JPH08158909A - Air fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE: To adjust air fuel ratio automatically according to humidity so as to improve operating capabilities, etc., by setting a target air fuel ratio in lean burn operation based on air fuel ratio learned values obtained immediately before high humidity condition is reached when the humidity of sucked air becomes high. CONSTITUTION: An air fuel ratio control part 28 learns a deviation between a target air fuel ratio and an actual air fuel ratio in stoic operation based on the detected signals of an air fuel ratio sensor 14, and the learned values are stored in a first memory 30. Also, based on the on/off conditions of a wiper switch 15, an updating judgment part 32 judges whether the content of a second memory 31 referred to during lean operation is updated or not in the content of storage of the first memory 30. By this, based on the learned values learned under normal humidity, the target air fuel ratio is set during lean operation under high humidity so as to fix the amount of fuel injection. Thus the air fuel ratio becomes high according to humidity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention operates at a stoichiometric air-fuel ratio while learning the deviation between the target air-fuel ratio and the actual air-fuel ratio, while reducing the air-fuel ratio when the engine enters a predetermined operating condition. TECHNICAL FIELD The present invention relates to an air-fuel ratio control device for an internal combustion engine that causes lean combustion to occur, and particularly to an air-fuel ratio control device for an internal combustion engine that can cope with a change in humidity of air.

[0002]

2. Description of the Related Art In recent years, when an engine enters a predetermined operating condition such as a low load running range, lean combustion is performed by making the air-fuel ratio thinner than the stoichiometric air-fuel ratio, thereby reducing fuel consumption and exhaust emission. Various so-called lean burn engines have been proposed which are intended to be improved. Generally, in this type of lean-burn engine, for example, when operating under conditions other than lean burn conditions such as a high load running range, based on the detection signal of the air-fuel ratio sensor, while performing air-fuel ratio control near the theoretical air-fuel ratio, When the lean-burn condition such as the low load running range is satisfied, the air-fuel ratio (fuel ratio) during lean-burn (ie, “lean”) operation is calculated based on the air-fuel ratio learned in the stoichiometric operation (so-called stoichiometric operation). The injection amount) is set, and thereby the air-fuel ratio during lean operation is controlled by open loop.

That is, as shown in the following formula 1, at the time of stoichiometric operation, based on the engine speed N detected by the crank angle sensor and the intake air amount Q detected by the air flow meter,
Calculating a basic injection quantity _{T P (T P = Q /} N), the basic injection quantity T _P, the various correction coefficients C _OEF including low water temperature during enrichment coefficient K _TW, etc. and the air-fuel ratio feedback correction coefficient α By correcting, the fuel injection amount T _i of the predetermined pulse width
(Reactive voltage pulse is omitted).

[0004]

## EQU1 ## Ti = T _P × C _oef × α The air-fuel ratio feedback correction coefficient α is a detection signal of the air-fuel ratio sensor that repeats inversion to rich and lean based on a predetermined slice level set near the theoretical air-fuel ratio. Based on the above, the deviation between the actual air-fuel ratio and the target air-fuel ratio (set air-fuel ratio) is eliminated by PI control. Therefore,
As shown by the solid line in the upper part of FIG. 9, during stoichiometric operation,
In order to realize the stoichiometric air-fuel ratio according to the engine load at that time, a fuel injection amount T _i having a predetermined pulse width is applied to the fuel injection valve.

When the engine reaches a predetermined operating condition such as a low load running range, lean combustion becomes possible. Therefore, the target air-fuel ratio is set to, for example, "22" which is thinner than the theoretical air-fuel ratio. Here, when using the air-fuel ratio sensor of the on-off detection type which inverts the detection signal based on the predetermined slice level set near the stoichiometric air-fuel ratio, it has only a fixed single slice level. Therefore, it is not possible to detect the air-fuel ratio during lean operation that deviates from this slice level.

Therefore, as shown by the dotted line in the upper part of FIG.
During lean operation, based on the fuel injection amount T _i for realizing the theoretical air-fuel ratio that is calculated on the stoichiometric operation, determine the fuel injection amount T _i for implementing the air-fuel ratio at the time of lean operation (e.g., stoichiometric The air-fuel ratio during lean operation is controlled in an open loop by this new fuel injection amount T _{i (} for example, it is set to 70% of the fuel injection amount).

Further, when the humidity of the intake air rises, that is, when the partial pressure of water vapor increases, the oxygen partial pressure decreases correspondingly. Therefore, as shown by the solid line in the lower part of FIG. 9, stoichiometric operation is performed in a high humidity state. The fuel injection amount T _i at that time is smaller than that in the normal humidity state by ΔT _i . Therefore, the target air-fuel ratio during lean operation in the high humidity state is also determined based on the fuel injection amount during stoichiometric operation under high humidity, as shown by the dotted line in the lower part of FIG. Also decreases by ΔT _iL .

By the way, in lean operation, if the air-fuel ratio becomes too thin, combustion becomes unstable and the surge worsens, while if the air-fuel ratio becomes too rich, NO _x (nitrogen oxide) is generated.
Since the emission amount increases, the range of the air-fuel ratio that the engine can take is limited to the so-called "adaptation region" between the "combustion stability limit" and the "NO _x emission limit", as shown in FIG. . Normally, the actual air-fuel ratio will vary to some extent (“air-fuel ratio control range” in the figure) due to the accuracy and control errors of each component such as the fuel injection valve, but under normal humidity conditions, this air-fuel ratio control Since the width is smaller than the width of the above-mentioned conformity region, even if some variation occurs in the air-fuel ratio, the engine can tolerate this variation, and the drivability is not affected at all.

However, during lean operation, the combustion stability limit and the NO _x emission limit tend to decrease as the humidity of the intake air rises, so during lean operation, the lean combustion operation is performed based on the air-fuel ratio learned during stoichiometric operation. In the first prior art in which the target air-fuel ratio is determined and is controlled by an open loop, when the humidity of the intake air reaches a humidity h% of about 90%, for example, as shown by the hatched pattern in FIG. A "combustion instability region" occurs in which a part of the control width exceeds the combustion stability limit, which may deteriorate drivability.

Therefore, for example, Japanese Patent Laid-Open No. 62-20394
In the second prior art shown in Japanese Patent Publication No. 2 or the like, a humidity sensor that detects the relative humidity of intake air is provided in the middle of the intake passage, and the air-fuel ratio is increased as the humidity of the intake air detected by this humidity sensor increases. By delaying the fuel injection timing or by delaying the fuel injection timing, closed-loop control is performed so that the air-fuel ratio increases according to the humidity, as indicated by the dotted line in FIG.

[0011]

In the prior art described above, feedback control of the air-fuel ratio during lean operation is performed based on the relative humidity of intake air to stabilize the combustion state and improve fuel efficiency. However, since the closed loop control has a more complicated control content than the open loop control, it has a drawback that the control system of the entire air-fuel ratio control device becomes complicated and the cost is increased.

That is, since the humidity sensor is required to have not only vibration resistance and heat resistance but also high-speed response and high accuracy, the price of the sensor alone tends to be high, and the wiring of the humidity sensor is high. As work is required, the assembly efficiency is also reduced.

The present invention has been made in view of the problems of the prior art, and an object thereof is to make it possible to easily control the air-fuel ratio during lean combustion even under a high humidity condition. To provide an air-fuel ratio control device of

[0014]

Therefore, the present invention was made by paying attention to the fact that as the humidity increases, the oxygen partial pressure relatively decreases due to the increase in the water vapor partial pressure. The air-fuel ratio under normal humidity learned in (Operating at air-fuel ratio) is used as the basis for the target air-fuel ratio during lean-burn operation under high humidity to easily correct the air-fuel ratio during lean-burn. It was decided to improve the combustion stability. That is, the configuration adopted by the air-fuel ratio control device for an internal combustion engine according to the present invention, an air-fuel ratio detection means for detecting the air-fuel ratio in the exhaust,
At least near the stoichiometric air-fuel ratio, learning control is performed on the deviation between the target air-fuel ratio and the actual air-fuel ratio based on the detection signal of the air-fuel ratio detecting means, and lean combustion is performed when the engine reaches a predetermined operating condition. An air-fuel ratio control device comprising: a humidity detecting means for detecting the humidity, and determining whether or not the humidity is high based on a detection signal of the humidity detecting means, and the humidity is high. When judged,
It is characterized in that the air-fuel ratio during lean-burn operation is calculated based on the air-fuel ratio during stoichiometric air-fuel ratio operation that was learned before the high humidity state.

Further, according to a more specific aspect, the target air-fuel ratio is detected based on the air-fuel ratio detecting means for detecting the air-fuel ratio in the exhaust gas and the detection signal of the air-fuel ratio detecting means at least near the stoichiometric air-fuel ratio. An air-fuel ratio control device equipped with air-fuel ratio control means for performing lean control of a deviation between a fuel ratio and an actual air-fuel ratio and performing lean combustion when the engine reaches a predetermined operating condition, and is referred to by the air-fuel ratio control means. First storage means for storing the learned value of the air-fuel ratio during the stoichiometric air-fuel ratio operation, second storage means for storing the learned value of the air-fuel ratio referred to during the lean-burn operation by the air-fuel ratio control means, and humidity And a humidity detecting unit for detecting whether or not the humidity is high based on a detection signal of the humidity detecting unit. When it is determined that the high humidity is detected, the empty space stored in the second storage is stored. Fuel ratio learning Prohibit updating to the air-fuel ratio learning value stored in the first storage means, and when it is determined that the high humidity state is not established, the air-fuel ratio learning value stored in the second storage means is changed to the first air-fuel ratio learning value. It is characterized in that update determining means for permitting updating to the air-fuel ratio learned value stored in the storage means is provided.

Further, a wiper switch for operating the wiper device may be used as the humidity detecting means.

A raindrop sensor for detecting raindrops provided on the wiper device may be used as the humidity detecting means.

[0018]

[Function] When the humidity becomes higher, the oxygen partial pressure decreases as much as the steam partial pressure increases. Therefore, based on the air-fuel ratio at the theoretical air-fuel ratio operation learned before the high humidity condition, If the target air-fuel ratio is calculated, the air-fuel ratio can be automatically increased, and the combustion state can be improved. In other words, as the humidity increases, the oxygen partial pressure decreases by the amount corresponding to this humidity, so the target air-fuel ratio during lean combustion is based on the air-fuel ratio during theoretical air-fuel ratio operation obtained under normal humidity conditions before high humidity. As a result, the air-fuel ratio at the time of lean combustion becomes rich according to the humidity.

Further, when it is determined that the high humidity condition exists, the stored content of the second storage means used for reference during the lean burn operation becomes the stored content of the first storage means stored during the stoichiometric air-fuel ratio operation. According to the configuration of claim 2 in which updating is prohibited, the storage content stored in the second storage means is always the air-fuel ratio learning value during the stoichiometric air-fuel ratio operation in the normal humidity state under the high humidity condition. Therefore, the air-fuel ratio during lean burn operation can be made rich according to the humidity.

On the other hand, when rainfall occurs, a puddle on the road surface evaporates and the humidity in the air rises. Therefore, if a wiper switch for operating the wiper device is used as the humidity detecting means, the wiper switch is turned on. As a result, it can be estimated that it is in a high humidity state, and the air-fuel ratio during lean burn operation can be corrected according to humidity with a simpler configuration.

Similarly, if a raindrop sensor provided in the wiper device is used as the humidity detecting means, it can be judged whether or not the humidity is high based on the detection signal of the raindrop sensor.

[0022]

Embodiments of the present invention will now be described in detail with reference to FIGS.

First, FIG. 1 is a structural explanatory view showing the overall structure of an air-fuel ratio control system for an internal combustion engine according to a first embodiment of the present invention. For example, a plurality of cylinders such as four cylinders are provided. A piston 2 is movably provided in one (only one is shown), and a combustion chamber 4 is defined between a crown surface of the piston 2 and a cylinder head 3 that covers an upper opening of the cylinder 1. Has been done. Further, an intake passage 5 and an exhaust passage 6 are connected to the cylinder head 3 so as to face each other via a pair of intake ports 5A and exhaust ports 6A, respectively, thereby forming a 4-valve pentroof type combustion chamber. Defined.

The downstream side of the intake passage 5 is bifurcated to be connected to each intake port 5A, the upstream side thereof is collectively connected to the air filter 7, and an intake air is provided in an intermediate portion near the cylinder 1 side. Collector part 5B for absorbing pulsation
Are formed. Further, in the intake passage 5, a fuel injection valve 8 located upstream of the bifurcating branch point, a throttle valve 9 located upstream of the collector portion 5B, the throttle valve 9 and the air filter 7. Between the air flow meter 10, the collector portion 5B and the fuel injection valve 8
And a swirl control valve 11 located between and. The swirl control valve 11 is formed as a butterfly valve having a notch, and is closed during lean combustion to generate swirl in the intake air flow, while it is opened during normal stoichiometric operation to stop swirl. like,
It is adapted to be opened and closed by the swirl control valve actuator 12.

On the other hand, the exhaust passage 6 has its upstream side bifurcated and connected to each exhaust port 6A, and its downstream side is collectively connected to a muffler (not shown). Further, H in the exhaust gas is provided downstream of the bifurcating point of the exhaust passage 6.
A catalytic converter 13 including a three-way catalyst that purifies C, CO, and NO _x is provided, and an air-fuel ratio sensor 14 that outputs a detection signal according to the oxygen concentration in the exhaust gas is provided on the upstream side of the catalytic converter 13. Is provided. The air-fuel ratio sensor 14 is, for example, provided with electrodes on a zirconia tube, and is configured to repeat inversion every rich or lean of the air-fuel ratio around a predetermined slice level corresponding to the theoretical air-fuel ratio.

Normally, the wiper switch 15 provided in the vicinity of the steering wheel in the vehicle compartment is provided with a wiper motor 1 via a wiper amplifier 16 as shown in the circuit configuration diagram of the wiper device in FIG.
7 is connected to the wiper blade 7 and drives the wiper blade (not shown) at a plurality of speeds such as intermittent, low speed, and high speed. A raindrop sensor 18 that detects the presence of raindrops based on, for example, a change in capacitance is connected to the wiper amplifier 16 via a wiper sub-amplifier 19 in the wiper device. The raindrop sensor 18 is provided, for example, near the wiper blade and is provided in a substantially central portion of the hood. When the raindrop sensor 18 detects a raindrop based on a change in electrostatic capacitance between opposed electrodes, for example, the wiper amplifier is used. 16 is
The wiper motor 17 is automatically driven. In addition, 20 shown in FIG. 2 is a washer pump for injecting a washer liquid, and 21 is a fuse for preventing overcurrent.

Reference numeral 22 shown in FIG. 1 is a throttle sensor for detecting the throttle opening of the throttle valve 9, and 23.
Are crank angle sensors for detecting the crank angle and the engine speed N of the engine, respectively. The throttle sensor 22 and the crank angle sensor 23 are an air flow meter 10, an air-fuel ratio sensor 14, a wiper switch 15, and a water temperature (not shown). It is connected to the control unit 27 together with a sensor, an ignition switch and the like.

Further, 24 is an intake valve that opens and closes each intake port 5A, and 25 is an exhaust valve that opens and closes each exhaust port 6A. These intake valves 24 and exhaust valves 25 are operated by a valve operating mechanism (not shown). Driven. Reference numeral 26 denotes an ignition plug provided on the cylinder head 3 such that the electrode portion on the tip side thereof faces the inside of the combustion chamber 4.
Is connected to a distributor (not shown).

The control unit 27 for electrically centrally controlling the engine includes an arithmetic processing circuit such as a CPU, ROM, and R.
It is configured as a microcomputer system including a storage circuit such as AM and an input / output circuit (neither is shown). The control unit 27 includes an air-fuel ratio control unit 28, an air-fuel ratio learning unit 29, a first memory 30, a second memory 31, and an update determination unit 32 as functions, as will be described later. There is.

Air-fuel ratio control unit 28 as air-fuel ratio control means
Is to determine the operating condition of the engine based on the engine speed N detected by the crank angle sensor 23, the intake air amount Q detected by the air flow meter 10, etc., and control the air-fuel ratio according to this operating condition. When the engine enters an operating condition such as a high load region, the stoichiometric control unit 28 for controlling the air-fuel ratio to near the stoichiometric air-fuel ratio based on the detection signal of the air-fuel ratio sensor 14.
A, and a lean control unit 28B for executing lean combustion by making the target air-fuel ratio thinner than the stoichiometric air-fuel ratio when the engine enters a predetermined operating condition such as a low load region.

The air-fuel ratio learning section 29 learns the deviation between the target air-fuel ratio and the actual air-fuel ratio generated during the stoichiometric operation to calculate the air-fuel ratio learning value. The air-fuel ratio learning section 29 calculates the air-fuel ratio. The learning value is stored in the first memory 3 as the first storage means.
Stored in 0.

Second memory 31 as second storage means
Stores the air-fuel ratio learning value that is referred to by the lean control unit 28B during lean operation. In the normal humidity state, the contents of the first memory 30 are sequentially updated and stored. The update determination unit 32 as the update determination means
The wiper switch 15 is connected between the first memory 30 and the second memory 31. Then, the update determination unit 32 determines that the wiper switch 15 is in the normal humidity state when the wiper switch 15 is in the off state, and updates the storage content of the second memory 31 with the storage content of the first memory 30. On the other hand, while permitting, when the wiper switch 15 is turned on, it is determined that it is in a high humidity state, and the updating of the second memory 31 is prohibited.

Here, "the wiper switch 15 is in the ON state" means all the cases when the wiper motor 17 is driven, and includes all the intermittent, low speed and high speed states. Further, the "high humidity state" referred to in the present specification means a state in which the humidity is high to a certain extent that the allowable level of the engine may be exceeded, specifically, a state in which the humidity is about 75% or more (see FIG. 5),
Furthermore, the "normal humidity condition" refers to a daily normal humidity condition other than this high humidity condition.

Next, the operation of this embodiment will be described with reference to FIGS. First, FIG. 3 shows a flow chart of the air-fuel ratio control processing according to the present embodiment. When the stoichiometric operation is started, the detection signal of the air-fuel ratio sensor 14 is read in step 1, and the target air-fuel ratio is read in the next step 2. . Then, in step 3, the deviation ΔA / F between the target air-fuel ratio and the actual air-fuel ratio is obtained by the air-fuel ratio learning unit 29,
In step 4, the correction amount as the air-fuel ratio learning value is calculated based on the deviation ΔA / F, and in step 5, the correction amount is stored in the first memory 30.

Next, in step 6, the wiper switch 1
The on / off state of No. 5 is read, and in step 7, it is determined whether or not the wiper switch 15 is in the on state. When it is determined to be “YES” in this step 7, since the wiper switch 15 is in the on state and it can be estimated that the high humidity state is caused by rainfall, the process moves to step 8 and the stored contents of the second memory 31 are The contents stored in the first memory 30 are prohibited from being updated, and the contents stored in the second memory 31 are maintained.

On the other hand, when the result of the determination in step 7 is "NO", it means that the wiper switch 15 is in the off state. Therefore, the process proceeds to step 9, and a predetermined time T _S has elapsed since the wiper switch 15 was turned off. Or not. That is, even if the wiper switch 15 is turned off, the evaporation of raindrops from the road surface or the like still continues, so it cannot be estimated that the high humidity state has been immediately eliminated. Therefore, in step 9, waits for a predetermined time the wiper switch 15 from the off state T _S has elapsed, the predetermined time T _S
It is presumed that the high humidity condition disappeared when the temperature passed. The predetermined time T _S is the time from the end of rainfall to the vicinity of the time when the high-humidity state is resolved, which is obtained in advance by experiments, state models, or the like. However, rather than waiting for the humidity to completely return to the normal state, the time required until the time when it can be estimated that the humidity will decrease to some extent is set.

When it is determined to be "NO" in the step 9, since the predetermined time T _S has passed since the wiper switch 15 was turned off and it can be estimated that the high humidity condition is resolved, the storage of the second memory 31 is performed. The contents are updated to the contents stored in the first memory 30. As a result, the correction amount during the stoichiometric operation learned before the high humidity state is stored in the second memory 31.

Then, in step 11, it is judged whether or not the engine is in lean operation, and in this step 11, "Y
When it is determined to be “ES”, since the lean operation is being performed, the target air-fuel ratio at the lean operation is set based on the correction amount stored in the second memory 31, and the air-fuel ratio is controlled by the open loop. On the other hand, if it is determined to be “NO” in step 11, it means that the engine is in stoichiometric operation, so the process moves to step 13 and the air-fuel ratio is referred to while referring to the first memory 13 that stores the correction amount during stoichiometric operation. Feedback control.

That is, according to the air-fuel ratio control process shown in FIG. 3, the first control referred to by the stoichiometric control unit 28A is performed.
The memory 30 stores the latest correction amount learned during the stoichiometric operation regardless of whether or not a high humidity condition has occurred. On the other hand, if it can be estimated that the high humidity state does not occur in the second memory 31 referred to by the lean control unit 28B, the contents of the first memory 30 are updated and stored,
If it can be estimated that a high humidity condition is occurring,
It is prohibited to update with the latest stored content (first correction amount obtained after rainfall) stored in the memory 30, and the stored content immediately before the high humidity state occurs (“YES” in step 7).
The contents updated in the program cycle one before the time when it is determined) are held.

As a result, during lean operation, the target air-fuel ratio is set on the basis of the correction amount learned in the normal humidity state immediately before rainfall, so that the fuel injection amount is in the high humidity state as shown in FIG. It becomes larger by ΔT _iL than when the target air-fuel ratio during lean operation is set based on the correction amount. That is, as described in the section of the prior art, in the high humidity state, the oxygen partial pressure is reduced by the amount of increase in the water vapor partial pressure. Therefore, it is only necessary to maintain the fuel injection amount T _i in the normal humidity state. The air-fuel ratio becomes rich.

The above-described air-fuel ratio control process will be described more specifically with reference to FIG. 4 showing the relationship between humidity change and air-fuel ratio change.

First, when rain suddenly occurs at a certain time T ₁ , the driver operates the wiper switch 15 to turn it on. Here, at the time point T ₁ when the rainfall starts, the moisture content in the air is absorbed by the falling raindrops and the evaporation amount from the road surface is small, so the humidity is not yet high. Therefore, even if the update prohibition process is performed at the start of rainfall, the operability of the engine is not impaired. Then, at time T ₁ when the wiper switch 15 is turned on by the start of the rainfall, it is determined to be “YES” in the step 7, and the stored content of the second memory 31 is maintained at the previous value in step 8. Therefore, during lean operation, the target air-fuel ratio is always set based on the correction amount learned in the normal humidity state immediately before rainfall.

As a result, as shown in the middle part of FIG. 4, the air-fuel ratio automatically increases as the humidity rises, and combustion stability and the like are secured. Further, since the fuel injection amount in the normal humidity state before the rainfall and the fuel injection amount in the high humidity state after the rainfall start time T ₁ are the same amount as long as other operating conditions such as the rotation speed are the same, As shown in the lower part of FIG. 4, the ratio of the amount of fuel to the total amount of gas drawn by the engine (G /
F) does not change before and after the rainfall.

Next, as time elapses from time T ₁ to time T ₂ , the amount of water vapor evaporated from the road surface increases, so that the humidity of the intake air rapidly rises. Then, if further time passes and the rainfall ends at time T ₃ , the wiper switch 15 is turned off by the driver,
Since the evaporation from the road surface is still continuing, the atmosphere of the intake air is still in the high humidity state even after the rain ends. Therefore, in step 9, the wiper switch 1
It is monitored that a predetermined time T _S has passed from when 5 was turned off,
Until the predetermined time T _S elapses, the updating of the second memory 31 is prohibited, and the target air-fuel ratio during lean operation is set by the correction amount in the normal humidity state. However, although the evaporation from the road surface continues, the humidity has gradually decreased because the rain has ended. Therefore, since the gradual oxygen partial pressure in accordance with the humidity decreases increases, even for the same fuel injection amount and the previous time T _3, the air-fuel ratio is gradually thinner (time T ₃ to time T ₄ Up curve between).

Then, from the rain end time T ₃ to a predetermined time T _S
Is reached and time T ₄ is reached, in step 9 described above, “Y
ES ”, the stored content of the second memory 31 is the first
Since the stored content of the memory 30 is updated, the lean control unit 28B sets the target air-fuel ratio during lean operation based on the latest correction amount obtained in step 4. However, even at this time T ₄ , the evaporation from the road surface is still continuing to some extent, so that the humidity of the intake air is slightly high and the oxygen partial pressure is low. Therefore, the fuel injection amount required to achieve the target air-fuel ratio in the normal humidity state decreases,
The ratio of the amount of fuel to the total amount of gas inhaled by the engine decreases, and the G / F increases slightly (sawtooth characteristic at time T ₄ ).

According to the present embodiment configured as described above,
The following effects are obtained.

First, when the wiper switch 15 as the humidity detecting means is turned on, it is presumed that the wiper switch 15 is in the high humidity state (step 7), and the air-fuel ratio learning section 29 learned before the high humidity state. Since the target air-fuel ratio during lean operation is calculated based on the correction amount during step operation (step 4) (steps 8, 11, 12), as shown by the solid line in FIG. The target air-fuel ratio during lean operation can be automatically thickened according to the humidity and can be controlled by open loop. In other words, as the humidity increases, the partial pressure of water vapor increases and the partial pressure of oxygen decreases, so if the target air-fuel ratio is set based on the correction amount (air-fuel ratio learning value) before the high humidity state, fuel injection Since the amount is fixed to the value before the high humidity state, the air-fuel ratio naturally increases as the oxygen partial pressure decreases (air-fuel ratio = oxygen partial pressure / fuel injection amount). As a result, the operability of lean operation under high humidity can be ensured with a simple and low-cost configuration without relying on closed loop control using an expensive humidity sensor.

Second, the first that is referred to during stoichiometric operation
The memory 30 and the second memory 31 referred to during lean operation
, And the first memory 30 always stores the latest correction amount, and the second memory 31 stores the first memory in the normal humidity state (the humidity state before the high humidity state). While the same correction amount as the memory 30 is updated and stored, in the high humidity state, the updated storage is prohibited and the immediately previous stored content is retained. Therefore, the stored content of the second memory 31 is
The correction amount learned immediately before the high humidity state can be always set. Therefore, when the lean operation is started under high humidity, the target air-fuel ratio can be easily set based on the correction amount in the normal humidity state, so that the first effect can be easily obtained.

Thirdly, since the wiper switch 15 is used as the humidity detecting means, it can be estimated that the wiper switch 15 is in the high humidity state when it is on, and is in the normal humidity state when it is off. It can be estimated that Therefore, it is possible to easily detect whether or not the humidity is high without using a separate expensive humidity sensor,
The entire structure can be simplified.

Fourth, in the present embodiment, the wiper switch 1
When 5 is turned off, the content of the second memory 31 is not immediately updated to the latest value, but is updated after waiting a predetermined time T _S. Therefore, high humidity is still caused by evaporation from the road surface or the like. Even when the above condition continues, it is possible to prevent the target air-fuel ratio from rising, and it is possible to secure the drivability during lean operation with higher reliability.

Next, a second embodiment of the present invention will be described with reference to FIGS. 6 and 7. In each of the following embodiments, the same components as those in the above-described first embodiment are designated by the same reference numerals, and the description thereof will be omitted. The feature of this embodiment is that, as the air-fuel ratio detecting means, an air-fuel ratio sensor that can detect the air-fuel ratio in an analog manner over a wide range is used.
The point is that the raindrop sensor 18 is used as the humidity detecting means.

That is, unlike the air-fuel ratio sensor 14 described in the first embodiment, the air-fuel ratio sensor 41 as the air-fuel ratio detecting means according to this embodiment covers a wide range from the stoichiometric operation to the lean operation. The air-fuel ratio in an analog manner (for example, the range of 12-24 is 1-5V or 4-20V).
It is configured as a wide-range air-fuel ratio sensor that can be detected by a signal such as mA. Further, the raindrop sensor 18 is connected to the update determination unit 32 instead of the wiper switch 15.

Next, the air-fuel ratio control processing according to this embodiment will be described with reference to the flowchart in FIG. First, at step 21, the operating state of the engine is detected based on the rotational speed N detected by the crank angle sensor 23, the intake air amount Q detected by the air flow meter 10, etc., and at step 22, stoichiometric operation is performed from this operating state. Determine if there is. If "YES" is determined in this step 22, the process proceeds to step 23, the deviation between the target air-fuel ratio and the actual air-fuel ratio is learned, this air-fuel ratio learning value is stored in the first memory 30, and then the step described later. Execute 25. On the other hand, when it is determined to be "NO" in step 22, it means that the lean operation is being performed, so that steps 23 and 24 are bypassed and the process proceeds to step 25.

Then, in step 25, the raindrop sensor 1
8 signal is read, and in step 26, the raindrop sensor 18
It is determined whether or not the signal is in the ON state, and thereafter, the same processing as the flowchart described in the first embodiment is performed. That is, steps 26 to 32 are the same as step 7 in FIG.
Since the same processing as that of steps 1 to 13 is performed, the duplicated description will be omitted. The raindrop sensor 18 is
Step 2 to detect the presence or absence of raindrops on and off
7 and 28, the raindrop sensor 18 is displayed as "SW".

Also in this embodiment having such a configuration, the same effect as that of the above-mentioned first embodiment can be obtained. In addition to this, the present embodiment also has the following effects.

First, since the raindrop sensor 18 is used as the humidity detecting means in place of the wiper switch 15, it is possible to reliably detect the occurrence of a high humidity state due to rainfall, and the reliability is improved. That is, in the case of the wiper switch 15, since it is operated by the driver, the switch operation may be delayed or forgotten, but since the raindrop sensor 18 detects raindrops without the intervention of the driver, reliability is high. Further improve.

Secondly, in the present embodiment, the wide-range air-fuel ratio sensor 41 capable of detecting the air-fuel ratio over a wide range is used. Therefore, although not shown, the air-fuel ratio can be feedback-controlled even during lean operation. It is also possible to easily change the control system according to the market demand (because only the rewriting of the control program is required).

Next, a third embodiment of the present invention will be described with reference to FIG. The feature of this embodiment is that the wiper switch 15
Both of the raindrop sensor 18 and the raindrop sensor 18 are used as humidity detecting means, and when either of them is turned on, it is presumed to be in a high humidity state, and updating of the second memory 31 is prohibited. In the flowchart of the first embodiment shown in FIG. 3, step 6 is "reading of wiper switch and raindrop sensor", step 7 is "at least one is on?", And step 9 is "on". If a predetermined time T _{S has} passed since the switch that turned off the switch, the processing contents are changed, and the flow chart of the present embodiment is provided. Therefore, the illustration thereof is omitted.

That is, in this embodiment, the wiper switch 1
5 and the raindrop sensor 18 are connected under the OR condition, and when either one is in the ON state, it is estimated to be in the high humidity state, so that the same effect as the first embodiment can be obtained. Further, since both the manual switch (wiper switch 15) and the automatic switch (raindrop sensor 18) are monitored, even if the driver forgets to operate the wiper, or if the raindrop sensor 18 malfunctions, Either one is
Since there is an extremely high possibility of normal operation, reliability can be further improved.

Although the wiper switch 15 and the raindrop sensor 18 are used as the humidity detecting means in each of the above embodiments, the present invention is not limited to this. For example, a crystal humidity sensor, a semiconductor humidity sensor, or the like. The humidity sensor may be used.

The raindrop sensor 18 may be used in place of the wiper switch 15 in the first embodiment, and the wiper switch 15 may be used in place of the raindrop sensor 18 in the second embodiment. Furthermore, the third embodiment,
It can also be applied to the second embodiment.

[0062]

As described in detail above, according to the air-fuel ratio control system for an internal combustion engine according to the present invention, the lean burn operation is performed based on the air-fuel ratio at the theoretical air-fuel ratio operation learned before the high humidity state. Since the target air-fuel ratio at the time of operation is calculated, the air-fuel ratio can be automatically increased by decreasing the oxygen partial pressure due to the increase in humidity, which improves the combustion state and operability during lean burn operation. can do.

Further, when it is determined that the high humidity condition exists, the stored content of the second storage means used for reference during the lean burn operation becomes the stored content of the first storage means stored during the stoichiometric air-fuel ratio operation. Since the update is prohibited, the storage content stored in the second storage means is always the air-fuel ratio learning value during the theoretical air-fuel ratio operation in the normal humidity state under the high humidity condition, and the lean burn operation is performed. The air-fuel ratio at that time can be easily increased depending on the humidity.

On the other hand, when rain occurs, a puddle on the road surface evaporates and the humidity in the air rises. Therefore, if a wiper switch for operating the wiper device is used as the humidity detecting means, the wiper switch is turned on. As a result, it can be estimated that it is in a high humidity state, and the air-fuel ratio during lean burn operation can be corrected according to humidity with a simpler configuration.

Similarly, if a raindrop sensor provided in the wiper device is used as the humidity detecting means, it can be easily determined whether or not it is in the high humidity state based on the detection signal of the raindrop sensor.

[Brief description of drawings]

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

FIG. 2 is a circuit configuration diagram showing a wiper device including a wiper switch and a raindrop sensor.

FIG. 3 is a flowchart of air-fuel ratio control processing.

FIG. 4 is an explanatory diagram showing a relationship between humidity change and air-fuel ratio change.

FIG. 5 is a characteristic diagram showing the characteristics of the air-fuel ratio control width during lean burn operation in comparison with the second conventional technique.

FIG. 6 is a configuration explanatory view showing an overall configuration of an air-fuel ratio control device for an internal combustion engine according to a second embodiment of the present invention.

FIG. 7 is a flowchart of an air-fuel ratio control process.

FIG. 8 is a configuration explanatory view showing an overall configuration of an air-fuel ratio control device for an internal combustion engine according to a third embodiment of the present invention.

FIG. 9 is an explanatory diagram showing changes in the fuel injection amount under high humidity and normal humidity.

FIG. 10 is a characteristic diagram showing the characteristics of the air-fuel ratio control width of the first conventional technology and the second conventional technology in comparison.

[Explanation of symbols]

 14, 41 ... Air-fuel ratio sensor (air-fuel ratio detection means) 15 ... Wiper switch (humidity detection means) 18 ... Raindrop sensor (humidity detection means) 28 ... Air-fuel ratio control section (air-fuel ratio control means) 30 ... First memory (first) 1 storage unit) 31 ... Second memory (second storage unit) 32 ... Update determination unit (update determination unit)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display area F02D 45/00 340 D

Claims (4)

[Claims] 1. An air-fuel ratio detecting means for detecting an air-fuel ratio in exhaust gas, and learning control of a deviation between a target air-fuel ratio and an actual air-fuel ratio based on a detection signal of the air-fuel ratio detecting means at least near the stoichiometric air-fuel ratio. An air-fuel ratio control device including an air-fuel ratio control means for performing lean combustion when the engine reaches a predetermined operating condition, and a humidity detection means for detecting humidity is provided, and based on a detection signal of the humidity detection means. If it is in the high humidity state, and if it is in the high humidity state, the air-fuel ratio in the lean burn operation is based on the air-fuel ratio in the stoichiometric air-fuel ratio operation learned before the high humidity state. An air-fuel ratio control device for an internal combustion engine, characterized in that: 2. A deviation between a target air-fuel ratio and an actual air-fuel ratio is learned and controlled on the basis of an air-fuel ratio detecting means for detecting an air-fuel ratio in exhaust gas and a detection signal of the air-fuel ratio detecting means at least near the stoichiometric air-fuel ratio. An air-fuel ratio control device comprising an air-fuel ratio control means for performing lean combustion when the engine reaches a predetermined operating condition together with an air-fuel ratio learning value during stoichiometric air-fuel ratio operation referred to by the air-fuel ratio control means. And a second storage means for storing an air-fuel ratio learning value referred to by the air-fuel ratio control means during lean burn operation, a humidity detection means for detecting humidity, and this humidity detection means. If it is determined that the high humidity condition is present, the air-fuel ratio learning value stored in the second storage means is stored in the first storage means. Air-fuel ratio When it is determined that it is not in the high humidity state, the air-fuel ratio learning value stored in the second storage means is updated to the air-fuel ratio learning value stored in the first storage means. An air-fuel ratio control device for an internal combustion engine, comprising: 3. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein a wiper switch for operating a wiper device is used as the humidity detecting means. 4. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein a raindrop sensor for detecting raindrops provided in a wiper device is used as the humidity detecting means.