JPH061051B2 - 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-
As disclosed in Japanese Patent No. 158329, 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.

In such a two-cycle engine, in order to prevent the exhaust gas from flowing back to the scavenging port, the opening timing of the scavenging port is set to be later than the opening timing of the exhaust port when the piston is descending, and the exhaust gas begins to be discharged. The air-fuel mixture is supplied to the cylinder after the pressure has dropped sufficiently.

(Problems to be Solved by the Invention) However, in the above-described conventional two-cycle engine, since the scavenging port and the exhaust port are opened and closed by the piston,
The opening / closing timing of each port is symmetrical with respect to the piston bottom dead center on the trailing side and the leading side. Therefore, if the opening timing of the scavenging port is set later than the opening timing of the exhaust port as described above, the closing timing of the scavenging port will be set earlier than the closing timing of the exhaust port when the piston rises after the bottom dead center. . As a result, the period in which the scavenging port is open becomes short, the mixture cannot be sufficiently filled in the cylinder, and improvement in engine output cannot be expected. Moreover, since the open period of the scavenging port overlaps with the open period of the exhaust port, there is also a problem that the air-fuel mixture sucked from the scavenging port blows through to the exhaust port as it is, leading to an increase in fuel consumption and deterioration of emission performance. .

The present invention has been made in view of the above points, 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 increase the filling amount of the air-fuel mixture and prevent blow-through of the air-fuel mixture.

However, in such a two-cycle engine, when the fuel supply amount is set based on the intake air amount of the engine in order to make the air-fuel ratio of the air-fuel mixture an appropriate air-fuel ratio, the intake air flow rate of the engine is Not only the flow rate, but the total flow rate of the air blown from the scavenging port to the exhaust port is the total flow rate, so the fuel supply amount is set based on the flow rate value that is higher than the flow rate of the air that actually fills the cylinder. As a result, the air-fuel ratio of the air-fuel mixture becomes rich, which causes deterioration of emission performance. Further, in a multi-cylinder engine, since air is blown from the scavenging port to the exhaust port in the combustion cylinder order, the difference between the total intake air flow rate and the air flow rate actually filled in the cylinders of each cylinder is further increased. It becomes remarkable.

Therefore, another object of the present invention is to accurately detect the flow rate of the air actually filled in the cylinder by appropriately setting the detection timing of the intake air flow rate, and to set the fuel supply amount based on the detected flow rate of the air-fuel mixture. It is to control the air-fuel ratio to an appropriate air-fuel ratio accurately and accurately.

(Means for Solving the Problems) In order to achieve the above-mentioned object, the solution means of the present invention is such that a scavenging port opened and closed by a piston is opened in the cylinder peripheral wall of each cylinder, and the piston top dead of the cylinder of each cylinder is opened. The intake passage and the exhaust passage branched for each cylinder above the point position open via the intake / exhaust ports,
An intake / exhaust valve for opening and closing each port is provided in each exhaust port, and each scavenging port is connected to an intake passage for each cylinder by a scavenging passage or to an upstream side of a branch portion of the intake passage. The intake / exhaust valve opening / closing timing 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 intake valve closing timing is later than the scavenging port closing timing. . Further, an intake air flow rate detecting means for detecting an intake air flow rate to each cylinder is provided on the upstream side of the branch portion of the intake passage for each cylinder and on the upstream side of the scavenging passage connecting portion, and the intake passage downstream of the intake passage is detected. Is provided with fuel supply means for supplying fuel to each cylinder. Then, the fuel supply amount is set based on the intake air flow rate detected by the intake air flow rate detection means in the period from the closing of the exhaust valve of one cylinder to the opening timing of the scavenging port of the next combustion cylinder. And a control means for controlling each of the fuel supply means.

(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 intake port and the open period of the exhaust port is narrowed, and the intake port to the exhaust port is closed. The mixture is prevented from passing through. On the other hand, the closing timing of the intake valve is set to be later than the closing timing of the scavenging port, so that the opening period of the intake port becomes longer and the amount of the air-fuel mixture charged in the cylinder increases. 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, after the exhaust valve of one cylinder is closed and the blow-through of air from the scavenging port to the exhaust port in the cylinder is completed, the scavenging port of the next combustion cylinder is opened and the scavenging port of the next combustion cylinder is changed to the exhaust port. The intake air flow rate detected during the period until the start of the blow-out of air into the cylinder is the air flow rate that is actually filled in the cylinder of one specific cylinder, so the fuel supply amount is set based on this intake air flow rate. By doing so, the air-fuel ratio of the air-fuel mixture is accurately and accurately controlled to the proper air-fuel ratio.

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

FIG. 1 shows a 4-cylinder 2-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.・ Exhaust port 8,
9 through which the intake / exhaust ports 8 and 9 are provided.
Intake / exhaust valve 1 for opening / closing each port 8 and 9 respectively
0 and 11 are provided. In addition, each scavenging port 4
Is connected by a scavenging passage 12 to the branch intake passage 5a for each cylinder. An air pump 13 for supercharging air is arranged in the main intake passage 5 upstream of the branch portion 5b of each branch intake passage 5a. The air supercharged by the air pump 13 is supplied with fuel from an injector 22 described later. It is injected and supplied to generate a mixture, and each intake port 8 cylinder 1
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 middle of each scavenging passage 12 and the main intake passage 5 upstream of the air pump 13.
And a bypass passage 16 communicating with the bypass passage 16
5 is a relief valve which is disposed in No. 5 and which controls the supercharging pressure to be maintained below a predetermined value. 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.

As shown in FIG. 2, the intake / exhaust valves 10 and 11 are opened / closed at the same time as the intake valve 10 is opened and the exhaust valve 11 is closed near the piston bottom dead center.
The valve opening timing of 1 is earlier than the opening timing of the scavenging port 4, and the closing timing of the intake valve 10 is set later than the closing timing of the scavenging port 4.

Further, on the upstream side of the branch portion 5b of the main intake passage 5 and on the upstream side of the air pump 13, a hot wire type air flow sensor 21 is arranged as an intake air flow rate detecting means for detecting the intake air flow rate to each cylinder. There is. Further, an injector 22 as a fuel supply means for supplying fuel to each cylinder is disposed downstream of the scavenging passage connecting portion of each branch intake passage 5a. A control unit 23 including a CPU for driving and controlling each injector 22 is connected to each injector 22, and each signal of the air flow sensor 21 and a crank angle sensor 24 for detecting a crank angle is input to the control unit 23. The injectors 22 are driven and controlled in accordance with the intake air flow rate and the crank angle, and the air flow sensor 21 as shown in FIG. Period T until the opening time of port 4,
Control means 25 is configured to control each of the injectors 22, 22 ... To set the fuel supply amount based on the intake air flow rate detected at T.

When the intake air flow rate is detected, the time delay t required for the air to reach each cylinder 1 after passing through the air flow sensor 21 is taken into consideration when the time t is longer than the time period T.
It is preferable to perform the correction processing such as detecting the intake air flow rate as soon as possible because the control accuracy can be improved.

Next, the operation of the above 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. Compressed, spark plug 19 at 20 degrees before top dead center
When is ignited, the air-fuel mixture explodes and burns. Then, when the piston 2 descends to 80 degrees before bottom dead center due to expansion of combustion gas, the exhaust valve 11 opens and exhaust starts, and when it descends to 50 degrees before bottom dead center, the scavenging port 4 opens and the scavenging port 4 starts The pressurized air supercharged by the air pump 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 no fuel component is contained in this air, it is possible to reduce fuel consumption and improve emission efficiency while reliably and efficiently scavenging exhaust gas. 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 and the exhaust valve 11 closes 10 degrees after the bottom dead center. The supplied air-fuel mixture is supplied into the cylinder 1 to start air supply. By thus narrowing the overlap between the open period of the intake port 8 and the open period of the exhaust port 9,
Blow-through of the air-fuel mixture from the intake port 8 to the exhaust port 9 is suppressed as much as possible, and fuel efficiency can be reduced and emission characteristics can be effectively improved.

Furthermore, when the piston 2 rises to 50 degrees after bottom dead center,
Although the scavenging port 4 is closed, the intake valve 10 continues to open up to 80 degrees after bottom dead center and the mixture 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, a specific cylinder (for example, the first cylinder
(Cylinder) exhaust valve 11 is closed, the scavenging port 4 in the cylinder
To the exhaust port 9 ends. On the other hand, when the scavenging port 4 of the next combustion cylinder (third cylinder) opens, blow-through from the scavenging port 4 to the exhaust port 9 starts in this cylinder. Therefore, the intake air flow rate detected in the period T, T ... Between the closing of the exhaust valve 11 of the specific cylinder and the opening timing of the scavenging port 4 of the next combustion cylinder is transferred to the cylinder 1 of the specific cylinder. 4 or the flow rate of the air that is actually filled from the intake port 8, the fuel supply amount is set based on this intake air flow rate, and the fuel is injected and supplied from the injector 22 so that the air-fuel ratio of the air-fuel mixture is adjusted to the proper air-fuel ratio. Therefore, it is possible to control the engine accurately and with high accuracy, and at the same time to improve the engine output and reduce the fuel consumption, it is possible to prevent the air-fuel ratio from becoming rich and further improve the emission property.

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

(Effect of the Invention) As described above, according to the multi-cylinder two-cycle engine of the present invention, the closing timing of the intake valve can be set later than the closing timing of the scavenging port, so that the opening period of the intake port becomes longer. The output of the engine can be improved by increasing the filling amount of the air-fuel mixture in the cylinder. Also, since it is possible to set the intake valve to open and the exhaust valve to close near the bottom dead center of the piston, it is possible to suppress blow-through of the air-fuel mixture from the intake port to the exhaust port, and to send only air to the scavenging port. Only air is blown from the scavenging port to the exhaust port, so that it is possible to reduce fuel consumption and improve emission performance.

Further, in any cylinder, the intake air flow rate is detected when the air is not blown from the scavenging port to the exhaust port, and the fuel supply amount is substantially determined based on the intake air flow rate filled in each cylinder. I set it, so
The air-fuel ratio of the air-fuel mixture can be accurately and accurately controlled, and the emission performance can be further improved while achieving both improved engine output and reduced 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. FIG. 4 and FIG. 4 are explanatory diagrams showing the detection timing of the intake air flow rate with respect to the open period of the scavenging port and the intake / exhaust valve. 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, 8 ... Intake port, 9 ... Exhaust port, 10 ... Intake valve,
11 ... Exhaust valve, 12 ... Scavenging passage, 21 ... Air flow sensor, 22 ... Injector, 23 ... Control unit, 25 ... 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 / closing timing of the intake / exhaust valve of each cylinder is such that the intake valve opens and the exhaust valve closes near the piston bottom dead center, and the intake valve closing timing A multi-cylinder two-cycle engine set to be later than the closing timing of the scavenging port, which is provided upstream of the branch portion of the intake passage for each cylinder and upstream of the scavenging passage connecting portion, And intake air flow rate detecting means for detecting an intake air flow rate to the cylinder, is provided to the transfer passage connecting portion downstream of the intake passage, a fuel supply means for supplying fuel to each cylinder,
The intake air flow rate detecting means sets the fuel supply amount based on the intake air flow rate detected during the period from the closing of the exhaust valve of one cylinder to the opening timing of the scavenging port of the next combustion cylinder. A multi-cylinder two-cycle engine provided with control means for controlling each fuel supply means.