three-way catalyst 14 of the exhaust pipe 13, an oxygen concentration sensor 16 (hereinafter referred to as "O2 sensor 16") as an air-fuel ratio detecting means is mounted. Is detected, and an electric signal corresponding to the detected value is output and supplied to the ECU 5.

The ECU 5 is connected to a vehicle speed sensor 19 for detecting a running speed (vehicle speed VP) of a vehicle on which the engine 1 is mounted, and a detection signal is supplied to the ECU 5.

The ECU 5 shapes input signal waveforms from various sensors, corrects a voltage level to a predetermined level, and converts an analog signal value to a digital signal value. The CPU 5b includes a storage unit 5c for storing various calculation programs executed by the CPU 5b, calculation results, various map tables, and the like, an output circuit 5d for supplying a drive signal to the fuel injection valve 6, and the like. .

CPU 5b as supply fuel amount calculation means
Based on the above-described various engine parameter signals, determine various engine operation states such as a feedback control operation area and an open loop control operation area according to the oxygen concentration in the exhaust gas, and according to the engine operation state,
The fuel injection time TOUT of the fuel injection valve 6 synchronized with the TDC signal pulse is calculated based on the following equation 1.

[0022]

## EQU00001 ## TOUT = TI.times.KTiCYL.times.KO2.times.K1 + K2 Here, TI is the basic fuel amount, and specifically, the current engine speed NE and the intake pipe absolute pressure PBA And the basic fuel injection time determined based on the TI map stored in the storage means 5c.

KTiCYL is a correction coefficient for correcting the air-fuel ratio of the supplied air-fuel mixture.
It is calculated by the L calculation process.

KO2 is an air-fuel ratio correction coefficient (amount) calculated based on the output of the O2 sensor 16 by the CPU 5b as an air-fuel ratio correction amount calculating means, and is detected by the O2 sensor 16 during the air-fuel ratio feedback control. The air-fuel ratio (oxygen concentration) is set to match the target air-fuel ratio,
During the open loop control, it is set to a predetermined value according to the engine operating state.

K1 and K2 are other correction coefficients and correction variables calculated in accordance with various engine parameter signals, respectively, to optimize various characteristics such as fuel consumption characteristics and engine acceleration characteristics according to the engine operating state. Is set to such a value.

The CPU 5b outputs a signal for driving the fuel injection valve 6 via the output circuit 5d based on the result calculated as described above.

The O2 sensor 16 constitutes the air-fuel ratio detecting means in the present invention, and the ECU 5 comprises the basic fuel amount determining means, the air-fuel ratio correction amount calculating means, the supplied fuel amount calculating means and the cruise state detecting means in the present invention. Means, an average value calculating means, and a fuel variation correction coefficient calculating means.

FIG. 2 is a flowchart showing the KO2 feedback control process. This process is executed in synchronization with the generation of the TDC signal pulse.

First, it is determined whether or not the last air-fuel ratio control was an open loop control (step S301). If the result of the determination is that the last air-fuel ratio control was not an open loop control, Is determined to be in the idling operation region (step S302). Whether the engine is in the idling operation range is determined from the engine speed NE and the intake pipe absolute pressure PBA. As a result of the determination, when the previous control region is the idle operation region, it is determined whether the current control region is the idle operation region (step S303).

As a result, if the result of the determination in step S302 indicates that the previous control region was not the idle operation region, or if the result of the determination in step S303 indicates that the current control region is the idle operation region, The process also proceeds to step S304, and it is determined whether or not the magnitude relationship between the output level of the O2 sensor 16 and the reference value VREF has been reversed. As a result of the determination, when the magnitude relationship between the output level of the O2 sensor 16 and the reference value VREF is reversed,
Proportional control (P-term control) or KO2
While performing processing such as calculating the average of the values, the O2 sensor 1
If the output level of No. 6 is not inverted, step S315
In the following, integral control (I-term control) is executed.

In step S305, the addition proportional term PR is added to the previously calculated KO2 value based on the magnitude comparison between the output level of the O2 sensor 16 and the reference value VREF.
Alternatively, processing such as subtraction of the subtraction proportional term PL is performed, and in the subsequent step S306, a limit check of the KO2 value is performed.

Next, it is determined whether or not the control region is the idling operation region (step S307). If the result of the judgment is that the control region is the idling operation region, a third average value KREF0 is calculated. On the other hand, when the control region is not in the idle operation region, the second average value KREF1 is calculated (step S309), and the first average is calculated.
Is calculated by the process of FIG. 3 described later (step S310), and the process proceeds to step S311. Here, each of the average values KREF0, 1, and CRS is an average value of the correction coefficient KO2, and is calculated by the following equation (2). The KREFCRS value is calculated by the same formula in step S406 of FIG. 3 described later.

[0033]

KREF (n) = CREF × KO2 / A + (A
−CREF) × KREF (n−1) / A Here, (n) and (n−1) are added to indicate the current value and the previous value, respectively. A is a constant set to, for example, 10000 (hexadecimal). CR
EF is a smoothing coefficient set between 0 and A, but the CREF value may be changed in two stages, for example, in accordance with the engine coolant temperature TW every time the average values KREF0, 1, and CRS are calculated. As KO2, a correction coefficient value immediately after execution of proportional control (that is, immediately after the output of the O2 sensor 16 is inverted and immediately after addition and subtraction of the proportional term) is used.

Next, each of the average values KREF0, 1, CRS
Is performed (step S311), and this process ends.

On the other hand, if the result of determination in step S301 is that the previous air-fuel ratio control was open-loop control, it is determined whether or not the current control region is an idle operation region (step S312). As a result of the determination, when the current control region is the idle operation region, the correction coefficient KO2 is set to the third average value KREF0 (step S313), and the process proceeds to step S315. If not, the correction coefficient KO2
Is set to (second average value KREF1 × CR) (step S314), and the process proceeds to step S315. Here, the value CR is set to a value such that the overall exhaust gas characteristics of the engine 1 are improved according to the exhaust gas characteristics of the engine itself and the exhaust gas purification characteristics of the exhaust gas purification device.

If the result of determination in step S303 is that the current control region is not in the idle operation region, that is, if the vehicle has shifted from the idle operation region to outside the idle operation region, step S314 is executed, and the process proceeds to step S315. .

In step S315, the KO2 calculated last time is based on the comparison between the output level of the O2 sensor 16 and the reference value VREF and the count number of the TDC signal pulse.
Add the addition integral term IR to the value, or subtract the integration integral term I
A process such as subtraction of L is executed, and the subsequent step S316
Then, the KO2 value limit check is performed, and the process is terminated.

According to this processing, the third average value KREF0 is calculated in the idle operation region immediately after the occurrence of the P term, and the second average value KREF1 is calculated outside the idle operation region immediately after the occurrence of the P term. The value KREFCRS is calculated at the timing of calculating the second average value KREF1 by the processing of FIG. 3 described later.

FIG. 3 shows a first average value KREFCR of the air-fuel ratio correction coefficient KO2 executed in step S310 of FIG.
5 shows a flowchart of an S calculation process.

First, a deviation (| KREF1-KREF) between the second average value KREF1 and the first average value KREFFCRS
CRS |) is smaller than a predetermined value DKRCRS (step S401), and as a result of the determination, | KRE
When F1−KREFCRS | <DKRCRS,
The engine speed NE is lower limit value NECRRFL and upper limit value N
It is determined whether or not it is within the range between ECRRFH (step S402), and as a result of the determination, NECRRFL <
When NE <NECRRFH, the absolute pressure P in the intake pipe
It is determined whether BA is within the range between the lower limit value PBCRRFL and the upper limit value PBCRRFH (step S40).
3) As a result of the determination, PBCRRFL <PB <PBC
When RRFH, the cruise flag FCR indicating by "1" that the vehicle is running at a constant speed (cruise state).
It is determined whether or not S is set to "1" (step S404). As a result of the determination, the cruise flag FCRS
Is set to “1”, the first average value KRE
FCRSREF is newly calculated, that is, the learning execution flag FCRSREF indicating that learning is to be performed is set to "1" (step S405), and the first average value KREFC is set.
RS is calculated by the above equation (step S40).
6) The counter value CKRCRS is incremented by "1" (step S409), and the process ends.

The cruise flag FCRS is set in a cruise determination process shown in FIG. Further, a hysteresis may be provided in the determination in steps S401 to S403.

On the other hand, NECRR in step S402
When FL <NE <NECRRFH is not satisfied, PBCRRFL <PB <PBCRRF in step S403.
When H is not established, or when the cruise flag FCRS is set to “0” in step S404, the process proceeds to step S408 in any case, the learning execution flag FCRSREF is set to “0”, and the present processing is performed. finish.

If | KREF1−KREFCRS | ≧ DKRCRS as a result of the determination in step S401, the KREFCRS value correction processing is performed by the following equation (3).
(Step S407), and the process ends.

[0044]

KREFCRS (n) = CREFCRS2 × K
REF1 / A + (A-CREFCRS2) × KREFC
RS (n-1) / A Here, (n) and (n-1) are added to indicate the current value and the previous value, respectively. A is a constant set to, for example, 10000 (hexadecimal), CREFC
RS2 is a smoothing coefficient set between 0 and A.

Here, the second average value KREF1 is calculated even when the vehicle is not in a cruise state if the engine 1 is in an operating state other than idling. Therefore, the calculation frequency is the first average value KREFFCRS. Higher than that of. Therefore, by correcting based on the deviation from the second average value KREF1, the learning accuracy of the first average value KREFFCRS can be improved.

According to the present processing, as described above, the first average value KREFFCRS is learned when the engine speed NE and the intake pipe absolute pressure PBA are within predetermined ranges and the vehicle is in a cruise state. When the deviation from the average value KREF1 of 2 is large, it is corrected by the KREF1 value. Further, each time the first average value KREFFCRS is calculated, the counter value CKRCRS increases by “1”.

The first average value KREFCRS learned by the process of FIG. 3 is held in a nonvolatile memory as a learned value even after the ignition key is turned off, and is used when the ignition key is turned on next time.

FIG. 4 shows a flowchart of the cruise determination process, which is executed by a timer process (for example, every 80 ms).

First, it is determined whether or not the state of the engine 1 is in the start mode (step S601). If the result of the determination is that the engine 1 is in the start mode, whether the fail-safe of the vehicle speed sensor 19 or the like is being executed. Is determined (step S
602) When the result of the determination is that failsafe is not being executed, the average value VPAVE of the vehicle speed VP is calculated by the following equation (4).
(Step S603).

[0050]

## EQU4 ## VPAVE (n) = (A-CCRS) × VP /
A + CCRS × VPAVE (n−1) / A Here, (n) and (n−1) are added to indicate the current value and the previous value, respectively. A is a constant set to 10,000 (hexadecimal), for example, and CCRS is a smoothing coefficient set between 0 and A.

Next, the vehicle speed average value VPAVE is changed to the lower limit value V.
It is determined whether or not the range is from CRSL (for example, 5 km) to the upper limit value VCRSH (for example, 255 km) (step S604).

As a result, when the engine 1 is in the start mode in step S601, when failsafe is being executed in step S602, or when VCRSL <VPAVE <VCRSH is not established in step S604, either In this case as well, the process proceeds to step S612, in which the countdown timer tmDVCRS stores the predetermined time T.
DVCRS (for example, 1.25 sec) is set and started, then a predetermined time TCRS (for example, 2 sec) is set in the down count timer tmCRS and started (step S613), and the cruise flag FCR is started.
S is set to “0” (step S614), and this processing ends.

On the other hand, in step S604, VCRSL
When <VPAVE <VCRSH holds, the timer t
It is determined whether or not the value of mDVCRS has reached "0" (step S605). If the value has not yet reached "0", this process is immediately terminated, while the value of the timer tmDVCRS has reached "0". When, the down count timer tmD
A predetermined time TDVCRS is set in VCRS and started (step S606), and a fluctuation amount (vehicle speed fluctuation amount) DVCRS of the vehicle speed average value VPAVE is calculated (step S606).
607). The vehicle speed fluctuation amount DVCRS is, for example, a current value and a previous value (stored value VPAVEBF) of the vehicle speed average value VPAVE.
Is calculated based on the deviation from.

Next, the stored value VPAVEBF is changed to the current V
The PAVE value is set (step S608), and the vehicle speed fluctuation amount DVCRS is set to a predetermined value DVCRSLMT (for example, 0.8 k
(equivalent to m / h / sec) (step S609). As a result of the determination, DVCRS ≧ DV
If CRSLMT, the process proceeds to step S613, while if DVCRS <DVCRSLMT, it is determined whether the value of the timer tmCRS has reached “0” (step S610). As a result of the determination, if the value has not yet reached “0”, the process proceeds to step S614,
When the value of the timer tmCRS has reached "0", the cruise flag FCRS is set to "1" (step S61).
1), end this processing.

According to this processing, as described above, the vehicle speed V
After the state in which the average value VPAVE of P is within the predetermined range continues for a predetermined time TDVCRS, and the amount of variation DVCRS of the average vehicle speed VPAVE is smaller than the predetermined value DVCRSLMT for a predetermined time TCRS, the cruise flag FCRS becomes "1". Is set to Therefore, FIG.
In step S406, learning of the first average value KREFFCRS is performed only when the vehicle travels in a stable state. This makes it possible to increase the reliability of the first average value KREFFCRS.

FIG. 5 is a flowchart showing a correction coefficient KTiCYL calculation process. This process is executed in synchronization with the generation of the TDC signal pulse.

First, it is determined whether the first average value KREFCRS is greater than a predetermined value KGASH (step S5).
01), and as a result of the determination, KREFCRS ≦ KGASH
When the first average value KREFCRS is equal to the predetermined value K
It is determined whether it is smaller than GASL (where KGASH> KGASL) (step S502). The predetermined value KGASH includes an upper value KGASHH and a lower value KGAS.
The predetermined value KGASL is provided with a hysteresis based on an upper value KGASLH and a hysteresis based on a lower value KGASHLL, respectively.

As a result of the determination in step S502, KR
When EFCRS ≧ KGASL, the counter value CK
RCRS is reset to "0" (step S503),
It is determined whether or not the flag FKGAS indicating that the fuel variation correction coefficient KGAS should be searched is indicated by "1" is set to "1" (step S504). As a result of the determination, the flag FKGAS is set to "1". If not, the fuel variation correction coefficient KGAS is set to "1.0" (step S505), and the process proceeds to step S506. If the flag FKGAS is set to "1", the process immediately proceeds to step S506. move on.

In the following step S506, the previous KTi
The current correction coefficient KTiCYL is calculated by multiplying the CYL value by the KGAS value, and the process ends. Then, the KTiCYL value calculated in step S506 is reflected in the calculation formula (formula 1) for the fuel injection time TOUT.

On the other hand, if the result of determination in step S501 is that KREFCRS> KGASH, the counter value CKRCRS has exceeded a predetermined value DKGAS (CKR
It is determined whether or not CRS> DKGAS) (step S507), and as a result of the determination, CKRCRS ≦ DKGA
If S, the process proceeds to step S504, while CK
When RCRS> DKGAS, the flag FKGAS
Is set to “1” (step S508), and the multiplication value KGA
SN is calculated as KGASN based on the first average value KREFCRS.
Search from the table (step S509).

FIG. 6 is a diagram showing the KGASN table. The table is set such that the larger the first average value KREFCRS, the larger the multiplied value KGASN.

Returning to FIG. 5, in the following step S510,
The fuel variation correction coefficient KGAS for this time is calculated by multiplying the multiplied value KGASN searched for by the previous KGAS value. As a result, when the first average value KREFCRS exceeds a predetermined value KGASH and the cruise state continues for a predetermined time (when the counter value CKRCRS exceeds a predetermined value DKGAS), the multiplied value KGASN is searched, and a new fuel A variation correction coefficient KGAS is calculated.

Next, the counter value CKRCRS is reset to "0" (step S511), and KREFn, that is, each of the average values KREF0, 1, and CRS are all set to "1.0".
And the KO2 value is initialized to "1.0" (step S512), and the process proceeds to step S506.

On the other hand, if the result of the determination in step S502 is that KREFCRS <KGASL, then in steps S513 and S514, steps S507 and S507 are executed.
The same processing as 508 is executed. That is, if CKRCRS ≦ DKGAS as a result of the determination in step S513, the process proceeds to step S504, while CKRCR
When S> DKGAS, the flag FKGAS is set to "1".
(Step S514), and the above-mentioned step S509 is set.
Proceed to.

It should be noted that the fuel variation correction coefficient KGAS calculated by this process and the set flag FKGAS are set.
Is retained in the non-volatile memory even after the ignition key is turned off, and is used when the ignition key is turned on next time.

FIG. 7 shows an operation example of the processing of FIG. 5, ie,
9 is a time chart illustrating an example of a change in a fuel variation correction coefficient KGAS and the like with respect to a change in a first average value KREFCRS.

When the flag FKGAS is set to "0" and the fuel variation correction coefficient KGAS is set to "1.0", the first average value KREFFCRS falls within a predetermined range (a predetermined value KGASH and a predetermined value KGASL). Between)
And when the deviation of the air-fuel ratio due to fuel is small (time t1
Before), the counter value CKRCRS is reset every time (step S503 in FIG. 5).

When the first average value KREFCRS gradually increases and exceeds the upper value KGASHH of the predetermined value KGASH (time t1), the counter value CKRCRS becomes the predetermined value DKG.
Until AS, it is increased without being reset, and the fuel variation correction coefficient KGAS maintains “1.0” (step S505 in FIG. 5). And the first average value KREFCR
When S falls below the lower value KGASHL of the predetermined value KGASH (time t2), the counter value CKRCRS is reset (step S503 in FIG. 5).

Next, the first average value KREFCRS again exceeds the upper value KGASHH of the predetermined value KGASH (time point t3), and the counter value CKRCRS remains in that state.
Exceeds the predetermined value DKGAS (time t4), the flag F
KGAS is set to “1” and the fuel variation correction coefficient K
The GAS is multiplied by the searched multiplication value KGAS, and the counter value CKRCRS is reset (step S in FIG. 5).
508-S511). Then, after calculating the fuel injection time TOUT based on the KTiCYL value, the first average value KRE is calculated.
FCRS changes so as to converge to the central value “1.0”. That is, the deviation of the control center is corrected.

Although the predetermined value KGASL is not shown in the figure, the first average value KREFCRS is equal to the predetermined value KG.
When the value falls below the ASL, the same processing is performed as when the first average value KREFCRS exceeds the predetermined value KGASH.

As described above, the first average value KREFCRS
Is over a predetermined range (when the value exceeds a predetermined value KGASH or falls below a predetermined value KGASL) and when the cruise state of the vehicle continues for a predetermined time (when the counter value CKRCRS exceeds a predetermined value DKGAS) In addition, assuming that the deviation of the air-fuel ratio due to fuel is large, the product KGASN
Is calculated, and a new fuel variation correction coefficient KGAS is calculated from the multiplied value KGASN.

As described above, according to the present embodiment, the first average value KREFCRS is learned during the cruise state of the vehicle during the air-fuel ratio feedback control (FIGS. 2 and 3), and the first average value KREFCRS is learned. Multiplied value KGA from value KREFCRS
SN is obtained (FIG. 6), and the fuel variation correction coefficient KGAS and the correction coefficient KTiCYL are calculated based on the multiplied value KGASN.
(FIG. 5), the fuel injection time TOUT is calculated (Equation 1 above).

Since the learning of the first average value KREFFCRS is performed during the cruise state of the vehicle in which the operation state of the engine 1 is relatively stable, the first average value KRFCRS is learned.
The EFCRS accurately reflects the effect of fuel composition variations. Therefore, it is possible to absorb the deviation of the air-fuel ratio from the target value due to the variation of the fuel composition, and it is possible to reduce the deviation of the center of the air-fuel ratio feedback control. Therefore, regardless of variations in fuel composition,
The air-fuel ratio of the air-fuel mixture can be appropriately controlled.

Further, as a result, the air-fuel ratio correction coefficient KO2
Moves so as to converge to the center value, so that a margin from the limit value in the limit processing (steps S306 and S316 in FIG. 2) for the air-fuel ratio correction coefficient KO2 can be sufficiently ensured.

Further, not only when the first average value KREFCRS exceeds the predetermined value KGASH or the like, but also when the cruise state of the vehicle continues for a predetermined time in that state (when the counter value CKRCRS exceeds the predetermined value DKGAS). Since the multiplication value KGASN is searched for, the fuel variation correction coefficient KGAS can be calculated in a more stable state, and the air-fuel ratio of the air-fuel mixture can be controlled more stably without causing hunting or the like. .

Since the first average value KREFCRS is corrected based on the deviation from the second average value KREF1 calculated during an operation state other than idling of the engine 1, learning of the first average value KREFCRS is performed. Accuracy can be improved, and the air-fuel ratio control can be more appropriately performed based on the more reliable KREFCRS value.

[0077]

As described above, according to the first aspect of the present invention,
According to the air-fuel ratio control apparatus for an internal combustion engine using natural gas, the basic fuel amount determining means for determining the basic fuel amount to be supplied to the internal combustion engine according to the operating state of the internal combustion engine, and the mixture supplied to the engine Air-fuel ratio detection means for detecting the air-fuel ratio of
Air-fuel ratio correction amount calculating means for calculating an air-fuel ratio correction amount according to the detected air-fuel ratio, and supply fuel to be supplied to the engine based on the determined basic fuel amount and the calculated air-fuel ratio correction amount. An air-fuel ratio control device for a natural gas-using internal combustion engine, comprising: a supply fuel amount calculation unit for calculating an amount; a cruise state detection unit for detecting a cruise state of a vehicle equipped with the engine; and the vehicle is in a cruise state. And an average value calculating means for calculating an average value of the calculated air-fuel ratio correction amount, and calculating a fuel variation correction coefficient based on the average value when the calculated average value exceeds a predetermined range. Fuel variation correction coefficient calculation means, and the supply fuel amount calculation means calculates the supply fuel amount based on the calculated fuel variation correction coefficient. That the deviation from the target value of the air-fuel ratio can be absorbed, it is possible to reduce the deviation of the center of the air-fuel ratio feedback control. Therefore, the air-fuel ratio of the air-fuel mixture can be appropriately controlled irrespective of the variation in the composition of the fuel.

Further, as a result, the air-fuel ratio correction amount moves so as to converge to the center value, so that a sufficient margin from the limit value in the limit processing for the air-fuel ratio correction amount can be secured.

According to the air-fuel ratio control apparatus for an internal combustion engine using natural gas of the second aspect of the present invention, the fuel variation correction coefficient calculation means calculates the average value of the air-fuel ratio correction amount calculated by the average value calculation means. When the vehicle exceeds the predetermined range and the cruise state of the vehicle continues for a predetermined time, the fuel variation correction coefficient is calculated based on the calculated average value. The calculated air-fuel ratio of the air-fuel mixture can be controlled more stably without hunting or the like.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an overall configuration of an air-fuel ratio control device for an internal combustion engine according to an embodiment of the present invention.

FIG. 2 is a diagram showing a flowchart of a KO2 feedback control process in the same embodiment.

FIG. 3 is a diagram showing a flowchart of a first average value KREFCRS calculation process of an air-fuel ratio correction coefficient executed in step S310 of FIG. 2 in the same embodiment.

FIG. 4 is a diagram showing a flowchart of a cruise determination process in the embodiment.

FIG. 5 is a diagram showing a flowchart of a correction coefficient KTiCYL calculation process in the same embodiment.

FIG. 6 is a diagram showing a multiplication value KGASN table in the same embodiment.

FIG. 7 is a time chart showing an example of a variation of a fuel variation correction coefficient KGAS and the like with respect to a variation of a first average value KREFCRS in the same embodiment.

[Explanation of symbols]

Reference Signs List 1 internal combustion engine 4 throttle valve opening (θTH) sensor 5 electronic control unit (ECU) (basic fuel amount determining means, air-fuel ratio correction amount calculating means, supplied fuel amount calculating means, cruise state detecting means, average value calculating means, and fuel Variation correction coefficient calculating means) 6 Fuel injection valve 8 Intake pipe absolute pressure (PBA) sensor 11 Engine speed (NE) sensor 16 O2 sensor (air-fuel ratio detecting means) 19 Vehicle speed (VP) sensor

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Eisaku Gosho 1-4-1 Chuo, Wako-shi, Saitama Prefecture Inside of Honda R & D Co., Ltd. (56) References JP-A-62-165555 (JP, A) JP-A-64-63645 (JP, A) JP-A-63-223348 (JP, A) JP-A-4-12151 ( JP, A) JP-A-63-36408 (JP, A) JP-A-4-116238 (JP, A) JP-A-63-57842 (JP, A) JP-A-2-1438 (JP, U) (58) ) Field surveyed (Int. Cl. ⁷ , DB name) F02D 41/00-45/00 F02D 19/00-19/12 F02M 21/02

Claims (2)

(57) [Claims] 1. A basic fuel amount determining means for determining a basic fuel amount to be supplied to an internal combustion engine in accordance with an operating state of the internal combustion engine; Air-fuel ratio correction amount calculating means for calculating an air-fuel ratio correction amount according to the detected air-fuel ratio; and supply to the engine based on the determined basic fuel amount and the calculated air-fuel ratio correction amount. An air-fuel ratio control device for a natural gas-using internal combustion engine, comprising: a supply fuel amount calculation unit that calculates a fuel amount; a cruise state detection unit that detects a cruise state of a vehicle equipped with the engine; In some cases, average value calculating means for calculating an average value of the calculated air-fuel ratio correction amount, and when the calculated average value exceeds a predetermined range, a fuel variation correction coefficient is calculated based on the average value. You An air-fuel ratio of the internal combustion engine using natural gas, wherein the supplied fuel amount calculation unit calculates the supplied fuel amount based on the calculated fuel variation correction coefficient. Control device. 2. The fuel-variation correction coefficient calculating means,
When the average value of the air-fuel ratio correction amount calculated by the average value calculation means exceeds a predetermined range and the cruise state of the vehicle continues for a predetermined time, the fuel variation is calculated based on the calculated average value. The air-fuel ratio control apparatus for an internal combustion engine using natural gas according to claim 1, wherein the correction coefficient is calculated.