JPH08144836A - Air-fuel ratio detection device of two-cycle engine - Google Patents

Abstract

PURPOSE: To provide the air-fuel ratio detection device of a two cycle engine by which the air-fuel ratio of mixed gas supplied to a combustion room can be detected accurately. CONSTITUTION: An air-fuel ratio detection device is composed of an O2 sensor 30 installed on the way of a sub-exhaust passage 29 for introducing burnt gas from a combustion room S to the outside and ECU (air fuel detection means) 15 for finding out the air fuel ratio of the mixed gas based on the signal from the O2 sensor 30 and the burnt gas can be introduced from the introduction port of a sub-exhaust passage 29 only in a term from ignition to the arrival of a scavenged gas flow to the introduction port of the sub-exhaust passage 29. As the burnt gas is introduced to the sub-exhaust passage 29 on above term, new gas is not included as a scavenged gas in the burnt gas flowing in the sub-exhaust passage 29 and the O2 density of this burnt gas is detected by the O2 sensor 30 and the air-fuel ratio of the mixed gas supplied to the combustion room S is found out accurately based on the detection value of the O2 density by ECU 15.

Description

Detailed Description of the Invention

[0001]

The present invention relates to relates to an air-fuel ratio detecting device of a two-stroke engine for detecting the air-fuel ratio of the mixture from the O ₂ concentration detected burnt gas by O ₂ sensors.

[0002]

2. Description of the Related Art It is desirable to keep the air-fuel ratio of an air-fuel mixture at an optimum value in accordance with the operating state of an engine, from the standpoint of improving engine performance and fuel efficiency.

As a method of detecting the air-fuel ratio of the air-fuel mixture, there is a method of obtaining the air-fuel ratio based on the O ₂ concentration in the air-fuel mixture detected by the O ₂ sensor provided in the intake passage. The unvaporized fuel in the air-fuel mixture flows along the wall surface of the intake passage, and this unvaporized fuel is vaporized during or after entering the combustion chamber, so in this method, the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber is increased. Cannot be detected accurately.

Therefore, an O ₂ sensor is arranged in the exhaust passage, and the air-fuel ratio of the air-fuel mixture before combustion is calculated based on the O ₂ concentration in the exhaust gas (burnt gas) detected by the O ₂ sensor, Air-fuel ratio control for controlling the amount of air or fuel supplied to the combustion chamber based on the calculated air-fuel ratio and engine operating condition has been conventionally performed in a 4-cycle engine.

Therefore, also in the air-fuel ratio control of the two-cycle engine, it is possible to arrange the O ₂ sensor in the exhaust passage.

[0006]

However, in a two-cycle engine, both the scavenging port and the exhaust port open during the scavenging / exhaust stroke, so that the fresh air supplied to the scavenging flows out from the combustion chamber to the exhaust passage. A so-called blow-through phenomenon occurs, and the exhaust gas irregularly contains fresh air containing unvaporized fuel, and even if the O ₂ sensor installed in the exhaust passage detects the O ₂ concentration of the exhaust gas flowing therethrough. However, there is a problem that the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber cannot be accurately detected because the unvaporized fuel is vaporized near the O ₂ sensor.

The present invention has been made in view of the above problems, and its object is to detect an air-fuel ratio of a two-cycle engine capable of accurately detecting the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber. To provide.

[0008]

In order to achieve the above-mentioned object, the invention according to claim 1 separates burned gas and fresh air by scavenging introduced into the cylinder from the scavenging port when the exhaust port is opened. An air-fuel ratio detecting device provided in a two-cycle engine that exchanges gas is provided in an O-position provided in the middle of an auxiliary exhaust passage that guides burned gas from the combustion chamber of the two-cycle engine to the outside.
₂ sensors and a mixture ratio detection means for obtaining the air-fuel ratio of the air-fuel mixture based on the signal from the O ₂ sensor,
It is characterized in that burned gas can be introduced from the inlet of the auxiliary exhaust passage only during a period from ignition until the scavenging air reaches the inlet of the auxiliary exhaust passage.

According to a second aspect of the present invention, in the first aspect of the present invention, the scavenging air flow after combustion is completed within a period from ignition to when the scavenging air flow reaches the inlet of the auxiliary exhaust passage. The burned gas can be introduced from the introduction port of the auxiliary exhaust passage only during a period until it reaches the introduction port of the auxiliary exhaust passage.

Further, the invention according to claim 3 has at least two cylinders in which the sliding of the pistons has a phase difference, and the scavenging air introduced into the cylinder from the scavenging opening when the exhaust port is opened in each cylinder. An air-fuel ratio detecting device provided in a two-cycle multi-cylinder engine for exchanging burnt gas and fresh air by means of an O ₂ sensor provided in the middle of a communication passage communicating two adjacent cylinders ₂ It is configured to include a mixture ratio detection means for obtaining the air-fuel ratio of the air-fuel mixture based on the signal from the _two sensors, and only from the ignition of one cylinder in the expansion stroke of two adjacent cylinders to the opening of the scavenging port. It is characterized in that both ends of the communication passage can be opened.

[0011]

According to the invention described in claim 1, since the burnt gas is introduced into the auxiliary exhaust passage only within a period from ignition until the scavenging airflow reaches the inlet of the auxiliary exhaust passage, Item 2
According to the invention described above, since the burnt gas is introduced into the auxiliary exhaust passage only within the period from the completion of combustion until the scavenging airflow reaches the inlet of the auxiliary exhaust passage, The burnt gas flowing does not include fresh air containing unvaporized fuel, the O ₂ concentration in this burnt gas is detected by the O ₂ sensor, and the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber is detected by the air-fuel ratio detecting means. Can be accurately obtained based on the detected value of the O ₂ concentration.

According to the third aspect of the present invention, the burned gas of one cylinder in the expansion stroke flows through the communication passage to the other cylinder in the compression stroke, and in this case, the scavenging gas of the cylinder in the expansion stroke. Since the mouth is closed, the burned gas flowing through the communication passage does not include fresh air containing unvaporized fuel, and therefore the O ₂ concentration of this burned gas is detected by the O ₂ sensor, and the combustion chamber of each cylinder is detected. The air-fuel ratio of the air-fuel mixture supplied to is accurately obtained by the air-fuel ratio detecting means based on the detected value of the O ₂ concentration.

[0013]

【Example】

[First invention] An embodiment of the first invention will be described below with reference to the accompanying drawings.

<First Embodiment> FIG. 1 is a cutaway side view of an essential part of a motorcycle showing a two-cycle engine equipped with an air-fuel ratio detecting device according to the present embodiment. FIG. 2 is an enlarged sectional view of the essential part of the two-cycle engine. FIG. 3 is a timing chart of ignition and opening / closing of the sweep / exhaust port and the auxiliary exhaust passage.

A two-cycle engine 1 shown in FIG. 1 is a water-cooled single-cylinder engine, which is arranged in a space surrounded by a main frame 51 and a down tube 52 of a motorcycle and is formed in a cylinder body 2 of the same. Further, an intake pipe 4, a carburetor 5 and an air cleaner 6 connected to the rear of the vehicle body (right side in FIG. 1) are connected to the intake passage 3, and an exhaust pipe 8 is connected to a main exhaust passage 7 formed in the cylinder body 2 as well. It is connected. The intake passage 3 is provided with a reed valve 9, and the exhaust pipe 8 is provided with an exhaust valve 11 which is opened / closed by an exhaust valve opening / closing actuator 10. The carburetor 5 has a valve provided therein. A throttle valve driving actuator 12 that functions as a sensor for opening and closing the illustrated throttle valve and detecting the opening thereof, and a variable main jet driving actuator 13
And a variable air jet drive actuator 14 is provided.

Thus, the on-off valve actuator 10,
The sensor / throttle valve drive actuator 12, the variable main jet drive actuator 13, and the variable air jet drive actuator 14 are electrically connected to an engine control device (hereinafter referred to as ECU) 15.
In FIG. 1, 53 is a rear arm, 54 is a chain sprocket, and 55 is a drive chain.

Here, the structure of the two-cycle engine 1 will be described.

A piston 16 is slidably fitted in a cylinder 2a formed in the cylinder body 2 of the two-cycle engine 1, and the piston 16 is rotatably housed in a crank chamber 17a in a crankcase 17. The crankshaft 18 is connected via a connecting rod 19. A rotation sensor 20 for detecting the engine speed is attached to the bottom of the crankcase 17, and the rotation sensor 20 is electrically connected to the ECU 15.

The cylinder head 21 attached to the upper portion of the cylinder body 2 is provided with a recess 21a which forms a combustion chamber S between the cylinder head 21 and the top surface of the piston 16.
An ignition plug 22 is screwed to the center of the cylinder head 21. The spark plug 22 is the ignition control circuit 23.
The ignition timing is controlled by, and the ignition control circuit 23 is electrically connected to the ECU 15.

Further, as shown in FIG. 2, a main scavenging passage 24 and a sub-scavenging passage 25 are formed in the cylinder body 2 in addition to the intake passage 3 and the main exhaust passage 7. The main exhaust passage 7 is communicated with the inside of the crank chamber 17a via the intake port 3a, and the main exhaust passage 7 is connected to the cylinder 2a via the main exhaust port 7a.
It has an opening inside. Further, one end of the main scavenging passage 24 opens into the cylinder 2a through the main scavenging port 24a,
The other end is connected to the crank chamber 17a through the main scavenging passage inlet 24b.
It has an opening inside. The auxiliary scavenging passage 25 connected to the intake passage 3 opens into the cylinder 2a via the auxiliary scavenging port 25a. As shown in the figure, the upper edge of the main exhaust port 7a is located above the main scavenging port 24a and the sub-scavenging port 25a.

Now, the air-fuel ratio detecting device according to the present invention will be described.

As shown in detail in FIG. 2, a chamber 26 is formed above the main exhaust passage 7 of the cylinder body 2, and the chamber 26 is connected to the inside of the cylinder 2 a via a first passage 27. At the same time, it communicates with the main exhaust passage 7 through the second passage 28. Therefore, in the cylinder body 2, the first passage 27, the chamber 26 and the second passage 2 are provided.
The auxiliary exhaust passage 29 is constituted by 8.

An O ₂ sensor 30 is attached to the chamber 26, and a first passage 27 is provided with a first O ₂ sensor 30.
The check valve 31 has the second check valve 3 in the second passage 28.
2 are provided.

The O ₂ sensor 30 is the ECU 1
5 is electrically connected. The first check valve 31 permits the flow of burnt gas from the cylinder 2a toward the chamber 26. It does not open at the compression pressure after the sweeping / exhaust stroke, but the combustion after the ignition combustion is completed. Its spring load is set to open under pressure. On the other hand, the second check valve 32 permits the flow of burnt gas from the chamber 26 toward the main exhaust passage 7, and opens at a pressure lower than the opening pressure of the first check valve 31. The spring load is set so that the main exhaust passage 7 is not opened by the negative pressure generated in the main exhaust passage 7.

Further, the inlet 27a of the first passage 27
Is above the main exhaust port 7a, and the combustion chamber S
During combustion of the air-fuel mixture, the piston 16 closes it, and opens at a position where it opens after the timing when the air-fuel mixture combustion is completed.

Thus, the air-fuel ratio detecting device according to the present invention is
The auxiliary exhaust passage 29, the O ₂ sensor 30 provided in the middle of the auxiliary exhaust passage 29 (the chamber 26), the first and second check valves 31, 32, and the ECU 15 that also functions as an air-fuel ratio detecting means are configured. Next, the operation will be described below with reference to FIG.

In the compression process in which the piston 16 moves upward in the cylinder 2a, the negative pressure generated in the crank chamber 17a pulls the fresh air from the air cleaner 6, and the carburetor 5 mixes the fuel with the fresh air. A mixture is formed, and this mixture is introduced from the intake passage 3 into the crank chamber 17a through the intake pipe 4 and the reed valve 9. The air-fuel mixture introduced into the crank chamber 17a is primarily compressed by the piston 16 moving downward in the expansion stroke.

On the other hand, when the main scavenging port 24a, the sub-scavenging port 25a, and the main exhaust port 7a are closed by the piston 16 in the compression process, the air-fuel mixture supplied into the cylinder 2a is compressed by the piston 16 and the piston 16 moves upward. Immediately before reaching the dead center (TDC), the air-fuel mixture in the combustion chamber S is ignited by the ignition plug 22 and ignited and burned (see FIG. 3). Since the first check valve 31 of the first passage 27 is not opened by the compression pressure as described above, the unburned air-fuel mixture does not flow to the auxiliary exhaust passage 29 side.

When the piston 16 moves downward in the expansion process due to the high combustion pressure generated by the combustion of the air-fuel mixture in the combustion chamber S, first, the first passage 27 which constitutes the auxiliary exhaust passage 29 is introduced. The opening 27a opens after the completion of the combustion of the air-fuel mixture (see FIG. 3), and the first check valve 31 of the first passage 27 is pushed open by the combustion pressure. Then, the burned gas generated by the combustion of the air-fuel mixture flows into the chamber 26 from the first passage 27, and the burned gas pushes the second check valve 32 open by the pressure of the burned gas from the second passage 28 to the main exhaust passage. 7, the O ₂ sensor 30 detects the O ₂ concentration of the burnt gas flowing through the auxiliary exhaust passage 29 (chamber 26).

After that, when the piston 16 further moves downward,
Next, the main exhaust port 7a is opened, and the burnt gas is blown from the main exhaust port 7a to the main exhaust passage 7 and discharged into the atmosphere through the exhaust pipe 8. After that, the main scavenging port 24a and the sub scavenging port are discharged. 25
When a is opened (see FIG. 3), the air-fuel mixture in the crank chamber 17a that has been primarily compressed in the previous cycle has the main scavenging passage 24.
Through the sub-scavenging passage 25 and the main scavenging port 24a and the sub-scavenging port 2
There is a scavenging action that pushes out the burned gas remaining in the cylinder 2a into the main exhaust passage 7 from 5a into the cylinder 2a, and a part of the scavenging gas blows into the main exhaust passage 7.

Thus, the main scavenging port 24a and the sub-scavenging port 25a
From the inside of the cylinder 2a until it reaches the inlet 27a of the first passage 27.
The pressure of the burnt gas remaining in a is sufficiently reduced, and the pressure of the air-fuel mixture flowing into the cylinder 2a is low, so that the burned gas and the air-fuel mixture are opened by the time the first check valve 31 of the first passage 27 is opened. Therefore, at least before the air-fuel mixture reaches the inlet 27a of the first passage 27, the detection of the ₂ concentration of the burned gas by the O ₂ sensor 30 is completed. Therefore, the burned gas flowing through the auxiliary exhaust passage 29 does not include the air-fuel mixture (fresh air),
The O ₂ sensor 30 detects the O ₂ concentration of the burned gas that does not include the air-fuel mixture (fresh air).

In FIG. 3, A3 is a period from the completion of the combustion of the air-fuel mixture to the arrival of the scavenging air flow at the inlet 27a of the auxiliary exhaust passage 29. During this period A3, the inlet 27 is introduced.
When a is opened and the burnt gas is guided to the O ₂ sensor 30, it is possible to detect the O ₂ concentration of the burned gas that does not include the air-fuel mixture (fresh air).

In this embodiment, the crank angle at which the inlet 27a formed on the side surface of the cylinder 2a is opened by the piston 16 is in the period A3, and the valve opening pressure P1 of the first check valve 31 is equal to the inlet pressure. The internal pressure p ₁ of the cylinder 2a when the scavenging air reaches the port 27a and the internal pressure p ₂ of the cylinder 2a when the piston 16 closes the inlet port 27a in the compression stroke are set to be higher.

Then, in the engine in which p ₁ ≧ p ₂ , by setting P1 = p ₁ , it becomes possible to introduce the burnt gas into the auxiliary exhaust passage 29 during the period of a ₁ shown in FIG. . If the P1> p _1, which during termination of the introduction period of a ₁ has been advanced is the introduction period of the burnt gas. Also, p
_{In the} engine with ₁ <p ₂ , it is necessary to satisfy P1 ≧ p _3, and similarly, the advanced period of the introduction period of a ₁ is the burned gas introduction period. The main exhaust port 7a
Since the internal pressure p ₃ of the cylinder 2a when the valve starts to open is usually higher than p ₁ and p ₂ , it is possible to introduce burnt gas during the period of a ₂ by setting P1 = p _3. Becomes The longer the introduction period is, the longer the period for the O ₂ sensor 30 to detect the O ₂ concentration of the burnt gas is, which is desirable. However, by increasing the detection performance of the O ₂ sensor 30, P1> p ₃ is set, and more reliably. Burned gas containing no air-fuel mixture (fresh air) can be guided to the auxiliary exhaust passage 29. Here, the valve opening pressure P1 of the first check valve 31 is always set higher than the valve opening pressure P2 of the second check valve 32 (P1> P2).

When the O ₂ sensor 30 detects the O ₂ concentration of the burnt gas as described above, the signal is EC
Inputted to U15, the ECU 15 obtains the air-fuel ratio of the air-fuel mixture from the detected value of the O ₂ concentration, and the variable main jet drive actuator 13 and the variable air jet drive actuator 14 so that the obtained air-fuel ratio becomes the target air-fuel ratio.
To adjust the amount of fuel supplied. The target air-fuel ratio is
It is given to the engine speed detected by the rotation sensor 20 and the throttle valve opening (engine load) detected by the sensor / throttle valve drive actuator 12.

Therefore, according to the present embodiment, the O ₂ concentration of the burnt gas which does not contain the air-fuel mixture (fresh air) is O ₂ sensor 30.
Since the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber S is accurately obtained by the ECU 15 based on the detected value of the O ₂ concentration, highly accurate air-fuel ratio control becomes possible and the two-cycle engine 1 It is possible to improve the performance of the vehicle, improve fuel efficiency, and drive stably.

When the mixture is burned, the first passage 27
Since the introduction port 27a of is closed by the piston 16, the heat load of the O ₂ sensor 30 can be suppressed to a small level.

By the way, the piston 16 moves to the bottom dead center (BD
When it passes through C) and moves upward, as shown in FIG.
By the piston 16, the main scavenging port 24a and the sub scavenging port 2
5a is first closed, and subsequently, the main exhaust port 7a and the inlet port 27a of the auxiliary exhaust passage 29 (first passage 27) are closed. When the main exhaust port 7a is closed, the cylinder 2
The air-fuel mixture supplied to the inside of a is compressed by the piston 16, and thereafter, the same operation as described above is repeated to continuously operate the two-cycle engine 1.

By the way, the introduction port 27a of the first passage 27 is located at a position where the main exhaust port 7 is opened and the main / sub scavenging ports 24a, 25.
It is also possible to arrange it between the positions where a is open, and by doing so, the combustion of the air-fuel mixture is almost completely completed and the internal pressure of the combustion chamber S decreases by the time the inlet 27a opens.
The valve opening pressure of the first check valve 31 can be set low. Also, when the inlet 27a is opened, the main / sub scavenging port 2
Since 4a and 25a are closed, the air-fuel mixture (fresh air) does not mix with the burned gas being measured.

<Second Embodiment> Next, a second embodiment of the first invention will be described with reference to FIGS. FIG. 4 is a schematic cross-sectional view of a main part of a two-cycle engine equipped with the air-fuel ratio detection device according to this embodiment. In this figure, the same elements as those shown in FIG. 2 are designated by the same reference numerals.

In this embodiment, the main exhaust passage 7 and the auxiliary exhaust passage 29 are formed in the cylinder head 21, and the inlet 29a of the auxiliary exhaust passage 29 is always opened in the combustion chamber S. The main exhaust port 7a of the main exhaust passage 7 is configured to be opened / closed by an exhaust valve 34 operated by a cam 33, and an opening / closing control valve 35 controlled to be opened / closed by the ECU 15 is provided in the middle of the sub exhaust passage 29. .

A scavenging valve 36 and a roots-type supercharger 37 are provided in the middle of the scavenging passage 24. The auxiliary exhaust passage 29
The outlet of is connected to the middle of the downstream side of the main exhaust passage 7,
You may open directly to the atmosphere.

As a result, as shown in FIG. 3, the opening period of the main exhaust port 7a can be made asymmetric with respect to the bottom dead center (BDC) as B2. In the present embodiment, the main scavenging port 24a is opened on the side surface of the cylinder 2a, and the opening period of the main scavenging port 24a is the bottom dead center (BD) like C1.
It becomes symmetric with respect to C). If scavenging is possible even after the exhaust valve 34 is closed in this way, the efficiency of filling the air-fuel mixture (fresh air) can be increased. In the engine where the main exhaust port is provided on the side surface of the cylinder, the scavenging port is provided on the cylinder head, and the scavenging valve that opens and closes by a cam drive is provided on the scavenging port, the main exhaust port opening period and the scavenging port opening period are respectively set. The setting can be made as shown by B and C2 in FIG. 3, and the charging efficiency of the air-fuel mixture (fresh air) can be increased in the same manner as described above.

Thus, according to this embodiment, the opening / closing control valve 3
The valve opening of No. 5 can be arbitrarily set during the period A3 in FIG. For example, if the burned gas introduction period is set as a ₄ , even if the time when the scavenging air reaches the introduction port 29a changes depending on the operating state, the air-fuel mixture will always be reliably discharged.
It is possible to guide the burnt gas that does not include the gas to the O ₂ sensor 30.

By increasing the detection performance of the O ₂ sensor 30, the burned gas introduction period can be set as shown by a ₃ . As a result, even if the operation state changes and the time at which the air-fuel mixture completes combustion varies, the main exhaust passage 7
Even if a backflow of burnt gas due to exhaust pulsation occurs at
The O ₂ sensor 30 can always be made to detect the O ₂ concentration in the burnt gas.

Further, A1 in FIG. 3 (from ignition to main scavenging port 24a
O ₂ during the period from the ignition to the time when the scavenging flow reaches the inlet 29a), that is, during the combustion stroke.
It is also possible to guide the gas in the combustion chamber S to the sensor 30. In this case, because it contains unburned gas in addition to the burned gas, in order to obtain an accurate air-fuel ratio is to be corrected according to the O ₂ concentration value detected by the O ₂ sensor 30 to the operating state There is. Since at least after ignition, there is no unvaporized fuel, and the air-fuel ratio can be easily obtained by correction. By setting the introduction period as indicated by a ₅ in FIG. 3, even if the unburned gas ratio at each crank angle changes according to the operating state, correction can be relatively easily performed.

<Third Embodiment> Next, a third embodiment of the first invention will be described with reference to FIG. Note that FIG. 5 is a schematic cross-sectional view of a main part of a two-cycle engine equipped with the air-fuel ratio detection device according to the present embodiment, and in this figure as well, the same elements as those shown in FIG.

In this embodiment, the main exhaust passage 7 is connected to the auxiliary exhaust passage 29 that bypasses the main exhaust passage 7, and the dynamic pressure of the burned gas is guided to the inlet port 29a of the auxiliary exhaust passage 29 in the middle of the main exhaust passage 7. A protrusion 7b for preventing the burned gas from reaching the inlet 29a of the auxiliary exhaust passage 29 by opening the main exhaust port 7 and the pressure p ₁ of the burned gas and the valve opening pressure P1 of the first check valve 31. between, so that the relationship of P1> p ₁ is satisfied.
The period during which the burnt gas is introduced into the auxiliary exhaust passage 29 in this case is approximately a ₆ in FIG.

<Fourth Embodiment> Next, a fourth embodiment of the first invention will be described with reference to FIG. FIG. 6 is a schematic cross-sectional view of a main part of a two-cycle two-cylinder engine equipped with the air-fuel ratio detection device according to the present embodiment. In this figure, the same elements as those shown in FIG. There is.

In this embodiment, the cylinder 2a of each cylinder is connected to the common main exhaust passage 7, and when the crank angle has a phase difference between the cylinders, the O ₂ sensor 30 is used.
It is possible to lengthen the period of contact with burnt gas. [Second Invention] An embodiment of the second invention will be described below with reference to the accompanying drawings.

<First Embodiment> FIG. 7 is a schematic cross-sectional view of a main part of a two-cycle two-cylinder engine equipped with an air-fuel ratio detecting device according to a first embodiment of the second invention. FIG. 8 shows ignition, sweep and exhaust ports. 7 is a timing chart of opening and closing of the communication path, and in FIG. 7, the same elements as those shown in FIG. 2 are denoted by the same reference numerals.

In the two-cycle two-cylinder engine according to this embodiment, the sliding (crank angle) of the piston 16 has a phase difference between the cylinders, and the first cylinder 2A and the second cylinder 2B have a continuous cylinder 2a. The passages 38 communicate with each other. The inlets 38a and 38b at both ends of the communication passage 38 are connected to the exhaust port 7
An O ₂ sensor 30 is installed in the chamber 26 provided in the middle of the communication passage 38, which is open above a.
The O ₂ sensor 30 is electrically connected to the ECU 15.

Then, as shown in FIG. 8, the first cylinder 2A
For, the exhaust port 7a, the scavenging port 24a, and the inlet port 38a are opened during the periods B1, C1, and E1. Therefore, the first
Period E1 when the inlet 38a of the cylinder 2A is open and the second cylinder 2B
In the periods e ₁ and e ₂ in which the introduction port 38b of the cylinder 2a and the introduction port 38b of the cylinder 2a overlap, the both introduction ports 38a and 38b are opened and the inside of the cylinder 2a of the two cylinders 2A and 2B is the communication passage 38
Communicate with each other via. At this time, the timing at which the inlet 38b of the second cylinder 2B closes is earlier than the timing at which the scavenging port 24a of the first cylinder 2A opens, so that the residual pressure in the cylinder 2a of the first cylinder 2A in the expansion stroke becomes the compression stroke. It becomes higher than the compression pressure of a certain second cylinder 2B, and the period e
_{In 1} , the burnt gas flows from the first cylinder 2A to the communication passage 38.
Through to the second cylinder 2B. In this case, since the scavenging port 24a of the first cylinder 2A is closed, the communication passage 3
The burnt gas flowing through 8 does not include fresh air (or air-fuel mixture) as scavenging gas, so that the O ₂ concentration of this burned gas is O _2.
2 Detected by the sensor 30.

The timing at which the scavenging port 24a of the first cylinder 2A is closed is the inlet port 38b of the second cylinder 2B.
Since it is earlier than the timing at which the
The first residual pressure in the cylinder 2a of the cylinder 2B is in the compression stroke.
It becomes higher than the compression pressure of the cylinder 2A, and burned gas flows from the second cylinder 2B to the first cylinder 2A during the period e ₂ , and in this case, since the scavenging port 24a of the second cylinder 2B is closed, The burnt gas flowing through the passage 38 does not include fresh air (or air-fuel mixture) as scavenging gas, so the O ₂ concentration of this burned gas is detected by the O ₂ sensor 30.

It should be noted that both of the inlets 38a and 38b are located farther from the top dead center (TDC) so that the combustion in each cylinder is completed at each start timing of the periods E1 and E2. It is arranged. In FIG. 8, G1 and G2 are periods from ignition to completion of combustion in each cylinder.

Both inlets 38a and 38b are at the top dead center (T
Since both of the inlets 38a, 38b are opened before the combustion in each cylinder is completed, the O ₂ detected as described in the first aspect of the invention is opened to the DC side.
The air-fuel ratio is calculated based on the corrected concentration value.

<Second Embodiment> Next, a second embodiment of the second invention will be described with reference to FIGS. 8 and 9. Incidentally, FIG. 9 is a schematic sectional view of a main part of a two-cycle two-cylinder engine equipped with the air-fuel ratio detection device according to the present embodiment, and in FIG.
The same elements as those shown in are given the same reference numerals.

In this embodiment, the tops of the cylinders 2a of the respective cylinders are communicated with each other by the communication passage 38, and the communication passage 38 is formed.
A chamber 26 is provided in the middle of the chamber 26, an O ₂ sensor 30 is installed in the chamber 26, and the ECU 15 is provided between the chamber 26 of the communication passage 38 and each cylinder 2A, 2B.
An opening / closing control valve 35, whose opening / closing is controlled by the above, is provided.

By opening the open / close control valve 35 during the period of e ₁ and e _{2 in} FIG. 8, the air-fuel ratio can be accurately obtained based on the detected value of the O ₂ concentration.

It should be noted that one cylinder 2A (2
During the period from the ignition of B) to the opening of the scavenging port 24a (the period indicated by F in FIG. 8), the ECU 15 controls the double opening / closing control valve 3
If 5 is opened at the same time, the unburned gas and the burned gas of one cylinder 2A (2B) in the expansion stroke will flow through the communication passage 38 to the other cylinder 2B (2A) in the compression stroke. In this case, the scavenging port 24 of the cylinder 2A (2B) in the expansion stroke
Since a is closed, the burnt gas flowing through the communication passage 38 does not include fresh air (or air-fuel mixture) as scavenging gas containing unvaporized fuel. Therefore, the O ₂ concentration of this gas is O ₂ sensor 3
0, and the air-fuel ratio can be accurately detected by the correction according to the operating state.

In the above embodiments, the second invention is applied to a two-cylinder engine.
It goes without saying that the second invention is similarly applicable to a multi-cylinder engine having three or more cylinders.

[0062]

As is apparent from the above description, claim 1
According to the invention described above, the burnt gas is introduced into the auxiliary exhaust passage only within a period from ignition until the scavenging air flow reaches the inlet of the auxiliary exhaust passage. According to this, since the burnt gas is introduced into the sub exhaust passage only within the period after the combustion is completed until the scavenging air reaches the inlet of the sub exhaust passage, the burned gas flowing through the sub exhaust passage Does not include fresh air including unvaporized fuel, and O _{2 in} this burned gas
The concentration is detected by the O ₂ sensor, and the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber can be accurately obtained by the air-fuel ratio detection means based on the detected value of the O ₂ concentration.

According to the third aspect of the present invention, the burnt gas of one cylinder in the expansion stroke flows through the communication passage to the other cylinder in the compression stroke, and in this case, the scavenging gas of the cylinder in the expansion stroke. Since the mouth is closed, the burned gas flowing through the communication passage does not include fresh air containing unvaporized fuel, and therefore the O ₂ concentration of this burned gas is detected by the O ₂ sensor, and the combustion chamber of each cylinder is detected. It is possible to obtain the effect that the air-fuel ratio of the air-fuel mixture supplied to is accurately obtained by the air-fuel ratio detecting means based on the detected value of the O ₂ concentration.

[Brief description of drawings]

FIG. 1 is a cutaway side view of a motorcycle essential part showing a two-cycle engine including an air-fuel ratio detection device according to a first embodiment of the first invention.

FIG. 2 is an enlarged cross-sectional view of a main part of a two-cycle engine including the air-fuel ratio detection device according to the first embodiment of the first invention.

FIG. 3 is a timing chart of ignition and opening / closing of a scavenging / exhaust port and an auxiliary exhaust passage of the two-cycle engine according to the first aspect of the present invention.

FIG. 4 is a schematic cross-sectional view of a main part of a two-cycle engine equipped with an air-fuel ratio detection device according to a second embodiment of the first invention.

FIG. 5 is a schematic cross-sectional view of a main part of a two-cycle engine equipped with an air-fuel ratio detection device according to a third embodiment of the first invention.

FIG. 6 is a schematic cross-sectional view of a main part of a two-cycle two-cylinder engine including an air-fuel ratio detection device according to a fourth embodiment of the first invention.

FIG. 7 is a schematic cross-sectional view of a main part of a two-cycle two-cylinder engine equipped with the air-fuel ratio detection device according to the first embodiment of the second invention.

FIG. 8 is a timing chart of ignition of a two-cycle two-cylinder endon and opening / closing of a sweep / exhaust port and a communication passage according to a second aspect of the present invention.

FIG. 9 is a schematic cross-sectional view of a main part of a two-cycle two-cylinder engine including an air-fuel ratio detection device according to a second embodiment of the second invention.

[Explanation of symbols]

1 2 cycle engine 2 cylinder body 2a cylinder 7 main exhaust passage 7a main exhaust port 15 ECU (mixing ratio detection means) 16 piston 24 scavenging passage 24a main scavenging port 25 auxiliary scavenging passage 25a auxiliary scavenging port 27 first passage 27a introducing port 28 Second passage 29 Secondary exhaust passage 30 O ₂ sensor 31 First check valve 32 Second check valve 38 Communication passage 38a, 38b Inlet S S Combustion chamber

Claims (3)

[Claims] 1. A device provided in a two-cycle engine for exchanging burned gas and fresh air by scavenging air introduced into a cylinder from a scavenging port when an exhaust port is opened. It is configured to include an O ₂ sensor provided in the middle of an auxiliary exhaust passage for guiding the burnt gas from the combustion chamber to the outside, and a mixing ratio detecting means for obtaining an air-fuel ratio of the air-fuel mixture based on a signal from the O ₂ sensor. An air-fuel ratio detecting device for a two-cycle engine, wherein burned gas can be introduced from an inlet of the auxiliary exhaust passage only during a period from ignition to arrival of a scavenging air flow to the inlet of the auxiliary exhaust passage. 2. The sub-exhaust gas during the period from ignition to the introduction port of the sub-exhaust passage, of the period from ignition until the scavenging flow reaches the introduction port of the sub-exhaust passage. The air-fuel ratio detecting device for a two-cycle engine according to claim 1, wherein burned gas can be introduced from an inlet of the passage. 3. A burned gas and a fresh air are provided by scavenging air introduced into the cylinder from the scavenging port when the exhaust port is opened in each cylinder. a device provided in two-cycle multi-cylinder engine for gas exchange, and O ₂ sensor provided in the middle of the communication passage for communicating two adjacent cylinders, mixing based on the signal from the O ₂ sensor It is configured to include a mixture ratio detection means for obtaining an air-fuel ratio of air, and it is possible to open both ends of the communication passage only during a period from ignition of one cylinder in an expansion stroke of two adjacent cylinders to opening of a scavenging port. An air-fuel ratio detection device for a two-cycle engine, which is characterized in that