JP3853747B2 - Air-fuel ratio control method and apparatus for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an air-fuel ratio control method for an internal combustion engine that purifies exhaust gas, for example, by maintaining the exhaust gas in the vicinity of the theoretical air-fuel ratio, and an apparatus suitable for implementing the method.
[0002]
[Prior art]
Conventionally, air-fuel ratio control has been performed for the purpose of purifying exhaust gas for environmental considerations. In particular, in an internal combustion engine of a type equipped with an electronic fuel injection device (Electronic Fuel Injection), various attempts have been made since complex control over fuel injection is possible.
[0003]
In the air-fuel ratio control, the air-fuel ratio (mass ratio) obtained by dividing the supply air amount per combustion supplied to the internal combustion engine by the supply fuel amount (that is, “fuel injection amount” in the fuel injection type), Regardless of changes in the operating state of the internal combustion engine, it is maintained at a constant target value (in a gasoline engine, the theoretical air-fuel ratio is often about 14.7).
[0004]
In this specification, for simplification of description, only the case of a single cylinder is referred to, but the basic principle is the same even in the case of multiple cylinders.
[0005]
In order to comply with exhaust gas regulations that are becoming more stringent in recent years, exhaust purification devices provided in exhaust systems of gasoline engines have conventionally been subject to regulated substances (for example, CO, HC, NO). _x ) Is efficiently removed from the exhaust gas, and the purification efficiency of this three-way catalyst is the highest in the vicinity of the theoretical air-fuel ratio. Maintaining it is very important.
[0006]
In the air-fuel ratio control, various oxygen sensors such as a linear sensor (Linear Air Fuel Ratio Sensor) and a lambda sensor (Lambda Oxygen Sensor) are used.
[0007]
In general, the air-fuel ratio control is to feed back the output value of the oxygen sensor as described above and adjust the fuel injection amount from the fuel injection device, but due to the response delay, the fuel injection amount is In fact, it has fluctuated.
[0008]
When this variation increases, the variation of the air-fuel ratio increases, and as a result, the variation of the output torque of the internal combustion engine increases. Therefore, when the internal combustion engine is mounted on a vehicle, the riding comfort deteriorates.
[0009]
Therefore, various techniques have been developed in order to suppress fluctuations in the fuel injection amount. For example, in Patent Documents 1 to 10, the basic fuel injection amount obtained based on the throttle opening, the engine speed, and the like is disclosed. Is increased or decreased by the fuel injection amount obtained based on the output value of the oxygen sensor, and is forced to the fuel injection amount by the oxygen sensor or the entire fuel injection amount after the increase or decrease by the fuel injection amount by the oxygen sensor. A feedback control technique (so-called “perturbation”) for applying vibrations is disclosed.
[0010]
In many of the above-mentioned patent documents, the amplitude and frequency of forced vibration are fixed, and in order to cause the oxygen sensor to vibrate at the forced vibration frequency when the integral constant is set large in order to improve the followability to the theoretical air-fuel ratio, The amplitude fluctuation of the forced vibration must be fixed at a large value, and the torque fluctuation increases.
[0011]
For this reason, for example, Patent Document 8 discloses that the ignition advance angle is adjusted according to the forced vibration of fuel injection to reduce torque fluctuation.
[0012]
Other patent documents disclose a technique for adjusting the frequency of forced vibration of fuel injection itself according to various evaluation criteria.
[0013]
[Patent Document 1]
Japanese Patent No. 2962987
[Patent Document 2]
JP 56-118535 A
[Patent Document 3]
Japanese Patent No. 1078486
[Patent Document 4]
Japanese Patent No. 2855963
[Patent Document 5]
JP-A-64-53042
[Patent Document 6]
Japanese Patent No. 2014465
[Patent Document 7]
JP-A-6-229308
[Patent Document 8]
JP-A-6-137242
[Patent Document 9]
Japanese Patent No. 2531525
[Patent Document 10]
JP-A-5-39741
[0014]
[Problems to be solved by the invention]
However, since the integration constant is fixed in the conventional technology that performs the control with the integration operation described above, the setting value of the integration constant is increased in advance for the purpose of improving the followability to the change in the required fuel injection amount. In this case, it is necessary to increase the amplitude of the forced vibration accordingly. As a result, as described above, there is a problem that the fluctuation of the air-fuel ratio becomes large and the fluctuation of the engine torque becomes large.
[0015]
The present invention has been made in view of such circumstances.For example, by increasing or decreasing the integral constant or the amplitude of forced vibration based on the output value of the λ-type oxygen sensor, the followability to the stoichiometric air-fuel ratio is improved. It is possible to suppress fluctuations in the air-fuel ratio while ensuring it, so that it is possible to purify the exhaust gas, and furthermore, there is little fluctuation in engine torque and to improve the ride comfort when applied to vehicles. It is an object of the present invention to provide an air-fuel ratio control method for an internal combustion engine and a device suitable for the implementation.
[0016]
[Means for Solving the Problems]
In order to solve the above-described problem, an air-fuel ratio control method for an internal combustion engine according to a first aspect of the present invention is based on the composition of exhaust gas from an internal combustion engine equipped with a fuel injection device, with the vicinity of the theoretical air-fuel ratio as a boundary. An output value of a sensor having the characteristic of detecting an actual air-fuel ratio rich state or lean state is received, and based on the received output value of the sensor, the duration of the rich state or lean state of the sensor output value is determined. The actual air-fuel ratio of the internal combustion engine is maintained in the vicinity of the stoichiometric air-fuel ratio based on the obtained rich state or lean state duration of the sensor output value.
[0017]
An air-fuel ratio control apparatus for an internal combustion engine according to a second aspect of the present invention provides a composition of exhaust gas from the internal combustion engine so as to maintain the air-fuel ratio of the internal combustion engine provided with the fuel injection device in the vicinity of the theoretical air-fuel ratio. An air-fuel ratio control apparatus for an internal combustion engine that performs feedback control accompanied by an integral operation that applies forced vibration to fuel injection by the fuel injection device based on an output value of a sensor to be measured, the output value of the sensor On the basis of this, a forced vibration adjusting means for changing the integral constant or the amplitude of the forced vibration is provided.
[0018]
According to the first aspect of the present invention, based on the output value of the sensor that detects the composition of exhaust gas (particularly, the oxygen content), the duration of the rich value or lean state of the output value of this sensor is obtained Based on the obtained duration, the actual air-fuel ratio of the internal combustion engine is maintained near the stoichiometric air-fuel ratio.
[0019]
Further, according to the second aspect of the present invention, feedback control (I control, PI) with an integral operation for applying a forced vibration to the fuel injection by the fuel injection device based on the output value of any type of sensor. Control, PID control, etc.) Increase or decrease the integral constant or the amplitude of forced vibration.
[0020]
According to each of the above inventions, it is possible to suppress fluctuations in the air-fuel ratio while ensuring follow-up to the stoichiometric air-fuel ratio. Therefore, it is possible to purify the exhaust gas, and further reduce fluctuations in the engine torque and reduce the vehicle. In the case of application to the vehicle, the ride comfort can be improved. In the above-described invention, either the integral constant or the amplitude of forced vibration may be made variable, but a further effect can be expected by changing both the integral constant and the amplitude of forced vibration.
[0021]
Specifically, the sensor according to the second aspect is a sensor having the characteristic of detecting the rich state or lean state of the actual air-fuel ratio (with the stoichiometric air-fuel ratio as a boundary), as in the first aspect. For example, a λ-type oxygen sensor.
[0022]
The λ-type oxygen sensor outputs based on the composition of the exhaust gas, particularly the oxygen content, and can indirectly detect the actual air-fuel ratio. As shown in FIG. 1, the λ-type oxygen sensor has a characteristic that its output value changes abruptly around the theoretical air-fuel ratio (about 14.7) as a boundary.
[0023]
FIG. 1 shows an example of the output characteristics of the λ-type oxygen sensor. In the example shown in the figure, the λ-type oxygen sensor is about 0.5 when the actual air-fuel ratio is lower than the theoretical air-fuel ratio (rich state). A voltage of V to about 0.9 V is output, and the output voltage rapidly approaches 0.9 V as it becomes richer than the theoretical air-fuel ratio. Similarly, the λ-type oxygen sensor outputs a voltage of about 0.5 V to about 0.1 V in a state where the actual air-fuel ratio is higher than the theoretical air-fuel ratio (lean state), and the output voltage is As it becomes leaner than the theoretical air-fuel ratio, it suddenly approaches 0.1V.
[0024]
In the present invention, in order to further improve the followability to the theoretical air-fuel ratio, the integral constant is increased when the duration of the rich state or lean state of the output value of the oxygen sensor is longer than a predetermined time. On the other hand, when the duration is shorter than the predetermined time, the integration constant may be decreased. The predetermined time can be realized by, for example, obtaining a relationship between the engine speed, the throttle opening, the intake pipe pressure, and the like through a test performed in advance and creating an appropriate map. Is possible.
[0025]
It is also possible to increase the amplitude as the integral constant increases, while decreasing the amplitude as the integral constant decreases.
[0026]
Furthermore, in the second aspect of the present invention described above, the integration constant and / or the amplitude are changed. However, in addition to these, it is possible to change the frequency of the forced vibration. is there.
[0027]
Note that the present invention can be applied to a type in which the forced oscillation of fuel injection is feedback-controlled with an integral operation using the output value of the λ-type oxygen sensor, and I control, PI control , And PID control can be employed.
[0028]
Further, the present invention is not limited to a general fuel injection type internal combustion engine, but can also be applied to a direct injection type internal combustion engine, and also to a fuel injection type internal combustion engine other than a gasoline engine such as a diesel engine. Is possible.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an apparatus suitable for implementing an air-fuel ratio control method for an internal combustion engine according to an embodiment of the present invention will be specifically described with reference to the accompanying drawings.
[0030]
(First embodiment)
FIG. 2 is a block diagram showing the overall configuration of the air-fuel ratio control apparatus for an internal combustion engine according to the embodiment of the present invention. As shown in FIG. 2, the air-fuel ratio control device according to the present embodiment mainly includes an internal combustion engine (engine) 1 and an engine control device 3 that controls a fuel injection device 2 of the engine 1.
[0031]
In the present embodiment, the engine 1 is a single-cylinder gasoline engine for clarity of explanation, but the present invention is an engine of a type using other fuel capable of controlling fuel injection, It can also be applied to multi-cylinder engines.
[0032]
The fuel injection device 2 includes a fuel injection valve (for example, consisting of an electromagnetic valve) connected to a pressurized fuel supply system (not shown), and opens the fuel injection valve based on a fuel injection command given from the engine control device 3 In addition, a predetermined amount of fuel is injected.
[0033]
Further, the engine 1 includes a throttle opening sensor 4 for detecting the throttle opening, an intake pipe pressure sensor 5 for detecting the pressure in the intake pipe 1a, an engine speed sensor 6 for detecting the engine speed, and an exhaust gas Various sensors such as the λ-type oxygen sensor 7 are provided that output in accordance with the composition (particularly the oxygen content). However, in the present invention, the sensor that outputs in accordance with the composition of the exhaust gas is not limited to the λ-type oxygen sensor 7, but has a characteristic of detecting the rich state or lean state of the actual air-fuel ratio. Any sensor may be used.
[0034]
The λ-type oxygen sensor 7 is installed on the exhaust upstream side of the three-way catalyst 8 as an exhaust purification device provided in the exhaust pipe 1b of the engine 1.
[0035]
The detection result of each sensor is given to the engine control device 3, and the engine control device 3 outputs a fuel injection command to the fuel injection device 2 based on the detection result of each sensor. More specifically, the engine control device 3 is configured to output a fuel injection command that causes the fuel injection device 2 to perform appropriate energization (energization time, energization timing, etc.).
[0036]
As shown in FIG. 3, the engine control apparatus 3 according to the present embodiment includes a basic fuel injection time calculation block 31, a rich / lean determination block 32, an integration block 33, adders 34 and 35, and a periodic signal generation block 36. The fuel injection command that defines the fuel injection time is output to the fuel injection device 2. In this embodiment, the fuel injection amount is controlled by time. However, in the present invention, the fuel injection amount may be directly controlled.
[0037]
The basic fuel injection time calculation block 31 calculates the basic fuel injection time based on the output values of sensors other than the λ-type oxygen sensor 7 such as the throttle opening sensor 4, the intake pipe pressure sensor 5, and the engine speed sensor 6. On the other hand, the rich / lean determination block 32 determines whether the air-fuel ratio is on the rich side or the lean side based on the output value of the λ-type oxygen sensor 7. A value of “1” is output, and if it is on the lean side, a value of “1” is output. The integration block 33 multiplies the output value of the rich / lean determination block 32 by a predetermined integration constant (variable) and integrates it, and supplies the value to the adder 34.
[0038]
The adder 34 adds the fuel injection time output from the periodic signal generation block 36 to the output value of the integration block 33 and supplies the result to the next adder 35. The adder 35 adds the output value of the basic fuel injection time calculation block 31 described above to the output value of the adder 34, and calculates the fuel injection time to be output to the fuel injection device 2.
[0039]
The engine control device 3 according to the present embodiment further includes an oxygen sensor output value duration measurement block 37, a forced vibration amplitude calculation block 38, an integral constant calculation block 39, and the like (the portion surrounded by a broken line in FIG. 3). A) With these blocks, the integration constant of the integration block 33 and the forced vibration amplitude of the periodic signal generation block 36 are changed.
[0040]
The oxygen sensor output value duration measurement block 37 measures the duration based on the output value of the λ-type oxygen sensor 7, and in the present embodiment, an integrator (not shown) having a reset function. ) Etc. For example, when the value 0.5 is subtracted from the output value of the λ-type oxygen sensor 7 (rich: 0.9V, lean: 0.1V) and the subtraction result rises from a negative value to a positive value, a timer (not shown) is set to zero. The duration from this point to the next reset is set as the duration.
[0041]
In the present invention, it goes without saying that any method other than the method exemplified here can be applied as long as the duration of the λ-type oxygen sensor 7 can be obtained.
[0042]
The forced vibration amplitude calculation block 38 refers to a map created in advance based on the output value of the oxygen sensor output value duration measurement block 37 and calculates the forced vibration amplitude. This map can be easily realized by conducting a test or the like in advance and obtaining the map in consideration of the relationship between the engine speed, the throttle opening, the intake pipe pressure, and the like.
[0043]
Therefore, the periodic signal generation block 36 described above generates a forced vibration signal based on the output value (forced vibration amplitude) of the forced vibration amplitude calculation block 38 and the forced vibration frequency, and outputs it to the adder 34.
[0044]
The output value (forced vibration amplitude) of the forced vibration amplitude calculation block 38 is also supplied to the integral constant calculation block 39, and the integral constant calculation block 39 performs integration such that it increases as the forced vibration amplitude increases. The value is calculated and output to the integrator 33.
[0045]
Such a relationship between the forced vibration amplitude and the integral value can be provided, for example, by the integral constant calculation block 39 as an integral constant map, and this relationship allows the integral constant to be set in a transient region where followability is required. On the other hand, the integral constant can be reduced in the steady region where the forced vibration amplitude is required to be small.
[0046]
Next, an effect comparison between the air-fuel ratio control apparatus according to the present invention and a conventional apparatus with a fixed integral constant and forced oscillation amplitude will be described based on experimental results with reference to FIGS. In this experiment, T ₀ ~ T _Ten Integral constant Ki [% / s], forced oscillation amplitude AMP [%], λ-type oxygen sensor output value rich state duration dT [s], fuel injection time INJ [μs], air-fuel ratio A / F [ −], And λ-type sensor output value O ₂ While observing each parameter of out [V] and examining the state of torque fluctuation, _Five At this point, the fuel injection time for changing the air volume stepwise to reach the stoichiometric air-fuel ratio is deliberately INJ ₁ To INJ ₂ (INJ ₁ > INJ ₂ ), The follow-up property was also investigated. In FIG. 4 to FIG. 8, the vertical axis represents the above parameters, and the horizontal axis represents a time axis (Time [sec]) common to the parameters. In addition, the broken line in the graph of the fuel injection time INJ indicates the theoretical fuel injection time at the theoretical air-fuel ratio.
[0047]
4 to 6 show experimental results for a conventional apparatus in which the integral constant and the forced vibration amplitude are fixed.
[0048]
<Case 1>
First, as an example of the experimental result of the prior art (case 1), in FIG. 4, the integration constant Ki = Ki ₁ [% / S] and forced vibration amplitude AMP = AMP ₁ [%] Is fixed. In this case, λ-type oxygen sensor output value O ₂ out is the same frequency as the forced vibration (about 4 / (T _{n + 1} -T _n ) [Hz]). It can also be seen that the air-fuel ratio A / F also vibrates at the same frequency.
[0049]
Where, for example, T _Five When the required fuel injection time INJ is suddenly changed by temporarily closing the throttle of engine 1 at the time (INJ ₁ → INJ ₂ ), There is a region where the air-fuel ratio A / F is constantly rich (<14.7), about 1/2 (T _{n + 1} -T _n ) Second, O-type oxygen sensor output value O ₂ It can be seen that out is in a steady state.
[0050]
<Case 2>
Next, as another example of the experimental result of the prior art (case 2), in FIG. 5, the integration constant Ki = Ki. ₁ [% / S] and forced vibration amplitude AMP = AMP ₂ (AMP ₁ > AMP ₂ ) [%] Is fixed. In this case, the forced vibration amplitude AMP is set smaller than that in case 1 with the same integral constant Ki as in case 1 described above. In this case, since the forced vibration amplitude AMP is too small, a limit cycle phenomenon occurs, and the forced vibration is reduced to about 4 / (T _{n + 1} -T _n ) Oxygen sensor output value O even though it is input in [Hz] ₂ It can be seen that out vibrates at a smaller frequency than in case 1.
[0051]
<Case 3>
Next, as yet another example (case 3) of the experimental result of the prior art, in FIG. 6, the integration constant Ki = Ki ₂ (Ki ₁ > Ki ₂ ) [% / S] and forced vibration amplitude AMP = AMP ₂ [%] Is fixed. In this case, the integral constant Ki and the forced vibration amplitude AMP are set smaller than in the case 1 described above. In this case, the λ-type oxygen sensor output value O ₂ It can be seen that out vibrates at the same frequency as the forced vibration. However, as a result of setting the integral constant Ki small, T _Five Λ-type oxygen sensor output value O at the time ₂ The steady state of out is about (T _{n + 1} -T _n ) Will continue for a second.
[0052]
As shown in Case 1 to Case 3, there is a close relationship between the integral constant Ki and the forced oscillation amplitude AMP. When the integral constant Ki is increased to increase the convergence to the air-fuel ratio, a predetermined forced In order to vibrate the λ-type oxygen sensor at the vibration frequency, the forced vibration amplitude AMP must be increased. If the integral constant Ki is excessively increased or the forced vibration amplitude AMP is excessively decreased, the λ-type oxygen sensor does not vibrate at the forced vibration frequency.
[0053]
In the present invention, when the rich state duration dT becomes larger than the set value, only the integration constant Ki is changed, only the forced vibration amplitude AMP is changed, and both the integration constant Ki and the forced vibration amplitude AMP are changed. The characteristics of each case will be described below.
[0054]
When only the integral constant Ki is increased when the rich state duration dT of the λ-type oxygen sensor output value becomes larger than the set value, the rich state duration dT of the λ-type oxygen sensor output value may be decreased. Is possible.
[0055]
Similarly, when only the forced vibration amplitude AMP is increased when the rich state duration dT of the λ-type oxygen sensor output value is larger than the set value, the rich state duration time of the λ-type oxygen sensor output value is similarly increased. It is possible to reduce dT.
[0056]
On the other hand, if both the integration constant Ki and the forced vibration amplitude AMP are changed when the rich state duration dT of the λ-type oxygen sensor output value becomes larger than the set value, the rich value of the λ-type oxygen sensor output value It is possible to simultaneously reduce the state duration dT and the air-fuel ratio fluctuation.
[0057]
Cases 4 and 5 shown below show experimental results when both the integration constant Ki and the forced vibration amplitude AMP are changed.
[0058]
<Case 4>
Next, as an example of the experimental results of the present invention (Case 4), in FIG. ₁ >Ki> Ki ₂ , And the forced vibration amplitude AMP is also AMP ₁ >AMP> AMP ₂ The range is variable. Initial experiment (T ₀ At the same time, as in Case 1, the integration constant Ki = Ki ₁ [% / S], forced vibration amplitude AMP = AMP ₁ [%] Was set for each.
[0059]
T ₀ From the time point, the steady state is reached, and both the integral constant Ki and the forced vibration amplitude AMP are smaller than in the case 1. From this, it is understood that the effect of forced vibration can be obtained even with a forced vibration amplitude AMP smaller than that in case 1.
[0060]
T _Five Λ-type oxygen sensor output value O at the time ₂ The steady state of out is approximately 3/4 (T by increasing the integral constant and the forced vibration amplitude temporarily. _{n + 1} -T _n ) Continuation of seconds and improvement, better results than in case 3.
[0061]
<Case 5>
Furthermore, as another example of the experimental results of the present invention (Case 5), in FIG. 8, the integration constant Ki is Ki. _Three >Ki> Ki ₂ (Ki _Three > Ki ₁ ) Is variable within the range, and the forced vibration amplitude AMP is also AMP _Three >AMP> AMP ₂ (AMP _Three > AMP ₁ ) Is variable. Initial experiment (T ₀ ), The integration constant Ki = Ki _Three [% / S], forced vibration amplitude AMP = AMP _Three [%] Was set for each.
[0062]
T ₀ From the time point to the steady state, both the integral constant Ki and the forced vibration amplitude AMP are reduced to the same values as in the case 4. From this, it can be seen that in the steady state, the same effect as in case 4 is obtained.
[0063]
T _Five Λ-type oxygen sensor output value O at the time ₂ The steady state of out is approximately 1/2 (T by increasing the integral constant Ki and the forced vibration amplitude AMP temporarily. _{n + 1} -T _n ) Continuation of seconds and improvement, better results than in case 4.
[0064]
(Second Embodiment)
FIG. 9 is a block diagram showing another embodiment of the engine control device 3 shown in FIG. As shown in FIG. 9, the engine control apparatus 3 according to the present embodiment differs from the forced vibration adjustment unit A of the first embodiment in the configuration of the forced vibration adjustment unit B surrounded by a broken line. Are substantially the same. Therefore, common parts are denoted by the same reference numerals, and detailed description thereof is omitted.
[0065]
The forced vibration adjustment unit B of the engine control device 3 according to the present embodiment includes an oxygen sensor output value duration measurement block 37, a forced vibration frequency calculation block 30a, a forced vibration amplitude calculation block 38a, an integral constant calculation block 39a, and the like. These blocks change the forced vibration frequency in addition to the integration constant of the integration block 33 and the forced vibration amplitude of the periodic signal generation block 36.
[0066]
The oxygen sensor output value duration measurement block 37 is the same as that in the first embodiment, and the output value is obtained from the forced vibration frequency calculation block 30a, the forced vibration amplitude calculation block 38a, and the integration constant. Each is given to the calculation block 39a.
[0067]
The forced vibration frequency block 30a calculates the forced vibration frequency based on the output value of the oxygen sensor output value duration measurement block 37.
[0068]
The forced vibration amplitude calculation block 38a calculates the forced vibration amplitude based on the output value of the duration measurement block 37 of the oxygen sensor output value.
[0069]
The periodic signal generation block 36 according to the present embodiment includes a forced vibration signal based on the output value (forced vibration frequency) of the forced vibration frequency block 30a and the output value (forced vibration amplitude) of the forced vibration amplitude calculation block 38a. Is output to the adder 34.
[0070]
The integral constant calculation block 39a calculates an integral value based on the output value of the oxygen sensor output value duration measurement block 37 and outputs the integral value to the integrator 33.
[0071]
These forced vibration frequency calculation block 30a, forced vibration amplitude calculation block 38a, and integral constant calculation block 39a are the optimum forced vibration frequency, forced vibration amplitude, and output value of the oxygen sensor output value duration measurement block 37. The integral value is stored as a map. Each map is obtained in advance by experiments or the like.
[0072]
In the present embodiment, the output value of the oxygen sensor output value duration measurement block 37 is input to the forced vibration frequency calculation block 30a, the forced vibration amplitude calculation block 38a, and the integral constant calculation block 39a, respectively. However, the forced vibration frequency may be fixed as in the first embodiment, and the forced vibration frequency calculation block 30a may be omitted from the structure of the second embodiment shown in FIG. Is possible.
[0073]
【The invention's effect】
As described above, according to the air-fuel ratio control method for an internal combustion engine according to the present invention and the apparatus suitable for the implementation, for example, the integration constant and / or the amplitude is increased or decreased based on the output value of the λ-type oxygen sensor. Thus, it is possible to suppress fluctuations in the air-fuel ratio with less amplitude while ensuring follow-up to the theoretical air-fuel ratio, so that exhaust gas can be purified, and further, fluctuations in engine torque are small, In the case of application to a vehicle, the present invention has an excellent effect that the ride comfort can be improved.
[Brief description of the drawings]
FIG. 1 is a graph showing output characteristics of a λ-type oxygen sensor used in an air-fuel ratio control apparatus for an internal combustion engine according to the present invention.
FIG. 2 is a block diagram showing a configuration of an air-fuel ratio control apparatus for an internal combustion engine according to an embodiment of the present invention.
FIG. 3 is a block diagram showing a detailed configuration of the engine control device shown in FIG. 2;
FIG. 4 is an experimental result (case 1) of a conventional air-fuel ratio control apparatus in which an integral constant and a forced vibration amplitude are fixed.
FIG. 5 is an experimental result (case 2) of a conventional air-fuel ratio control apparatus in which an integral constant and a forced vibration amplitude are fixed.
FIG. 6 is an experimental result (case 3) of a conventional air-fuel ratio control apparatus in which an integral constant and a forced vibration amplitude are fixed.
FIG. 7 is an experimental result (case 4) of the air-fuel ratio control apparatus according to the present invention;
FIG. 8 is a graph showing experimental results (case 5) of the air-fuel ratio control apparatus according to the present invention;
FIG. 9 is a block diagram showing a detailed configuration according to another embodiment of the engine control device shown in FIG. 2;
[Explanation of symbols]
1 engine
1a Intake pipe
1b Exhaust pipe
2 Fuel injector
3 Engine control device
4 Throttle opening sensor
5 Intake pipe pressure sensor
6 Engine speed sensor
7 λ type oxygen sensor
8 Catalyst (Exhaust gas purification device)
30a Forced vibration frequency calculation block
31 Basic fuel injection time calculation block
32 Rich / lean judgment block
33 Integration block
34 Adder
35 Adder
36 Periodic signal generation block
37 Oxygen sensor output value duration measurement block
38, 38a Vibration amplitude calculation block
39, 39a Integral constant calculation block
A, B Forced vibration adjuster

Claims (4)

In order to maintain the air-fuel ratio of the internal combustion engine provided with the fuel injection device in the vicinity of the theoretical air-fuel ratio, the fuel injection by the fuel injection device is forcibly oscillated based on the output value of the sensor that measures the composition of the exhaust gas from the internal combustion engine. An air-fuel ratio control method for an internal combustion engine that performs feedback control with integral operation,
Based on the output value of the sensor, calculate the duration of the rich state or lean state of the sensor output value,
Determine whether the calculated duration is longer than a predetermined time,
When it is determined that it is longer than the predetermined time, the integral constant and the amplitude of the forced vibration are increased. On the other hand, when it is determined that the time is shorter than the predetermined time, the integral constant and the forced vibration are increased. An air-fuel ratio control method for an internal combustion engine, wherein the amplitude is decreased . In order to maintain the air-fuel ratio of the internal combustion engine provided with the fuel injection device in the vicinity of the theoretical air-fuel ratio, the fuel injection by the fuel injection device is forcibly oscillated based on the output value of the sensor that measures the composition of the exhaust gas from the internal combustion engine. An air-fuel ratio control apparatus for an internal combustion engine that performs feedback control with integral operation,
Based on the output value of the sensor, comprising a forced vibration adjusting means for changing the integral constant and the amplitude of the forced vibration ,
The forced vibration adjusting means includes
Based on the output value of the sensor, comprising a duration calculating means for calculating the duration of the rich state or lean state of the sensor output value,
Based on the duration calculated by the duration calculation means, the integral constant and the amplitude of the forced vibration are changed,
A determination unit for determining whether the duration calculated by the duration calculation unit is longer than a predetermined time;
If the determination means determines that the time is longer than the predetermined time, the integral constant and the amplitude of the forced vibration are increased,
An air-fuel ratio control apparatus for an internal combustion engine configured to reduce the integral constant and the amplitude of the forced vibration when it is determined that the time is shorter than the predetermined time . The forced vibration adjusting means, said integration constant and in addition to the amplitude of the forced vibration, the air-fuel ratio according to claim 2 Symbol placement of the internal combustion engine, characterized in that it is configured to change the frequency of the forced vibration Control device. The sensor, the air-fuel ratio control apparatus for an internal combustion engine according to claim 2 or 3, wherein the a λ-type oxygen sensor.

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