JP2827428B2 - Intake device for two-cycle engine - Google Patents

Description

Description of the Invention [Object of the Invention] (Industrial application field) The present invention relates to an intake device for a two-stroke engine in which a sub-scavenging passage and a reed valve are arranged at substantially the same position.

(Prior Art) For example, the scooter shown in FIG. 5 uses a unit swing type two-cycle engine, and a cylinder a is inclined substantially horizontally forward. In this case, from the layout of the carburetor d and the air cleaner e, the exhaust passage b is led downward from the lower part of the cylinder a, and the intake passage c is introduced from above.

As shown in FIG. 4, the intake passage c is connected to the crankcase f via a reed valve device g, and the carburetor d is buried in the crankcase f in order to position the carburetor d as low as possible. .

In the two-stroke engine, as shown in FIGS. 2 and 3, a main scavenging passage h is formed on both sides of the cylinder a with the exhaust passage b interposed therebetween, and a sub-scavenging passage i is provided at a position opposed to the exhaust passage b. The technology to be formed is customary. In the example shown,
Although one sub-scavenging passage i is arranged directly opposite to the exhaust passage b, there is a case where two sub-scavenging passages are arranged near the main scavenging passage.

Accordingly, the auxiliary scavenging passage i and the reed valve device g are in a close positional relationship, and in order to make the intake air flow smooth, care is taken that the tip of the reed valve device g does not protrude on the extended locus of the auxiliary scavenging passage i. Have been. Further, since the cylinder skirt portion j faces the front of the reed valve device g, a cutout portion k is formed to make it easier for the intake air flow to enter the main scavenging passage h from inside the cylinder skirt portion j.

However, in such a setting, the opening position of the reed valve device g is far from the main scavenging passage h, so that the intake air-fuel mixture hardly flows into the main scavenging passage h and may flow more through the sub-scavenging passage i. If the scavenging flow in the sub-scavenging passage i is large,
The amount of blow-through to the exhaust passage b increases, and there are many disadvantages in terms of fuel efficiency and output.

On the other hand, if the reed valve device g is separated from the cylinder skirt portion j, the flow is partially obstructed without the size of the notch k corresponding to the flow in which the intake air-fuel mixture diffuses, and the distance is long. Therefore, oil does not easily adhere to the inner surface of the cylinder, which is often disadvantageous for lubrication performance with the piston.

(Problems to be Solved by the Invention) In view of such problems, the present invention suppresses the amount of air-fuel mixture flowing into the sub-scavenging passage and increases the amount of oil adhering to the cylinder inner surface. Accordingly, it is an object of the present invention to provide an intake device for a two-cycle engine in which the output is increased and the lubrication performance is improved by reducing the blow-by.

[Configuration of the invention]

(Means for Solving the Problems) In the intake device for a two-stroke engine according to the present invention, in order to solve the above-described problems, the cylinder skirt portion protrudes into the crankcase from the mating surface of the cylinder and the crankcase, A sub-scavenging passage is formed in the cylinder on the opposite side of the exhaust passage with respect to the cylinder axis, and an intake passage is opened in the crankcase on the same side as the sub-scavenging passage, and a reed valve device that opens only into the crank chamber is provided. In the interposed two-stroke engine, the reed valve device is disposed so as to face a notch formed in the cylinder skirt portion such that a tip of the reed valve device protrudes into an extension locus of the auxiliary scavenging passage and approaches the cylinder skirt portion. The opening angle θ into the crank chamber defined by the valve seat surface and the valve stopper is at least partially Configured to direct the exhaust passage side of Sunda, in which the air-fuel mixture from the intake passage has flowed into the crank chamber so as to face the cylinder exhaust passage side.

(Operation) The reed valve device configured as described above is arranged closer to the outer periphery of the cylinder skirt portion.

As a result, the tip of the reed valve device protrudes into the extended locus of the sub-scavenging passage, the flow of the air-fuel mixture into the sub-scavenging passage is suppressed to some extent, and the amount of blow-by to the exhaust passage is reduced, which is advantageous in fuel consumption and output. .

At the same time, the notch in the cylinder skirt corresponding to the opening angle of the reed valve can be small, and the distance to the cylinder inner surface can be reduced, so that a sufficient amount of oil can adhere to the cylinder inner surface without obstruction. . In particular, the supply around the exhaust port becomes abundant, which advantageously acts on the lubrication performance.

(Embodiment) Hereinafter, a drawing which is an embodiment of the present invention will be described.

In FIG. 1, a cylinder 1 that is inclined forward substantially horizontally and a crankcase 2 that is connected to the rear thereof are connected by a mating surface 3, and a cylinder skirt portion 4 protrudes deeply into the crankcase 2.

The cylinder 1 has an exhaust passage 5 in the lower part and a main scavenging passage on both sides.
6, a sub-scavenging passage 7 is formed in the upper part, and an intake passage 9 is connected to the upper part of the crankcase 2 via a reed valve device 8 immersed in the case. Therefore, the reed valve device 8 is located on the opposite side of the exhaust passage 5 with respect to the cylinder axis and on the same side as the sub-scavenging passage 7, and the front end 8 a faces the outer peripheral surface of the cylinder skirt 4.

In this reed valve device 8, the tip 8a approaches the cylinder skirt portion 4 and the extended trajectory S of the sub-scavenging passage 7 is extended.
A notch 10 having a size corresponding to the opening angle θ defined by the valve seat 8b and the valve stopper 8c that regulates the lift amount is formed in the cylinder skirt portion 4.

Note that oil is injected into the carburetor by the oil pump 11, and the air-fuel mixture is supplied to the intake passage 9.

In this way, in the suction process by the rise of the piston 12, the air-fuel mixture is sucked into the crankcase 2 through the reed valve device 8, and then the interior of the crankcase 2 is compressed by the lowering of the piston 12, so that the air-fuel mixture sucked is mainly The upper portion of the cylinder 1 is charged through the scavenging passages 6 and 7 (scavenging). At this time, the exhaust passage 5 is open.

In the scavenging process, the flow of the air-fuel mixture to the sub-scavenging passage 7 is suppressed to some extent by the presence of the reed valve device tip 8a. Therefore, the amount of air-fuel mixture short-circuiting from the sub-scavenging passage 7 to the exhaust passage 5 across the cylinder 1 is reduced, and the so-called blow-by phenomenon is prevented.
Improvement of filling efficiency and output can be obtained.

On the other hand, the oil component of the air-fuel mixture flowing out of the reed valve device 8 flows substantially along the opening angle θ because of its large mass, and smoothly flows into the cylinder 1 because there is no barrier in front of the notch 10. The gas enters the exhaust passage 5 formed in the lower part of the cylinder 1 and is directed closer to the exhaust passage 5. This makes it possible to sufficiently cope with the most severe lubrication of this part. Therefore, the supply amount of oil can be reduced.

The invention is not limited to the engine in which the cylinder is inclined substantially horizontally forward as shown in the example of the drawing, but can be applied to a two-cycle engine having a cylinder in any posture. Also, due to layout problems, the number of parts does not increase, and no special processing or assembling is required, so that there is no disadvantage in cost increase.

〔The invention's effect〕

As described above, in the intake device for a two-stroke engine according to the present invention, the cylinder skirt portion protrudes into the crankcase from the mating surface of the cylinder and the crankcase, and the sub-scavenging passage passes through the cylinder on the opposite side with respect to the cylinder axis. Is formed, and an intake passage is opened in a crankcase on the same side as the sub-scavenging passage, and a reed valve device that opens only to the inside of the crank chamber is interposed. Projecting into the extension locus of the sub-scavenging passage so as to be closer to the cylinder skirt portion, facing the notch formed in the cylinder skirt portion, and opening into the crank chamber defined by the valve seat surface and the valve stopper. Angle θ is set so that at least a part thereof faces the exhaust passage side of the cylinder. Since the mixture is introduced into the crank chamber so as to face the cylinder exhaust passage, the amount of the mixture air flowing into the sub-scavenging passage is suppressed, and the amount of blow-through is reduced to enhance output and improve fuel efficiency. The air-fuel mixture (cold air flow and oil) is positively directed toward the exhaust passage side, which is thermally severe, and the amount of oil adhering to the inner surface of the cylinder on the exhaust passage side is increased to improve the cooling performance.
In addition, the lubrication performance between the cylinder and the piston can be improved.

[Brief description of the drawings]

FIG. 1 is a longitudinal side view of a two-stroke engine provided with an intake device according to an embodiment of the present invention, FIG. 2 is an end view showing a mating surface of a two-stroke engine cylinder with a crankcase, and FIG. FIG. 4 is a vertical cross-sectional view taken along the line AA, FIG. 4 is a vertical cross-sectional side view of a main part of a two-stroke engine showing a conventional intake device, and FIG. 5 is a side view of a motorcycle equipped with a two-stroke engine. is there. DESCRIPTION OF SYMBOLS 1 ... cylinder, 2 ... crankcase, 4 ... cylinder skirt part, 5 ... exhaust passage, 6 ... main scavenging passage, 7
… Auxiliary scavenging passage, 8… Reed valve device, 8a… End, 8b… Valve seat, 8c …… Valve stopper, 9…
... intake passage, 10 ... notch, 11 ... oil pump,
12 ... Carburetor.

Claims (1)

(57) [Claims] The cylinder skirt portion protrudes into the crankcase from the mating surface of the cylinder and the crankcase, and a sub-scavenging passage is formed in the cylinder opposite to the exhaust passage with respect to the cylinder axis. In a two-stroke engine in which an intake passage is opened in the crankcase on the same side as the scavenging passage and a reed valve device that opens only to the inside of the crank chamber is provided, the leading end of the reed valve device has an extension locus extending along the sub-scavenging passage. At an angle of at least a part of the opening angle θ into the crank chamber defined by the valve seat surface and the valve stopper. The cylinder is set so as to face the exhaust passage side, and the air-fuel mixture from the intake passage faces the cylinder exhaust passage side. Intake system of a two-stroke engine, characterized in that flowed into the sea urchin crank chamber.