JPH0138279Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a cylinder block for a two-stroke engine.

(Prior Art) As shown in Fig. 3, a cylinder block a that integrates a cylinder head portion and a cylinder portion, and a crankcase b that consists of left and right or upper and lower members are separated, and a pair of scavenging passages are connected to the crankcase. It is generally known that cylinder liners i are disposed opposite to each other in the direction of axis c and that cylinder liner i is cast into cylinder block a (see Japanese Utility Model Application No. 53-40105). In this case, since the cylinder block a and the crankcase b are separate bodies, the width W of the crankcase b in the direction of the crankshaft c is set to be the same as or smaller than the inner diameter D of the cylinder liner i. The engine output can be improved by increasing the preload ratio of the engine and increasing the scavenging air filling efficiency. In addition, the distance B between the journal bearings e and e on both sides of the crank web d can be made as narrow as possible to reduce the influence of the load on the crankshaft c due to the drive of the piston f, resulting in a compact crankshaft c.
As a result, its strength can be ensured.

However, since the cylinder block a and the crankcase b are separate bodies, and the crankcase b itself is made up of two parts, the number of parts increases, which increases the number of assembly steps, and the joint surfaces of each part also require high precision. This increases the number of machining steps and increases costs.

On the other hand, as shown in FIG. 4, the cylinder block a and the upper part k of the crankcase b are integrated, and as shown in FIG. (Refer to Utility Model Application Publication No. 51-26210), No. 6
As shown in the figure, there is also the above-mentioned integral structure in which the upper part of the crankcase b is narrowed.

(Problem to be solved by the invention) However, in the case shown in FIG. 4, in order to cut out the part forming the scavenging passage h, the width W of the crankcase b in the crankshaft direction is changed to the scavenging passage width S.
The crankcase must be larger than B
Due to the increase in the internal volume, the preload ratio becomes lower, which is disadvantageous in terms of engine output. At the same time, the distance B between the journal bearings e and e increases, and the shaft diameter of the crankshaft c is increased to ensure the strength of the crankshaft c. This becomes a disadvantage from the viewpoint of reducing the weight of the engine. Also, the cylinder liner i has its skirt part j
Because it has a simple cylindrical shape, it has low strength and deforms due to the high heat generated by engine operation, resulting in a reduction in engine output, blow-by of combustion gas, and engine seizure.

On the other hand, in the one shown in Fig. 5, either the intake system parts (carburizer and air cleaner) or the exhaust system muffler are in the same direction as the cooling fan attached to one end of the crankshaft c, so the muffler Due to heat dissipation, the cooling performance of the cooling fan decreases, and the installation space for parts of the intake system, exhaust system, and auxiliary equipment such as cooling fans (magnets) becomes narrow, making it difficult to install them. Especially when the engine is mounted vertically, such as on lawn mowers,
When this engine is attached to a working machine, engine parts or auxiliary equipment are disposed between the engine and the working machine, making it difficult to mount the engine on the working machine.

In addition, in the case shown in Fig. 6, although it is advantageous in terms of engine output because the upper part of the crankcase b is constricted, it is difficult to cut out the part that forms the scavenging passage h, and the cylinder bore g is Core (pull out in the Y direction) and core for scavenging passages h and h (X
It is necessary to use a special and expensive die-casting die that incorporates a die-casting die (in the direction of the die), and the molten metal enters the mating surfaces of the die-casting die, shortening the shot cycle and ultimately increasing costs.

In other words, the problem of the present invention is to integrate the cylinder head part, cylinder part, and upper part of the crankcase, and to cast the cylinder liner, so that even if the upper part of the crankcase is squeezed, the strength of the cylinder liner can be maintained, and the above-mentioned mold can be maintained. To prevent the problem of punching out and to ensure the positioning of a cylinder liner in a die-cast mold when casting the cylinder liner to form a cylinder block.

(Means for solving the problem) Therefore, the present invention solves the problem,
By integrally providing the scavenging passage forming wall and a positioning part for positioning the cylinder liner in a die-cast mold on the cylinder liner that is cast into the cylinder block, the strength of the cylinder liner is ensured while the upper part of the crankcase is tightened. This also prevents the problem of mold cutting mentioned above and facilitates casting.

That is, the method is as follows: In a cylinder block of a two-stroke engine in which a cylinder head part, a cylinder part, and an upper part of a crankcase are integrally molded by die-casting a cylinder liner, a scavenging hole is formed in the cylinder liner. A passage wall is integrally provided that bulges outward from the cylinder block and extends to the upper part of the crankcase to form a scavenging passage along its entire length. In order to constitute a part, a positioning part is integrally provided with a contact surface facing the cylinder head side that abuts on the outer surface molded part of the cylinder block in the die-cast mold for the cylinder block and positions the cylinder liner in the die-cast mold. This is a two-stroke engine cylinder block characterized by:

(Function) In the above cylinder block, the passage wall that forms the scavenging passage is integrally provided in the cylinder liner, so even if the upper part of the crankcase is squeezed, there is no need for a complex-shaped core to form the scavenging passage. Moreover, the passage wall acts as a reinforcement for the cylinder liner. In addition, when the cylinder head and cylinder are integrated, the cylinder liner can only be supported by the die-casting mold on the crankcase side because the molten metal for forming the cylinder head comes above it, and its positioning is difficult. Although it becomes difficult, in the case of the cylinder block mentioned above, the cylinder liner is provided with a positioning part, so by bringing this positioning part into contact with the externally formed part of the cylinder block in the die-casting mold, the cylinder liner can be easily positioned in the die-casting mold. death,
In this state, pouring can be performed.

That is, since the above-mentioned positioning part is located near the scavenging hole in the passage wall, that is, at a position away from the crankcase side, the cylinder liner is placed in a die-cast mold at a position close to the crankcase side and away from there towards the cylinder head side. Furthermore, since the contact surface of the positioning part that contacts the die-cast die faces the cylinder head side, the cylinder liner can be held between the die-cast die from both the crankcase side and the cylinder head side. The cylinder liner can be supported in the die-casting mold in a stable position.

(Effects of the invention) Therefore, according to the invention, in order to simplify or reduce the weight of the engine structure, the cylinder head part, the cylinder part, and the upper part of the crankcase are integrated.
In the case where the cylinder liner is cast into this,
The cylinder liner is integrally provided with a scavenging passage constituting wall and a positioning part having a contact surface that faces the cylinder head and abuts against the cylinder block outer surface molded part in the die-cast mold at a position of the passage constituting wall near the scavenging hole. Therefore, while ensuring the strength of the cylinder liner, it is possible to tighten the upper part of the crankcase without using a complex-shaped core to improve engine output and ensure the strength of the crankshaft. Positioning can be performed reliably, casting can be facilitated, and the quality of the cylinder block can be improved.

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

A cylinder block 5 for a two-stroke engine shown in FIG. 1 is formed by integrally forming a cylinder part 1, a cylinder head part 2, and an upper part 3 of a crankcase 4 by die-casting aluminum, and having a cylinder liner 6 cast therein. This cylinder liner 6 has a liner portion 7 on which a piston (not shown) slides, a passage wall 8 for a scavenging passage, and positioning portions 14, 14' for positioning the cylinder liner 6 in a die-cast type for a cylinder block. and are integrated. In this case, the passage wall 8 and the positioning parts 14, 14' are integrally molded when the liner part 7 is cast.

Scavenging holes 10 and 10' are formed in the liner portion 7 at opposite positions in the direction of the axis 9 of the crankshaft, and exhaust holes 11 and exhaust holes 11 are formed in opposite positions in the direction orthogonal to the axis 9 of the crankshaft. Intake hole 1 shown in
7 is formed.

The passage wall 8 for the scavenging passage bulges outward from the scavenging holes 10, 10' of the liner part 7, extends to the upper part 3 of the crankcase 4 via the lower inner surface 1a of the cylinder part 1, and extends from the lower part 12, 12. is curved inward and continues to the lower end of the liner portion 7, and constitutes the entire length of the scavenging passages 13, 13 between it and the skirt portion 7a of the liner portion 7.

The positioning portions 14, 14' are connected to the passage wall 8.
The scavenging holes 10, 10' are provided at positions near the scavenging holes 10, 10', that is, at the upper end, and contact the molded portion of the outer surface of the cylinder block in the die-cast mold for this cylinder block so as to form a part of the outer surface of the cylinder block 5. It has an abutment surface facing the cylinder head side. That is, this contact surface faces toward the cylinder head portion 2 at the position of the fins 15 formed on the outer periphery of the cylinder block 5, and contacts the outer surface of the cylinder block in the die-casting mold, that is, the portion where the fins 15 are formed. It is something that forces you to do something. In addition, in FIG. 1, 16 is a hole for a spark plug.

In addition, in FIG. 2, 11a is the exhaust hole end;
13a is a reinforcing rib for the scavenging passage 13, 17a is the end of the intake hole, and 18 and 18' are die-cast molds for the exhaust hole and the intake hole, respectively. Exhaust hole end 11a
The intake hole end portion 17a is machined to have a radius R larger than the radius of the outer surface of the scavenging passages 13, 13 portion of the cylinder liner 6.

Note that the reinforcing rib 13a of the skirt portion 7a can be omitted if the cylinder liner 6 has sufficient strength.

Next, a method of manufacturing the cylinder block 5 will be explained.

First, the cylinder liner 6, which is formed by integrally molding the liner part 7, the scavenging passage wall 8, and the positioning parts 14, 14' by casting, is assembled into a die-cast mold for a cylinder block. At this time, the positioning section 1
The cylinder liner 6 is positioned by bringing the contact surfaces of the fins 4 and 14' into contact with predetermined positions of the molded portion of the fin 15 in the die-casting mold. In this case, the lower end of the cylinder liner 6 can be supported by a die-casting die that is inserted into the cylinder liner 6 from the crankcase 4 side to form the inner surface 2a of the cylinder head portion 2. Therefore, the cylinder liner 6 can be held from both the cylinder head side and the crankcase side by the die-cast mold for forming the fins and the die-cast mold inserted inside, and its positioning state can be accurately maintained. As it becomes more stable, it becomes more stable.

In addition, the distance between the die-cast mold inserted into the cylinder liner 6 and the inner surface of the lower end 8a of the cylinder liner 6 is made sufficiently narrow, and the exhaust hole end 1
1a and the intake hole end 17a are die-cast type 18,
18' and a slight distance between them. Thereafter, molten aluminum alloy is injected to obtain the cylinder block 5 into which the cylinder liner 6 is cast.

The cylinder liner 6 may be made of cast iron, high-silicon aluminum casting, or aluminum casting with chrome plating on the inner surface.

Therefore, in the case of the cylinder block 5, since the cylinder part 1, cylinder head part 2, and upper part 3 of the crankcase 4 are integrally formed, the number of parts is reduced, and the number of cutting and assembly steps is reduced. Therefore, manufacturing costs can be reduced.

Since the scavenging passage wall 8 is integrally provided with the cylinder liner 6, a complex-shaped core is not required to form the scavenging passage, and a simple-shaped core is sufficient, reducing manufacturing costs. This also increases the degree of freedom in designing the shape of the scavenging passage.
Further, the scavenging passage wall 8 acts as a reinforcing member for the cylinder liner portion 7, and can prevent the cylinder liner portion 7 from deforming due to high heat generated by engine operation.

Furthermore, since the scavenging passages 13, 13 are arranged opposite to each other in the direction of the crankshaft, and the inner diameter of the lower part of the scavenging passage 13 in the cylinder block 5 can be made the same as the inner diameter of the upper part of the scavenging passage 13, both sides of the crank web can be By reducing the distance between the journal bearings in the engine, the strength of the crankshaft can be improved, and by reducing the internal volume of the crankcase, it is possible to increase engine output, which reduces the weight of the engine per unit output. By lowering the engine weight, it is possible to reduce the weight and cost of the engine. Also,
The distance between the die-cast mold inserted into the cylinder liner 6 and the inner surface of the lower end 8a of the cylinder liner 6, and the distance between the exhaust hole end 11a or the intake hole end 17a and the die-cast molds 18, 18' are narrowed. Therefore, it is possible to prevent the molten metal from entering the scavenging passage and the intake/exhaust holes, and it is possible to reduce the number of steps required for deburring after casting.

Furthermore, since the scavenging passages 13, 13 can be arranged opposite to each other in the direction of the crankshaft, it is easy to prevent interference between the cooling fan at one end of the crankshaft and parts of the intake system and exhaust system. In addition, the cooling performance of the cooling fan can be prevented from deteriorating due to heat radiation from the muffler, and the engine can be easily mounted on the working machine.

In addition, if the cylinder liner 6 is made of high-silicon aluminum casting or aluminum casting with chrome plating on the inner surface, the adhesion between the cylinder liner and the cylinder block body will be better, and the heat dissipation will be improved, which will reduce the engine output. It is possible to improve the fuel consumption rate and reduce the weight of the engine.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of a cylinder block according to an embodiment of the present invention, FIG. 2 is a sectional view taken along the line -- in FIG. 1, and FIGS. 3 to 6 are longitudinal sectional views of conventional examples. 1...Cylinder part, 2...Cylinder head part,
4... Crank case, 5... Cylinder block, 6... Cylinder liner, 7... Liner section, 8
...Aisle wall, 10,10'...Scavenging hole, 13...
Scavenging passage, 14, 14'...positioning part.

Claims (1)

[Claims for Utility Model Registration] A cylinder block for a two-stroke engine in which a cylinder head part, a cylinder part, and an upper part of a crankcase are integrally formed by die-casting a cylinder liner, A passage wall that bulges outward from the scavenging hole and extends to the upper part of the crankcase and constitutes the entire length of the scavenging passage is integrally provided, and a part of the outer surface of the cylinder block is located on the passage wall near the scavenging hole. In order to configure this, a positioning part is integrally provided with a contact surface facing the cylinder head side for abutting against the outer surface molded part of the cylinder block in the die-casting mold for the cylinder block and for positioning the cylinder liner on the die-casting mold. A two-stroke engine cylinder block characterized by: