JP3352819B2 - Combustion control device for two-cycle engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art In engines such as automobiles and outboard motors, controlling the air-fuel ratio improves the combustion state of the engine, thereby improving engine output and reducing harmful components in exhaust gas. I am trying to do it. In the control of the air-fuel ratio, 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. It is.

On the other hand, a two-stroke engine has a scavenging stroke for discharging burned gas by fresh air.
In a cycle engine, there is a blow-by phenomenon in which fresh air is mixed in exhaust gas. Therefore, when the oxygen concentration in the exhaust gas flowing in the exhaust pipe is detected, an accurate air-fuel ratio cannot be obtained. Therefore, in the air-fuel ratio control of the two-cycle engine, the oxygen concentration of the burned gas in the combustion chamber is detected, and the air-fuel ratio is obtained based on the detected oxygen concentration. In the detection of the oxygen concentration, adjacent cylinders having a phase difference are connected to each other through a detection passage, an O ₂ sensor is interposed in the passage, and burned gas flows from one cylinder to the other cylinder. It is conceivable to collect the gas to be detected. In the present invention, the burned gas refers to a gas containing only a combustion gas that does not include a blow-by gas, or a gas when the content of the blow-by gas is such that the oxygen concentration detection is not so hindered. Means a mixed gas of blow-through gas and combustion gas. Further, the mixture refers to a mixed gas of fresh air and fuel.

[0004]

However, in the above-mentioned conventional method, in general combustion control, particularly at the start of feedback control (generally, the air-fuel ratio largely deviates from the target air-fuel ratio). However, there is a problem that the convergence time required to reach the target air-fuel ratio is long. To shorten the convergence time, a large control coefficient may be set. However, if the control coefficient is simply increased, the A / F
There is a problem that hunting of values occurs and the combustion state of the engine becomes unstable.

In the air-fuel ratio detection method for collecting burned gas, the amount of gas to be collected varies depending on the operating state of the engine, and the response of the detection sensor changes. As a result, the air-fuel ratio tends to hunt. There's a problem.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and it is possible to converge and stabilize an air-fuel ratio in a short period of time, so that the combustion control of a two-cycle engine can always be stabilized. It is intended to provide a device.

[0007]

According to a first aspect of the present invention, there is provided a combustion control apparatus for a two-stroke engine, comprising: an air-fuel ratio detecting means for obtaining an air-fuel ratio of an air-fuel mixture from properties of burned gas; And a control coefficient before convergence 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. Control coefficient calculating means for setting the previous control coefficient larger than the post-convergence control coefficient, and setting the pre-convergence control coefficient and the post-convergence control coefficient to be larger as the engine speed is lower and smaller as the engine speed is higher;
Feedback control means for feedback-controlling the fuel supply amount with the control coefficient calculated by the control coefficient calculation means so that the air-fuel ratio determined by the air-fuel ratio detection means matches the target air-fuel ratio. Features.

[0008]

According to a second aspect of the present invention, in the first aspect, the air-fuel ratio detecting means detects the oxygen concentration of the burned gas.
_The O ₂ sensor is provided in the middle of a detection passage that connects one cylinder having the phase difference and the other cylinder, and the introduction port of the detection passage is connected to the one cylinder. The exhaust port is located between the exhaust port and the scavenging port of the other cylinder, the exhaust port is located closer to the bottom dead center than the exhaust port of the other cylinder, and the inlet port and the exhaust port are located at the exhaust port of one cylinder. The phase difference is set so as to open simultaneously during a certain period after the start of the stroke and a certain period before the start of the compression stroke of the other cylinder, and during this period, the burned gas in one cylinder flows toward the other cylinder. It is characterized by being.

Here, the control coefficient in the present invention means, for example, the values of the proportional component P and the integral component I in PI control. 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 at a stroke by P, and then the detected A / F is changed 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 reduced at once by P, and thereafter,
It gradually decreases by I.

[0011]

According to the first aspect of the present invention, when the difference between the detected air-fuel ratio and the target air-fuel ratio is equal to or greater than a predetermined value, the control coefficient is set higher than when the difference is within a predetermined range. Since the setting is large, for example, when the feedback control is started when the air-fuel ratio is largely on the rich side due to the start-up increase in which the feedback is not applied, 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.
When the detected air-fuel ratio reaches a predetermined range near the target air-fuel ratio, control is performed with a small post-convergence control coefficient, so that hunting of the air-fuel ratio can be avoided. As described above, since the fuel injection width is changed in accordance with the difference between the detected air-fuel ratio and the target air-fuel ratio, the convergence time of the detected value can be shortened, and the hunting of the A / F after convergence can be reduced. .

Further, since the control coefficients before and after convergence are set to be larger as the engine speed is lower and smaller as the engine speed is higher, the convergence time can be further shortened.
A / F hunting can be reduced.

That is, in the operating range where the engine speed is low, the burned gas amount (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 to target. It is considered that the actual air-fuel ratio has already significantly changed to the lean side when the air-fuel ratio has changed to lean. Therefore, by making the control coefficient larger and increasing the fuel amount, it is possible to more quickly invert the target air-fuel ratio.

On the other hand, in the operating range where the engine speed is high, the amount of burned 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 making the amount of increase in fuel conservative without making the control coefficient too large, it is possible to invert the target air-fuel ratio more quickly.

According to the combustion control device for a two-stroke engine of the second aspect of the present invention, one of the cylinders having a phase difference and the other from the scavenging port of the other cylinder on the combustion chamber side, and one of the cylinders starts the 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 that detects the oxygen concentration of the burned gas is provided in the middle of the passage, almost only the burned gas is used. Can detect the air-fuel ratio of
The accuracy of the feedback control can be improved, and the combustion state of the engine can always be stabilized.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIGS. 1 to 9 are views for explaining a combustion control device for a two-stroke engine according to one embodiment of the present invention.
FIG. 1 is a schematic configuration diagram of the above-described embodiment device, 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, an in-cylinder pressure, and the opening and closing of the detection passage. 4 is a characteristic diagram showing the relationship between the A / F value and the output value of the O ₂ sensor, FIG. 5 is a characteristic diagram showing the relationship between the detected A / F value and the fuel injection width, and FIG. 6 is a graph showing the relationship between the engine speed and the feedback coefficient. FIG. 7 is a functional block diagram, FIG. 8 is a characteristic diagram showing a modification of the relationship between the detected A / F value and the fuel injection width, and FIG. 9 is a diagram showing the relationship between the engine speed and the feedback coefficient. FIG.

In FIG. 1, reference numeral 1 denotes an engine for a three-cylinder, two-stroke outboard motor having a vertically mounted crankshaft, in which a piston 3 is slidably disposed in a cylinder bore 3a of a cylinder block 2, and the piston 3 is connected to a connecting rod. 4 is connected to the crankshaft 5. In the AA cross section in FIG. 1, indicates a 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 into 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 provided with a pressure sensor 31 for measuring an 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 of the cylinder block 2 opposite to the head. 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 (one cylinder).
0 is provided, and an O ₂ sensor 35 for detecting the air-fuel ratio of the burned gas is provided at an intermediate portion of the passage 40. In this case, as shown in FIG. 2, the introduction port 65 of the bypass passage 40 is connected between the opening timing position H1 of the exhaust port 2a of the cylinder No. and the opening timing position H2 of the scavenging port 2b, for example, with the exhaust port 2a. It is arranged to be opened and closed at the same time. The discharge port 68 of the passage 40 opens at a position advanced (closed to the bottom dead center) from the closing timing position H1 of the exhaust port 2a of the cylinder No., for example, immediately before the scavenging port 2b opens, and closes immediately after the closing. The inlet 65 and the outlet 68 are opened and closed by the pistons 3 of the respective cylinders.

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

Here, when the inlet port 65 is disposed between the exhaust port 2a and the scavenging port 2b of the cylinder No. 2 when it is disposed closer to the top dead center than the exhaust port 2a, it is compressed in the compression process of the cylinder No. 2. This is because the fresh air to be escaped through the passage 40, and the compression efficiency is reduced. In addition, if it is located closer to the bottom dead center 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 cylinder number to the cylinder number becomes shorter.

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

Further, since the passage 40 is formed to have a uniform diameter without a constricted portion, carbon or sludge is generated due to incomplete combustion when the engine 1 is operated at an extremely low speed such as a trolling operation of the outboard motor. Even so, the inside of the passage 40 is not blocked by the carbon or the like.

Further, the inlet port 65 and the discharge port 68 of the passage 40 are opened and closed by the respective pistons 3 of the cylinder No. and cylinder No. 2, and are simultaneously opened 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 one 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, and therefore, for example, the air-fuel ratio for each cycle can be detected even during excessive operation, and the optimal air-fuel ratio control can be performed during excessive operation. .

In the above embodiment, the case where the engine 1 is a three-cylinder two-stroke engine has been described. However, since there is a phase difference between the cylinders, the inlet 65 and the outlet 68 of the passage 40 are set at appropriate timing positions. V type 4
The present invention is also applicable to a two-stroke engine of a cylinder or a V-type six cylinder.

The output of the O ₂ sensor 35 is shown in FIG.
As shown by the characteristic line 7-1, when A / F is ab near the stoichiometric air-fuel ratio, a'b 'is obtained. In the present embodiment, the target A / F value is set in accordance with the above (a to b) according to the engine operating state.
Is variably controlled within the range. Note that a linear sensor having a linear output characteristic as shown by a characteristic line 7-2 in FIG. 4 may be used as the O ₂ sensor. 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 through a cylinder bore 3a. A reed valve 11 for preventing backflow of the intake air is disposed near the opening of the intake passage 10 near the crank chamber. Each of the intake passages 10 is provided with an injector 12 for injecting fuel into the intake passage, and a fuel supply device 13 is connected to the injector 12. The injector may be common to all cylinders. In this case, it is provided at the gathering portion of the intake manifold. A throttle valve 15 is provided in the intake passage 10.
, Ie, the throttle angle is detected by the sensor 41. Further, the outboard motor body 50 includes:
A trim angle detection sensor 42 for detecting the trim angle β is provided.

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

As shown in FIG. 7, the ECU 30 sets a 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 state of the engine. As well as O
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 feedback coefficient before convergence before the detected A / F reaches the target A / F, and IB is a post-convergence feedback coefficient after the detected A / F once reaches the target A / F. Where IA is I
B is set larger than B. As shown in FIG. 6, the feedback coefficients IA and IB are set so as to increase as the engine speed decreases and to decrease as the engine speed increases.
When the difference between the detected A / F and the target A / F is equal to or more than a predetermined value, the pre-convergence feedback coefficient IA may be employed, and when the difference is less than the predetermined value, the post-convergence feedback coefficient IB may be employed.

Next, the operation of this embodiment will be described with reference to FIG. In the present embodiment, the A / F value of the air-fuel mixture is obtained from the detection value of the O ₂ sensor 35, and the feedback before convergence shown in 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 a characteristic curve indicating a change in the coefficient IA. After the calculated A / F value reaches the target A / F value for the first time, 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 change amount than the IA. .

More specifically, as shown in FIG. 5, when feedback control is started when the air-fuel ratio is large and rich due to an increase in engine start-up amount or an increase in acceleration time, the convergence occurs. Previous feedback coefficient IA
The feedback control is performed using the 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 reaching the target A / F value, the post-convergence feedback coefficient I smaller than the IA
In B, the fuel injection amount is feedback-controlled to stabilize the target air-fuel ratio with a small fluctuation width. In this feedback control, when the target A / F is reached from the rich side, the fuel injection width is increased at once, while the target A / F is increased 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, when the difference between the detected air-fuel ratio and the target air-fuel ratio is large, such as when feedback control is started after starting, after acceleration, or the like, the control coefficient is set large. With this configuration, when the difference is large, the fuel injection amount can be largely changed to converge the detected air-fuel ratio to the target air-fuel ratio in a short time. 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 set smaller as the engine speed is higher, the amount of sampled gas supplied to the O ₂ sensor 35 decreases when the engine speed is low. The above sensor 3
5, the convergence delay and hunting of the A / F due to the decrease in the responsiveness of the sensor 35 can be avoided, 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. When the performance is high, it is possible to avoid an excessive change in the fuel amount.

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

Although the magnitude of the feedback coefficient I is changed before and after convergence in the above embodiment, the feedback coefficient P may be changed. Specifically, as shown in FIG. 8, until the detected A / F value reaches the target A / F value for the first time at the start of feedback, the fuel injection width is reduced at once by the pre-convergence feedback coefficient PA, and thereafter, the fuel injection width is fixed. It is reduced at the rate of the feedback coefficient I. The detected A / F value is equal to the target A / F.
After the F value has been reached (converged), the fuel injection width is increased at a stretch 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, the above PA, PB
Is set higher as the engine speed is lower, as shown in FIG. In FIG. 8, the feedback coefficient I is the same in both regions before and after 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. The convergence time can be further reduced, and the hunting of the A / F can be prevented.

[0038] In the above embodiment, although the case in which the O ₂ sensor in the middle of the detection path communicating one cylinder and the other cylinder, the method can also be employed placed in other O ₂ sensor is there. In other words, already the one end of the passageway connected to the second cylinder, connected to the accumulator chamber having a larger cross-sectional area than the cross-sectional area of the passage, to face the O ₂ sensor in the accumulator, which accumulated in the accumulation chamber A method of detecting the oxygen concentration of the combustion gas can be adopted. Here, the way of providing a passage for discharging the burned gas led to the accumulator chamber is as follows. The cylinder is connected to another cylinder, connected to the exhaust passage, and the inlet passage through which the burned gas enters. (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-stroke engine according to the first aspect of the present invention, when the difference between the detected air-fuel ratio and the target air-fuel ratio is equal to or greater than a predetermined value, the difference is within a predetermined range. Since the control coefficient is set to be larger than usual, there is an effect that the convergence time of the detected A / F value can be shortened, and there is an effect that the stability of the A / F after convergence is improved and hunting can be prevented. .

Further, since the control coefficients before and after convergence are set to be larger as the engine speed is lower and smaller as the engine speed is higher, the convergence caused by a decrease in the response of the sensor when the engine speed is low is set. This has the effect of avoiding the extension of time and hunting, and the effect of avoiding hunting of the A / F caused by excessive fuel change when the response of the sensor is high when the rotation speed is high.

In the combustion control device for a two-stroke engine according to the second aspect of the invention, one of the cylinders having a phase difference is
One is at the start the exhaust stroke, the other is connected by detecting passage communicating only a predetermined period before starting the compression stroke, in the middle of the detection passage, is provided with the O ₂ sensor for detecting the oxygen concentration in the burnt gas, There is an effect that the air-fuel ratio of only the burned gas that does not include the blow-by fresh air can be detected. Thus, the feedback control based on the air-fuel ratio of only the burned gas has an effect that the operation state of the engine can always be stabilized.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a combustion control device of a two-cycle engine according to one 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 a relationship among a cylinder crank angle, an in-cylinder pressure, and the opening and closing of a detection passage in the apparatus of the 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 embodiment device.

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

FIG. 7 is a functional block diagram of the device of the 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 embodiment device.

FIG. 9 is a characteristic diagram illustrating a relationship between an engine speed and a feedback coefficient according to the modification.

[Explanation of symbols]

1 Two-cycle engine 2a Exhaust port 2b Scavenging port 30 ECU (control coefficient calculating means, feedback control means) 35 O ₂ sensor (air-fuel ratio detecting means) 40 Detection passage 65 Inlet port 68 Discharge port One cylinder The other cylinder

Continuation of the front page (56) References JP-A-63-21342 (JP, A) JP-A-2-75738 (JP, A) JP-A-60-50242 (JP, A) JP-A-58-48741 (JP) JP-A-4-81538 (JP, A) JP-A-57-73840 (JP, A) JP-A-63-314341 (JP, A) JP-A-60-198348 (JP, A) 3-117644 (JP, A) JP-A-3-117645 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F02D 41/14

Claims (2)

(57) [Claims] An air-fuel ratio detecting means for obtaining an air-fuel ratio of an air-fuel mixture from properties of burned gas, a control coefficient in feedback control, and a detected air-fuel ratio being a predetermined value from a target air-fuel ratio. The pre-convergence control coefficient is divided into a pre-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 to be larger than the post-convergence control coefficient. Control coefficients before and after convergence.
A control coefficient calculating means for setting the higher the gin rotation speed and a smaller value for the higher gin rotation speed, and a control coefficient calculated by the control coefficient calculating means such that the air-fuel ratio obtained by the air-fuel ratio detecting means coincides with the target air-fuel ratio. A combustion control device for a two-stroke engine, comprising: feedback control means for performing feedback control of a fuel supply amount using a coefficient. 2. An air-fuel ratio detecting means according to claim 1, wherein said air-fuel ratio detecting means has an O ₂ sensor for detecting the oxygen concentration of the burned gas, and said O ₂ sensor has one phase having a phase difference and the other having a phase difference. It is interposed in the middle of the detection passage communicating with the 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 located at the bottom dead center side of the exhaust port of the other cylinder. The port and the discharge port are simultaneously opened during a certain period after the start of the exhaust stroke of one cylinder and during a certain period before the start of the compression stroke of the other cylinder, and during this period, the burned gas in one cylinder is released from the other cylinder. The combustion control device for an engine according to claim 1, wherein the phase difference is set so as to flow toward the engine.