JPH02307663A - 2-cycle engine cylinder block manufacturing method - Google Patents

Abstract

PURPOSE:To obtain sliding surface precisely worked by forming a core part with an insert which is inserted into a core mold separated to right and left sides from the upper part and successively drawn out to the upper part. CONSTITUTION:The insert 28 arranging cavity 29 for housing valve connecting with cavity 25 for exhaust passage at lower face, is inserted between the core molds 22a, 22b of right and left sides into cavity 26 for inserting the insert from the upper part. The core sand is packed into inner part of a sleeve 2. Successively, the inert 28 is drawn out to the upper part and also the core molds 22a, 22b are separated to right and left sides to take out the core 31, which integrates the cylinder 2 and exhaust passage. This core 31 is set in a mold and a cylinder block integratedly formed with the sleeve 2 is cast. By this method, annular recessed part along upper edge part of exhaust port in the sleeve can be formed.

Description

[Detailed Description of the Invention] Main millet support skin! The present invention relates to a method for manufacturing a cylinder block for a two-stroke engine, which is formed by integrally casting a sleeve and has an exhaust timing control valve mounted on an exhaust port.

In a two-stroke engine, the sleeve that slides against the piston is integrally cast into the cylinder block, and the upper edge of the exhaust port can be opened and closed using a valve to control the exhaust timing according to the engine speed. This has been known in the past (for example, see Japanese Utility Model Application Publication No. 158535/1983).

FIGS. 1 and 2 show an example of such a conventional cylinder block for a two-stroke engine.

In the figure, 01 is a cylinder block, a sleeve 02 is integrally cast, and a piston 03 is fitted into the sleeve 02.
are in sliding contact. The sleeve 02 is provided with an exhaust port 04 and a scavenging port 05, and the cylinder block 01 has an exhaust passage 06 and a scavenging passage 0 communicating with these ports.
7 is provided. A valve storage part 08 is recessed in the upper part of the exhaust passage 06 near the exhaust port, and this valve storage part 0
At 8, an exhaust timing control valve 09 is rotatably provided around a shaft 010. This exhaust timing control valve 09 is for controlling the start and end timing of exhaust by opening and closing the upper edge portion of the exhaust bow 04, and its tip surface 09a has an arc shape along the outer peripheral surface of the sleeve 02. It has a planar shape.

Further, on the sleeve 02 side, a sliding surface 011 having an arcuate cross section is provided which slides into contact with the tip end surface 09a when the valve 09 swings around the shaft 010 to perform opening/closing operations.

When the valve 09 is fully opened, it is drawn into the valve housing part 08, but the upper end of the part of the valve housing part 08 that is in contact with the outer peripheral surface of the sleeve 02 is defined by an annular horizontal upper wall 012, and the trajectory of the tip of the valve 09 is An unnecessary space 014 is formed on the sleeve 02 side of 013. This has traditionally occurred unavoidably during the manufacturing process of the cylinder block 01. In other words, the core used to prevent molten metal from entering the valve storage portion 08 during casting of the cylinder block 01 is a mold for molding the core, which is divided into left and right halves by a plane corresponding to the cross section in FIG.
Sand is molded using a sand core (core mold), but when separating the core mold into left and right sides to take out the molded sand core, the surface (corresponding to the upper wall 012 having an arcuate planar shape) is The surface of the core mold must be at least parallel to the moving direction of the core mold, and an annular portion (space 0
14), the molded sand core will be destroyed by this annular portion when the core molds are separated.

The heat generated in the sleeve 02 due to combustion in the cylinder is diffused into the cylinder block body, which is made of aluminum alloy or the like and has good heat conductivity, and which is in close contact with the outer peripheral surface of the sleeve, and the water flowing through the cooling channel 015 is effective. cooled down. However, the back of the portion of the sleeve 02 adjacent to the upper edge of the exhaust port 04 is a space 014 due to the above-mentioned manufacturing reasons, so that heat is not diffused to the cylinder block main body portion and is easily overheated. In other words, this part has poor heat conductivity.

Furthermore, since the sliding surface 011 of the sleeve 02 serves as a sealing surface for the control valve 09, its shape and position precisely match the distal end surface 09a of the valve 09, and it is finished to have a sufficiently smooth surface. However, it is impossible to machine this sliding surface 011 after the sleeve 02 is cast into the cylinder block 01.

An object of the present invention is to provide a method for producing a sleeve-integrated cylinder block in which there is no space on the outer periphery of the sleeve part and the sliding surface of the sleeve with the exhaust timing control valve is machined with sufficient precision. It is.

According to the present invention, a cylinder block of a two-stroke engine is formed by integrally casting a sleeve and has an exhaust timing control valve attached to the exhaust port, and the cylinder block is formed by integrally casting a sleeve and having an exhaust timing control valve mounted on the exhaust port. A step of finishing the sliding surface of the exhaust port with the exhaust timing control valve, a sleeve cavity that cooperates with the opposing surface to hold the sleeve, and the exhaust port of the sleeve. A core divided into right and left sides, having an exhaust passage cavity corresponding to an exhaust passage connected to the sleeve cavity, and a cavity for insertion of a nest provided adjacent to the sleeve cavity and above the exhaust passage cavity. In the step of attaching it to the mold, in the space for inserting the insert,
the step of inserting an insert having a valve case 6 one-handle space on the lower surface corresponding to an exhaust timing control valve storage part continuous with the exhaust passage space from above, straddling the left and right core molds; Filling the inside of the sleeve, the exhaust passage cavity, and the valve housing cavity with core sand; then, the insert is pulled out upward and the core mold is separated into left and right sides, and the sleeve and the exhaust passage are separated. The cylinder block is manufactured through the following steps: removing the core with the integrated core, and placing the core in a mold to cast the cylinder block with the sleeve integrally cast therein.

According to the present invention, the core portion corresponding to the valve storage portion is formed by the insert that is inserted from above into the core mold that is separated into left and right sides and can be pulled out upward. Even if an annular recess (a cavity into which molten metal flows during casting) is formed along the upper edge of the exhaust port of the sleeve, by pulling the insert upward after molding the core,
The molded core can be taken out from the core mold without damaging the recessed portion. Therefore, in a cylinder block cast using this core, there is no space at the outer periphery of the sleeve portion adjacent to the upper edge of the exhaust port, which improves heat dissipation of the sleeve portion.

Furthermore, the sliding surface of the sleeve with respect to the exhaust timing control valve is finished before the sleeve is cast into the cylinder block, so that a sliding surface machined with sufficient precision can be obtained.

Each step of the method of the present invention will be sequentially explained below with reference to FIGS. 3 to 11.

FIG. 3 shows the first step of the method of the invention. In this step, the exhaust port 4, the scavenging port 5, etc. are machined into the material of the sleeve 2, and the sliding surface 11 along the upper edge of the exhaust port 4 is finished.

This finishing process is performed on the fixed sleeve 2 by adjusting the axis 010 of the sleeve o2 and the control valve o9 in FIG. 1.2.
The rotating shaft 21 of the rotary tool 20 (see Fig. 3a) is set at a position that matches the relationship between By cutting (grinding) 11, this can be done easily and precisely.

Next, as shown in FIGS. 4 and 8, this sleeve 2 is sandwiched and attached to the left and right divided core molds 22a and 22b. Matching surface 2 of core molds 22a and 22b
3a and 23b are respectively recessed with sleeve cavity portions 24a and 24b that hold half of the sleeve 20, and these cavity portions 24a and 24b meet to form a sleeve cavity 24 that completely surrounds the sleeve 2. form. The mating surfaces 23a, 23b are also recessed with exhaust passage cavity portions 25a, 25b, respectively, which define an exhaust passage cavity 25 that communicates with the sleeve cavity 24 through the exhaust port 4 of the sleeve 2 when the sleeve 2 is installed. It is set up.

Above the portion of the exhaust passage cavity 25 adjacent to the sleeve cavity 24 is a cavity 26 for inserting an insert which opens upward and spans the left and right core molds 22a, 22b. On the side opposite to the exhaust passage cavity 25 with respect to the sleeve cavity 24, there is a scavenging passage cavity 27 that communicates with the sleeve cavity 24 through the scavenging port 5 of the sleeve 2, and has left and right core molds 22a, 22.
It is formed across b.

As shown in FIG. 8, the insert 28 is inserted into the insert inserting space 26 from above after the left and right core molds 22a and 22b are closed with the sleeve 2 between them. FIG. 6 is a bottom view of the insert 28, and FIG. 7 is a sectional view of the center thereof. As can be seen from these drawings, the insert 28 has a rectangular parallelepiped shape with one side having a cylindrical surface 28a along the outer peripheral surface of the sleeve 2, and the insert 28 is formed by a core mold 22a and a core mold 221]. It is inserted into the insertion cavity 26 in a tight fit. A valve housing cavity 29 corresponding to the valve housing part 08 in FIG. 1 is recessed in the lower surface 28b of the insert 28. However, in this valve housing cavity 29, a space 014 formed behind the portion adjacent to the upper edge of the exhaust port 04 in the valve housing 08 in FIG. Buried.

After the sleeve 2, the core molds 22a, 22b, and the insert 28 are assembled as described above, a sleeve cavity 24, an exhaust passage cavity 25, and a valve housing connected to the exhaust passage cavity 25 are formed in the sleeve 2. The hollow space 29 and the scavenging passage space 27 are filled with sand, and then the insert 28 is pulled out upward to form the core mold 22a.
, 22b are separated into left and right sides, a core 31 in which the sleeve 2 and the filled sand are integrated is obtained as shown in FIG. 32 is an exhaust passage forming portion, 33 is a valve storage portion forming portion, and 34 is a scavenging road forming portion. A recessed portion 35 is formed in the valve storage portion forming portion 33 along the upper edge of the exhaust port 4 of the sleeve 2 by a projecting edge portion 30 provided on the insert 28 .

The recessed portion 35 has an arcuate planar shape along the outer circumferential surface of the sleeve 2, and the insert 28 that molds this portion is pulled out upward in the axial direction of the sleeve 2 after molding the core.
The shape of the recessed portion 35 does not collapse during die cutting.

Next, as shown in FIG. 10, this core 31 is installed at a predetermined position in the cylinder block forming cavity 37 of the mold 36, and other cores 38 for forming cooling channels are also installed. Then, a molten metal 39 of a cylinder block material, for example, an aluminum alloy, is injected into the cavity 37 through a sprue 40, and a cylinder block having the sleeve 2 integrally cast therein is cast.

FIG. 11 shows a cylinder block 1 cast in this manner, in which an exhaust passage 6 similar to that of the cylinder block 01 of FIG. The portion 33 forms the valve storage portion 8, the scavenging road forming portion 34 forms the scavenging road 7, and the core 38 forms the cooling water channel 15. However, on the outside of the portion 2a along the upper edge of the exhaust port 4 of the sleeve 2, there is a cylinder block 01 shown in FIG.
There is no space 014, and the portion corresponding to the space 014 is filled with a hanging portion 41 of the cylinder block material, and the hanging portion 41 is in close contact with the outer peripheral surface of the sleeve portion 2a. Therefore, the heat of the sleeve portion 2a is transferred to the hanging portion 41.
It is diffused into the cylinder block body through
The portion 2a does not locally become hot. Drooping part 41
is formed by molten metal entering the concave portion 35 of the core 31, and by employing the cylinder block manufacturing method described above G4, such a hanging portion 41 can be formed.

Next, a shaft hole 10 for pivotally supporting a control valve similar to the exhaust timing control valve 09 shown in FIG. 1 is precisely positioned and machined in the valve storage portion 8 with reference to the sleeve 2.

The distal end surface of the control valve supported by the shaft hole 10 comes into sliding contact with the sliding surface 11 formed on the sleeve 2, but since the sliding surface 11 is first precisely finished as described above, the control valve Sufficient sealing performance is ensured between the tip surface and the sliding surface 11,
It is possible to effectively prevent deterioration in engine performance due to leakage of gas inside the cylinder through this.

As described above, according to the method of the present invention, the core portion for forming the exhaust timing control valve storage portion of the cylinder block is inserted from above into the core mold that is separated into the left and right sides, and is therefore Since it is molded with a removable insert, it is possible to form an annular recessed portion along the upper edge portion of the exhaust port of the sleeve in the core portion. Therefore, in a cylinder block cast using this core, there is no space at the outer periphery of the sleeve portion adjacent to the upper edge of the exhaust port, which improves heat dissipation of the sleeve portion. Furthermore, the sliding surface of the sleeve with respect to the exhaust timing control valve is finished before the sleeve is cast into the cylinder block, so that a sliding surface machined with sufficient precision can be obtained.

=12-

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional view of a conventional cylinder block for a two-stroke engine, Fig. 2 is a cross-sectional view thereof, Fig. 3 is a perspective view of a sleeve showing the first step of the present invention, and Fig. 3a is a top view thereof. , Fig. 4 is a top view showing the sleeve sandwiched between the left and right core molds, Fig. 5 is a front view showing the mating surface of one of the core molds, and Fig. 6 is a bottom view of the insert. Figure 7 shows ■-■ of Figure 6.
8 is a perspective view showing the left and right core molds and the insert in a separated state; FIG. 9 is a longitudinal sectional view of the core molded by the core mold and the insert; FIG. 10 is a cross-sectional view taken along the line; 11 is a longitudinal sectional view of a mold incorporating the core described above, showing a cylinder block casting process, and FIG. 11 is a longitudinal sectional view of a cylinder block cast by the method of the present invention. 1... Cylinder block, 2... Sleeve, 4...
・Exhaust port, 5...Scavenging port, 6...Exhaust passage, 7...Scavenging passage, 8...Valve storage part, 10...Shaft hole, 11...Sliding surface, 15.・・Cooling channel, 20・・
・Rotating tool, 21... Rotating shaft, 22... Core mold, 2
3...Mating surface, 24...Sleeve void, 25...
Exhaust passage cavity, 26...Vacancy for inserting insert, 27...
Scavenging passage void, 28... Insert, 29... Valve storage space, 30... Flange portion, 31... Core, 32... Exhaust passage forming portion, 33... Valve storage part forming part, 34.
...Scavenging passage forming part, 35...Recessed part, 36...
Mold, 37... Vacancy, 38... Core, 39... Molten metal, 40... Sprue, 41... Drooping part.

Claims (1)

[Scope of Claim] A method for manufacturing a cylinder block for a two-stroke engine in which a sleeve is integrally cast and an exhaust timing control valve is installed in an exhaust port, the method comprising: machining a port, etc. in the sleeve; The sliding surface of the port with the exhaust timing control valve is finished, and the sleeve is provided with a sleeve cavity that cooperates with the sleeve to hold the sleeve on the opposing surface, and a sleeve space that is connected to the exhaust port of the sleeve. A core mold divided into right and left parts, having an exhaust passage cavity corresponding to an exhaust passage, and a cavity for inserting a insert provided adjacent to the sleeve cavity and above the exhaust passage cavity. The insert, which has a valve storage space corresponding to the exhaust timing control valve storage part that is continuous with the exhaust passage space, is inserted into the insert insertion space from above, and is inserted into the insert insertion space from above. The inside of the sleeve, the exhaust passage cavity and the valve housing cavity are filled with core sand, and then the core sand is pulled out upward and the core mold is moved left and right. A two-stroke engine characterized in that the cylinder block and the exhaust passage are separated, a core in which the cylinder and the exhaust passage are integrated is taken out, and this core is placed in a mold to cast a cylinder block in which the sleeve is integrally cast. cylinder block manufacturing method.