The present invention relates to a scavenging passage structure for a two-stroke engine having a scavenging passage communicating a scavenging port provided in a cylinder with a crank chamber inside a crankcase, the scavenging passage extending through respective fastening surfaces of the cylinder and the crankcase.
In two-stroke engines, scavenging passages that open to the crank chamber formed inside the crankcase extend as smoothly curved passages inside the crankcase to the fastening surfaces of the crankcase and the cylinder, through the scavenging passages, and connect to scavenging ports provided in the cylinder.
In
Reference numeral 102 denotes the crankcase, inside which a crank chamber 106 is formed. Reference numeral 140 denotes two scavenging ports provided in side portions of the cylinder 101 to face opposite each other,
Reference numeral 118 denotes air passages for supplying leading air, connected midway of the scavenging passages 104b so that leading air from an air cleaner is supplied to the scavenging ports 140 through the air passages 118 and scavenging passages 104b.
Reference numeral 132 denotes an insulator for thermally insulating the intake system from the engine body, the insulator 132 being fastened to a side face of the cylinder 2 with bolts. An upper passage 132a inside the insulator 132 forms an air passage for supplying leading air. This air passage is connected midway of the scavenging passages 104b, so that leading air is supplied to the scavenging ports 140 via the air passages 118 and scavenging passages 104b. A lower passage 132b inside the insulator 132 forms an air/fuel mixture passage for supplying an air/fuel mixture into the crank chamber 106. This air/fuel mixture passage communicates with inside of the cylinder 101 via an intake port 142.
In
Reference numeral 103 denotes a flat and smooth cylinder mounting surface formed at the top of the crankcase 102. The cylinder 101 is fastened with a plurality of bolts 114, with its lower face 103′ making contact with this cylinder mounting surface 103.
The scavenging passages 104a and the scavenging passage inlets 104c are each formed inside the front crankcase 102a and rear crankcase 102b symmetrically about the front and back split surface 125. The upper ends of the scavenging passages 104a are open in the cylinder mounting surface 103.
Reference numeral 110 denotes guide members, inserted from the openings in the cylinder mounting surface 103, their upper faces forming part of the cylinder mounting surface 103. The guide members 110 are formed with passage surfaces that smoothly connect to the scavenging passages 104a. The guide members 110 are provided with protrusions, for example, in their upper faces and sides, while grooves are cut in the crankcase 102, so that the guide members are fastened to the crankcase 102 with these protrusions fitted in the grooves.
In the two-stroke engine equipped with the scavenging passage structure configured as shown in
The conventional scavenging passage structure for a two-stroke engine using the guide members described using
Patent Document 1: Japanese Patent No. 4031602
However, with the conventional scavenging passage structure for a two-stroke engine using the guide members 110 disclosed in Patent Document 1 and described using
Also, the use of the slide cores increases the number of steps for forming the scavenging passages for the two-stroke engine, causing the problem of increased cost required for the formation of the scavenging passages.
Accordingly, in view of such a problem encountered by the conventional technique, an object of the present invention is to provide a scavenging passage structure for a two-stroke engine, with which scavenging passages communicating scavenging ports provided in the cylinder with the crank chamber inside the crankcase can be formed without using slide cores, so that the production cost arising from the use of slide cores is cut down.
To solve the problem mentioned above, the present invention provides a scavenging passage structure for a two-stroke engine, having a scavenging passage communicating a scavenging port provided in a cylinder with a crank chamber formed inside a crankcase, the scavenging passage being formed to extend through respective fastening surfaces of the cylinder and the crankcase, characterized in that the scavenging passage structure further has a cover member attached inside the crankcase to be in contact with an inner wall surface of the crankcase, and a groove formed in a contact surface between the inner wall surface of the crankcase and the cover member, and forming part of the scavenging passage connecting to the crank chamber and to an upper face of the crankcase.
Thereby, even though the crankcase is produced by die casting, there is no need to use slide cores, which are slid toward the cylinder mounting surface to allow extraction of the casting. As there is no need to use slide cores, the production cost for slide cores is made unnecessary. Accordingly, the production cost required for configuring the scavenging passages for a two-stroke engine can be reduced.
The groove may be recessed in the inner wall surface of the crankcase and the cover member may be attached in contact with the inner wall surface of the crankcase so as to close an open part of the groove.
This way, as grooves need not be provided in the cover member, a general-purpose component can be used as the cover member. This allows inexpensive replacement of cover members when failure occurs.
The groove may be recessed in the cover member, and the cover member may be attached in contact with the inner wall surface of the crankcase so as to close an open part of the groove.
Thereby, the production cost can be reduced as the slide cores are made unnecessary, and also, the die design used for producing the crankcase can be made simpler, as no grooves are formed in the crankcase.
The groove may be recessed both in the inner wall surface of the crankcase and in the cover member, and the cover member may be attached in contact with the inner wall surface of the crankcase so that respective open parts of the grooves provided in the inner wall surface of the crankcase and in the cover member face opposite each other.
Thereby, the production cost can be reduced as the slide cores are made unnecessary, and also, the cover member can be positioned to the crankcase more easily since the mounting position of the cover member to the crankcase is determined by the positions of the grooves each provided in the crankcase and the cover member.
The cover member may be attached to the inner wall surface at a mounting position determined by being fitted in between opposite inner wall surfaces of the crankcase.
This allows simple and reliable positioning between the cover member and the crankcase, ensuring correct formation of the scavenging passage.
The present invention can provide a scavenging passage structure for a two-stroke engine, which allows formation of scavenging passages communicating the scavenging ports in the cylinder with the crank chamber inside the crankcase without using slide cores, whereby the production cost incurred by the use of slide cores can be cut down.
Preferred embodiments of the present invention will be hereinafter illustratively described in detail with reference to the drawings. It should be understood that the sizes, materials, and shapes of the constituent elements described in the embodiments, and their positions relative to each other, are given for illustrative purposes only and not meant to limit the scope of this invention, unless specifically stated otherwise.
(Embodiment 1)
The crankcase 2 is made up of a front crankcase 2a (a front crankcase portion) and a rear crankcase 2b (a rear crankcase portion) that are front and back parts divided at a front and back split surface 25 orthogonal to the crankshaft axis 80. After the crankshaft 8 and others have been assembled inside, the front crankcase 2a and rear crankcase 2b are fastened together and united with a plurality of bolts 26.
In
Reference numeral 40 denotes two scavenging ports provided in side portions of the cylinder 12 to face opposite each other,
Reference numeral 18 denotes an air passage for supplying leading air, connected midway of the scavenging passages 4b so that leading air from an air cleaner (not shown) is supplied to the scavenging ports 40 through the air passage 18 and scavenging passages 4b.
The scavenging passages 4a inside the crankcase 2 are formed as described below. The crankcase 2 is provided with grooves 21 in contact surfaces with cover members 22, the grooves being recessed into the direction of the crankshaft axis 80 as shown in
On the open side of the grooves 21 formed in the crankcase 2, the cover members 22 are attached in contact with inner wall surfaces 2c of the crankcase 2. The cover members 22 close the open side of the grooves 21, attached in contact with the inner wall surfaces of the crankcase 2, and fastened to the crankcase 2 with fastening members 23 such as bolts.
The crankcase 2 further includes two inner wall surfaces 2d opposite each other at both ends of the inner wall surfaces 2c in which the grooves 21 are provided, the cover members 22 being fitted in between the two inner wall surfaces 2d. As the cover members 22 are fitted in between the two opposing inner wall surfaces 2d, the mounting position of the cover members 22 is determined.
The open side of the grooves 21 recessed into the direction of the crankshaft axis 80 in the crankcase 2 is thus closed by the cover members 22 so that the grooves 21 and cover members 22 together form passages, these passages being the scavenging passages 4a.
In the two-stroke engine with the scavenging passage structure having the configuration shown in
With Embodiment 1, the scavenging passages 4a inside the crankcase 2 are formed by the grooves 21 and the cover members 22, the grooves being provided in the contact surfaces 2c between the crankcase 2 and the cover members 22. Therefore, the rear crankcase 2b can be produced by die casting, using a die set designed to form a groove 21, the cover member 22 then being brought into contact with the inner wall surface 2c of the rear crankcase 2b so as to close the open side of the groove 21 from the side of the front and back split surface 25 and fastened there with the bolts 23. The front crankcase 2a is produced similarly with the rear crankcase 2b, after which the front crankcase 2a and the rear crankcase 2b are fastened together and united with the bolts 26, so that the crankcase 2 is complete.
Therefore, even though the crankcase is produced by die casting, there is no need to use slide cores, which are slid toward the cylinder mounting surface 3 on the upper face of the crankcase 2 that is the fastening surface with the cylinder 12, to allow extraction of the casting, for forming the scavenging passages 4a.
As there is no need to use slide cores, the production cost for slide cores is made unnecessary. Accordingly, the production cost required for configuring the scavenging passages for a two-stroke engine can be reduced.
The cover members 22 take up part of the space inside the crankcase 2. An extremely large space left inside the crankcase 2 would cause a reduction in compression ratio of the crankcase 2. The provision of the cover members 22 can prevent such reduction in the compression ratio.
(Embodiment 2)
In Embodiment 2, no grooves are formed in the crankcase 2, and instead, grooves 21a are formed in the contact surfaces of the cover members 22 contacting the inner wall surfaces of the crankcase so as to be recessed in the direction of the crankshaft axis 80. The grooves 21a are open on the side opposite the inner wall surfaces 2c of the crankcase 2 that is in contact with the cover members 22. The remaining parts are formed in smooth curves to form the scavenging passages 4a.
The cover members 22 are attached so that the open side of the grooves 21a thereof makes contact with the inner wall surfaces of the crankcase 2. The cover members 22 are attached in contact with the inner wall surfaces of the crankcase 2 so that the open grooves 21a are closed, and fastened in position with fastening members such as bolts to the inner wall surfaces 2c of the crankcase 2.
Thus the open side of the grooves 21a provided in the cover members 22 is closed by the inner wall surfaces 2c of the crankcase 2 so that the grooves 21a and the inner wall surfaces 2c of the crankcase 2 together form passages, these passages being the scavenging passages 4a.
As in Embodiment 2 described using
Thereby, the production cost can be reduced as the slide cores are made unnecessary, as with Embodiment 1, and also, the die design used for producing the crankcase can be made simpler.
(Embodiment 3)
In Embodiment 3, grooves 21b and 21c are formed each in the contact surface of the crankcase 2 contacting the cover members 22 and in the contact surfaces of the cover members 22 contacting the inner wall surfaces of the crankcase so as to be recessed in the direction of the crankshaft axis 80. The grooves 21b are open in the inner wall surfaces 2c of the crankcase 2 contacting the cover members 22. The grooves 21c are open in the contact surfaces of the cover members 22 contacting the crankcase 2. The grooves 21b and 21c are formed in the crankcase 2 and the cover members 22, respectively, so that, when the cover members 22 are attached to the crankcase 2 to be in contact with the inner wall surfaces of the crankcase so that the respective open sides of the grooves 21b and grooves 21c are faced opposite each other, the grooves 21b and 21c together form smoothly curved scavenging passages 4a.
The cover members 22 are fastened in position, with fastening members such as bolts, to the inner wall surfaces of the crankcase 2.
Thus the grooves 21b and 21c provided in the crankcase 2 and cover members 22 are faced opposite each other in the direction of the crankshaft axis 80 so that the grooves 21b and 21c together form passages, these passages being the scavenging passages 4a.
As in Embodiment 3 described using
Thereby, the production cost can be reduced as the slide cores are made unnecessary, as with Embodiment 1, and in addition, the cover members 22 can be positioned to the crankcase 2 more easily since the mounting position of the cover members 21b to the crankcase 2 is determined by the positions of the grooves 21b and 21c.
The present invention is applicable as a scavenging passage structure for a two-stroke engine, which allows formation of scavenging passages communicating the scavenging ports in the cylinder with the crank chamber inside the crankcase without using slide cores.
Number | Date | Country | Kind |
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2010-102148 | Apr 2010 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2011/056870 | 3/23/2011 | WO | 00 | 8/30/2012 |
Publishing Document | Publishing Date | Country | Kind |
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WO2011/135948 | 11/3/2011 | WO | A |
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Number | Date | Country | |
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20120325191 A1 | Dec 2012 | US |