Stratified scavenging two-cycle engine

Abstract: The present invention relates to a stratified scavenging two-cycle engine which enables a reduction in size and an improvement in productivity. To this end, a carburetor (6) is provided between an air cleaner (7) and a suction pipe (4), within which a mixture flow passage (6B) and an air flow passage (6A) are formed in parallel and an air control valve (6a) and a mixture control valve (6b) are disposed in the air flow passage (6A) and the mixture flow passage (6B) respectively. The suction pipe (4) is provided between the carburetor (6) and an outer face of a cylinder (2), in which an air flow passage (4a) connected to the air flow passage (6A) in the carburetor (6) and a mixture flow passage (4b) connected to the mixture flow passage (6B) in the carburetor (6) are formed.

Description: Technical Field The present invention relates to a stratified scavenging two-cycle engine, and more particularly to a stratified scavenging two-cycle engine in which a carburetor and an air control valve are integrally formed. Background Art An example of a conventional stratified scavenging two-cycle engine is disclosed in Japanese Patent Laid-open No. 9-268917 , and Fig. 12 shows a side sectional view of a stratified scavenging two-cycle engine 10 described in the aforesaid Japanese Patent Laid-open. In Fig. 12 , a muffler 80 is attached to an exhaust port 26 which is formed in a cylinder 20 of the engine 10. Formed in an outer face of a crankcase 90 attached to the underside of the cylinder 20 is a suction port 90a for sucking mixture into a crank chamber. A heat insulating pipe (suction pipe) 40 is connected to the suction port 90a, and a carburetor 60 is disposed through the heat insulating pipe 40. An air control valve 50 is provided between the carburetor 60 and an air cleaner 70. The air control valve 50 is connected to a scavenging port 20a, which is provided in the cylinder 20, through an air supply valve 55. A check valve 20b is provided in the scavenging port 20a. An ignition plug 30 is attached to the top of the cylinder 20. A length in a cross direction between an outer face of the cylinder 20 and an outer face of the air cleaner 70 is set to be a dimension LA. In the aforesaid art, however, the air control valve 50 is provided between the carburetor 60 and the air cleaner 70. Therefore, the dimension LA in a cross section between the outer face of the cylinder 20 and the outer face of the air cleaner 70 is made longer and the space area of the stratified scavenging two-cycle engine 10 is enlarged. Consequently, there arises a disadvantage that the workability of a shoulder hanging, hand-held, or knapsack-type mower for mowing grass, a chain sew, or the like with the engine 10 is inferior. The distance from the air control valve 50 to the scavenging port 20a of the cylinder 20 is far. Therefore, the air supply pipe 55 is made longer, which results in lack of compact disposition. In addition, there is a disadvantage that the air supply pipe 55 is a hindrance to a workman because it touches his body. There is another disadvantage that the air control valve 50 and the carburetor 60 are manufactured separately, thus causing high manufacturing costs. Moreover, since the check valve 20b is provided within the cylinder 20 in the engine assembly process, productivity is low. JP 580 054 23 A and JP 62 11 3824 disclose a suction section for a two-cycle internal combustion engine, comprising an air cleaner mounted to a scavenge pipe and a carburetor which is directly mounted to the cylinder of the two-cycle internal combustion engine and supplies mixture directly into the engine. At the side of the cylinder the carburetor comprises a flange like neck at which the scavenge pipe coming from the air cleaner is mounted. The two-cycle internal combustion engine is scavenged via the air cleaner, the scavenge pipe and the flange like neck of the carburetor. Summary of the Invention In view of the aforesaid disadvantages, an object of the present invention is to provide a stratified scavenging two-cycle engine which enables the reduction in size of an engine, compact disposition, improvement in workability of a mower, a chain sew, or the like with the stratified scavenging two-cycle engine, and improvement in productivity. This problem is solved with a stratified scavenging two-cycle engine according to claim 1. A stratified scavenging two-cycle engine according to the invention includes a piston, a cylinder in which said piston is disposed to be vertically slidable, a crankcase connected to said cylinder, a scavenging flow passage having a scavenging port formed in a side wall of said cylinder and connecting said scavenging port and a crank chamber in said crankcase, an air supply flow passage connected to said scavenging flow passage and supplying air through a check valve, a carburetor supplying mixture into said crank chamber through a mixture flow passage of the carburetor, a mixture control valve disposed in said mixture flow passage, an air cleaner connected to said carburetor,an air flow passage forming a part of said air supply flow passage in parallel with said mixture flow passage, an air control valve disposed in said air flow passage, wherein said carburetor is provided between said air cleaner and a separate suction pipe, and said suction pipe is provided between said carburetor and an outer face of said cylinder, said air flow passage is formed in said carburetor such that said mixture control valve and said air control valve and are integrally formed in said carburetor, said suction pipe serving as a heat insulating material and including a suction pipe air flow passage connected to said air flow passage of said carburetor and a suction pipe mixture flow passage connected to said mixture flow passage of said carburetor. According to the aforesaid configuration, the mixture flow passage and the air flow passage in parallel with the mixture flow passage are formed in the carburetor. The air control valve and the mixture control valve are disposed correspondingly in the respective flow passages, and the carburetor is attached to the outer face of the cylinder through the suction pipe which serves also as a heat insulating material. Consequently, the dimension in a cross section between the outer face of the cylinder and the outer face of the air cleaner is made smaller, thereby reducing the space area of the stratified scavenging two-cycle engine and the size thereof. Accordingly, the handling of a shoulder hanging, hand-held, or knapsack-type mower for mowing grass, a chain sew, or the like with the stratified scavenging two-cycle engine according to the present invention is facilitated, thereby improving workability. In addition, the carburetor, the air control valve, and the mixture control valve can be integrally formed, thus decreasing the number of parts and lowering manufacturing costs. The suction pipe has a plurality of exhaust ports for exhausting air, a plurality of the scavenging flow passages are provided in the cylinder, and the plurality of exhaust ports and the plurality of scavenging flow passages are connected with a plurality of air supply pipes. According to the aforesaid configuration, as to the conventional disadvantages shown in Fig. 12 , the suction pipe attached to the outer face of the cylinder and the scavenging flow passage are connected with the air supply pipe, whereby the air supply pipe is made shorter and compact and satisfactory piping can be obtained. As a result, the conventional disadvantage that "the air supply pipe is a hindrance to a workman because it touches his body" is eliminated, thus improving workability and lowering manufacturing costs. A plurality of connecting pipes may be disposed between the plurality of air supply pipes and the plurality of scavenging flow passages, and check valves may be provided respectively in the plurality of connecting pipes. According the aforesaid configuration, as against the conventional configuration in which "the check valve is disposed in the cylinder", the check valve is provided in the connecting pipe, thereby decreasing the number of parts. Consequently, assembly man-hours in the engine assembly process are decreased and productivity can be improved. Brief Description of the Drawings Fig. 1 is a front view of a stratified scavenging two-cycle engine according to the present invention; Fig. 2 is a sectional view taken along the 2-2 line in Fig. 1 ; Fig. 3 is a front view of a suction pipe according to the present invention; Fig. 4 is a sectional view taken along the 4-4 line in Fig. 3 ; Fig. 5 is a rear view of the suction pipe in Fig. 3 ; Fig. 6 is a sectional view taken along the 6-6 line in Fig. 5 ; Fig. 7 is a sectional view taken along the 7-7 line in Fig. 3 ; Fig. 8 is a perspective view of the suction pipe in Fig. 3 ; Fig. 9 is a perspective view of principal portions of a carburetor, the suction pipe, an air supply pipe, and a connecting pipe according to the present invention; Fig. 10 is a fragmentary sectional view for explaining an air cleaner, the carburetor, and the suction pipe according to the present invention; Fig. 11 is a sectional view of a cylinder according to the present invention; and Fig. 12 is a side sectional view of a stratified scavenging two-cycle engine according to a prior art. Best Mode for Carrying out the Invention A preferable embodiment of a stratified scavenging two-cycle engine according to the present invention will be described in detail with reference to the attached drawings. A schematic configuration of a stratified scavenging two-cycle engine 1 will be explained on the basis of Fig. 1 and Fig. 2 . A piston (not shown) is disposed to be vertically slidable in a cylinder 2 for the stratified scavenging two-cycle engine 1. An exhaust port (not shown) is provided in the right side face of the cylinder 2, and a muffler 8 is attached to the exhaust port. A suction pipe 4 is provided between the left side face of the cylinder 2 and a carburetor 6, and an air cleaner 7 is attached to an outer face of the carburetor 6. A crankcase 3 is connected to the underside of the cylinder 2. An ignition plug 2d is attached to the top of the cylinder 2. A length between an outer face of the cylinder 2 and an outer face of the air cleaner 7 is a dimension L. Air flow passages 4a and 4a which are formed in the suction pipe 4 are connected to air supply pipes 5 and 5. The air supply pipes 5 and 5 are connected to plural scavenging flow passages 2b and 2b (See Fig. 11 ), which are formed in the cylinder 2, through connecting pipes 5a and 5a. The configuration of the suction pipe 4 will be explained by Figs. 3 to 8 with reference to Figs. 1 and 2 . The suction pipe 4 is formed integrally with the air flow passages 4a and 4a and a mixture flow passage 4b. The air flow passages 4a and 4a are connected to the plural scavenging flow passages 2b and 2b (See Fig. 11 ) formed in the cylinder 2 through the air supply pipes 5 and 5 connected to exhaust ports 4A and 4A and the connecting pipes 5a and 5a, respectively. The mixture flow passage 4b is connected to a mixture supply flow passage (not shown) which is provided in the cylinder 2. In Fig. 9 , the suction pipe 4 is attached to the carburetor 6 and connected to the plural scavenging flow passages 2b and 2b (See Fig. 11 ) through the plural air supply pipes 5 and 5 and the connecting pipes 5a and 5a, respectively. The connecting pipes 5a and 5a respectively have check valves 2B and 2B (See Fig. 2 ) therein. The air supply pipes 5 and 5 may be made of metal, but if they are made with flexible materials, assembly becomes easier, thus improving productivity. The principal part of the present invention will be explained by Figs. 10 and 11 with reference to Figs. 1 to 9 . As shown in Fig. 10 , an air control valve 6a and a mixture control valve 6b are integrally formed in the carburetor 6, and the carburetor 6 and the suction pipe 4 are connected. Air 7B which is introduced into the air cleaner 7 branches into two flows by a shielding plate 7a provided almost at the center of the air cleaner 7 and flows toward the carburetor 6 along the directions shown by arrows in Fig. 10 . In the carburetor 6 connected to the air cleaner 7, an air flow passage 6A and a mixture flow passage 6B are formed in parallel. Mixture generated by fuel and the air 7B flows through the mixture flow passage 6B. In addition, the air flow passage 6A is provided with the air control valve 6a therein and the mixture flow passage 6B is provided with the mixture control valve 6b therein. Accordingly, in the flow passages 6A and 6B in the carburetor 6, the respective control valves 6a and 6b are integrally formed. The suction pipe 4 includes the air flow passage 4a and the mixture flow passage 4b. The air flow passage 4a and the mixture flow passage 4b are connected to the air flow passage 6A and the mixture flow passage 6B, respectively. Mixture flows into a crank chamber (not shown) from the mixture flow passage 4b through the mixture supply flow passage (not shown) provided in the cylinder 2. The suction pipe 4 is connected to the outer face of the cylinder 2 through the air supply pipes 5 and 5 (See Fig. 2 ) which are connected to the exhaust ports 4A and 4A for the air 7B and the connecting pipes 5a and 5a shown in Fig. 11 . The connecting pipes 5a and 5a respectively communicate with the plural scavenging flow passages 2b and 2b provided in the cylinder 2. Check valves 2B and 2B are provided between the connecting pipes 5a and 5a and the scavenging flow passages 2b and 2b, respectively. Plural scavenging ports 2a and 2a provided in the cylinder 2 are connected to the crank chamber in the crankcase 3 through the scavenging flow passages 2b and 2b respectively. Suction and scavenge of air are conducted by way of the scavenging flow passages 2b and 2b and the scavenging ports 2a and 2a in synchronization with upward and downward movements of a piston 2A which is disposed to be vertically slidable in the cylinder 2. The check valves 2B and 2B operate to allow the air 7B which is introduced along the directions of the arrows shown in Fig. 10 to flow into the air flow passages 4a and 4a in the suction pipe 4, the air supply pipes 5 and 5, the connecting pipes 5a and 5a, and the scavenging flow passages 2b and 2b respectively, but not to allow combustion gas in the cylinder 2 to flow into the connecting pipes 5a and 5a sides. As described above, in the stratified scavenging two-cycle engine 1 of the present invention, the carburetor 6, the air control valve 6a, and the mixture control valve 6b are integrally formed. Moreover, in the stratified scavenging two-cycle engine 1, the carburetor 6 is attached to the outer face of the cylinder 2 through the suction pipe 4 which serves also as a heat insulating material, thereby shortening a dimension L in a cross direction between the outer face of the cylinder 2 and the outer face of the air cleaner 7 and making the space area of the engine 1 smaller as shown in Fig. 1 . Consequently, the handling of a shoulder hanging, hand-held, or knapsack-type mower for mowing grass, a chain sew, or the like with the stratified scavenging two-cycle engine 1 is facilitated, thereby improving workability. In addition, the carburetor 6, the air control valve 6a, and the mixture control valve 6b are integrally formed, thus decreasing the number of parts and assembly man-hours and lowering manufacturing costs. Hitherto, as shown in Fig. 12 , there has been a disadvantage that satisfactory disposition can not be obtained since an air supply pipe 55 is made longer due to a long distance from an air control valve 50 to a scavenging port 20a of a cylinder 20. Contrary to this, in the present invention, the suction pipe 4 attached to the outer face of the cylinder 2 and the scavenging flow passages 2b and 2b are connected with the air supply pipes 5 and 5, thereby shortening the air supply pipes 5 and 5 and obtaining satisfactory disposition. As a result, a conventional disadvantage that the air supply pipes 5 and 5 are hindrances to a workman because they touch his body is eliminated, thus improving the workability and lowing manufacturing costs. Moreover, since the check valves 2B and 2B are provided in the connecting pipes 5a and 5a respectively, assembly man-hours in the assembly process are decreased, thereby improving productivity.

Claims: A stratified scavenging two-cycle engine including a piston (2A), a cylinder (2) in which said piston (2A) is disposed to be vertically slidable, a crankcase (3) connected to said cylinder (2), a scavenging flow passage (2b) having a scavenging port (2a) formed in a side wall of said cylinder (2) and connecting said scavenging port (2a) and a crank chamber in said crankcase (3), an air supply flow passage connected to said scavenging flow passage (2b) and supplying air through a check valve (2B), a carburetor (6) supplying mixture into said crank chamber through a mixture flow passage (6B) of the carburetor (6), and a mixture control valve (6b) disposed in said mixture flow passage (6B), an air cleaner (7) connected to said carburetor (6), an air flow passage (6A) forming a part of said air supply flow passage in parallel with said mixture flow passage (6B), an air control valve (6a) disposed in said air flow passage (6A), characterised in that said carburetor (6) is provided between said air cleaner (7) and a separate suction pipe (4), and said suction pipe (4) is provided between said carburetor (6) and an outer face of the cylinder (2), said air flow passage (6A) is formed in said carburetor (6) such that said mixture control valve (6b) and said air control valve (6a) are integrally formed in said carburetor (6), said suction pipe (4) serving as a heat insulating material and including a suction pipe air flow passage (4a) connected to said air flow passage (6A) of said carburetor (6) and a suction pipe mixture flow passage (4b) connected to said mixture flow passage (6B) of said carburetor (6), wherein said suction pipe (4) has a plurality of exhaust ports (4A, 4A) for exhausting air, a plurality of said scavenging flow passages (2b, 2b) are provided in said cylinder (2), and said plurality of exhaust ports (4A, 4A) and said plurality of scavenging flow passages (2b, 2b) are connected with a plurality of air supply pipes (5, 5). The stratified scavenging two-cycle engine in accordance with Claim 1, characterised in that a plurality, of connecting pipes (5a, 5a) are disposed between said plurality of air supply pipes (5, 5) and said plurality of scavenging flow passages (2b, 2b), and check valves (2B, 2B) are provided respectively in said plurality of connecting pipes (5a, 5a).

Inventors: KATO HIROSHI, SAWADA TOSHIHARU, WATANABE TAKESHI, KATO, HIROSHI, SAWADA, TOSHIHARU, WATANABE, TAKESHI
Applicants: KOMATSU ZENOA KK, KOMATSU ZENOAH CO.
Application year: 1999
Main classification: F02B17
IPC codes: F02B17, F02B25, F02B63, F02M35, F02B75, F02M19, F02M11, F02B33