JPH0814086A - Combustion control device for two-cycle engine - Google Patents

Abstract

PURPOSE:To converge and stabilize an air-fuel ratio in a short time and to always stabilize the combustion state of an engine by setting a control factor to a higher value than a control factor when a difference between a detecting air-fuel ratio and a target air-fuel ratio is within a given range when the difference therebetween exceeds a given value. CONSTITUTION:An ECU is functioned as a control factor computing means 71 to set a control factor to control a fuel injection width according to a difference between a target air-fuel ratio and a detecting air-fuel ratio and the operation state of an engine. Further, the ECU is functioned as a feedback control means 60 to effect feedback control of a fuel injection amount form a fuel injection valve by means of a control factor so that a detecting value (an air- fuel ratio) from an O2 sensor 35 is adjusted to a target air-fuel ratio. From the detecting value of the O2 sensor 35, an A/F value of air-fuel mixture is determined, and a feedback factor 1A before convergence is computed until the A/F value attains a target A/F value. After the A/F value attains the target value, a feedback factor after convergence having a change amount being lower than the 1A is computed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine combustion control device.

[0002]

2. Description of the Related Art In engines for automobiles, outboard motors, etc., the air-fuel ratio is controlled to improve the combustion state of the engine, thereby improving engine output and reducing harmful components in exhaust gas. I am trying to do it. In this air-fuel ratio control, it is common to install an exhaust gas sensor to detect the amount of oxygen in the exhaust gas, obtain the air-fuel ratio from the detected value, and control the fuel supply amount so that this matches the target air-fuel ratio. Is.

On the other hand, the two-cycle engine has a scavenging stroke for discharging burnt gas by fresh air, and therefore, two
In a cycle engine, there is a blow-by phenomenon in which fresh air mixes with the exhaust gas. Therefore, when the oxygen concentration in the exhaust gas flowing through the exhaust pipe is detected, it is not possible to obtain an accurate air-fuel ratio. Therefore, in the air-fuel ratio control of the two-cycle engine, the oxygen concentration of the burnt gas in the combustion chamber is detected, and the air-fuel ratio is obtained from this. In detecting the oxygen concentration, adjacent cylinders having a phase difference are connected to each other through a detection passage, an O ₂ sensor is provided in the passage, and burned gas is caused to flow from one cylinder to the other cylinder. It is possible to collect the gas to be detected. In the present invention, the burnt gas means a gas containing only combustion gas that does not include blow-through gas, or a gas in a case where the content of the blow-through gas is such that it does not hinder oxygen concentration detection so much, exhaust gas Means a mixed gas of blow-through gas and combustion gas. Further, the air-fuel mixture means a gas mixture of fresh air and fuel.

[0004]

However, in the above-mentioned conventional method, in the general combustion control, the air-fuel ratio is increased especially at the start of the feedback control (the air-fuel ratio usually deviates largely from the target air-fuel ratio). There is a problem that it takes a long convergence time to reach the target air-fuel ratio. A large control coefficient may be set to reduce the convergence time. However, if the control coefficient is simply increased, the A / F after the convergence is reduced.
There is a problem that hunting of the value occurs and the combustion state of the engine becomes unstable.

Further, in the case of the air-fuel ratio detecting method for sampling the burnt gas, the amount of sampled gas varies depending on the operating state of the engine, so that the response of the detection sensor changes, and as a result, the air-fuel ratio tends to hunt. There's a problem.

The present invention has been made in view of the above problems, and is capable of converging the air-fuel ratio in a short time and stabilizing it, so that the combustion state of the engine can always be stabilized. The purpose is to provide a device.

[0007]

According to a first aspect of the present invention, in a combustion control device for a two-cycle engine, an air-fuel ratio detecting means for obtaining an air-fuel ratio of an air-fuel mixture based on a property of burnt gas, and a control coefficient for feedback control are provided. It is divided into a pre-convergence control coefficient when the detected air-fuel ratio deviates from the target air-fuel ratio by a predetermined value or more, and a post-convergence control coefficient when the detected air-fuel ratio is within a predetermined range near the target air-fuel ratio. A control coefficient calculation means for setting the control coefficient larger than the post-convergence control coefficient and a control coefficient calculated by the control coefficient calculation means so that the air-fuel ratio calculated by the air-fuel ratio detection means matches the target air-fuel ratio. Therefore, a feedback control means for feedback controlling the fuel supply amount is provided.

According to a second aspect of the present invention, in the first aspect, the control coefficient computing means is configured to set the pre-convergence and post-convergence control coefficients larger as the engine speed is lower and smaller as the engine speed is higher. It is characterized by that.

According to a third aspect of the present invention, in the first or second aspect, the air-fuel ratio detecting means has an O ₂ sensor for detecting the oxygen concentration of the burned gas, and the O ₂ sensor has a phase difference. One of the cylinders is provided in the middle of a detection passage that communicates with the other cylinder, and the inlet of the detection passage is located between the exhaust port and the scavenging port of the one cylinder. The outlet is located at the bottom dead center side of the exhaust port of the other cylinder, and the introduction port and the exhaust port have a certain period after the start of the exhaust stroke of one cylinder and before the start of the compression stroke of the other cylinder. The phase difference is set so that the burned gas in one cylinder flows toward the other cylinder in this period at the same time.

Here, the control coefficient in the present invention means the value of the proportional component P and the integral component I in PI control, for example. In the PI control, for example, when the detected A / F reaches the target A / F from the rich side, the fuel injection width up to that point is increased by P at once, and then the detected A / F changes from the lean side to the target A / F. The fuel injection width is gradually increased by I until returning, and when the target A / F is reached from the lean side, the fuel injection width is decreased by P at once, and then,
It gradually decreases by I.

[0011]

According to the combustion control device for a two-cycle engine of the first aspect of the present invention, when the difference between the detected air-fuel ratio and the target air-fuel ratio is a predetermined value or more, the control coefficient is set higher than when the difference is within the predetermined range. Since it is set to a large value, for example, when the feedback control is started when the air-fuel ratio is greatly on the rich side due to the starting increase without feedback, the feedback control is performed with a large pre-convergence control coefficient. The detected air-fuel ratio reaches the target air-fuel ratio in a short time.
Then, when the detected air-fuel ratio reaches a predetermined range in the vicinity of the target air-fuel ratio, it is controlled with a small post-convergence control coefficient, so that hunting of the air-fuel ratio can be avoided. As described above, the fuel injection width is changed according to the difference between the detected air-fuel ratio and the target air-fuel ratio, so that the convergence time of the detected value can be shortened and the hunting of the A / F after convergence can be reduced. .

According to the combustion control apparatus for a two-cycle engine of the second aspect of the present invention, the control coefficient before and after convergence is set to be larger when the engine speed is lower and smaller when the engine speed is higher. And A / F hunting can be reduced.

That is, in an operating region where the engine speed is low, the amount of burned gas (collected gas amount) introduced into the detection passage is small and the response of the sensor is low. Therefore, for example, the sensor output exceeds the target air-fuel ratio from rich. It is considered that the actual air-fuel ratio has already changed considerably to the lean side when it changes to lean. Therefore, by increasing the control coefficient and increasing the fuel amount, it is possible to invert faster toward the target air-fuel ratio side.

On the other hand, in an operating range where the engine speed is high, the amount of burnt gas introduced into the detection passage is large and the response of the sensor is high. Therefore, for example, when the sensor output changes from rich to lean, the actual air-fuel ratio becomes It is considered that it is still near the target air-fuel ratio. Therefore, by conserving the amount of increase in the fuel without increasing the control coefficient too much, the target air-fuel ratio can be reversed more quickly.

According to the combustion control device for a two-cycle engine of the third aspect of the present invention, when one cylinder having a phase difference and the other combustion chamber from the scavenging ports of the other cylinder are located on the combustion chamber side, when one cylinder starts an exhaust stroke. Since the other cylinder is connected by a detection passage that communicates only for a predetermined period before the start of the compression stroke, and an O ₂ sensor for detecting the oxygen concentration of the burned gas is provided in the middle of the passage, only the burned gas is used. Can detect the air-fuel ratio of
The accuracy of feedback control can be improved, and the combustion state of the engine can always be stabilized.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. 1 to 9 are views for explaining a combustion control device for a two-cycle engine according to an embodiment of the present invention,
FIG. 1 is a schematic configuration diagram of the apparatus of the above embodiment, FIG. 2 is a schematic diagram for explaining a mounting position of a detection passage, FIG. 3 is a characteristic diagram showing a relationship between a cylinder crank angle, a cylinder pressure, and opening / closing of a detection passage, FIG. 4 is a characteristic diagram showing the relationship between the A / F value and the O ₂ sensor output value, FIG. 5 is a characteristic diagram showing the relationship between the detected A / F value and the fuel injection width, and FIG. 6 is the engine speed and the feedback coefficient. FIG. 7 is a functional block diagram, FIG. 8 is a characteristic diagram showing a modified example of the relationship between the detected A / F value and the fuel injection width, and FIG. 9 is a relationship between the engine speed and the feedback coefficient. It is a characteristic view to show.

In FIG. 1, reference numeral 1 is an engine for a vertically arranged three-cylinder two-cycle outboard motor having a crankshaft, in which a piston 3 is slidably arranged in a cylinder bore 3a of a cylinder block 2 and the piston 3 is connected to a connecting rod. It has a structure in which it is connected to the crankshaft 5 at 4. In addition, in the AA cross section of FIG. 1, indicates the cylinder number, and the phase difference between the cylinders is set to 120 °.

A cylinder head 6 is mounted on the mating surface of the cylinder block 2, and a spark plug 7 is inserted in a combustion recess formed in the cylinder head 6. 2a is an exhaust port and 2b is a scavenging port. The cylinder head 6 is equipped with a pressure sensor 31 for measuring in-cylinder pressure, and the crankshaft 5 is provided with an angle sensor 33 for detecting a crank angle (engine speed). A crank chamber 8 is provided on the side opposite to the head of the cylinder block 2. The crank chamber 8 is provided with a temperature sensor 32 for measuring intake air temperature or engine temperature and a pressure sensor 34 for measuring crank chamber pressure.

A bypass passage (detection passage) 4 is provided between the numbered cylinder (the other cylinder) and the numbered cylinder (the one cylinder).
0 is provided, and an O ₂ sensor 35 for detecting the air-fuel ratio of the burned gas is provided in the middle of the passage 40. In this case, as shown in FIG. 2, the introduction port 65 of the bypass passage 40 is provided, for example, with the exhaust port 2a between the open timing position H1 of the exhaust port 2a of the No. cylinder and the open timing position H2 of the scavenging port 2b. It is arranged so that it can be opened and closed at the same time. Further, the discharge port 68 of the passage 40 is opened at a position on the advance side (bottom dead center side) of the closing timing position H1 of the exhaust port 2a of the cylinder # 2, for example, immediately before opening the scavenging port 2b and immediately after closing. The inlets 65 and the outlets 68 are opened and closed by the pistons 3 of the respective cylinders.

Here, as shown in FIG. 3, the cylinder internal pressure P2 of the No. cylinder and the cylinder internal pressure P1 of the No. cylinder fluctuate with a phase difference of 120 ° between the two cylinders. Further, the introduction port 65 is the exhaust port 2a in the cylinder #.
From the open timing crank angle A to the closing timing crank angle B, the engine is opened. On the other hand, the discharge port 68 is opened from the opening timing crank angle (not shown) of the scavenging port 2b of the No. cylinder to the crank angle D immediately after the closing timing.
Therefore, the inlet port 65 and the outlet port 68 are opened simultaneously during the crank angles A to D, and during this period, the gas flows from the number cylinder to the number cylinder due to the pressure difference. The symbol E indicates the closing timing crank angle of the exhaust port 2a of the No. cylinder.

Here, the introduction port 65 is arranged between the exhaust port 2a and the scavenging port 2b of the No. cylinder when it is arranged at the top dead center side of the exhaust port 2a, and it is compressed in the compression process of the No. cylinder. This is because the fresh air escapes through the passage 40 and the compression efficiency is reduced. In addition, if it is arranged closer to the bottom dead center side than the scavenging port 2b, the introduction port 65 and the discharge port 68 are opened at the same time, and the period during which the burned gas flows from the No. cylinder to the No. cylinder is shortened.

Since the positions of the inlet port 65 and the outlet port 68 of the passage 40 are set as described above, when the inlet port 65 is opened immediately after the start of the exhaust stroke by the piston 3 of the cylinder No. 3, the outlet port 68 of the cylinder No. Since the piston 3 located immediately before the start of the compression stroke is still open, the burned gas in the number cylinder is introduced at the same time as the opening of the introduction port 65 due to the pressure difference between the cylinder number and the cylinder pressure between the number cylinders. Flowing through the passage 40 from the port 65 toward the exhaust port 68, the sensor 35 measures the amount of oxygen in the burned gas. Since the exhaust port 68 is closed immediately before the scavenging port 2b is opened in the cylinder # 2, the burned gas flowing through the passage 40 does not contain fresh air. Therefore, the sensor 35 can measure the oxygen amount in the burned gas that does not include blow-through fresh air, and can detect the air-fuel ratio of the burned gas that does not include blow-through fresh air.

Further, since the passage 40 is formed to have a uniform diameter without a narrowed portion, carbon, sludge, etc. are generated due to incomplete combustion during extremely low speed operation of the engine 1 such as during trolling operation of the outboard motor. However, the inside of the passage 40 is not blocked by the carbon or the like.

Further, the inlet port 65 and the outlet port 68 of the passage 40 are opened / closed by the pistons 3 of the No. cylinder and No. cylinder, respectively, so that they can be opened at the same time only during the crank angles A to D as described above. That is, since one of the openings is almost always closed, the burned gas in any of the cylinders does not flow backward from the inlet 65 or the outlet 68 into the passage 40.

Further, since the passage 40 has a simple structure, the fluid resistance is small. Therefore, for example, the air-fuel ratio for each cycle can be detected even during the transient operation, and the optimum air-fuel ratio control can be performed during the transient operation. .

In the above embodiment, the case where the engine 1 is a 3-cylinder 2-cycle engine has been described. However, there is a phase difference between the cylinders, and the inlet 65 and the outlet 68 of the passage 40 are set at appropriate timing positions. V type 4 because it can be arranged
It can also be applied to a 2-cycle engine having a cylinder or a V-type 6 cylinder.

The output of the O ₂ sensor 35 is shown in FIG.
As indicated by the characteristic line 7-1 of No. 3, when the A / F is ab near the stoichiometric air-fuel ratio, it becomes a'-b '. In the present embodiment, the target A / F value is set to the above (ab) according to the engine operating state.
Is variably controlled in the range of. As the O ₂ sensor, a linear sensor having a linear output characteristic as shown by the characteristic line 7-2 in FIG. 4 may be used. When this linear sensor is used, the variable range of the target A / F can be greatly expanded.

An intake passage 10 is connected to each of the crank chambers 8 so as to communicate with each other through a cylinder bore 3a. A reed valve 11 for preventing backflow of intake air is arranged near the opening of each intake passage 10 on the crank chamber side. An injector 12 for injecting fuel into the intake passage is attached to each intake passage 10, and a fuel supply device 13 is connected to the injector 12. The injector may be common to all cylinders. In this case, it will be provided at the collecting portion of the intake manifold. Further, a throttle valve 15 is arranged in the intake passage 10, and the throttle valve 15
The amount of rotation, that is, the throttle angle, is detected by the sensor 41. In addition, the outboard motor body 50
A trim angle detection sensor 42 for detecting the trim angle β is provided.

The engine 1 is an ECU 3 as a control unit.
It has 0. The ECU 30 includes a cylinder pressure detection sensor 31, an intake air temperature detection sensor 32, a crank angle detection sensor 33, a crank chamber pressure detection sensor 34, an O ₂ sensor 35, a back pressure detection sensor 36, and an engine temperature detection sensor 3.
7, throttle angle detection sensor 41, atmospheric pressure detection sensor,
The detection signals of the shift switch, cooling water temperature detection sensor, and engine vibration sensor are input.

As shown in FIG. 7, the ECU 30 sets the control coefficient for controlling the fuel injection width in accordance with the difference between the target air-fuel ratio and the detected air-fuel ratio and the operating condition of the engine, as shown in FIG. Functioning as
₂ Feedback control means 6 for feedback-controlling the fuel injection amount from the fuel injection valve 12 with the control coefficient so that the detection value (air-fuel ratio) from the sensor 35 becomes the target air-fuel ratio.
Functions as 0. Then, the ECU 30 has the configuration shown in FIG.
Engine speed and feedback coefficient (IA, I
A characteristic diagram showing the relationship with B) is stored as map data. Here, the feedback coefficient IA is a pre-convergence feedback coefficient before the detection A / F reaches the target A / F, and IB is a post-convergence feedback coefficient after the detection A / F once reaches the target A / F. , IA is I
It is set larger than B. Further, as shown in FIG. 6, the feedback coefficients IA and IB are set to be larger as the engine speed is lower and smaller as the engine speed is higher.
If the difference between the detected A / F and the target A / F is a predetermined value or more, the pre-convergence feedback coefficient IA may be adopted, and if the difference is less than the predetermined value, the post-convergence feedback coefficient IB may be adopted.

Next, the operation of this embodiment will be described with reference to FIG. In the apparatus of this embodiment, the A / F value of the air-fuel mixture is obtained from the detection value of the O ₂ sensor 35, and the pre-convergence feedback of FIG. 6 is performed until the A / F value first reaches the target A / F value. A feedback coefficient corresponding to the engine speed is calculated based on the characteristic curve indicating the change in the coefficient IA. Then, after the calculated A / F value first reaches the target A / F value, the control coefficient is calculated in the same manner as described above from the characteristic curve of the post-convergence feedback coefficient IB having a smaller variation amount than the IA. .

More specifically, as shown in FIG. 5, when the feedback control is started when the air-fuel ratio is large and is on the rich side due to an increase in the starting amount at the time of starting the engine, an increase in the acceleration amount, etc., the above convergence is achieved. Previous feedback coefficient IA
Feedback control is performed with a large control coefficient shown in (1), the fuel injection amount is greatly reduced, and the detected A / F value quickly converges to the target A / F value. After the target A / F value is reached, the post-convergence feedback coefficient I smaller than the above IA.
The fuel injection amount is feedback-controlled by B to stabilize the target air-fuel ratio within a small fluctuation range. In this feedback control, the fuel injection width is increased at once when the target A / F is reached from the rich side, while the target A is reached from the lean side.
When / F is reached, the fuel injection width is reduced at once, so-called PI control is performed.

As described above, in this embodiment, the control coefficient is set to a large value when the difference between the detected air-fuel ratio and the target air-fuel ratio is large, such as when the feedback control is started after starting or after acceleration. With this configuration, when the difference is large, the fuel injection amount can be greatly changed to converge the detected air-fuel ratio to the target air-fuel ratio in a short time. Further, after the convergence, the control coefficient is set small, so that the fuel injection amount can be controlled with a small change amount, and thus the stability of the A / F value can be improved.

Further, since the control coefficient is set to be larger as the engine speed is lower and smaller as the engine speed is higher, the amount of sampled gas supplied to the O ₂ sensor 35 is reduced when the engine speed is low. By the above sensor 3
5 can avoid A / F convergence delay and hunting due to a decrease in responsiveness, and when the engine speed is high, the amount of sampled gas supplied to the sensor 35 increases and the response of the sensor 35 increases. It is possible to avoid an excessive change in the fuel amount when the property is high.

Further, since the O ₂ sensor 35 is arranged in the detection passage 40, the air-fuel ratio of only the burnt gas can be accurately detected, and the accuracy of feedback control can be improved.

Here, in the above embodiment, the magnitude of the feedback coefficient I is changed before and after convergence, but the feedback coefficient P may be changed. Specifically, as shown in FIG. 8, until the detected A / F value first reaches the target A / F value at the start of the feedback, the fuel injection width is reduced by the pre-convergence feedback coefficient PA at a stretch, and then the fuel injection width is kept constant. The feedback coefficient I is decreased. The detected A / F value is the target A /
After reaching (converging) the F value, the fuel injection width is increased at once with a post-convergence feedback coefficient PB smaller than the pre-convergence feedback coefficient PA so as not to deviate significantly from the target value. In this case, PA, PB
Is set to be larger as the engine speed is lower, as shown in FIG. In FIG. 8, the feedback coefficient I is the same both before and after the convergence.

In the above embodiment, only one of the control coefficients P and I is changed according to the difference between the detected A / F and the target A / F. It may be changed, and if this is done, the convergence time can be further shortened and A / F hunting can be prevented.

In the above embodiment, the case where the O ₂ sensor is provided in the middle of the detection passage that communicates one cylinder with the other cylinder has been described, but other O ₂ sensor installation methods can also be adopted. is there. That is, one end of the passage connected to the second cylinder is connected to a pressure accumulating chamber having a cross-sectional area larger than the cross-sectional area of the passage, and the O ₂ sensor is exposed to this pressure accumulating chamber to store the accumulated pressure in the pressure accumulating chamber. A method of detecting the oxygen concentration of the fuel gas can be adopted. Here, as a method of providing a passage for discharging the burnt gas led to the accumulator, the inlet side passage connected to another cylinder, connected to the exhaust passage, and containing the burned gas is used as it is, and the own cylinder ( It is possible to adopt a method such as returning to the second cylinder). By doing so, the degree of freedom in providing the discharge passage, that is, the degree of freedom in layout can be increased.

[0039]

As described above, in the combustion control device for a two-cycle engine according to the invention of claim 1, when the difference between the detected air-fuel ratio and the target air-fuel ratio is a predetermined value or more, the difference is within a predetermined range. Since the control coefficient is set to be larger than that at the time, there is an effect that the convergence time of the detected A / F value can be shortened, and the stability of the A / F after convergence can be improved and hunting can be prevented. .

In the combustion control device for a two-cycle engine according to the second aspect of the present invention, the control coefficient before and after convergence is set to be larger as the engine speed is lower and smaller as the engine speed is higher. Has the effect of avoiding the extension of the convergence time and hunting due to the deterioration of the sensor responsiveness, and the excess of the fuel change amount when the responsiveness of the sensor is high when the rotational speed is high. This has the effect of avoiding F hunting.

In the combustion control device for a two-cycle engine according to a third aspect of the present invention, one cylinder having a phase difference and the other cylinder having
One is at the start of the exhaust stroke and the other is connected by a detection passage communicating only for a predetermined period before the start of the compression stroke, and an O ₂ sensor for detecting the oxygen concentration of the burned gas is provided in the middle of the detection passage. This has the effect of being able to detect the air-fuel ratio of only the burnt gas that does not include blow-through fresh air, and therefore has the effect of always stabilizing the operating state of the engine by performing feedback control based on the air-fuel ratio of the burnt gas only.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a combustion control device for a two-cycle engine according to an embodiment of the present invention.

FIG. 2 is a schematic diagram for explaining a mounting position of a detection passage of the apparatus of the embodiment.

FIG. 3 is a characteristic diagram showing the relationship between the cylinder crank angle, the cylinder pressure, and the opening and closing of the detection passage in the apparatus of the above embodiment.

FIG. 4 is a characteristic diagram showing a relationship between an A / F value and an O ₂ sensor output value of the apparatus of the embodiment.

FIG. 5 is a characteristic diagram showing a relationship between a detected A / F value and a fuel injection width (feedback coefficient) of the apparatus of the above embodiment.

FIG. 6 is a characteristic diagram showing a relationship between an engine speed and a feedback coefficient of the apparatus of the above embodiment.

FIG. 7 is a functional block diagram of the apparatus of the above embodiment.

FIG. 8 is a characteristic diagram showing a modified example of the relationship between the detected A / F value and the fuel injection width (feedback coefficient) of the apparatus of the above embodiment.

FIG. 9 is a characteristic diagram showing a relationship between an engine speed and a feedback coefficient in the modified example.

[Explanation of symbols]

1 2 cycle engine 2a exhaust port 2b scavenging port 30 ECU (control coefficient calculation means, feedback control means) 35 O ₂ sensor (air-fuel ratio detection means) 40 detection passage 65 inlet port 68 exhaust port one cylinder the other cylinder

Claims (3)

[Claims] 1. In a combustion control device for a two-cycle engine, an air-fuel ratio detecting means for obtaining an air-fuel ratio of an air-fuel mixture from the properties of burnt gas, and a control coefficient in feedback control, wherein a detected air-fuel ratio is a predetermined value from a target air-fuel ratio. It is divided into a pre-convergence control coefficient when there is a deviation above and a post-convergence control coefficient when the detected air-fuel ratio is within a predetermined range near the target air-fuel ratio, and the pre-convergence control coefficient is set larger than the post-convergence control coefficient. So that the air-fuel ratio obtained by the control-coefficient calculating means and the air-fuel ratio detecting means coincides with the target air-fuel ratio,
A combustion control device for a two-cycle engine, comprising: feedback control means for feedback-controlling the fuel supply amount with the control coefficient obtained by the control coefficient calculation means. 2. The control coefficient calculation means according to claim 1, wherein the control coefficient before and after the convergence is set to be larger as the engine speed is lower and smaller as the engine speed is higher. Combustion control device for 2-cycle engine. 3. The air-fuel ratio detecting means according to claim 1 or 2, wherein the air-fuel ratio detecting means has an O ₂ sensor for detecting the oxygen concentration of the burned gas, and the O ₂ sensor is connected to one cylinder having a phase difference. It is provided in the middle of a detection passage that communicates with the other cylinder, the inlet of the detection passage is located between the exhaust port and the scavenging port of the one cylinder, and the outlet is the other one. It is located on the bottom dead center side of the exhaust port of the cylinder, and the inlet and the outlet are in a fixed period after the start of the exhaust stroke of one cylinder and a fixed period before the start of the compression stroke of the other cylinder. A combustion control device for an engine, wherein the phase difference is set so that the burned gas in one cylinder flows toward the other cylinder in the same period when opened simultaneously.