JP3046847B2 - Air-fuel ratio control device for internal combustion engine - 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 device for an internal combustion engine, and more particularly to an air-fuel ratio control device for an internal combustion engine using a fuel mixed with alcohol.

[0002]

2. Description of the Related Art In recent years, research and development of an internal combustion engine using a fuel mixed with an alcohol represented by methanol has been actively carried out for the purpose of reducing harmful exhaust gas such as NOx and reducing the cost of fuel used. I have.

Conventionally, in this type of internal combustion engine,
The air-fuel ratio of the air-fuel mixture supplied to the engine has been controlled to be a stoichiometric air-fuel ratio according to the alcohol concentration in the fuel detected by the alcohol sensor (for example, Japanese Patent Application Laid-Open No. 1-244133).

[0004]

However, in the above-described conventional control method, particularly when the output (detection value) of the alcohol sensor fluctuates due to ignition noise or drift and deviates from the actual alcohol concentration at the time of starting, the above-mentioned control method is used. The air-fuel ratio of the air-fuel mixture is also controlled to a value that deviates from the stoichiometric air-fuel ratio in accordance with the output of the alcohol sensor, and there has been a problem that the exhaust gas characteristics deteriorate.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has been made in an internal combustion engine using a fuel mixed with alcohol, and has an air-fuel ratio caused by fluctuations in the output of an alcohol sensor due to disturbances such as noise and drift. It is an object of the present invention to provide an air-fuel ratio control device for an internal combustion engine that can prevent fluctuations in exhaust gas characteristics and avoid deterioration of exhaust gas characteristics.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides an air-fuel ratio control device for an internal combustion engine using a fuel mixed with alcohol, which comprises: A correction coefficient calculating means for calculating a correction coefficient in accordance with the alcohol concentration detected by the means, an operating state detecting means for detecting an operating state of the engine, and the operating state detected by the operating state detecting means. An average value calculating means for calculating an average value of the correction coefficient, and an air-fuel ratio controlling means for controlling an air-fuel ratio in accordance with the average value calculated by the average value calculating means.

Further, the average value calculating means calculates the average value of the correction coefficient during the engine start and within a predetermined period after the engine is started.

Further, in the first invention and the second invention, the calculation speed of the average value of the correction coefficient in the average value calculating means is different between during and after the start of the engine.

Further, the average value calculation speed of the correction coefficient during the start of the engine in the average value calculation means is faster than the average value calculation speed after the start of the engine.

According to the present invention, the average value of the correction coefficient depending on the output of the alcohol concentration detecting means is calculated by the average value calculating means in accordance with the driving state, and the air-fuel ratio is controlled by the air-fuel ratio control means in accordance with the average value. Control is exercised.

The average value of the correction coefficient is calculated during the start of the engine and within a predetermined period after the start of the engine.

The speed of calculating the average value differs between during and after the start of the engine. Preferably, the average value during the start of the engine is calculated faster than the average value after the start of the engine.

[0012]

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

FIG. 1 is an overall configuration diagram showing one embodiment of a rotation speed control device for an internal combustion engine according to the present invention.

Reference numeral 1 denotes an internal combustion engine having, for example, four cylinders (hereinafter simply referred to as "engine"). An engine water temperature (TW) sensor comprising a thermistor or the like is provided on a cylinder wall of a cylinder block of the engine 1 which is filled with cooling water. 2 is inserted, and an electric signal corresponding to the engine coolant temperature TW detected by the TW sensor 2 is supplied to an electronic control unit (hereinafter, referred to as “ECU”) 3.

An engine speed (NE) sensor 5 is mounted around a camshaft (not shown) or around a crankshaft of the engine 1. The NE sensor 5 outputs a signal pulse (hereinafter referred to as a “TDC signal pulse”) at a predetermined crank angle position every time the crankshaft of the engine 1 rotates by 180 degrees. These TDC signal pulses are supplied to the ECU 3.

A throttle body 7 is provided in the middle of an intake pipe 6 of the engine 1, and a throttle valve 7 'is provided therein.
Is arranged. A throttle valve opening (θTH) sensor 8 is connected to the throttle valve 7 ′, and supplies an electric signal corresponding to the opening of the throttle valve 7 ′ to the ECU 3.

An absolute pressure (PBA) sensor 10 is connected to the intake pipe 6 downstream of the throttle valve 7 ′ via a branch pipe 9. The PBA sensor 10 is electrically connected to the ECU 3, and an electric signal corresponding to the absolute pressure PBA in the intake pipe 6 detected by the PBA sensor 10 is transmitted to the EC 3.
It is supplied to U3.

An intake air temperature (TA) sensor 11 is mounted on the pipe wall of the intake pipe 6 downstream of the branch pipe 9, and an electric signal corresponding to the intake air temperature TA detected by the TA sensor 11 is sent to the ECU 3. Supplied.

The fuel injection valve 12 is provided for each cylinder between the engine 1 and the throttle valve 7 'and slightly upstream of an intake valve (not shown) of the intake pipe 6.

The fuel injection valve 12 has a first fuel supply pipe 13
The ECU 3 is connected to the fuel pump 14 through
The valve opening time is controlled by a drive signal from the ECU 3 electrically connected to the ECU. Further, the fuel pump 14 is connected to a fuel tank 16 via a second fuel supply pipe 15.

A fuel pressure (PAL) sensor 18 is connected to the first fuel supply pipe 13 downstream of the fuel pump 14 via a branch pipe 17. The PAL sensor 18 is electrically connected to the ECU 3, and an electric signal corresponding to a detection value of the PAL sensor 18 is supplied to the ECU 3.

The bypass pipe 19 is provided so as to branch off from the middle of the first fuel supply pipe 13 between the fuel pump 14 and the branch pipe 17, and a part of the alcohol fuel discharged from the fuel pump 14 is supplied to the fuel tank. Refluxed to 16. Specifically, the ECU 3 sends a control signal corresponding to the value detected by the PAL sensor 18 to the pressure regulating valve 20 provided in the pipeline of the bypass pipe 19, and adjusts the valve opening of the pressure flow regulating valve 20. Thus, the fuel pressure supplied from the fuel tank 16 to the fuel injection valve 12 is controlled to a predetermined value.

An alcohol concentration (ALC) sensor 2 is provided on the wall of the first fuel supply pipe 13 downstream of the branch pipe 17.
1 is attached. The ALC sensor 21 is the ECU 3
, And supplies an electric signal corresponding to the detection value of the ALC sensor 21 to the ECU 3.

Further, an exhaust gas concentration detector such as an O ₂ sensor is mounted in the exhaust pipe 22 of the engine 1, and an electric signal corresponding to the oxygen concentration in the exhaust gas detected by the O ₂ sensor is sent to the ECU 3. Supplied.

The ECU 3 shapes the input signal waveforms from the various sensors described above, corrects the voltage level to a predetermined level,
An input circuit 3a having a function of converting an analog signal value to a digital signal value and the like;
U ") 3b, a storage means 3c comprising a ROM for storing various calculation programs executed by the CPU 3b, a predetermined map and the like, and a RAM for storing calculation results and the like; the fuel injection valve 12 and the pressure regulating valve 21; And an output circuit 3d for supplying a drive signal to the output circuit 3d.

The CPU 3b determines various engine operating conditions based on various engine parameter signals, and opens the fuel injection valve 12 in synchronization with the TDC signal in accordance with the determined engine operating conditions. The fuel injection time Tout to be calculated is calculated based on Equation 1.

First, during the start of the engine, the fuel injection time Tout is calculated based on the following equation 1 according to the start mode.

[0028]

Tout = TiCR × KNE × KALCCR × K₁+ K_Two  Here, TiCR is the fuel injection valve 12 in the start mode.
This is the reference value for the injection time of
It is determined according to the engine cooling water temperature Tw. KNE is KN
Determined according to the engine speed NE by the E table
You.

KALCCR is an alcohol concentration correction coefficient in the starting mode, which is determined according to the alcohol concentration detected by the ALC sensor 21 in the KALCCR table, and as described later, its average value is used as the actual KALC value in the above equation (1). Applied to

K ₁ and K ₂ are other correction coefficients and correction variables, which are determined according to the battery voltage and the like.

Next, after the start of the engine is completed, the basic mode is entered, and the fuel injection time Tout is calculated by the following equation (2).

[0032]

## EQU2 ## Tout = Ti × KALC × K_Three+ K_Four  Here, Ti represents the injection of the fuel injection valve 12 in the basic mode.
This is the reference value of the firing time, and the engine speed is determined based on the Ti map.
It is determined according to the number NE and the intake pipe absolute pressure PBA.

KALC is an alcohol concentration correction coefficient in the basic mode. In the basic mode, the KALC table is used in accordance with the detection value of the ALC sensor 21 according to the detection value of the ALC sensor 21 when the engine is in a steady state and when the engine is accelerating in the KALCT table. , KALCT. Equation 2 above also applies to KAL in the basic mode.
The average value is applied as the C value.

K ₃ and K ₄ are a correction coefficient and a correction variable which are set by the throttle valve opening and other parameter values indicating the engine operation state, and are set so that the starting characteristics, acceleration characteristics and the like are optimized. You.

In this case, the CPU 3 b
c, based on the correction coefficient tables (KALCCR table, KALC table, KALCT table), according to the methanol concentration ALC detected by the ALC sensor 21, the correction coefficients KALCCR, KALC, K
ALCT (hereinafter "KALC" unless otherwise specified)
), Average value calculating means for calculating the average value of the correction coefficients, and air-fuel ratio control means for controlling the air-fuel ratio in accordance with the average value.

The correction coefficient table used for calculating the correction coefficient KALC is stored in the storage means 3c (RO
M) and is selected according to the operating state of the engine.

FIG. 2 shows an example of the correction coefficient table, which is a correction coefficient K at the time of a steady state of the engine in the basic mode.
FIG. 4 is a diagram illustrating an ALC table, in which the horizontal axis indicates an alcohol concentration value detected by an ALC sensor, and the vertical axis indicates a value of a correction coefficient KALC.

As is apparent from FIG. 2, the correction coefficient table includes a plurality of predetermined methanol concentration values ALC1,.
The predetermined correction coefficient values KALC,.
An ALC 6 is provided. When the value is between the predetermined methanol concentration values, the correction coefficient value is calculated by performing a linear interpolation calculation. The other correction coefficient tables such as the start mode and the acceleration mode state of the basic mode have the same settings as described above.

FIG. 3 shows the average value KALC of the correction coefficient KALC.
9 is a flowchart illustrating a calculation procedure for calculating ave.

First, it is determined whether or not the operating state of the engine is in the start mode (step S1). Whether or not the engine is in the start mode is determined based on whether or not a starter switch (not shown) of the engine is turned on and whether or not the engine speed is equal to or lower than a predetermined start speed (cranking speed).

Since the first loop is in the start mode, the hold timer TALCH is set to a predetermined time (for example, 90 seconds) to start counting of the timer TALCH (step S2).
It is determined whether the LCS is “0” (step S3). This sample timer TALCS is a timer for sampling the alcohol concentration correction coefficient KALC at regular intervals, and the first loop is a sample timer TALCS.
Since H is "0", the detected value of the methanol concentration ALC from the ALC sensor 12 is read and stored in the storage means 3c.
(Step S4). Next, the methanol concentration A
A correction coefficient KALC value corresponding to the LC detection value is calculated based on the above-described correction coefficient table (step S5). In this case, since the engine is in the start mode, the correction coefficient KAL is calculated using the KALCCR table for the start mode.
The CCR is calculated.

Next, based on Equation 3, the average value K of the correction coefficient is calculated.
ALCave (n) is calculated.

[0043]

(Equation 3) Here, KALCave (n- ₁₎ is the average value calculated in the previous loop, in the starting mode is set to a predetermined initial value KALCave _0.

CKALC (n) is an averaging coefficient, which is set to a different value between the start mode and the basic mode. Therefore, the average value KALCave (n) of the correction coefficient is calculated at a different calculation speed between the two modes. Is done. That is, by making the averaging coefficient CKALC ( ₀ ) in the start mode different from the averaging coefficient CKALC ( ₁ ) in the basic mode, the calculation speed of the average value KALCave (n) of the correction coefficient is made different. More specifically, the averaging coefficient CKALC ( ₀ ) in the start mode is equal to the averaging coefficient CK in the basic mode.
It is set to a value larger than ALC ( ₁ ), and the desired average value KALCave (n) is calculated faster in the start mode by increasing the calculation speed than that in the basic mode. This is for the following reason. That is, in the start mode, there is a possibility that the fuel stored in the fuel tank 16 may not be uniformly mixed. Therefore, the fuel composition ratio (methanol / gasoline) in the fuel tank 16 before the engine stops and the engine stop The component ratio (methanol / gasoline) of the fuel supplied later may be different. In addition, when the methanol concentration is high, the engine 1 does not start unless the supplied fuel is increased. Therefore, in the start mode, the calculation speed of the average value KALCave (n) is increased to detect the methanol concentration rapidly.

After the start-up mode, even if the detection of the methanol concentration is delayed, the air-fuel ratio is feedback-controlled to the stoichiometric air-fuel ratio by the O ₂ sensor 23 as described later.

Next, the correction coefficient KA calculated as described above.
The average LC value KALCave (n) is stored in the storage means 3c (backup RAM) (step S7), then the sample timer TALCS is set (for example, 80 ms) to start counting, and the final correction coefficient KALC is calculated as the average value K
ALCave is set (step S10), and this program ends. This average value KALCave is expressed by K
Applied as ALC value.

Next, in the next loop, it is determined again in step S1 whether or not the engine is in the start mode. When the start mode is completed and the start of the engine is completed, the process proceeds to step 9 and is set in step S2. Hold timer TA
It is determined whether or not LCH has become “0”. If it is determined that the hold timer TALCH has not become “0”, it is determined whether or not the sample timer TALCS set in the above-described step S8 has become “0”. If not “0”, the average value K calculated in the loop
ALCave is set to the final correction coefficient KALC, and the program ends.

On the other hand, in step S3, the sample timer TA
If the LCS is "0", the respective steps of S4 → S5 →... → S8 → S9 are executed as in the start mode, and the program is terminated. In this case, KALCave (n- ₁ ) in the second term on the right side of Equation 3 uses the value calculated in the previous loop, that is, in the start mode. The averaging coefficient CKALC is set to a value smaller than the start mode as described above.

In the subsequent loop, when it is determined that the hold timer TALCH set in step S2 has become "0", it is considered that the fuel in the fuel tank 16 has already been uniformly mixed, and methanol There is almost no change in density, and the correction coefficient K calculated in the basic mode
The average value of ALC KALCave ₁ is converted to the final correction coefficient KALCav
This is set to e (n) (step S10) and the program ends. By stopping the detection of the methanol concentration after the elapse of the set time of the hold timer TALCH, the average value KALCav calculated and stored immediately before the elapse of the set time is set.
e is applied to the subsequent calculation of the Tout value to avoid the effects of noise and drift.

[0050]

As described above in detail, according to the present invention, in an air-fuel ratio control device for an internal combustion engine using a fuel mixed with alcohol, a concentration detecting means for detecting the alcohol concentration and the concentration detected by the concentration detecting means. Correction coefficient calculating means for calculating a correction coefficient according to the alcohol concentration; operating state detecting means for detecting an operating state of the engine; and an average value of the correction coefficient according to the operating state detected by the operating state detecting means. And the air-fuel ratio control means for controlling the air-fuel ratio according to the average value calculated by the average value calculation means, it is possible to calculate an averaged correction coefficient, Even if the output of the alcohol sensor fluctuates due to noise or drift, the fluctuation of the correction coefficient is suppressed, and the air-fuel ratio can be controlled to almost the stoichiometric air-fuel ratio. It is possible to avoid the deterioration of the gas-gas properties.

The average value calculating means calculates the average value of the correction coefficient during the engine start and within a predetermined period after the engine is started. Averaging is performed, and unnecessary calculation of an average value after the fuel is uniformly mixed can be omitted, and the calculation program can be simplified.

Further, since the calculation speed of the average value of the correction coefficient by the average value calculation means differs between during and after the start of the engine, it is necessary to calculate the average value at an appropriate calculation speed according to the operating state of the engine. Can be. That is, for example, the average value calculating means executes the calculation of the average value of the correction coefficient during the engine start and within a predetermined period after the engine is started, so that the average value during which the fuel during the engine start is not uniformly mixed is calculated. By increasing the speed, the alcohol concentration in the fuel can be detected very quickly, and deterioration of exhaust gas characteristics and the like can be avoided more quickly.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating an example of a correction table for calculating a correction coefficient KALC.

FIG. 3 is a flowchart illustrating a calculation procedure for calculating an average value of correction coefficients.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 3b CPU (correction coefficient calculation means, average value calculation means, air-fuel ratio control means) 5 Revolution (NE) sensor (operating state detection means) 21 Alcohol concentration (ALC) sensor (concentration detection means)

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-1-244133 (JP, A) JP-A-57-44752 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F02D 41/14 F02D 19/08 F02D 45/00

Claims (4)

(57) [Claims] In an air-fuel ratio control device for an internal combustion engine using fuel mixed with alcohol, a concentration detecting means for detecting an alcohol concentration and a correction coefficient are calculated in accordance with the alcohol concentration detected by the concentration detecting means. Correction coefficient calculating means, operating state detecting means for detecting an operating state of the engine, average value calculating means for calculating an average value of the correction coefficient according to the operating state detected by the operating state detecting means, Air-fuel ratio control means for controlling an air-fuel ratio according to the average value calculated by the average value calculation means. 2. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein the average value calculation means calculates the average value of the correction coefficient during the engine start and within a predetermined period after the engine is started. . 3. The air-fuel ratio control of an internal combustion engine according to claim 1, wherein the calculation speed of the average value of the correction coefficient in the average value calculating means is different between during and after the engine is started. apparatus. 4. The air-fuel ratio control device for an internal combustion engine according to claim 3, wherein the average value calculation speed of the correction coefficient during engine start is faster than the average value calculation speed after engine start.