JP2591045B2 - Fuel injection control device for alcohol-containing fuel internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a fuel injection control device for an internal combustion engine that uses gasoline mixed with alcohol as a fuel.

(Prior art)

Generally, fuel injection control in an internal combustion engine refers to the amount of intake air
Q / The target fuel injection amount (time) is calculated by integrating the air-fuel ratio correction coefficient FAF with the basic fuel injection amount (time) determined according to the engine load represented by the engine speed Ne and the intake pipe pressure PM. In the air-fuel ratio feedback control, the air-fuel ratio is determined from the oxygen concentration in the exhaust gas based on the stoichiometric air-fuel ratio (for example,
14.7) The oxygen sensor (O ₂ sensor) and a comparator determine whether the value is smaller (over-concentration side) or larger (lean side), and the FAF is reduced when the signal is over-concentration (rich). By the way, when different kinds of fuels such as alcohol are mixed into gasoline as fuel for automobiles, avoiding deterioration of the internal combustion engine operation performance and exhaust emission if the target air-fuel ratio etc. is maintained at a value when no different kinds of fuels are mixed. Can not.

Therefore, a device for detecting the mixing ratio of different types of fuel in the fuel and correcting the basic fuel injection amount in accordance with the mixing ratio of different types of fuel has already been proposed (Japanese Patent Laid-Open No. 58-96139, Japanese Utility Model Application Laid-Open No. 58-96139). No. 108343).

That is, since the apparatus according to the above proposal directly controls the fuel amount in accordance with the degree of mixing of different kinds of fuel in order to control the control air-fuel ratio to the target air-fuel ratio (for example, the stoichiometric air-fuel ratio), Deviation from the stoichiometric air-fuel ratio can be corrected.

[Problems to be solved by the invention]

The above-mentioned O ₂ sensor has a zirconia element inside, utilizing the inherent properties of the zirconia element that generates an electromotive force by the passage of oxygen ions, the inside of the zirconia element has a high oxygen concentration atmosphere, the outside When the oxygen concentration in the exhaust gas passing outside is high, that is, when the actual air-fuel ratio is larger than the stoichiometric air-fuel ratio (lean), the electromotive force is generated because the oxygen concentration difference is small. Is small, and when the oxygen concentration in the exhaust gas is low (rich), the electromotive force increases due to the large concentration difference.

By the way, when the fuel used in the internal combustion engine is mixed with alcohol, the amount of hydrogen (H ₂ ) contained in the combustion gas of the alcohol becomes larger than the amount of H ₂ contained in the normal gasoline combustion gas. Therefore, H ₂ having a smaller molecular weight than O ₂ is easily diffused into the zirconia element of the O ₂ sensor,
The detected O ₂ concentration tends to be determined to be lower than the actual O ₂ concentration. Therefore, as shown in FIG. _{2, the} output of the O ₂ sensor becomes rich, for example, while the actual air-fuel ratio is the stoichiometric air-fuel ratio. As a result, the control air-fuel ratio deviates from the stoichiometric air-fuel ratio to the lean side, and NOx Etc., the exhaust emissions will deteriorate. This tendency becomes more pronounced as the proportion of alcohol contained in the fuel is higher.

However, in the device according to the above proposal, it is not possible to avoid the shift of the control air-fuel ratio to the lean side caused by the shift of the detection characteristic of the O ₂ sensor to the lean side due to the mixing of different types of fuel.

This, O ₂ sensor also controls the air-fuel ratio is a stoichiometric air-fuel ratio when the detection characteristics of the O ₂ sensor due to contamination of the improper fuel is shifted to the lean side fuel injection amount is reduced by a feedback control for shift to the rich side This is because the control air-fuel ratio eventually shifts to the lean side by the same amount as the shift of the detection characteristic of the O ₂ sensor.

The present invention was made in view of the斯Ru problems, inherently air-fuel ratio control by the O ₂ sensor for detecting the actual less O ₂ concentration in the internal combustion engine using an alcohol-containing fuel, around the theoretical air-fuel The present invention provides a fuel injection control device that approaches the air-fuel ratio feedback control described above and thereby improves exhaust emissions.

[Means for solving the problem]

FIG. 1 illustrates a fuel injection control device according to the present invention.

According to the present invention, the target fuel injection amount is obtained by correcting the basic fuel injection amount calculated according to the engine load with the air-fuel ratio correction coefficient corresponding to the output value of the oxygen sensor, and determining the target fuel injection amount. A fuel injection device for an internal combustion engine that uses an alcohol-containing fuel and performs an air-fuel ratio feedback control that approximates an air-fuel ratio to a stoichiometric air-fuel ratio. The fuel injection device is provided in an engine exhaust system and detects an oxygen concentration in exhaust gas. Oxygen sensor
Alcohol concentration detecting means for detecting the concentration of alcohol contained in the fuel, and an air-fuel ratio feedback control constant for calculating the air-fuel ratio correction coefficient such that the target fuel injection amount increases as the detected alcohol concentration increases. , An air-fuel ratio correction coefficient calculating unit that calculates an air-fuel ratio correction coefficient according to the oxygen sensor output and the air-fuel ratio feedback control constant, and the air-fuel ratio correction coefficient calculating unit. There is proposed a fuel injection control device for an alcohol-containing fuel-fuel engine, comprising: a fuel injection amount calculating means for calculating a fuel injection amount using an air-fuel ratio correction coefficient.

(Operation)

According to the above configuration, the deviation of the detection characteristics of the oxygen sensor due to the alcohol being mixed into the fuel is determined by the air-fuel ratio feedback control constant, for example, the rich / lean delay time, detected by the oxygen sensor in accordance with the alcohol concentration. The direction is changed in the direction of correcting the characteristic deviation, and the feedback around the stoichiometric air-fuel ratio is achieved.

〔Example〕

FIG. 3 is an overall schematic diagram showing one embodiment of a fuel injection control device for an internal combustion engine according to the present invention. In FIG. 3, an air flow meter 3 is provided in an intake passage 2 of an engine body 1. The air flow meter 3 directly measures the intake air amount Q, and has a built-in potentiometer to generate an output signal of an analog voltage proportional to the intake air amount Q. This output signal is supplied to the A /
It is supplied to the D converter 101. Further, the distributor 4 has a crank angle sensor 4a whose axis generates a reference position detection pulse signal every 720 ° when converted into a crank angle, and an angular position detection pulse every 30 ° when converted into a crank angle. A crank angle sensor 4b for generating a signal is provided. The pulse signals of these crank angle sensors 4a and 4b are supplied to the input / output interface 102 of the control circuit 10, and the output of the crank angle sensor 4b is supplied to the interrupt terminal of the CPU 103.

Further, the intake passage 2 is provided with a fuel injection valve 5 for supplying pressurized fuel from a fuel supply system to an intake port for each cylinder.

A fuel filter 7 and an alcohol concentration sensor 8 for detecting the alcohol concentration in the fuel are provided between the fuel tank 6 and the fuel injection valve 5. The alcohol concentration sensor 8 generates an electric signal of an analog voltage corresponding to the alcohol concentration DA contained in the fuel.

Further, the exhaust manifold, that is, upstream of the catalytic converter (not shown) and O ₂ (oxygen) sensor 9 is provided, the O ₂ sensor 9 corresponding to the oxygen component concentration in the exhaust gas electrical Generate a signal. That is, the O ₂ sensor 9 outputs different output voltages to the A / D converter 101 of the control circuit 10 depending on whether the air-fuel ratio is lean or rich with respect to the stoichiometric air-fuel ratio.
Occurs.

The control circuit 10 is configured as a microcomputer, for example, and includes an A / D converter 101, an input / output interface 102,
In addition to PU103, ROM104, RAM105, backup RAM106,
A clock generation circuit 107 and the like are provided. The backup RAM 106 is directly connected to a backup battery (not shown). Therefore, even if the ignition switch is turned off or the vehicle battery is removed,
The storage contents of the backup RAM 106 do not disappear.

In the control circuit 10, the down counter 108, the flip-flop 109, and the driving circuit 110
Is to control the That is, when the fuel injection amount TAU is calculated in a routine described later, the fuel injection amount TAU is preset in the down counter 108 and the flip-flop 109 is also set. As a result, the drive circuit 110 starts energizing the fuel injection valve 5. On the other hand, when the down counter 108 counts a clock signal (not shown) and its carry-out terminal finally becomes “1” level, the flip-flop 109 is reset and the drive circuit 110 is reset.
Stops the energization of the fuel injection valve 5. That is, the fuel injection valve 5 is energized by the above-described fuel injection amount TAU, so that an amount of fuel corresponding to the fuel injection amount TAU is sent to the combustion chamber of the engine body 1. The CPU 103 generates an interrupt when the A / D converter 101 ends A / D conversion, when the input / output interface 102 receives a pulse signal from the crank angle sensor 4b, and the like.

The intake air amount data Q of the air flow meter 3 and the concentration data DA of the alcohol concentration sensor 8 are fetched by an A / D conversion routine executed every predetermined time and stored in a predetermined area of the RAM 105. That is, the data Q in the RAM 105
And DA are updated every predetermined time. The rotation speed data Ne is calculated by an interruption of the crank angle sensor 4b at every 30 ° CA, and is stored in a predetermined area of the RAM 105.

 Hereinafter, the operation of the control circuit of FIG. 3 will be described.

Figure 4 represents an air-fuel ratio feedback control routine for calculating the air-fuel ratio correction coefficient FAF based on the output of the O ₂ sensor 9, a predetermined time is performed, for example, every 4 ms.

In step 401, the air-fuel ratio of the closed loop by the O ₂ sensor 9 (feedback) condition is determined whether or not satisfied. During engine start, during fuel increase operation after start, during warm-up increase operation, during power increase operation, during lean control, O ₂ sensor 9
In any of the inactive states and the like, the closed loop condition is not satisfied, and in other cases, the closed loop condition is satisfied. If the closed loop condition is not satisfied, the routine proceeds to step 423, where the air-fuel ratio correction coefficient FAF is set to the average value of the FAF immediately before the stop of the closed loop control. On the other hand, if the closed loop condition is satisfied, the process proceeds to step 402.

In step 402, the output V of the O ₂ sensor 9 is A / D converted and taken in. In step 403, it is determined whether or not V is equal to or lower than a comparison voltage V _R (for example, 0.45 V) as shown in FIG. That is, it is determined whether the air-fuel ratio is rich or lean. Lean (V
If ≦ V _R), the delay counter CDL at step 404
It is determined whether or not Y is positive. If CDLY> 0, CDLY is set to 0 in step 405, and the process proceeds to step 406. In step 406, the delay counter CDLY is decremented by one, and then in step 407, it is determined whether CDLY <TDL. TDL is O ₂
This is a lean delay time for maintaining the determination of the rich state even when the output of the sensor 9 changes from rich to lean, and is defined as a negative value. Therefore, CD
Only when LY <TDL, CDLY is set to TDL in step 408,
In step 409, the air-fuel ratio flag F is set to "0" (lean). On the other hand, if rich (V> V _R ), it is determined in step 410 whether the delay counter CDLY is negative or not, and CDLY <0.
If so, in step 411 CDLY is set to 0 and the process proceeds to step 412. In step 412, 1 is added to the delay counter CDLY, and then, in step 413, it is determined whether CDLY <TDR. Incidentally, TDR is a rich delay time for holding the judgment that even if there is a change from the lean at the output of the O ₂ sensor 9 to rich is lean condition, is defined by a positive value. Therefore, only when CDLY> TDR, step 414
At step 415, the air-fuel ratio flag F is set to "1" (rich).

In step 416, it is determined whether or not the sign of the air-fuel ratio flag F has been inverted, that is, whether or not the air-fuel ratio after the delay processing has been inverted. If the air-fuel ratio has been inverted, it is determined in step 417 whether the air-fuel ratio is inverted from rich to lean or from lean to rich. If the transition is from rich to lean (F = “0”), then in step 418, FAF ← FAF
+ RSR in a skip-like manner. Conversely, if the inversion is from lean to rich (F = “1”), the FAF
← Skip to FAF-RSL. That is, skip processing is performed.

If the sign of the air-fuel ratio flag F is not inverted at step 416, the integration processing is performed at steps 420, 421, and 422.
In other words, if F = “0” (lean) in step 420, FAF ← FAF + KIR is set in step 421, while F = “1”
If (rich), FAF is set to FAF-KIL in step 422. Here, the integration constants KIR, KIL are set smaller than the skip constants RSR, RSL. Therefore, step 421 is to gradually increase the fuel injection amount in the lean state (F = “0”),
In step 422, the fuel injection amount is gradually reduced in the rich state (F = “1”).

Then, the air-fuel ratio correction coefficient FAF calculated in steps 418, 419, 421, and 422 is stored in the RAM 105, and the routine ends in step 424. The FA calculated as described above
In order to prevent over-rich or over-lean when F becomes too large or too small, a step of guarding with a maximum value or a minimum value between steps 422 and 424 may be provided.

FIG. 5 is a timing chart for supplementarily explaining the operation according to the flowchart of FIG. When the air / fuel ratio signal A / F for rich / lean determination is obtained from the output of the O ₂ sensor 9 as shown in FIG. 5 (A), the delay counter CDLY becomes rich as shown in FIG. 5 (B). It counts up and counts down in a lean state. As a result, as shown in FIG. 5 (C), the air-fuel ratio signal A /
F 'is formed. For example, the air-fuel ratio signal A / F is changed from lean to rich at time t _1, the air-fuel ratio signal A / F which is delayed processed 'at time t ₂ after being held lean only the rich delay time TDR Change richly. Even the air-fuel ratio signal A / F at time t ₃ is changed from rich to lean, the delayed air-fuel-fuel ratio signal A / F 'is the time after being held rich only equivalent lean delay time (-TDL) t It changes to lean at ₄ .
However, when the air-fuel ratio signal A / F 'is reversed at time t _5, shorter period of time than the rich delay time TDR as the t _6, t _7, takes time delay counter CDLY reaches the rich delay time TDR, As a result, the air-fuel ratio signal after delay processing at time t ₈ a /
F 'is inverted. That is, the air-fuel ratio signal A /
F ′ becomes more stable than the air-fuel ratio signal A / F before the delay processing.
Thus, the air-fuel ratio signal correction coefficient FAF shown in FIG. 5D is obtained based on the stable air-fuel ratio signal A / F 'after the delay processing.

As shown in FIG. 5, the control air-fuel ratio can be changed by changing the air-fuel ratio feedback control constant, for example, TDR, TDL; RSR, RSL; KIR, KIL. For example, rich delay time
If TDR> lean delay time (-TDL) is set, the control air-fuel ratio can shift to the rich side, and conversely, the lean delay time (-TDL)
If L)> rich delay time TDR is set, the control air-fuel ratio can shift to the lean side. When the rich skip amount RSR is increased, the control air-fuel ratio can be shifted to the rich side.
Even if the lean skip amount RSL is reduced, the control air-fuel ratio can be shifted to the rich side, while if the lean skip amount RSL is increased, the control air-fuel ratio can be shifted to the lean side, and even if the rich skip amount RSR is reduced. The control air-fuel ratio can be shifted to the lean side. Furthermore, if the rich integration constant KIR is increased, the control air-fuel ratio can shift to the rich side, and if the lean integration constant KIL is reduced, the control air-fuel ratio can shift to the rich side, while the lean integration constant KIL increases. Then, the control air-fuel ratio can be shifted to the lean side, and the control air-fuel ratio can be shifted to the lean side even if the rich integration constant KIR is reduced.

Therefore, in the present invention, the tendency of the air-fuel ratio to lean due to alcohol is compensated by changing the air-fuel ratio feedback control constant according to the alcohol concentration DA contained in the fuel.

FIG. 6 is a routine for changing an air-fuel ratio feedback control constant, for example, a delay time TDR, −TDL,
It is executed every predetermined time. That is, in step 601, the alcohol concentration DA is read from the alcohol concentration sensor 8, and in step 602, the delay times TDR, -TDL corresponding to the detected alcohol concentration DA are obtained using a map as shown in the drawing. Become. This map is stored in a predetermined area of the ROM 104 in advance, and the respective delay times TDR and −TDL are set corresponding to the alcohol concentration DA. Thus, the map is set so that the higher the alcohol concentration DA, the greater the rich delay time TDR and the lean delay time (-TDL) decrease in proportion thereto.
By increasing the lean state (F = “0”) in FIG. 9C, the FAF is increased, so that the fuel injection amount is increased, in other words, the control air-fuel ratio shifts to the rich side. It has become. This is because the control of the air-fuel ratio leaner than the stoichiometric air-fuel ratio (for example, 15) due to the bad alcohol in the fuel is returned to the rich direction by increasing the FAF. Intended to be. The respective delay times TDR, (-TDL) determined in this way are stored in the RAM 105 in step 603, and this routine ends in step 604.

FIG. 7 is a routine for calculating a target fuel injection amount from the FAF that varies with the air-fuel ratio feedback control constant variably set as described above, and is executed at predetermined crank angles, for example, every 360 ° CA. In step 701, RA
Intake air amount data Q and rotation speed data Ne by M105
Is read to calculate the basic injection amount TAUP. For example TAUP ←
Let KQ / Ne (K is a constant). In step 702, the target fuel injection amount TAU is calculated by TAU ← TAUP · FAF · α + β. Note that α and β are correction amounts determined by other operating state parameters, for example, correction amounts determined by a signal from a throttle position sensor (not shown), a signal from an intake air temperature sensor, a battery voltage, and the like. Is stored in Next, in step 703, the injection amount TAU is set by the down counter 108 and the flip-flop 109 is set to start fuel injection. Then, in step 704, this routine ends. As described above, when the time corresponding to the injection amount TAU has elapsed, the flip-flop 109 is reset by the carry-out signal of the down counter 108, and the fuel injection ends.

In the above-described embodiment, Q / Ne is read.
Instead, use the intake pipe pressure PM as the intake pipe pressure sensor (not shown)
And may be used as a load. In the routine of FIG. 6, the delay time TDR, (−TDL) is variable.
Either the rich delay time TDR or the lean delay time (-TDL) may be made variable. In addition, delay time TDR,
Instead of making (−TDL) variable, skip amounts RSR, RSL,
The integration constants KIR and KIL may be variable.

〔The invention's effect〕

As described above, according to the present invention, the air-fuel ratio feedback control constant is changed in accordance with the alcohol concentration, and the higher the alcohol concentration, the larger the air-fuel ratio correction coefficient, that is, the higher the target fuel injection amount. The leaning tendency of the air-fuel ratio by the oxygen sensor that detects O ₂ less than the actual amount is compensated according to the alcohol concentration, and therefore helps prevent the deterioration of exhaust emissions. .

[Brief description of the drawings]

FIG. 1 is an overall block diagram for explaining a configuration of the present invention, FIG. 2 is a graph for explaining output characteristics of an O ₂ sensor, and FIG. 3 is a diagram of an air-fuel ratio control device for an internal combustion engine according to the present invention. 4, 6 and 7 are flow charts for explaining the operation of the control circuit of FIG. 3, and FIG. 5 is a supplementary description of the flow chart of FIG. FIG. 1 ...... engine body, 3 ...... air flow meter, 4 ...... distributor, 4a, 4b ...... crank angle sensor, 8 ...... alcohol concentration sensor, 9 ...... O ₂ sensor, 10 ...... control circuit.

Claims (1)

(57) [Claims] 1. A target fuel injection amount is obtained by correcting a basic fuel injection amount calculated according to an engine load with an air-fuel ratio correction coefficient according to an output value of an oxygen sensor to determine a target fuel injection amount. A fuel injection device for an internal combustion engine that uses an alcohol-containing fuel and performs an air-fuel ratio feedback control that approximates an air-fuel ratio to a stoichiometric air-fuel ratio. The fuel injection device is provided in an engine exhaust system and detects an oxygen concentration in exhaust gas. Oxygen sensor, and alcohol concentration detecting means for detecting the concentration of alcohol contained in the fuel, the higher the detected alcohol concentration,
Air-fuel ratio feedback control constant calculating means for calculating a feedback control constant for calculating an air-fuel ratio correction coefficient so that the target fuel injection amount increases; and air-fuel ratio correction according to the oxygen sensor output and the air-fuel ratio feedback control constant. Alcohol-containing air-fuel ratio correction coefficient calculating means for calculating the coefficient, and fuel injection amount calculating means for calculating the fuel injection amount using the air-fuel ratio correction coefficient determined by the air-fuel ratio correction coefficient calculating means. Fuel Injection device for internal combustion engine.