WO2012010144A2 - Method for producing a cylinder for a two-stroke engine and casting core therefor - Google Patents

Abstract

The invention relates to a method for producing a cylinder (10, 110) for a two-stroke engine, comprising the following steps: producing a casting core (30, 130), wherein a central core slide (31, 131) for the cylinder chamber (11, 111) and at least one salt core (33, 133) for an overflow channel (18, 19; 118, 119) are produced and the at least one salt core (33, 133) is connected to the central core slide (31, 131), inserting the casting core (30, 130) into a casting mold, casting the cylinder (10, 110) in a die-casting process, removing the central core slide (31, 131) from the cylinder (10, 110), wherein the at least one salt core (33, 133) is separated from the central core slide (31, 131), and flushing the at least one salt core (33, 133) out of the cylinder (10, 110). The invention further relates to a casting core (30, 130) for such a method.

Description

 Method for producing a cylinder for a two-stroke engine as well as

 Casting core for this

The present invention relates to a method for producing a cylinder for a two-stroke engine and a casting core for this method.

Such cylinders are typically cast from an aluminum alloy in a gravity casting process using sand cores. The problem here is that form very easily casting defects and inclusions. Therefore, it is desirable to cast such cylinders in a die-casting process. Sand cores, however, can not be used for this because they do not withstand the pressure conditions prevailing during casting.

DE 33 31 664 A1 describes a cylinder with closed overflow channels for a two-stroke engine, which is produced by die-casting. To form the overflow channels divided steel cores are used, which are connected to the central core valve for the cylinder chamber. Both the design of the multi-part cores and the distance of the split steel cores for the overflow from the cast cylinder make very complex and cumbersome.

It is also known to use cores made of a wood fiber material (see DE 198 20 246 A1). However, such cores have not been proven for the die casting process, since they are not stable enough for this purpose.

The object of the present invention is to develop a generic method or a generic casting core so that the casting core can be easily removed from the cast cylinder and is nevertheless suitable for a die-casting process. The solution is that initially a casting core is produced, wherein a central core slide for the cylinder space and at least one salt core for a transfer channel is made and the at least one salt core is connected to the central core slider, that the casting core then introduced into a mold and the Cylinder is poured in a die-casting process, then that the central core slider is removed from the cylinder, wherein the at least one salt core is separated from the central core slider and finally the at least one salt core is flushed out of the cylinder.

The casting core according to the invention is characterized in that it has a central core slide for the cylinder chamber, to which at least one salt core is connected for an overflow channel.

Surprisingly, it has been found by a person skilled in the art that a salt core connected to a central core slide is so stable that it can withstand the conditions, in particular the pressure conditions, of a die casting process. The at least one salt core can be particularly easily flushed out of the cast cylinder in a conventional manner. The inventive method or the Gusskem invention thus make it possible to produce cylinders for two-stroke engines, which have at least one overflow, with little effort in the die-casting process.

Advantageous developments emerge from the subclaims.

The at least one salt core can be produced in a manner known per se by pressing, by injection molding or by sintering. Suitable main components are, for example, sodium chloride and / or potassium chloride. If necessary, at least one binder can be added, for example at least one alkali metal carbonate and / or at least one alkaline earth carbonate.

The central core slider can be made of any materials. Preference is given to metallic materials, in particular steel materials. The at least one salt core is preferably connected in a form-fitting manner and without binders to the central core slider.

The inventive method or the casting core according to the invention are particularly suitable for the production of cylinders which are cast in a die-casting process from an aluminum alloy.

Embodiments of the present invention are explained in more detail below with reference to the accompanying drawings. In a schematic, not to scale representation:

Figure 1 is an exemplary overall view of a cylinder for a two-stroke engine in section;

Figure 2 shows a cylinder for a two-stroke engine with a first embodiment of a casting core according to the invention therein in section;

FIG. 3 shows the cylinder according to FIG. 1 after removal of the casting core;

Figure 4 shows another embodiment of a casting core according to the invention in a perspective oblique view;

FIG. 5 shows the casting core according to FIG. 4 in a front view;

6 shows a further cylinder for a two-stroke engine in section, manufactured with a casting core according to FIGS. 4 and 5;

7 shows a section along the line VII - VII in Figure 6.

Figure 1 shows a schematic representation of a cylinder 10 for a two-stroke engine. In the exemplary embodiment, a piston-edge-controlled two-stroke engine is shown. as used, for example, for hand tools such as power saws. Such a two-stroke engine has at least one cylinder 10 with a cylinder chamber 11, in which a piston 12, which has a piston head 16, is guided movable up and down. The cylinder 10 is closed at one end by a cylinder head 13. The other end of the cylinder 10 is attached to a crankcase 14, which is shown only schematically in Figure 1. In known manner, the piston 12 is connected by means of a piston pin and a connecting rod with a crankshaft which is rotatably mounted in the crankcase 14 (not shown).

In the cylinder 10, a combustion chamber 15 is formed, which is bounded by the cylinder head 13, the piston head 16 of the piston 12 and the cylinder wall 17 of the cylinder chamber 11. In the exemplary embodiment, an overflow channel 18 is shown, which connects the combustion chamber 15 with the crankcase 14. The cylinder chamber 11 also has an outlet channel 21 for discharging the resulting combustion gases from the combustion chamber 15. Below the junction of the overflow channel 18 into the combustion chamber 15, the cylinder chamber 11 also has an inlet channel 22, via which a fuel-air mixture is introduced into the crankcase 14. The outlet channel 21, the inlet channel 22 and the junction of the overflow into the combustion chamber 15 are opened and closed by the reciprocating piston 12 in response to its stroke position.

In the position of the piston 12 shown in FIG. 1 in the region of its bottom dead center, the outlet channel 21 and the junction of the overflow channel 18 into the combustion chamber 15 are opened. In this position, the fuel-air mixture compressed by the piston 12 in the crankcase flows into the combustion chamber 15 (see arrow S) and displaces combustion gases located in the combustion chamber 15, which exit from the combustion chamber 15 via the outlet channel 21. In the following upward movement of the piston 12 in the direction of the cylinder head 13, first the mouth of the overflow channel 18 into the combustion chamber 15 and then the outlet channel 21 is closed. At the same time, the intake passage 22 is opened, so that fresh fuel-air mixture is sucked into the crankcase 14. The piston 12 compresses on its way to top dead center in the combustion chamber 15th During the subsequent downward stroke of the inlet channel 22 is closed and compressed into the crankcase 14 sucked fresh fuel-air mixture. Then first the outlet channel 22 and then the mouth of the overflow 18 are opened into the combustion chamber 15, and the cycle begins again.

Figures 2 and 3 show an embodiment of the present invention in a simplified representation. FIG. 2 shows a cylinder 10 for a two-stroke engine made from an aluminum casting alloy. The cylinder 10 was cast in a conventional manner in a die-casting process.

The casting core 30 used according to the invention has a central core slide 31 and a foot plate 32 provided thereon. The core slide 31 serves to form the cylinder space 11. The foot plate 32 essentially serves to close the casting mold and, after casting, pull the core slide 31 out of the cast cylinder 10 in the direction of the arrows A. The core slide 31 and the base plate 32 are made in the embodiment of the steel material X37CrMoV5-1 cured to 48-52 HRC.

In the embodiment, two salt cores 33 are connected to the core slide 31, which serve to form two overflow channels 18,19. The salt cores 33 in the exemplary embodiment consist of pressed sodium chloride or compressed potassium chloride.

The Anbind ung the salt cores 33 to the core slide by means of a positive connection.

The salt cores 33 are based on the base plate 32 in the exemplary embodiment. The finished casting core 30 is placed in a casting mold. The cylinder 10 is cast from an aluminum material in a die-casting process. When pulling out the core slide 31 after casting of the cylinder 10, the salt cores 33 are sheared off from the core slide 31 and separated from the base plate 32. The salt cores 33 are then flushed out of the cylinder 10 in a manner known per se, so that two overflow channels 18, 19 result. The support of the salt cores 33 on the base plate 32 causes the transfer channels to have an opening 18a, 19a in the direction of the crankcase to be added later. After adding the crankcase, the transfer ports open into the crankcase.

FIGS. 4 to 7 show a further exemplary embodiment of a cylinder 110 produced by the method according to the invention and of a cast core 130 used therefor. The cylinder 110 has a cylinder space 111, two overflow channels 118, 119, an outlet channel 121 and an inlet channel 122. The casting core 130 has, for forming the cylinder space 111, a core slide 131 made of a steel material, in particular made of hot-work steel X37CrMoV5-1 hardened to 48-52 HRC. Two core cores 133 for forming the overflow channels 118, 119 are connected to the core slide 131. Further, a mold part 121a for forming an exhaust passage 121 and a mold part 122a for molding an intake passage 122 are provided on the central core valve 131.

Claims

claims A method of making a cylinder (10, 110) for a two-stroke engine, comprising the steps of:  Producing a casting core (30, 130), wherein a central core slide (31, 131) for the cylinder space (11, 111) and at least one salt core (33, 133) for an overflow channel (18, 19, 118, 119) is produced, and the at least one salt core (33, 133) is connected to the central core slide (31, 131),  Inserting the casting core (30, 130) into a casting mold,  Casting the cylinder (10, 110) in a die-casting process,  Removing the central core slide (31, 131) from the cylinder (10, 110), the at least one salt core (33, 133) being separated from the central core slide (31, 131),  Rinsing out the at least one salt core (33, 133) from the cylinder (10, 110). 2. The method according to claim 1, characterized in that the at least one salt core (33, 133) is pressed. 3. The method according to claim 1, characterized in that the at least one salt core (33, 133) is sintered. 4. The method according to claim 1, characterized in that the at least one salt core (33, 133) is produced by injection molding. 5. The method according to claim 1, characterized in that the at least one salt core (33, 133) is prepared from sodium chloride as the main component. 6. The method according to claim 1, characterized in that the at least one salt core (33, 133) is made of potassium chloride as the main component. 7. The method according to claim 1, characterized in that the at least one salt core (33, 133) is prepared using at least one alkali carbonate and / or at least one alkaline earth carbonate. 8. The method according to claim 1, characterized in that the central core slide (31, 131) is made of a steel material. 9. The method according to claim 1, characterized in that the cylinder (10, 110) is cast from an aluminum alloy. 10. casting core (30, 130) for producing a cylinder (10, 110) for a two-stroke engine, with a central core slide (31, 131) for the cylinder chamber (11, 111), characterized in that the central core slide ( 31, 131) at least one salt core (33, 133) for an overflow channel (18, 19, 118, 119) is connected. 11. Cast core according to claim 10, characterized in that the at least one salt core (33, 133) is pressed. 12. Cast core according to claim 10, characterized in that the at least one salt core (33, 133) is sintered. 13. Cast core according to claim 10, characterized in that the at least one salt core (33, 133) is produced by injection molding. 14. Cast core according to claim 10, characterized in that the at least one salt core (33, 133) consists of sodium chloride as the main constituent. 15. Cast core according to claim 10, characterized in that the at least one salt core (33, 133) consists of potassium chloride as the main constituent. Cast core according to claim 10, characterized in that the at least one salt core (33, 133) contains at least one alkali carbonate and / or at least one alkaline earth carbonate. 17. Cast core according to claim 10, characterized in that the central core slide (31, 131) consists of a steel material.