JPH0727004A - Controller of alcohol engine - Google Patents

Abstract

PURPOSE:To suppress the unstable combustion state of an engine caused by the decrease in the air-fuel ratio accompanying alcohol, evaporated in a clank chamber, being reduced by an intake system. CONSTITUTION:An air-fuel ratio control means 61 operates the quantity of feedback control for bringing this air-fuel ratio close to the logical air-fuel ratio, based on the air-fuel ratio being detected with an O2 sensor 34, and outputs a pulse signal to an injector 20, based on this quantity of control. A timer 63 outputs an operation command signal during the specified period after the water temperature of an engine reaches the boiling point of methanol. During output of this operation command signal, a judgment inhibition means 65 inhibits the abnormality judgment by an abnormality judging means 62 and the stop operation of air-fuel feedback control based on the abnormality judgment by an abnormality judging means 62, and a control range enlarging means 66 enlarges the range where the quantity of feedback control is operated, and a fuel jet reduction means 67 compulsorily reduces the set quantity of jetted fuel by a specified quantity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a controller for an alcohol engine equipped with a crankcase ventilation system.

[0002]

2. Description of the Related Art In recent years, an alcohol engine using a fuel containing alcohol has been provided for the purpose of a clean engine or the like. Some of these alcohol engines have the same O
There is known one provided with a control device for feedback-controlling the fuel injection amount based on an air-fuel ratio detection signal from _two sensors or the like (see, for example, Japanese Patent Application Laid-Open No. 1-244133).

[0003]

In the above alcohol engine, the fuel injection amount is set to be larger than that in the normal operation in consideration of the fact that the fuel adheres to the wall surface at the time of starting, and the fuel that does not contribute to the combustion is the oil. Fall into bread. When the engine water temperature rises from such a state and reaches the boiling point of alcohol (for example, 65 ° C. for methyl alcohol), the alcohol component in the fuel evaporates at once and P as the blow-by gas.
Since the air-fuel ratio is rapidly reduced by being returned to the intake system by the CV system, the feedback control cannot catch up with such a sharp decrease in the air-fuel ratio, and the combustion state of the engine becomes unstable. In the worst case, The engine may stop. In particular, an abnormality determination means is provided for determining that an abnormal situation such as a sensor failure has occurred when the air-fuel ratio detected by the O ₂ sensor has fallen below the stoichiometric air-fuel ratio for a certain period or longer, and forcibly canceling the feedback control. In the device, an abnormal judgment is made even though the air-fuel ratio is actually lower than the stoichiometric air-fuel ratio for a long time due to the evaporation of alcohol, and feedback control is stopped based on this judgment, so engine stop Is likely to occur.

In view of such circumstances, it is an object of the present invention to provide a controller for an alcohol engine which can effectively suppress the instability of combustion of the engine due to the reduction of the air-fuel ratio due to the evaporation of alcohol. And

[0005]

As a means for solving the above problems, the present invention relates to an alcohol engine equipped with a crankcase ventilation system, which can prevent an unstable combustion state of the engine due to a decrease in air-fuel ratio. Combustion instability suppressing means for suppressing and combustion actuating suppressing means for operating the combustion instability suppressing means for a predetermined period from a time corresponding to a time when the engine water temperature reaches the boiling point of alcohol in the fuel (claim) 1).

The combustion instability suppressing means may be an air-fuel ratio decrease suppressing means for suppressing a decrease in the air-fuel ratio (Claim 2) or an output increasing means for increasing the output of the engine. (Claim 6).

As the air-fuel ratio reducing means, there are provided air-fuel ratio detecting means for detecting a value corresponding to the air-fuel ratio, and fuel supply control means for feedback controlling the fuel supply amount based on the detected air-fuel ratio. In the apparatus, as the air-fuel ratio reduction suppressing means, a control range expanding means for relaxing the restriction on the small air-fuel ratio side of the feedback control amount calculated by the fuel supply control means, and a fuel supply amount are set in advance. The fuel-supply reducing means for forcibly reducing the amount of fuel consumption (claim 4), the air-fuel ratio detecting means and the fuel supply control means, and the air-fuel ratio by the air-fuel ratio detecting means are continuously lower than the theoretical air-fuel ratio for a certain period. In the case of an apparatus provided with an abnormality determining means for determining that there is an abnormality and forcibly stopping the feedback control by the fuel supply control means, It is preferable to use a judgment prohibiting means for prohibiting the above-mentioned abnormality judgment (claim 5), and the output increasing means includes an idling speed control means for controlling the engine speed during idling to approach a target value. In addition, as the output increasing means, target value increasing means for increasing the target value above the normal value is preferable (claim 7).

Further, according to the present invention, in an alcohol engine having a crankcase ventilation system, air-fuel ratio detecting means for detecting a value corresponding to the air-fuel ratio,
Fuel supply control means for feedback-controlling the fuel supply amount based on the detected air-fuel ratio, learning control means for calculating a learning control amount based on the feedback control amount calculated by the fuel supply control means, and engine water temperature Is provided with learning prohibition means for prohibiting the calculation of the learning control amount by the learning control means for a predetermined period from the time corresponding to the time when the boiling point of the alcohol is reached (claim 9).

Each of the above devices is provided with operating period varying means for setting the operating period of the combustion instability suppressing means by the operating means and the learning inhibiting period by the learning inhibiting means to be longer as the set fuel injection amount at the time of engine start is larger. Is more preferable (claims 8 and 10).

[0010]

According to the apparatus of the present invention, the combustion instability suppressing means is operated for a predetermined period from the time when the engine water temperature reaches the boiling point of the alcohol, so that the engine resulting from the decrease in the air-fuel ratio is activated. The combustion destabilization of is automatically suppressed.

Specifically, in the apparatus according to the second aspect, the unstable combustion state is suppressed by suppressing the decrease of the air-fuel ratio during the predetermined period.

More specifically, in the apparatus according to claim 3,
While the fuel supply amount is feedback controlled within a predetermined control range based on the detected air-fuel ratio, during the predetermined period,
The restriction on the small air-fuel ratio side of the control range is relaxed, that is, the control range in the air-fuel ratio increasing direction is expanded,
Control of reduction of air-fuel ratio decrease is promoted.

Further, in the apparatus according to the fourth aspect, the decrease in the air-fuel ratio is suppressed by forcibly reducing the fuel supply amount by a preset amount during the predetermined period.

Further, in the apparatus according to the fifth aspect, when the air-fuel ratio detected by the air-fuel ratio detecting means is continuously lower than the stoichiometric air-fuel ratio for a certain period of time, it is determined to be abnormal and the feedback control is forcibly stopped. On the other hand, by prohibiting the abnormality determination by the abnormality determination means during the predetermined period, the forced stop of the feedback control based on the abnormality determination is avoided, and the feedback control, that is, the control of suppressing the air-fuel ratio is executed. Is secured.

On the other hand, in the apparatus according to the sixth aspect, the unstable combustion state of the engine is suppressed by increasing the output of the engine during the predetermined period.

More specifically, in the apparatus according to claim 7,
By increasing the target value of the engine speed control during idling only during the predetermined period, the engine output during idling increases.

According to the ninth aspect of the present invention, while the learning control amount is calculated based on the feedback control amount of the fuel supply, the learning control amount is calculated for a predetermined period from the time when the engine water temperature reaches the boiling point of the alcohol, that is, the alcohol. By prohibiting the learning control amount from being calculated by the learning control means during a special period during which the water vapor is evaporated, it is automatically prevented that the learning is inappropriate for the control during the normal operation.

In each of the above-mentioned devices, the invention as set forth in claim 8
In the apparatus described in 10, the relatively short combustion instability suppression period and the learning prohibition period are set while the fuel injection amount at the time of starting is relatively small, that is, when the alcohol evaporation does not require a long period of time, the starting is performed. When the fuel injection amount at this time is relatively large, that is, when it takes a long period to evaporate alcohol, a relatively long combustion instability suppression period or learning prohibition period is set. That is, the combustion instability suppression period and the learning prohibition period are set corresponding to the time required for the actual evaporation of alcohol.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIGS.

An intake passage 12 and an exhaust passage 14 are connected to the engine body 10 shown in FIG. 1, and an intake valve 16, an exhaust valve 18 and a spark plug 19 are provided at positions facing the combustion chamber 15. There is.

An injector 20, which is a fuel injection means, is provided in the middle of the intake passage 12. On the other hand, an alcohol fuel containing a considerable amount of methanol (methyl alcohol) is contained in the fuel tank 22, and a fuel pump 24 is installed inside the fuel tank 22. The fuel pump 24 is connected to the injector 20 via a fuel supply pipe 26.
A fuel filter 28 and a methanol sensor 30 for detecting the concentration of methanol in the fuel are provided in the middle of 6. Further, the injector 20 is connected to the fuel tank 22 via a fuel return pipe 32, and a predetermined amount of the fuel pumped from the fuel pump 24 is injected into the injector 2.
The remaining fuel that has been injected into the intake passage 12 from 0 and not injected is returned to the fuel tank 22 through the fuel return pipe 32.

[0022] in the middle of the exhaust passage 14, O ₂ sensor (air-fuel ratio detecting means) 34 and a catalyst 36 is provided by the O ₂ sensor 34, the oxygen concentration in the exhaust gas, the air-fuel ratio of the thus mixed air It is supposed to be detected.

This engine has an IS as shown in FIG.
A C (idle speed control) system and a PCV (positive crankcase ventilation) system are provided.

Specifically, a throttle valve 36 is provided in the middle of the intake passage 12, and an IS for bypassing the throttle valve 36 and communicating the upstream side and the downstream side thereof.
A C passage 38 is provided, and an ISC valve 40 is provided in the ISC passage 38. The idle speed is controlled by changing the opening of the ISC valve 40 while the throttle valve 36 is fully closed.

On the other hand, the inside of the crank chamber 42 is the engine body 1.
The head cover 46 is communicated with the inside of the head cover 46 through the passage 44 formed in 0. The inside of the head cover 46 is connected to the surge tank 52 through the PCV valve 48 and the PCV passage 50, and the above through the fresh air introduction passage 54. It is connected to the intake passage 12. The blow-by gas in the crank chamber 42 passes through the passage 44, the head cover 46, and the PCV.
The air is returned to the surge tank 52 through the valve 48 and the PCV passage 50, and at the same time, fresh air is replenished into the head cover 46 through the fresh air introduction passage 54.

In such an engine, among the fuel injected from the injector 20 when it is cold, the unburned fuel enters the crank chamber 42 through the gap between the piston and the cylinder and mixes with the lubricating oil 59. After that, when the temperature of the engine rises above the boiling point of methanol, the methanol in the fuel evaporates all at once and is returned to the intake system by the PCV system as blow-by gas, which causes the air-fuel ratio to decrease sharply.

In addition to the methanol sensor 30 and the O ₂ sensor 34, this engine includes a water temperature sensor 5 shown in FIG.
6, engine speed sensor 57, engine load sensor 5
Various sensors such as 8 are provided, and these are electrically connected to an ECU (engine control unit) 60. This ECU 60 uses the ignition timing of the spark plug 19 and the injector 2 based on the detection signals of various sensors.
The fuel injection amount is controlled by 0.

Specifically, the ECU 60 serves as a means for controlling the fuel injection amount, such as an air-fuel ratio control means 61, an abnormality determination means 62, a timer (operation means) 63, and an operation period as shown in FIG. Variable means 64, determination prohibition means 6
5, a control range expansion means 66, a fuel injection reduction means 67, a learning control means 68, and a learning prohibition means 69.

The air-fuel ratio control means 61 basically controls the fuel injection amount based on the air-fuel ratio detected by the O ₂ sensor 34 so that the actual air-fuel ratio approaches the stoichiometric air-fuel ratio. Specifically, as a general rule, as shown in FIG. 4, a feedback control amount that targets the above theoretical air-fuel ratio within a preset control range from an upper limit value (+ β ₁ ) to a lower limit value (−β ₁ ). It is configured to compute CFB.

The abnormality determining means 62, if constantly monitors the detection signal of the O ₂ sensor 34, falls below the stoichiometric air-fuel ratio detected by the O ₂ sensor 34 continuously period set in advance, or the When the stoichiometric air-fuel ratio is continuously exceeded for a period of time, it is determined that an abnormal situation such as a failure of the O ₂ sensor 34 has occurred, and the feedback control by the air-fuel ratio control means 61 is forcibly stopped.

The timer 63 operates from the time when the engine water temperature detected by the water temperature sensor 56 reaches the boiling point of methanol (about 15 ° C.), and from this time until a predetermined period elapses, the judgment prohibiting means 65, Control range expanding means 66,
And an operation command signal to the fuel injection reducing means 67.

The operation period changing means 64 is configured to change the predetermined period,
That is, the period in which the operation command signal is output by the timer 63 is changed based on the engine water temperature at the time of starting and the methanol concentration in the fuel. Specifically, a map as shown in FIG. 4 is stored, and a longer period is set as the predetermined period as the engine water temperature at start is lower and the methanol concentration is higher. Here, the higher the water temperature at the time of start, the more fuel is injected at the time of start in anticipation of the adherence to the wall surface of the fuel. Therefore, during the above predetermined period, the methanol water temperature after the engine water temperature reaches the methanol boiling point (about 65 ° C) The larger the amount of evaporation, the longer the setting.

The judgment prohibiting means 65 judges the fuel rich side abnormality by the abnormality judging means 62, that is, the detected air-fuel ratio continues for a certain period or more continuously only during the period when the operation command signal is received from the timer 63. It is forbidden to make an abnormality determination when the value is below the range.

The control range expanding means 66 is provided with the timer 63.
As shown in the right half of FIG. 5, the lower limit value of the feedback control amount CFB calculated by the air-fuel ratio control means 61 is (-β ₁ ) only while the operation command signal is received from
To (-β ₂ ) (increasing the absolute value).

The fuel injection reducing means 67 has the timer 63.
The set fuel injection amount calculated by the air-fuel ratio control means 61 is forcibly reduced by a preset amount only during the period in which the operation command signal is received from.

The learning control means 68 has a map for storing a learning value according to the operating state, and the air-fuel ratio control means 6
Feedback control amount CF calculated momentarily by 1
The learning value is stored and updated based on B. For example, the arithmetic operation is performed such that the learning value is changed by a value obtained by multiplying the average value of the feedback control amount during the predetermined period by a predetermined coefficient. This learned value will be reflected in the subsequent control.

The learning prohibiting means 69 controls the learning control means 68 (that is, the feedback control amount C only during the period in which the operation command signal is received from the timer 63).
FB storage and learning value calculation, update) are prohibited.

Next, the control operation performed by the ECU 60 will be described with reference to the flowcharts of FIGS.

First, various detection signals are read (step S1), and a basic pulse for fuel injection is calculated (step S2). Then, it is determined whether or not the current operating condition (engine speed, engine load, engine water temperature) satisfies a preset feedback condition (step S3), and only if it is satisfied, the feedback control is executed (step S3). Then YES).

As a feature of this apparatus, first, it is judged whether or not the detected engine water temperature is above the methanol boiling point (65 ° C.) (step S4), and when the engine water temperature exceeds 65 ° C. for the first time this time. Only (YES in step S4 and NO in step S4 '), the timer T is set (step S5). The timer T is set based on the map shown in FIG.

Next, when the timer T is 0 (NO in step S6), that is, when the water temperature is 65 ° C. or lower, or when the timer T has already expired, as a general rule,
As the limit value of the feedback control amount CFB, the first limit value, that is, the upper limit value (+ β ₁ ) and the lower limit value (−β ₁ ) shown in FIG. 5 are set (step S7). Also,
The basic pulse is not reduced (step S8).
Under these conditions, the feedback correction amount (feedback control amount) CFB is finally calculated (step S
9).

On the other hand, after the timer T is set, the period until the timer T becomes 0 (step S6
YES), that is, the period during which the timer T is operating,
The timer T is decremented (step S
At the same time, the second limit value is set as the limit value of the feedback control amount CFB (step S11). That is, the upper limit value remains (+ β ₁ ), but the lower limit value is set to −β ₂ (<−β ₁ ), and the range of the feedback control amount CFB (control range) is expanded accordingly. Further, the basic pulse is reduced (step S12), and the set fuel injection amount is basically reduced by that amount. Then, the feedback correction amount (feedback control amount) CFB is calculated under such conditions (step S9).

FIG. 7 shows a calculation routine for the feedback control amount. First, after reading various signals (step S31), it is determined whether the fuel in the air-fuel mixture is rich, that is, whether the detected air-fuel ratio is below the stoichiometric air-fuel ratio (step S32).

Here, while the current time is rich (YES in step S32), the previous time is not rich (NO in step S33), that is, the detected air-fuel ratio changes from the lean side to the rich side with the stoichiometric air-fuel ratio as a boundary. If it is reversed, the abnormality determination counter is reset (step S
34), the feedback control amount CFB is calculated by subtracting the constant amount P from the previous feedback control amount CFB (i-1) (step S35).

On the other hand, if both this time and the previous time are rich (YES in steps S32 and S33), whether or not the timer T is currently set, that is, the engine water temperature is
It is determined whether or not it is within a predetermined period after reaching 65 ° C. (step S36). If the timer T is not set (NO in step S36), the abnormality determination count C is incremented at a predetermined time interval (step S37) until the count C reaches a preset number α. (NO in step S38), an amount obtained by subtracting the predetermined amount ΔI from the previous feedback control amount CFB (i-1) is calculated as the current feedback control amount CFB (step S41). When the count C reaches the set number α, that is, when the fuel rich is continuously detected for a certain period (YES in step S38), it is determined that an abnormal situation such as a failure of the O ₂ sensor 34 has occurred (step S38). In step S39, the feedback control amount CFB is forcibly set to 0 and the feedback control is stopped (step S40).

If the timer T has not expired yet (YES in step S36), the above abnormality determination is forcibly prohibited, so that the count C is not performed, and the previous feedback control amount CFB (i-1) is not used. An amount obtained by subtracting the fixed amount ΔI is calculated as the current feedback control amount CFB (step S41).

On the other hand, if the detection result this time is fuel lean (NO in step S32) and rich last time (NO in step S42), it is rich this time and previous lean (YES in step S32). Further, similarly to (NO in step S33), the abnormality determination counter is reset (step S43), and a value obtained by adding a constant value P to the previous feedback control amount CFB (i-1) is calculated as the current feedback control amount CFB. (Step S4
4). On the other hand, if both this time and the previous time are rich (NO in step S32 and YES in step S42), the count C for abnormality determination is incremented regardless of the state of the timer T (step S45), Until the count C reaches a preset number α (step S
46, NO), the previous feedback control amount CFB (i-
An amount obtained by adding the predetermined amount ΔI to 1) is calculated as the current feedback control amount CFB (step S49). When the count C reaches the set number α, that is, when the fuel rich is continuously detected for a certain period (step S4).
(YES in 6), it is determined that an abnormal situation such as a failure of the O ₂ sensor 34 has occurred (step S47), the feedback control amount CFB is forcibly set to 0, and the feedback control is stopped (step S48).

After the feedback control amount is calculated in this manner, the current operating state is set to the preset learning condition (for example, the engine water temperature is 80 ° C. in the idling state).
The above is determined (step S1 in FIG. 6).
3). If it is the learning condition, it is determined whether or not the timer T has expired (step S14). Only when the timer T has expired (YES in step S14), the learning control is performed and the learning value is updated. (Step S1
5). Therefore, not only when there is no learning condition (NO in step S13), but also when there is a learning condition (YES in step S13) and the timer T has not expired (NO in step S14), the learning value The previous learning value is maintained without being updated (step S15).

After each control amount is calculated in this way,
The final pulse is calculated (step S17), and this pulse is output to the injector 20 (step S18), so that fuel injection is performed in an amount suitable for the actual operating conditions.

As described above, with this device, the following effects can be obtained.

(A) During a predetermined period after the engine water temperature reaches the boiling point of methanol, that is, during a period in which methanol in the fuel in the crank chamber 42 is simultaneously vaporized and returned to the intake system, the lower limit value of the feedback control amount CFB is set to a normal value. Lower limit (-
Since the control range is expanded by changing from β ₁ ) to the lower limit value −β ₂ below this, the feedback control amount C is conventionally used.
Since FB was not set below the lower limit value (-β ₁ ), the feedback control could not follow the sudden decrease in the air-fuel ratio due to the evaporation of methanol, which destabilized the combustion state and, in the worst case, stopped the engine. However, in this device, the feedback control amount CFB lower than the lower limit value (−β ₂ ) is set to further suppress the decrease in the air-fuel ratio and suppress the combustion instability. Engine stop can be prevented.

Further, in this device, the combustion instability suppressing effect can also be obtained by forcibly reducing the set fuel injection amount by a fixed amount during the predetermined period. Further, conventionally, as shown in FIG. 8 (b), an abnormality determination is made by keeping the air-fuel ratio detection result below the stoichiometric air-fuel ratio, and the feedback control amount CFB is returned to 0, causing an engine stop. However, in this device, as shown in FIG. 4A, the feedback control is continued by prohibiting the abnormality determination by keeping the air-fuel ratio detection result below the stoichiometric air-fuel ratio for the predetermined period. By doing so, it is possible to suppress the decrease in the air-fuel ratio and the destabilization of combustion resulting from this, and to reliably prevent the engine stop.

The present invention does not have to include all of the above means, and the combustion unstable state can be suppressed by providing any one of the means.

(B) In the above device, the water temperature at the start is low,
Also, the higher the methanol concentration, that is, the larger the amount of methanol evaporated after the engine water temperature reaches the methanol boiling point, the longer the timer operating period is set.
When the amount of evaporated methanol is relatively small, the above period is set short to start normal control earlier, while when the amount of evaporated methanol is relatively large, the period is set longer to make combustion instability more effective. Can be suppressed.

(C) Since the update of the learning value is forcibly prohibited during the above-mentioned timer operation period, that is, during the period when the air-fuel ratio abnormally decreases due to the evaporation of methanol, during the normal operation during this period. It is possible to prevent a learning value that is not suitable for control from being calculated.

Next, a second embodiment will be described with reference to FIGS.

In this embodiment, as means for suppressing the unstable combustion state for a predetermined period after the engine water temperature reaches the methanol boiling point, a means for increasing the engine output above the normal state is provided during the above period.

Specifically, as shown in FIG. 9, the ECU 6
In addition to the idle rotation speed control means 81, the target rotation speed changing means 80 is provided at 0. Here, as a general rule, the idle speed control means 81 is configured so that the engine speed sensor 5
Based on the engine speed detected in step 7, the speed of the ISC valve 40 shown in FIG. 2 is set so as to approach the target speed N1 determined according to the engine water temperature as shown in FIG. 10 (a). The target rotation speed varying means 80 is for controlling the opening degree, and the target rotation speed N1 is compulsorily set to the target rotation speed N1 only during the period in which the operation command signal is received by the timer 63 similar to the first embodiment. The target rotation speed is switched to N2 (> N1).

Next, the control operation performed by the ECU 60 will be described with reference to the flowchart of FIG.

Similar to the above-described embodiment, various signals are read (step S1), and the control amount corresponding to the operating state is calculated (step S19) except when idling (NO in step S3 '). On the other hand, during idling (YES in step S3 '), the operation control of the timer T is performed (steps S4, S4'S) as in the first embodiment.
5).

Here, before the timer T is set or after the timer T expires (NO in step S6), the normal target rotation speed N1 is set as the target rotation speed (step S6).
7 '), the ISC valve basic opening (initial opening; see FIG. 10 (b)) GB1 corresponding to this target rotational speed N1 is set (step S8'). On the other hand, while the timer T is operating (YES in step S6), the target rotation speed N2 higher than the target rotation speed N1 is set as the target rotation speed along with the decrement of the timer T (step S10) (step S11). ′), Corresponding ISC valve basic opening G
B2 (>GB1; see FIG. 10B) is set (step S12 '). As a result, the actual idle speed is increased more than in the normal state, and the combustion instability is suppressed and the engine stop is prevented as in the first embodiment.

The subsequent control operation (steps S9, S
17, S18) are the same as in the first embodiment.

In each of the above embodiments, the engine water temperature is actually detected by the water temperature sensor 56, and combustion instability suppression and learning control inhibition are executed within a predetermined period after the detected temperature reaches the methanol boiling point. However, the present invention is not limited to detecting the actual engine water temperature. For example, the relationship between the elapsed time from the engine start and the engine water temperature is investigated in advance, and the engine is started when a predetermined time elapses after the engine is started. Assuming that the water temperature has reached the boiling point of methanol, the combustion instability suppression and learning control prohibition may be performed for a predetermined period from this point.

[0064]

As described above, according to the present invention, the following effects can be obtained.

In the apparatus according to the first aspect of the present invention, the means for suppressing the unstable combustion state is operated for a predetermined period from the time corresponding to the time when the engine water temperature reaches the boiling point of the alcohol. During the period, it is possible to automatically and effectively suppress the unstable combustion state caused by the air-fuel ratio sudden decrease due to the evaporation of alcohol.

Specifically, in the apparatus according to the second aspect, the unstable combustion state of the engine can be suppressed by suppressing the decrease of the air-fuel ratio during the predetermined period.

More specifically, in the apparatus according to claim 3,
While performing feedback control of the fuel supply amount within a predetermined control range based on the detected air-fuel ratio, during the predetermined period, the restriction on the small air-fuel ratio side of the control range is relaxed, that is, the control range in the direction of increasing the air-fuel ratio. Only by enlarging, it is possible to suppress the decrease in air-fuel ratio.

Further, in the apparatus according to the fourth aspect, it is possible to suppress the decrease in the air-fuel ratio by forcibly reducing the fuel supply amount by the preset amount during the predetermined period.

Further, in the apparatus according to the fifth aspect, when the air-fuel ratio detected by the air-fuel ratio detecting means is continuously lower than the stoichiometric air-fuel ratio for a certain period of time, it is determined to be abnormal and the feedback control is forcibly stopped. On the other hand, by prohibiting the abnormality determination by the abnormality determination means during the predetermined period, the forced stop of the feedback control based on the abnormality determination is avoided, and the execution of this feedback control, that is, the control of suppressing the air-fuel ratio is secured. By doing so, the air-fuel ratio reduction suppressing operation can be continued.

On the other hand, in the apparatus according to the sixth aspect, the combustion instability of the engine can be suppressed by increasing the output of the engine during the predetermined period.

More specifically, in the apparatus according to claim 7,
By increasing the target value of the engine speed control during idling only during the predetermined period, it is possible to increase the engine output during idling and suppress combustion instability.

According to the ninth aspect of the present invention, the control response is improved by calculating the learning control amount based on the feedback control amount of the fuel supply calculated in the past, while the engine water temperature reaches the boiling point of the alcohol. During a predetermined period from the time corresponding to the above, that is, during a special period in which alcohol is evaporated and returned to the intake system, the learning control amount is prohibited from being calculated, so that it is not suitable for the control during normal operation. There is an effect that automatic learning can be automatically prevented and proper learning control can be secured.

In each of the above devices, the device according to claim 8,
In the device described in 10, when the fuel injection amount at the time of engine start is relatively small, that is, when the alcohol evaporation does not require a long period, a relatively short combustion instability suppression period and a learning prohibition period are set, While aiming for a quick transition to normal control, if the fuel injection amount at engine startup is relatively large, that is, if it takes a long period to evaporate alcohol, a relatively long combustion instability suppression period or learning prohibition period is used. By setting, there is an effect that the suppression of combustion instability and the prohibition of inappropriate learning control can be more reliably performed.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an engine according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a main part of the engine.

FIG. 3 is a block diagram showing a functional configuration of an ECU provided in the engine.

FIG. 4 is a graph showing the relationship between the timer operating period, the methanol concentration, and the engine starting water temperature set in the ECU.

FIG. 5 is a graph showing a range of an air-fuel ratio feedback control amount calculated by the ECU.

FIG. 6 is a flowchart showing a control operation actually performed by the ECU.

FIG. 7 is a flowchart showing a calculation routine of a feedback control amount in the above control operation.

FIG. 8A is a graph showing changes over time of the feedback control amount and the air-fuel ratio under the control of the apparatus of the above embodiment,
(B) is a graph showing the time variation of the feedback control amount and the air-fuel ratio under the control of the conventional device.

FIG. 9 is a block diagram showing a functional configuration of an ECU in the second embodiment of the present invention.

FIG. 10A is a graph showing a relationship between an idle speed target value set in the ECU and engine water temperature, and FIG. 10B is a basic ECU valve opening and engine set in correspondence with the target value. It is a graph which shows the relationship with water temperature.

FIG. 11 is a flowchart showing a control operation actually performed by the ECU.

[Explanation of symbols]

10 Engine Body 12 Intake Passage 14 Exhaust Passage 20 Injector 34 O ₂ Sensor (Air-Fuel Ratio Detection Means) 42 Crank Chamber 50 PCV Passage 60 ECU 61 Air-Fuel Ratio Control Means 62 Abnormality Determining Means 63 Timer (Actuating Means) 64 Operating Period Changing Means 65 Judgment prohibiting means 66 Control range expanding means 67 Fuel injection reducing means 68 Learning control means 69 Learning prohibiting means 80 Target speed changing means 81 Idle speed controlling means

Claims (10)

[Claims] 1. In an alcohol engine having a crankcase ventilation system, combustion instability suppressing means for suppressing an unstable combustion state of the engine due to a decrease in air-fuel ratio, and engine water temperature being the boiling point of alcohol in the fuel. A control device for an alcohol engine, comprising: an actuation unit that actuates the combustion instability suppression unit for a predetermined period from a time corresponding to the time when the alcohol engine reaches the time. 2. The controller for an alcohol engine according to claim 1, wherein the combustion instability suppressing means includes an air-fuel ratio reduction suppressing means for suppressing a decrease in air-fuel ratio. . 3. The alcohol engine control device according to claim 2, wherein air-fuel ratio detecting means for detecting a value corresponding to the air-fuel ratio, and fuel supply for feedback-controlling the fuel supply amount based on the detected air-fuel ratio. The alcohol engine is provided with a control means, and as the air-fuel ratio reduction suppressing means, a control range expanding means for relaxing a restriction on the small air-fuel ratio side of the feedback control amount calculated by the fuel supply control means. Control device. 4. The alcohol engine control device according to claim 2, wherein the air-fuel ratio reduction suppressing means includes a fuel supply reducing means for forcibly reducing the fuel supply amount by a preset amount. Control unit for alcohol engine. 5. The alcohol engine control device according to claim 2, wherein air-fuel ratio detecting means for detecting a value corresponding to the air-fuel ratio, and fuel supply for feedback controlling the fuel supply amount based on the detected air-fuel ratio. Control means, and an abnormality determination means for forcibly stopping the feedback control by the fuel supply control means by determining that the air-fuel ratio by the air-fuel ratio detection means is abnormal when the air-fuel ratio is continuously lower than the theoretical air-fuel ratio for a certain period. In addition to the above, the control apparatus for an alcohol engine is characterized by further comprising, as the air-fuel ratio reduction suppressing means, a determination prohibiting means for prohibiting the abnormality determination by the abnormality determining means. 6. The alcohol engine control device according to claim 1, further comprising, as the combustion instability suppressing means, an output increasing means for increasing an output of the engine. 7. The controller for an alcohol engine according to claim 6, further comprising idle speed control means for controlling the engine speed during idling to approach a target value, and the output increasing means as the target value. A controller for an alcohol engine, comprising: a target value increasing means for increasing the above-mentioned normal value. 8. The control device for an alcohol engine according to claim 1, wherein the operating period of the combustion instability suppressing means by the operating means is set longer as the set fuel injection amount at engine start is larger. A control device for an alcohol engine, comprising an operation period varying means. 9. In an alcohol engine equipped with a crankcase ventilation system, air-fuel ratio detecting means for detecting a value corresponding to an air-fuel ratio, and feedback control of a fuel supply amount based on the detected air-fuel ratio. A fuel supply control means, a learning control means for calculating a learning control amount based on the feedback control amount calculated by the fuel supply control means, and a predetermined period from a time corresponding to a time when the engine water temperature reaches the boiling point of the alcohol. ,
A control device for an alcohol engine, comprising: learning prohibition means for prohibiting the calculation of the learning control amount by the learning control means. 10. The control device for an alcohol engine according to claim 9, further comprising an operation period changing means for setting a longer operation period of the learning prohibition means as the set fuel injection amount at engine start increases. Control unit for alcohol engine.