JPH077577Y2 - Two-cycle engine decompression device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a decompression device that reduces starting torque when starting a two-cycle engine.

[Conventional technology]

FIG. 5 shows a spark-ignition two-cycle engine of the piston valve type, where 1 is a cylinder, 2 is a cylinder liner that constitutes the inner wall of the cylinder 1, 3 is a piston, 4 is a cylinder head, 5 is a combustion chamber, 6 Is an exhaust port, and the opening 6a on the cylinder inner wall side of the exhaust port 6 is opened and closed by sliding of the piston 3.

As shown in FIG. 6, a compressed gas leakage groove is formed on the inner wall of the cylinder 1 within a range in which the piston 3 slides from the upper end edge of the cylinder inner wall side opening 6a of the exhaust port 6 to the top dead center side. 7 are set up.

As shown in FIG. 7, the compressed gas leakage groove 7 has an inverted isosceles trapezoidal shape in plan view, and the exhaust port cylinder inner wall side opening portion thereof.
The communicating portion 7a with the 6a is formed to be narrower than the upper end starting end portion 7b.

As a modified example of the inverted isosceles trapezoidal compressed gas leakage groove 7, an egg-shaped compressed gas leakage groove 8 having a plan shape as shown in FIG. 8 and an inverted convex compression as shown in FIG. Gas leak groove 9, oblique gas hole shaped compressed gas leak groove as shown in FIG.
It may also be provided in the Christmas tree-shaped compressed gas leak groove 11 and the like as shown in FIG. 10 and FIG. 11, and the communication portions 8a, 9a, 10a and 11a with the exhaust port cylinder inner wall side opening 6a are narrowed respectively. Is forming.

Further, the compressed gas leakage grooves 7 to 11 may be arranged not only in one line but also in a plurality of lines in the opening 6a on the cylinder inner wall side of the exhaust port 6. In addition, the compressed gas leakage groove 7 to
It is desirable to provide the upper end start portion of 11 at a position where the crankshaft rotation angle is 40 ° or less.

Further, preferably, the compressed gas leak groove 7 (or 8 to 1)
As shown in FIG. 6, 1) is provided such that the depth of the groove on the upper end starting end portion 7b side is relatively shallow and the groove on the communicating portion 7a side is deep, and the exhaust gas passing through the compressed gas leakage groove 7 is It has the advantage of smoothing the flow.

In FIG. 5, 12 is a spark plug, 13 is an air supply port,
14, 15 are piston rings, and 16 is a gasket.

[Problems to be solved by the device]

In the conventional device as described above, the decompression passage (compressed gas leakage groove) 7 communicates with the exhaust port 6 and the combustion chamber 5.

Therefore, the incomplete combustion gas peculiar to the two cycles escapes from the exhaust port 6 via the decompression passage 7. At this time, charcoal is easily trapped in the passage and the function of the passage is impaired.

Further, technically, in order to provide the conventional groove 7, the core of the cylinder is pulled out to the side opposite to the plug. Therefore, the mold for forming the groove 7 must first be moved to the center, and the core must be removed in the lower part in the subsequent process, which increases the number of steps.

[Means for Solving the Problems]

A decompression groove that releases the air-fuel mixture in the cylinder chamber to the crankcase when the engine is started is provided in the axial direction at the upper end of the scavenging passage. Further, the decompression groove is provided in the scavenging passage on the windward side of the cylinder cooling air so that the decompression groove is not easily blocked by the soot.

On the other hand, the shape of the decompression groove is taken into consideration so that it is difficult to close it.

[Action]

1) Since the decompression groove communicates with the crankcase through the scavenging passage, when the piston moves from the top dead center to the bottom dead center, the combustion gas passes through the decompression groove and enters the crankcase. Since it enters the cylinder again through the scavenging passage and the decompression groove from the crankcase, soot is hard to be clogged.

2) A decompression groove can also be formed in the conventional process, which prevents an increase in cost due to mold construction.

〔Example〕

FIG. 1 is a longitudinal sectional view of an engine along a scavenging passage of a cylinder.

Reference numeral 19 is a cooling fan for cooling the cylinder, and cooling air flows as shown by the arrow. Reference numerals 20 and 20 'of the cylinder 1 are scavenging passages that connect the crankcase 23 and the combustion chamber 5 to each other. 6 is an exhaust port and 13 is an intake port.

A decompression groove for returning the air-fuel mixture into the crankcase 23 in the axial direction of the cylinder 1 at the upper end of the scavenging passage 20 on the windward side of the cooling wind.
21 is provided. The upper end of the decompression groove 21 is the piston 3
Therefore, the intake port 13 is in a position where it does not communicate with the combustion chamber 5 before opening. (FIG. 2) FIG. 3 and FIG. 4 are detailed views of the shape of the decompression groove.

FIG. 3 shows a straight shape that is sharp in the plug direction. FIG. 4 shows a fan-shaped configuration on the scavenging passage side.

In this case the _{h 2 ≦ h 1/2,} B ≦ A / 2, b ≦ a / 2.

[Effect of device]

1) By providing a decompression groove in the axial direction at the upper end of the scavenging passage in the cylinder chamber that communicates with the crankcase, the air-fuel mixture in the cylinder chamber returns to the crankcase through the decompression groove, and the starting torque at engine startup Is reduced.

2) By providing the decompression groove on the scavenging passage side on the windward side of the cylinder cooling air, the temperature around the decompression groove is reduced, and the soot in the decompression groove is prevented.

3) Even if the combustion gas passes through the decompression groove, fresh air flows into the combustion chamber from the crankcase through the scavenging passage, so the decompression groove is not blocked by the soot.

4) By changing the width and depth of the groove in the axial direction of the groove to taper the plug side, the flow velocity of the air-fuel mixture flowing in the decompression groove changes, and soot is less likely to adhere. Further, it becomes possible to control the output reduction and the starting torque reduction.

5) Since the decompression groove is formed at the upper end portion of the scavenging passage, the mold in the cylinder chamber can be molded in one step, so that the cost does not increase.

[Brief description of drawings]

1 (a) is a longitudinal sectional view of an embodiment of the present invention, FIG. 1 (b) is an overall sectional view of the cylinder of FIG. 1 (a), and FIG. 1 (c) is FIG. 1 (b). AA arrow view, FIG. 2 is a sectional view around the scavenging passage including the piston, FIG. 3 (a) (b) is a sectional view and a side view of the decompression groove, and FIG. 4 (a) (b) is another Fig. 5 is a vertical sectional view of a conventional device, Fig. 6 is an enlarged view of the compressed gas leak groove portion of Fig. 5, and Figs. 7 to 11 are conventional compression units. FIG. 6 is a view showing the shape of a gas leakage groove and is a view taken along the line BB in FIG. 1 …… Cylinder, 19 …… Cooling fan 20,20 ′ …… Scavenging passage, 21 …… Decompression groove 23 …… Crankcase

Claims (1)

[Scope of utility model registration request] 1. A cooling fan having a scavenging passage in an axial direction of a cylinder, which communicates an in-cylinder combustion chamber with an inside of a crankcase, formed on an inner wall of the cylinder, and provided at one end of a crankshaft supported by the crankcase. In an air-cooled two-cycle engine that cools the cylinder with cooling air guided by a wind guide cover from the above, a decompression groove that is continuous with an upper end portion of a scavenging passage formed in the cylinder inner wall on the windward side with respect to the flow direction of the cooling air is provided. The inner wall of the cylinder is provided so as to extend toward the cylinder head side along the cylinder axis direction, and the width and depth of the decompression groove are changed in the axial direction to form a tapered shape toward the cylinder head side. Characteristic 2-cycle engine decompression device.