JPH079199B2 - Multi-cylinder 2-cycle engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an improvement of a multi-cylinder two-cycle engine in which a scavenging port opened and closed by a piston is opened in a cylinder peripheral wall.

(Prior Art) Conventionally, as a two-cycle engine, for example, JP-A-59-158
As disclosed in Japanese Patent No. 329, an intake passage is opened in a crank chamber through an intake port, a scavenging passage communicating with the crank chamber is opened in a cylinder peripheral wall through the scavenging port, and an exhaust passage is exhausted. Opened through the port, the piston opens and closes the scavenging port and the exhaust port at a predetermined timing, and the air-fuel mixture sucked from the intake port into the crank chamber is compressed by the downward movement of the piston and supplied to the cylinder from the scavenging port. On the other hand, it is known that exhaust gas is discharged from an exhaust port.

(Problems to be Solved by the Invention) However, in the above-mentioned conventional two-cycle engine, in order to smoothly discharge exhaust gas, the open period of the scavenging port and the open period of the exhaust port are overlapped and supplied from the scavenging port. Since the exhaust gas of the cylinder is pushed out by the air-fuel mixture, there is a problem that the air-fuel mixture sucked from the scavenging port blows through to the exhaust port as it is, resulting in an increase in fuel consumption and deterioration of emission performance.

The present invention has been made in view of such a point, and an object thereof is to supply air-fuel mixture and discharge exhaust gas at a timing not controlled by a piston, and to supply only air to a scavenging port. The purpose is to prevent the air-fuel mixture from passing through while smoothly discharging the exhaust gas.

However, in such a two-cycle engine, when the air-fuel ratio of the engine is feedback-controlled to a target value by the oxygen concentration in the exhaust gas of the engine so that the air-fuel ratio of the air-fuel mixture becomes an appropriate air-fuel ratio, the exhaust gas burns in the cylinder. Since it contains not only the combustion gas but also the air that blows from the scavenging port to the exhaust port, the detected value of the air-fuel ratio will be a leaner value than the actual air-fuel ratio. When the air-fuel ratio is feedback-controlled, the air-fuel ratio of the air-fuel mixture supplied to the engine becomes excessive, which causes deterioration of emission performance and increase of fuel consumption. Further, in a multi-cylinder engine, since air is blown from the scavenging port to the exhaust port in the order of combustion cylinders, the difference between the oxygen concentration in the exhaust gas and the oxygen concentration of the gas actually burned in each cylinder is even greater. Therefore, the above problem becomes more prominent.

Therefore, a further object of the present invention is to accurately detect the air-fuel ratio of the engine by properly setting the detection timing of the oxygen concentration in the exhaust gas and detecting the oxygen concentration of the combustion gas by burning in the cylinder. Based on this, the air-fuel ratio of the air-fuel mixture supplied to the engine is accurately and accurately controlled to a proper air-fuel ratio.

(Means for Solving the Problems) In order to achieve the above object, the means for solving the problems of the present invention is to open a scavenging port opened and closed by a piston in a cylinder peripheral wall of each cylinder, and to cause piston top dead of the cylinder of each cylinder. The intake passage and the exhaust passage branched for each cylinder are opened above the point position through intake and exhaust ports,
An intake / exhaust valve that opens and closes each port is provided in the exhaust port, and each scavenging port is connected by a scavenging passage to the intake passage for each cylinder or to the upstream side of the branch portion of the intake passage. Further, the opening / closing timing of the intake / exhaust valve of each cylinder is set so that the intake valve is opened and the exhaust valve is closed near the piston bottom dead center, and the opening timing of the exhaust valve is earlier than the opening timing of the scavenging port. Further, oxygen concentration detection means for detecting the oxygen concentration in the exhaust gas from each cylinder is provided on the downstream side of the confluent portion of the exhaust passage for each cylinder, and each cylinder is provided downstream of the scavenging passage connection portion of the intake passage. Fuel supply means for supplying fuel is provided. Then, the air-fuel ratio of the air-fuel mixture supplied to each cylinder is set based on the oxygen concentration detected by the oxygen concentration detection means while the exhaust valve of at least one cylinder is open and the scavenging ports of all cylinders are closed. Thus, the control means for controlling the fuel supply means is provided.

(Operation) With the above configuration, in the present invention, the intake passage and the exhaust passage are opened above the piston top dead center position of the cylinder and opened and closed by the intake and exhaust valves, respectively.
It is possible to set the intake / exhaust timing that is not controlled by the piston. That is, by setting the intake valve to open and the exhaust valve to close in the vicinity of the piston bottom dead center, the overlap between the open period of the exhaust port and the open period of the exhaust port is narrowed and the mixture from the intake port to the exhaust port is reduced. Passage of air is suppressed. Further, since only air is supplied to the scavenging port, only air is blown out from the scavenging port to the exhaust port with good scavenging efficiency.

Further, by setting the opening timing of the exhaust valve to be earlier than the opening timing of the scavenging port, there is a period in which the exhaust valve of at least one cylinder is open and the scavenging ports of all cylinders are closed. In this period, the exhaust gas is only the combustion gas burned in the cylinder. Therefore,
The air-fuel ratio of the engine can be accurately detected according to the oxygen concentration detected during this period, and the air-fuel ratio of the air-fuel mixture is set by setting the air-fuel ratio of the air-fuel mixture supplied to each cylinder based on this air-fuel ratio. The air-fuel ratio will be controlled accurately and accurately.

(Example) Hereinafter, the Example of this invention is described based on drawing.

FIG. 1 shows a two-cylinder two-cycle engine according to an embodiment of the present invention. Reference numeral 1 is a cylinder formed in each cylinder of the engine body E, 2 is a piston slidably arranged in the cylinder 1, and the piston 2 is provided on the cylinder peripheral wall 3 of each cylinder of the engine body E. A scavenging port 4 that is opened and closed by the peripheral wall of the piston 2 as it descends and rises is opened. Further, in the engine body E, the branch intake passage 5a and the branch exhaust passage 6a branched for each cylinder are respectively sucked above the piston top dead center position (solid line position in FIG. 1) of the cylinder 1 of each cylinder. -Opening through the exhaust ports 8 and 9, intake / exhaust valves 10 and 11 for opening and closing the ports 8 and 9 are provided in the intake / exhaust ports 8 and 9, respectively. Further, each scavenging port 4 is connected to a branch intake passage 5a for each cylinder by a scavenging passage 12. In addition, the main intake passage 5 upstream of the branch portion 5b of each branch intake passage 5a
Is provided with an air pump 13 for supercharging air, and a fuel is injected and supplied from an injector 22 described later to the air supercharged by the air pump 13 to generate an air-fuel mixture. Meanwhile, the supercharged air is also supplied to the scavenging port 4 as each scavenging air. In addition, 6 is a main exhaust passage on the downstream side of the collecting portion of each branch exhaust passage 6a, 14 is an air cleaner arranged upstream of the main intake passage 5, and 15 is a main intake passage 5 in the middle of each scavenging passage 12 and upstream of the air pump 13. Reference numeral 16 denotes a bypass passage that communicates with the bypass passage 16. Reference numeral 16 denotes a relief valve that is disposed in each of the bypass passages 15 to control and maintain the supercharging pressure at a predetermined value or less. Further, 17 is a throttle valve arranged in each branch intake passage 5a, 18 is a control valve for adjusting the flow rate arranged in each scavenging passage 12, and 19 is an ignition plug arranged in each cylinder.

And, the opening and closing timings of the intake and exhaust valves 10 and 11 are as follows.
As shown in FIG. 2, the intake valve 10 is opened and the exhaust valve 11 is closed near the bottom dead center of the piston, the opening timing of the exhaust valve 11 is earlier than the opening timing of the scavenging port 4, and the intake valve 10 is closed. The valve closing timing is set to be later than the closing timing of the scavenging port 4.

Further, a hot wire type air flow sensor 21 for detecting the intake air flow rate to each cylinder is arranged upstream of the branch portion 5b of the main intake passage 5 and upstream of the air pump 13. Further, an injector 22 as a fuel supply means for supplying fuel to each cylinder is arranged downstream of the scavenging passage connection part of each branch intake passage 5a. On the other hand, an O ₂ sensor 23 as an oxygen concentration detecting means for detecting the oxygen concentration in the exhaust gas from each cylinder is arranged on the downstream side of the merging portion 6 of the main exhaust passage 6. A control unit 24 including a CPU for driving and controlling each injector 22 is connected to each of the injectors 22, and the control unit 24 includes an air flow sensor 21, an O ₂ sensor 23, and a crank angle sensor 25 for detecting a crank angle. Signals are input, the injectors 22 are driven and controlled according to the intake air flow rate, the oxygen concentration, and the crank angle, and the exhaust rim 11 of at least one cylinder is opened and the scavenging air of all cylinders is opened as shown in FIG. Control for controlling the injectors 22, 22, so that the air-fuel ratio of the air-fuel mixture supplied to each cylinder is set based on the oxygen concentration detected during the period T, T, ... While the port 4 is closed. Means 26 are configured.

When the oxygen concentration is detected, the time period t required for the exhaust gas (combustion gas) to reach the O ₂ sensor 23 after being discharged from each cylinder 1 is taken into consideration in the period T
It is preferable to perform a correction process such as detecting the oxygen concentration later than t, because the control accuracy can be improved.

Next, the operation of the above-described embodiment will be described with reference to FIG. 3. In each cylinder, the intake / exhaust valves 10, 11 and the scavenging port 4 are closed and the piston 2 is raised so that the air-fuel mixture in the cylinder 1 is removed. When it is compressed and the spark plug 19 ignites at 20 degrees before top dead center, the air-fuel mixture explodes and burns. When the piston 2 descends to 80 degrees before bottom dead center due to the expansion of combustion gas, the exhaust valve
When 11 is opened and exhaust begins, and when it descends to 50 degrees before bottom dead center, the scavenging port 4 opens. In this way, since the valve opening timing of the exhaust edge 11 is earlier than the valve opening timing of the scavenging port 4, air is supplied to the cylinder 1 after the cylinder pressure has sufficiently decreased due to the start of exhaust gas discharge. Can be prevented from flowing back to the scavenging port 4. In addition, during the period from the opening of the exhaust valve 11 to the opening of the scavenging port 4, the cylinder 1
Only the combustion gas burned in
Will be discharged to the branch exhaust passage 6a. And
When the exhaust port 4 opens, the scavenging port 4 starts the air pump.
The pressurized air supercharged by 13 is supplied into the cylinder 1, and the exhaust gas is efficiently scavenged and discharged from the exhaust port 9 to the branch exhaust passage 6a together with the pressurized air by the pressurized air. Although air is blown from the scavenging port 4 to the exhaust port 11 in this way, since the fuel component is not contained in this air, it is possible to reduce the fuel consumption and improve the emission property while scavenging the exhaust gas reliably and efficiently. Can be planned.

Next, when the piston 2 descends to the vicinity of the bottom dead center, the intake valve 10 opens 10 degrees before the bottom dead center, the exhaust valve 11 closes 10 degrees after the bottom dead center, and the intake air from the intake port 8 is exceeded by the air pump 13. The supplied air-fuel mixture is supplied into the cylinder 1 to start air supply. In this way, the overlap between the open period of the intake port 8 and the open period of the exhaust port 9 is narrowed, so that the intake port 8
Blow-through of the air-fuel mixture from the exhaust port 9 to the exhaust port 9 is suppressed as much as possible, and fuel efficiency can be reduced and emission characteristics can be improved effectively.

Further, when the piston 2 rises to 50 degrees after bottom dead center, the scavenging port 4 closes, but the intake valve 10 continues to operate at 80 degrees after bottom dead center.
The air-fuel mixture is continuously supplied to the cylinder 1 and is supplied to the cylinder 1. As a result, the opening period of the intake port 8 becomes longer, so that the amount of the air-fuel mixture filled can be increased. Moreover, since the air-fuel mixture sent by the air pump 13 is supplied to the intake port 8, the air-fuel mixture is forced to the cylinder 1 during the opening period of the intake port 8 regardless of the rise of the cylinder pressure due to the rise of the piston 2. Since the fuel can be charged into the cylinder, it is possible to reliably increase the amount to be charged and improve the engine output.

In this case, as shown in FIG. 4, the exhaust valve 11 of at least one cylinder (for example, the first cylinder) is open and all the cylinders (first cylinder).
Cylinder and second cylinder) scavenging port 4 is closed
The exhaust gas at T, T, ... Is the combustion gas itself burned in the cylinder (first cylinder) in which the exhaust valve 11 is open, and does not include the air blown from the scavenging port 4 to the exhaust port 9, The air-fuel ratio of the engine can be accurately detected by the oxygen concentration detected during this period T, T, .... As a result, by setting the air-fuel ratio of the air-fuel mixture to be supplied to each cylinder based on this air-fuel ratio and injecting and supplying the fuel from the injector 22, the air-fuel ratio of the air-fuel mixture is accurately and accurately set to an appropriate air-fuel ratio. It is possible to control, and it is possible to prevent the enrichment of the air-fuel ratio and further improve the emission performance while achieving both the improvement of the engine output and the reduction of the fuel consumption.

Further, FIG. 5 shows the oxygen concentration detection timing when the present invention is applied to a 3-cylinder 2-cycle engine,
As long as the open periods of the scavenging ports 4 of the cylinders adjacent to each other in the combustion order do not overlap, the period T for detecting the oxygen concentration is set to the same condition as in the above embodiment (exhaust valves of at least one cylinder are open and scavenging of all cylinders is performed). (Port is closed)
It is possible to set with, and the same operation and effect as those of the above-mentioned embodiment can be obtained.

Although the scavenging port 4 is connected to the branch intake passage 5a for each cylinder by the scavenging passage 12 in the above embodiment, the scavenging passage 12
Therefore, it may be connected to the main intake passage 5 upstream of the branch portion 5b and downstream of the air pump 13.

(Effect of the Invention) As described above, according to the multi-cylinder two-cycle engine of the present invention, it is possible to set the intake valve to open and the exhaust valve to close in the vicinity of the piston bottom dead center. It is possible to suppress blow-through of air-fuel mixture,
Since only the air is sent to the scavenging port, only the air is blown from the scavenging port to the exhaust port, so that the engine output can be improved, the fuel consumption can be reduced, and the emission property can be improved.

In addition, the oxygen concentration in the exhaust gas from each cylinder is detected when air is not blown from the scavenging port to the exhaust port in any cylinder, and the oxygen concentration in the combustion gas burned in each cylinder is detected. Since the air-fuel ratio of the air-fuel mixture supplied to each cylinder is set based on the accurate air-fuel ratio, it is possible to control the air-fuel ratio of the air-fuel mixture accurately and accurately, thus improving the engine output. While aiming, it is possible to further improve emission characteristics and fuel consumption.

[Brief description of drawings]

The drawings show an embodiment of the present invention, FIG. 1 is an overall schematic configuration diagram, FIG. 2 is an explanatory view showing opening / closing timings of a scavenging port and intake / exhaust valves, and FIG. 3 is an explanation explaining an operation stroke of an engine. FIGS. 4 and 5 are explanatory diagrams showing the detection timing of the oxygen concentration in the exhaust gas with respect to the open period of the scavenging port and the intake / exhaust valve in the two-cylinder two-cycle engine.
The figure is equivalent to FIG. 4 in a 3-cylinder 2-cycle engine. E ... Engine body, 1 ... Cylinder, 2 ... Piston, 3 ... Cylinder peripheral wall, 4 ... Scavenging port, 5 ... Main intake passage, 5a ... Branch intake passage, 6 ... Main exhaust passage, 6a
...... Branch exhaust passage, 6b ...... Merging section, 8 ...... Intake port,
9 ... Exhaust port, 10 ... Intake valve, 11 ... Exhaust valve, 12 ...
… Scavenging passage, 21 …… Air flow sensor, 22 …… Injector, 23 …… O ₂ sensor, 24 …… Control unit,
26 ... Control means.

Claims (1)

[Claims] 1. A scavenging port opened and closed by a piston is opened in a cylinder peripheral wall of each cylinder, and an intake passage and an exhaust passage branched for each cylinder are located above a piston top dead center position of each cylinder. An intake / exhaust valve that opens through the intake / exhaust port and opens / closes each port is provided in each intake / exhaust port, and each scavenging port is an intake passage for each cylinder by a scavenging passage, or its It is connected to the upstream side of the branch part of the intake passage, and the opening and closing timings of the intake and exhaust valves of each cylinder are as follows: the intake valve is open and the exhaust valve is closed near the piston bottom dead center, and the exhaust valve opening timing is A multi-cylinder two-cycle engine set to be earlier than the opening timing of a scavenging port, the multi-cylinder two-cycle engine being provided on the downstream side of a confluent portion of the exhaust passage for each cylinder, and in the exhaust gas from each cylinder. Oxygen concentration detecting means for detecting the elementary concentration, fuel supply means provided downstream of the scavenging passage connecting portion of the intake passage for supplying fuel to each cylinder, and the oxygen concentration detecting means opens the exhaust valve of at least one cylinder. And a control means for controlling the fuel supply means so as to set the air-fuel ratio of the air-fuel mixture supplied to each cylinder based on the oxygen concentration detected while the scavenging ports of all cylinders are closed. A multi-cylinder two-cycle engine characterized by the following.