JPH0335864Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to an improvement in the piston structure of an engine having a scavenging port opened and closed by a piston in the cylinder peripheral wall.

(Prior Art) Conventionally, as a two-stroke engine, as disclosed in Japanese Patent Application Laid-Open No. 59-158329, a scavenging port and an exhaust port are opened in the cylinder peripheral wall, and these ports are connected to a predetermined position by a piston. A device is known that opens and closes at different timings to supply the air-fuel mixture to the cylinder from the scavenging port, while exhausting exhaust gas from the exhaust port.

(Problem to be solved by the invention) However, in order to improve the output of the conventional two-stroke engine, a supercharger is installed upstream of the scavenging port, and the engine is supercharged by the supercharger. When the air-fuel mixture is supplied into the cylinder from the scavenging port, the scavenging port opens on the cylinder peripheral wall, so the high-pressure supercharged air-fuel mixture blows through the scavenging port into the crankcase, increasing the blow-by gas pressure inside the crankcase. increases, and as a result of this blow-by gas pressure, the piston is subjected to a large back resistance when it descends, and as a result, the engine output cannot be effectively improved due to the pumping loss.

In addition, some of the oil that is supplied from the oil reservoir in the crankcase to the cylinder circumferential wall to lubricate the piston rings (compression rings, etc.) provided at the piston top round part flows out to the scavenging port on the cylinder circumferential wall. However, there is a problem in that during scavenging, oil is supplied into the cylinder and burned and consumed, or is blown into the exhaust port, resulting in wasted oil consumption, leading to an increase in oil consumption.

The present invention has been developed in view of the above, and its purpose is to open a scavenging port in the cylinder peripheral wall that is opened and closed by a piston as described above, and to supply supercharged air-fuel mixture to the scavenging port. In a built-in engine, by sealing the communication between the scavenging port and the crankcase on the cylinder circumferential wall below the scavenging port, the supercharged air-fuel mixture is prevented from blowing into the crankcase, and the piston back resistance is reduced. The objective is to reduce oil consumption as much as possible by preventing oil in the crankcase from flowing out to the scavenging port.

(Means for solving the problem) In order to achieve the above object, the solution of the present invention is that a scavenging port opened and closed by a piston is opened in the cylinder peripheral wall, and a supercharger is disposed upstream of the scavenging port. The piston structure of the installed engine is such that a seal ring is provided on the piston skirt portion located below the scavenging port when the piston is at top dead center.

(Function) With the above configuration, in the present invention, the oil ring is located below the port opening in the cylinder circumferential wall and the scavenging port is sealed from the crankcase regardless of the piston position, so the supercharger This prevents the supercharged high-pressure air-fuel mixture from blowing into the crankcase, and also prevents the oil in the crankcase from flowing out to the scavenging port.

(Example) Hereinafter, an example of the present invention will be described based on the drawings.

FIG. 1 shows an embodiment in which the present invention is applied to a two-stroke engine. 1 is a cylinder formed in the engine body E, 2 is a piston slidably disposed within the cylinder 1, and the cylinder circumferential wall 3 of the engine body E is provided with a piston as the piston 2 descends and rises. A scavenging port 4 that is opened and closed by the peripheral wall of the piston 2 is opened. Further, in the engine body E, an intake passage 5 and an exhaust passage 6 each having an injector 7 as a fuel supply means are located above the piston top dead center position of the cylinder 1 (solid line position in FIG. 1).・Exhaust port 8,
The intake/exhaust ports 8, 9 are provided with intake/exhaust valves 10, 11 for opening and closing the respective ports 8, 9. Further, the scavenging port 4 is connected to the injector 7 by the scavenging passage 12.
It is communicatively connected to the upstream intake passage 5. An air pump 13 serving as a supercharger for supercharging air is disposed in the intake passage 5 upstream of the scavenging passage connection part, and the air supercharged by the air pump 13 injects and supplies fuel from the injector 7. The air-fuel mixture is generated and supplied into the cylinder 1 through the intake port 8, while the supercharging air is also supplied to the scavenging port 4 as scavenging air.

The opening/closing timing of the intake/exhaust valves 10 and 11 is as shown in FIG. Scavenging port 4
The closing timing of the intake valve 10 is set to be earlier than the opening timing of the intake valve 10, and the closing timing of the intake valve 10 is later than the closing timing of the scavenging port 4. Note that 14 is an air cleaner disposed upstream of the intake passage 5, 15 is a bypass passage that communicates the middle of the scavenging passage 12 with the intake passage 5 upstream of the air pump 13, and 16 is an air cleaner disposed in the bypass passage 15 for controlling the boost pressure. This is a relief valve that maintains and controls below a predetermined value. Further, 17 is a throttle valve disposed in the intake passage 5, 18 is a flow rate adjustment control valve disposed in the scavenging passage 12, and 19 is a spark plug.

In addition, as shown in FIG.
0 is formed, and oil scraped up from the oil surface provided in the crankcase 21 below the cylinder of the engine body E or oil injected from an oil jet is supplied.

On the other hand, first and second piston ring grooves 2 are formed on the outer peripheral surface of the top round portion 2a of the piston 2.
2, 23 are formed in each piston ring groove 22, 23, and a compression ring 24,
25 are attached to each cylinder 1 to ensure airtightness of the cylinder 1.

A seal ring groove 26 is formed on the outer peripheral surface of the skirt portion 2b of the piston 2 located below the scavenging port 4 when the piston 2 is at the top dead center as shown in FIG. A compression ring 27 serving as a seal ring is attached to the ring groove 26 to seal the scavenging port 4 to the crankcase 21 below the cylinder.

Furthermore, as shown in FIG. 3, the piston 2
A plurality of oil passages 29, 29, . ... are formed radially through the piston, and when the piston descends, the oil supplied to the inner space 20 is supplied from the second piston ring groove 23 to the piston top round part 2a by the blow-by gas pressure rising in the crankcase. When the piston rises, the oil collected in the second piston ring groove 23 by the second compression ring 25 is returned to the inner space 20 by the rising cylinder pressure and collected in the oil reservoir of the crankcase 21. .

Next, to explain the operation of the above embodiment, as shown in FIG. 2, the intake/exhaust valves 10 and 11 and the scavenging port 4 are closed, the piston 2 is raised, and the air-fuel mixture in the cylinder 1 is compressed. When the spark plug 19 ignites at 20 degrees before top dead center, the 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 11 opens and exhaust begins. When the piston 2 descends to 50 degrees before bottom dead center, the scavenging port 4 opens and the scavenging port 4 is air pump 1
3, the pressurized air is supplied into the cylinder 1, and the exhaust gas is efficiently scavenged and discharged from the exhaust port 9 to the exhaust passage 6 together with the pressurized air. At this time, the compression ring 27 provided on the piston skirt portion 2b, which is located below the scavenging port 4 at the top dead center of the piston, is located below the scavenging port 4 regardless of the piston position. The high-pressure supercharged air-fuel mixture supplied to the scavenging port 4 by the sealing action of the tension ring 27 is transferred to the crankcase 21.
This suppresses the increase in blow-by gas pressure within the crankcase 21 and reduces the rear resistance of the piston as much as possible, thereby reducing pumping loss and improving the supercharging effect of the air pump 13. This makes it possible to effectively improve engine output. Furthermore, although air blows from the scavenging port 4 to the exhaust port 11, this air does not contain fuel components, so exhaust gas is scavenged reliably and efficiently, reducing fuel consumption and improving emission performance. be able to.

Next, when the piston 2 descends to near the bottom dead center, the intake valve 10 opens 10 degrees before the bottom dead center, and after the bottom dead center
At 10 degrees, the exhaust valve 11 closes, and air-fuel mixture supercharged by the air pump 13 is supplied from the intake port 8 into the cylinder 1, and air supply begins. 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, and the blow-by of the air-fuel mixture from the intake port 8 to the exhaust port 9 is suppressed as much as possible, thereby reducing fuel consumption. It is possible to increase the effectiveness of reduction and improvement of emission properties.

Furthermore, when the piston 2 rises to 50 degrees after the bottom dead center, the scavenging port 4 closes, but the intake valve 10 continues to open thereafter until 80 degrees after the bottom dead center, and the air-fuel mixture is supplied to the cylinder 1. As a result, the period during which the intake port 8 is open becomes longer, so that the filling amount of the air-fuel mixture 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 supplied to the cylinder 1 during the open period of the intake port 8, regardless of the rise in cylinder pressure due to the rise of the piston 2. Since it can be forcibly filled, the amount of filling can be reliably increased and the engine output can be improved.

Furthermore, the sealing action of the compression ring 27 can prevent oil from flowing out from the crankcase 21 to the scavenging port 4. Furthermore, since the pressurized air and mixture for scavenging are supplied to the cylinder 1 from the scavenging port 4 and the intake port 8 without passing through the crankcase 21, there is a possibility that oil may get mixed into the pressurized air or mixture. Without,
Therefore, oil consumption can be reduced as much as possible.

In this case, although the compression ring 27 prevents oil from being supplied to the upper part of the cylinder peripheral wall above the scavenging port 4, the blow-by gas pressure in the crankcase 21 causes the oil to flow from the oil passages 29, 29... to the piston. Since oil is supplied to the top round portion 2a, the compression rings 24, 25 can be well lubricated, and seizure of the rings can be reliably prevented. In addition, since the oil passages 29, 29... are opened in areas that do not face the scavenging port 4, the oil supplied from the oil passages 29, 29... does not flow into the scavenging port 4, and the oil It is possible to increase the effectiveness of consumption reduction.

Furthermore, FIG. 4 shows a modification of the present invention when applied to another type of two-stroke engine. In this two-stroke engine, there are a plurality of scavenging ports 4' on the cylinder peripheral wall 3, which are opened and closed by the piston 2.
4',... are opened, and the scavenging ports 4', 4',...
A roots blower type supercharger 30 is disposed in the scavenging passage 12' connected to..., and an exhaust passage is installed in the engine body E above the piston top dead center position of the cylinder 1 (solid line position in Fig. 4). 6 is opened through two exhaust ports 9, 9 branched from the exhaust port 9, and exhaust valves 11, 11 for opening and closing each port 9 are provided in each exhaust port 9, and the scavenging port is supercharged by a supercharger 30. This is a uniflow scavenging type two-stroke engine in which the cylinder 1 is scavenged by the air-fuel mixture supplied to the cylinder 1 from the engine 4' and the cylinder 1 is filled with this air-fuel mixture. A compression ring 27' is provided on the piston cart portion 2b located below the scavenging ports 4', 4', . . . when the engine is at top dead center. In this example, blow-by of the supercharged mixture from the plurality of scavenging ports 4', 4', . . . to the crankcase 21 and prevention of oil leakage to the plurality of scavenging ports 4', 4', . It is possible to obtain the same effect as in the above embodiment.

This invention is applicable not only to 2-cycle engines, but also to
It is also widely applicable to four-stroke engines.

(Effect of the invention) As explained above, according to the invention, when the piston is at top dead center, the scavenging port is opened in the cylinder circumferential wall by a seal ring provided in the piston skirt portion located below the scavenging port. I decided to seal it against the case, so
It prevents the supercharged air-fuel mixture from blowing into the crankcase and reduces piston back resistance as much as possible.
Engine output can be improved, and oil consumption can be reduced as much as possible by preventing oil from flowing into the scavenging port.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention; FIG. 1 is a general schematic diagram, FIG. 2 is an explanatory diagram showing the opening/closing timing of scavenging ports and intake/exhaust valves, FIG. 3 is an enlarged sectional view of main parts, and FIG. The figure is a diagram corresponding to FIG. 3 showing a modified example. E... Engine body, 1... Cylinder, 2...
Piston, 2b...Skirt portion, 3...Cylinder peripheral wall, 4, 4'...Scavenging port, 5...Intake passage,
12, 12'... scavenging passage, 13... air pump,
21... Crank case, 27, 27'... Compression ring, 30... Supercharger.

Claims (1)

[Scope of utility model registration request] In an engine in which a scavenging port that is opened and closed by a piston opens on the cylinder peripheral wall and a supercharger is disposed upstream of the scavenging port, the piston skirt portion located below the scavenging port when the piston is at top dead center. An engine piston structure characterized by a seal ring.